ZOO 3210 Lecture 2: Metabolism & Thermoregulation
Write open-ended research questions leading to hypotheses
1.
Explain how MR changes with body size
2.
Draw graphs depicting relationship between environmental
and body temperatures
3.
Learning Outcomes:
First scientists weren't just looking for answers, they were
looking for good explanations
!
Logical
○
Not arbitrary
○
Internally consistent
○
Consistent with what we already know
○
Often able to make unexpected predictions
○
Good explanations are:
!
Aristotle
Ask a question --> come up with possible answers --> try to
disprove the answers
!
Where did like on Earth come from?
○
How can hibernating squirrels supercool without
freezing?
○
Why do some cold water fish species make antifreeze
proteins and other species do not?
○
Why is there variation in the length of time
amphibious fishes stay out of water?
○
Good questions are tough, open-ended questions
!
How does Science work?
Observe
!
Question
!
Hypothesis
!
Prediction(s)
!
Experiment(s)
!
Analyze & Conclude
!
Scientific Method:
Better: Why do deep sea animals have high
concentrations of organic osmolytes (e.g. TMAO) in
their blood and tissues?
○
Bad: What is the relationship between organic osmolytes
and water depth in ocean fishes?
!
Does it provide a satisfying possible answer to the
question asked?
○
Is it internally consistent?
○
Is it consistent with what we already know?
○
Does it pass the raised eyebrow test?
○
Quality Control for hypotheses and predictions:
!
Applying scientific method leads us to better and
better explanations
○
Scientific method was designed to help answer open-
ended questions
○
Hypotheses must explain the original observation
○
Predictions must be logical consequences of the
hypothesis and have the potential to disprove it
○
Imagination and creativity drive good science
○
Key points:
!
Applying the Scientific Method to these questions that don't
demand an explanation usually results in confusion.
What stages of development are shortened by an
increase in temperature during incubation?
○
Why can geckos that hatch later (incubated at lower
temperatures) withstand greater range of
temperature?
○
*How does temperature impact performance during
early development?
○
Possible Research Questions:
!
Activity: Gecko youngsters more at risk after incubating during a
heat wave
What is 'known', summarize previous findings that led to
current study
!
What is 'unknown', experiments are often based on
unanswered questions generated by earlier studies
!
Dissect each figure before reading text describing that
figure, use your own words (this helps you to interpret the
data independent of author's interpretation)
!
*see worksheet to prepare for assignment
Arctic animals face many challenges during the long, cold
dark winter months
!
Many different strategies have evolved to cope with low
temperature and/or lack of food during winter
!
Muskox, arctic fox, ground squirrels, ptarmigan, arctic cod,
and woolly caterpillars are some of the animals that survive
in the Canadian arctic
!
How do very cold temperatures impact these organisms?
!
What strategies are employed to survive arctic winter?
!
Metabolism & Thermoregulation
Endotherm: own production of metabolic heat used to
regulate body temperature
!
Ectotherm: environment influences body temperature
!
Homeotherm: thermoregulates by physiological means
!
Poikilothem: variable body temperature with environmental
change
!
Heterothem: regional/temporal (ex. Hibernating mammal)
!
Review:
Ex. A rhino that is 6x larger than a vole,
does not eat 6x less
"
NOT proportional --> more complex
relationship
!
Log -Log Plot
"
Y axis = mass-specific metabolic rate
"
Note:
!
Metabolic rate (e.g. O2 consumption) decreases with
increasing body mass (in vertebrates)
○
logMR = log a + b*logW
!
Advantage of a log-log plot is that one can
have a big range of numbers all on one graph
!
Weight specific MR = a*Weight(b-1) *a power
function relation
○
Surface 'law' stated that MR is
proportional to body-surface area and
related to maintaining a 37C body temp
(in mammals)
"
As animal gets bigger, ratio
decreases
!
Therefore, a smaller animal loses
heat faster than a larger animal
!
SA/volume is not proportional
"
*does not explain relationship between
metabolic rate and body mass in
ectotherms
"
Max Rubner (1900s)
!
All organisms show allometric relationship, not
just mammals
!
Has now been some-what
discredited
!
Fractal theory -related to transporting
material to/from cells
"
Multiple-causes theory -there are many
underlying processes
"
Other theories:
!
The explanation for allometric metabolism-weight
relations remains unknown
○
Body SizeA)
Body temperature also increases
"
Metabolic rate or oxygen uptake increases as
they digest food (and then declines post-
digestion)
!
*see slide
!
SDA = specific dynamic action
○
Food Intake & DigestionB)
Metabolic rate is affected by many factors:
02/06/18
Draw graphs depicting changes in MR with temperature1.
Explain the mechanisms that endotherms use to generate
heat in detail
2.
Write the results section for a graph on early development
of thermogenesis, draw a conclusion
3.
Learning Outcomes:
Allometry: pattern of change in a parameter (e.g. MR) with
change in body size
!
a,b = constants
○
W = weights
○
Allometric Equation: MR = a*Wb
!
O2 uptake or O2 consumption (mL O2/hr)
○
Heat produced (e.g. J/hr or kcal/hr)
○
Metabolic Rate:
!
Log-log plot
!
As body size increases, the amount of oxygen
consumption (per gram of tissue) decreases
!
Weight specific MR has a negative slop with body
mass
○
Weight-specific Metabolic Rate: amount of O2 consumed
or heat produced per gram or kilogram of body mass (e.g.
mL O1/hr/g or J/h/kg)
!
Terms:
Melting of ice --> heat produced
!
=direct calorimetry (oxygen uptake would be indirect
calorimetry)
!
Note: metabolic rate was first measured by putting animal within
a chamber covered in ice
Relationship is observed in all organisms
(unicellular/mutlicellular, ectotherm/endotherm)
!
*see slide
!
Log-log plot
!
Metabolic rate vs. body mass has a positive slop (~0.75)
Not a log-log plot
!
*see slide
!
Weight-specific metabolic rate vs. body mass has negative
hyperbolic? slope
Factor Change Impact on MR
Body Mass Increase Increases (but is not
proportional)
Food Increase Increases (SDA)
Activity Level Increase Increases
Temperature Increase Increases (in
ectotherms)
Age Increase Decreases (in
humans)
Reproductive State Active Increases
Hormones Increase (ex.
Thyroid)
Increases
Hypoxic
Environment
Low O2 Decreases
Time of Day
(circadian rhythms)
Becoming
more active
Increases
Metabolic Rate is impacted by many factors:
Arctic animals expend less energy to thermoregulate at cold
ambient temperatures, and can thermoregulate at lower
temperatures
!
Tropical species increase their metabolic rate more rapidly
in response to colder temperatures (sharper slope)
!
*see slide
!
Major adaptation: insulation
!
Note: animals have evolved to cope with temperature in different
parts of the planet
Allows them to generate heat
effectively
!
In newborns, BAT is found in discrete
regions
"
Brown adipose tissue (BAT) or brown fat is the
tissue involved in non-shivering thermogenesis
!
BAT is more vascularized to
deliver more O2 and help carry the
heat away
!
Vascularization
"
BAT contain more mitochondria
that tend to be larger --> more ATP
hydrolysis and heat produced
!
Mitochondria
"
Smaller in BAT
!
Size lipid droplet
"
Discrete deposits of BAT (usually
around neck, abdomen)
!
WAT is usually subcutaneous (in
abdomen)
!
Location
"
Brown colouration of BAT is due
to pigment
!
Yellowish colouration in WAT
!
Colour
"
WAT -diet
!
Acclimation to cold
increases content (in
mammals)
◊
Through development, BAT
content decreases with age
(in most mammals)
◊
Seasonal: hibernators
increase BAT content
◊
BAT
!
Change
"
Brown (vs. White) Adipose Tissue
!
ATP -energy currency of cell
"
*see figure on slide
"
Normal Cell: movement of H+ through ATP
synthase creates energy captured by ADP +
P --> ATP
!
Fat deposits --> free fatty acids + O2 (via
lipase)
"
O2 triggers movement of H+ across
mitochondrial membrane in oxidative
phosphorylation
"
Does not create ATP but creates
energy as heat when H+ lose their
charge through UCP
!
Mitochondrial membrane have
uncoupling protein or thermogenin (not
in normal cell) to move H+ into the cell
that creates HEAT
"
ATP synthase is present but is not used?
"
Generates 10x more heat than a normal
cell
"
BAT cells: heavily innervated from
sympathetic nervous system with
norepinephrine (bind to beta receptors on BAT
cell membrane)
!
BAT oxidative phosphorylation can be used for
hibernating arousal
!
*see figure
"
As the age of the reindeer
increases, the % change in O2
consumption with norepinephrine
decreases
!
Results:
"
Norepinephrine stimulates BAT
and increases the metabolic rate
!
Older animals show a decreased
response to norepinephrine
because non-shivering
thermogenesis and BAT decrease
with age
!
Conclusion:
"
Maximum change in rate of O2 consumption
(%) elicited by norepinephrine decreases
(hyperbolically) as reindeer age (0 days -30
days)
!
Non-shivering thermogenesis -futile cyclinga.
Involuntary contractions
!
High frequency with little net movement
!
Shivering*b.
Voluntary contractions
!
Inefficient reactions for heat is produced
!
Physical activity (movement)*c.
Digestion (SDA)d.
*these only last for a period of time (will become less
effective at generating heat; costly, burning through
fuel that is mostly muscle glycogen stores)
Increase Thermogenesis (heat produced)1.
Increase insulationa.
Huddlingb.
Counter-current heat exchangerc.
Peripheral vasoconstrictiond.
Drop in metabolic rate (in hibernators)e.
Decrease Heat Loss 2.
Strategies for Cold Tolerance in Endotherms
Will increase circulation to peripheral blood vessels to
increase heat loss while swimming
!
*seal has very thick layer of blubber
02/13/18
Asking a research question, then write a hypothesis and
prediction
1.
Explain multiple factors affecting heat loss in endotherms2.
Calculate Q10 or predict metabolic rate from Q10 data in
ectotherms
3.
Learning Outcomes:
Resting metabolic rate is significantly lower in
winter (vs. summer)
!
Steeper slope in metabolic rate in
summer at temperatures below the LCT
relative to winter
"
More constant metabolic rate in the winter
(decreases due to increasing air temperature
during the summer)
!
LCT is higher in the summer (~ 5C) than in the
winter (~ -30C)
!
Results:
○
Because the fur thickness is greater in the
winter, the animal is better insulated
!
Therefore, thermoregulation is more
energetically costly in the summer reindeer
!
Conclusion:
○
*See Figure 11.2
!
Question: Why does it require less energy to
thermoregulate in reindeers at 14 days relative to 1
days?
○
Hypothesis: Thermoregulation is more challenging in
newborn reindeer because they have less insulation
relative to older stages.
○
If so, then older individuals will have more
insulation (fur, fat), than newborns.
!
If so, then adding insulation (fur coat) to
newborns will lower the LCT and steepness of
the slope of the metabolic rate response.
!
Prediction:
○
*See resting MR vs. Air Temperature in the early life of
reindeer
!
Reindeer increase the thickness of their fur (--> guard hairs)
during winter to increase their insulation
Design an experiment to test this hypothesis
○
Start by writing a prediction
○
Explain your experimental design (How many
animals? Treatments? Protocol? Measurements?_
○
Expected result: draw a graph and label axes if
evidence for prediction
○
Penguins exposed to Antarctic winter temperatures (-30
to -40C) and high winds huddle to decrease heat loss
!
Possible Exam Question:
Colder blood in extremities --> smaller temperature
gradient between blood and environment so the
organism loses less heat
○
The arteries and veins are close together to allow
countercurrent heat exchange to occur
○
Therefore, the temperature of venous blood rises as
blood travels towards the body
○
Note: has to be followed by episodes of vasodilation
so tissues do not die by prevention of blood flow
(oscillating)
○
*see slide
!
Have red muscle (oxidative, used for swimming) into
the core of muscle body (usually in periphery)
○
Red muscle is generating heat
○
Usually this heat would be lost to environment
○
Venous blood carries this heat away and is then
transferred to arterial blood coming in
○
All heat is then captured in the muscle
○
Allows them to swim very fast for predatory
purposes
○
= regional heterothermy
○
Ex. Counter-current heat exchange in tuna muscle
!
Counter-current heat exchange permits restriction of heat flow to
appendages
When blood travels close to the surface of the animal, heat
is lost across the skin
!
When temperatures are cold, blood is diverted from the
skin through arteriovenous (AV) shunts = artiovenous
anastomes --> reducing heat loss
!
When an animal is in a hot environment, shunts are
constricted and blood moves through the vessels closer to
the skin surface, enhancing heat loss
!
Peripheral Vasoconstriction
*see figures on slide
!
Hummingbirds enter torpor at night
!
High MR relative to body size (increase SA:V) -->
lose heat faster than larger animals
○
Low air temperatures
○
Availability of food
○
Why do some small mammals hibernate/torpor? What are
the challenges in winter or overnight?
!
Body temp increases rapidly with arousal
○
While the groundhog was in hibernation, its body
temperature was almost equal to the ambient temperature
!
Temperature of soil in hibernaculum decreases over
time
○
Arousals -reboots brain
○
Brown fat is used for arousal --> increases body
temperature very quickly
○
Only conscious for 12 days during whole winter
○
Active Hibernati
ng
Body
Temp.
37C -3.0C
(supercoo
ling)
Can
supercool
Heart Rate 250 bpm 6 bpm 42 fold
decrease
Respiration
Frequency
100
breaths/m
in
6
breaths/m
in
17 fold
decrease
Metabolic
Rate
100% 4% 25 fold
decrease
Fluctuate between short and long arousals
○
Arctic ground squirrels have periodic arousals over
hibernation
!
Do not thermal conform -some regulation occurs
○
When ambient temperature is far below 0C,
metabolic rate production is elevated to keep body
temperature from falling close to the ambient
temperature
○
When the ambient temperature is above 0C,
metabolic rate is minimal, and the body temperature
virtually matches the ambient temperature (if in
TNZ)
○
*See slide: Metabolic Rate & Body Temperature vs.
Ambient Temperature
!
Hibernation and Daily Torpor
The Arctic woolly caterpillar will freeze completely for
years and thaw when ambient temperatures increase
!
O2 uptake (metabolic rate) increases linearly with ambient
temperature = thermo-conformer
!
Heart rate
!
Respiration rate
!
Enzyme activity rate
!
Aka how much change is observed in metabolic rate
with 10C temperature change
○
Q10 = Rate at T / Rate at T-10
○
*note Q10 ~ 2 is normal (will be larger if animals
hibernate or enter torpor)
○
Temperature coefficient = Q10
!
Metabolic rate at 15C = 8 mL O2/hour
!
Metabolic rate at 5C = 2 mL O2/hour
!
Q10 = 8/2 = 4
!
What is the Q10 of the woolly caterpillar?
○
3.0 = x / 100
!
Therefore, metabolic rate at 20C is 300
mL O2/g/hr
"
X = 3*100 = 300 mL O2/g/h
!
If the tiger moth caterpillar has a Q10 of 3.0 and
metabolic rate at 10C is 100 mL O2/g/h, then what is
the metabolic rate at 20C?
○
Questions:
!
Ectotherms:
Behavioural thermoregulation
!
Regional heterothermy
!
Ectotherms conform to environmental temperatures (generally),
however there are a few exceptions:
Kinetic energy increases with
temperature
"
Weak bonds (H-H) change, temperature
changes ionization state of water
"
Active site (amino acids with charges)
can change with temperature -->
substrate binding may change
"
Conformational changes requires
flexibility in molecule (temperature
changes can alter flexibility of protein or
enzyme)
"
Temperature changes enzymes kinetics
because:
!
Enzymes
○
Lipids
○
Temperature affects molecules, macromolecules, cells,
tissues
!
Ectotherms can experience temperature changes, resulting in big
physiological changes
02/15/18
Describe the influence of temperature change on enzymes
and cell membrane lipids
1.
Provide examples of animals that are freeze tolerant vs
intolerant and discuss strategies for survival in sub-zero
temperatures
2.
Learning Outcomes:
Goes through freeze-thaw winter-summer cycle
!
Enzymes need to function properly in short summer so they
can eat, grow and reproduce
!
Lipids in cell membranes are strongly influenced by
temperature changes
○
Cell membranes must also have integrity across a range of
temperatures
!
Ex. Woolly Caterpillar
Pyruvate (substrate) ---> lactate (product) via LDH
(NADH --> NAD+)
!
Conformational change occurs when it binds NADH and
pyruvate in the activate site
!
His193 and Arg-171 form weak bonds with pyruvate in
active site
!
Temperature can affect the active site and how things bind
!
Lactate Dehydrogenase (LDH)
Ectotherms have similar affinities at the temperature
of the environment where they usually reside
○
Enzyme-substrate affinity decreases with increasing
temperature in individual organisms
!
They have evolved different forms of LDH
(homologs)
○
How do animals maintain the affinity (Km) of LDH for the
substrate at different temperatures?
!
Alter the expression of different homologs
!
Change concentration of enzyme (gene
transcription changes that lead to changes in
protein translation --> new proteins)
!
Phenotypic plasticity --> acclimatization responses
between seasons
○
How do animals maintain the activity (Vmax) of LDH at
different temperatures?
!
Enzyme-substrate affinity (Km) is kept ~constant at the body
temperature of the natural habitat
*see slide
!
Polar heads on outside with non-polar fatty acid chains
inside
!
Acute decrease in temperature --> rigid membrane
with decreased fluidity (gel state)
○
Change head group
!
More double bonds, less packing, more space
(increase unsaturation)
!
Shorter FA tails, more mobile
!
Acclimation to colder temperature to increase
fluidity:
○
**remember we are talking about cell membranes
mostly of ectotherms, but some endotherms also have
decreased body temperature (heterothermy) and the
same processes would occur
○
Maintenance of a relative constant membrane fluidity
regardless of tissue temperature is called homeoviscous
adaptation
!
Lipid bilayer membrane fluidity is approximately the same
at natural body temp (is conserved)
!
Lipid bilayer membrane of cells:
Freezing point of seawater = -1.6 C
"
Freezing point of freshwater = 0C
!
If water is cooled to less than freezing point
with agitation, seed crystals, nucleators it is
said to be: supercooled
!
As ice forms, osmotic pressure increases
in the extracellular fluid
"
Protects against further freezing by
decreasing the freezing point
"
As water leaves down the osmotic
pressure gradient (cell--> ECF) there will
be an increase in the osmotic pressure of
the intracellular fluid, which also protects
against freezing by lowering the freezing
point
"
*see process of extracellular freezing in a
tissue
!
Intracellular ice formation almost always
kills the cell, and is therefore most often
fatal for animals
"
Extracellular ice formation can be
tolerated if the formation is controlled
"
Nucleating proteins lower freezing point
"
Ice nucleating agents (INA) = dissolved or
undissolved substance that promotes freezing
(e.g. macromolecules, calcium salts, membrane
components, microbes)
!
Freeze Tolerance1.
Ex. Turtles below the ice
"
Many ectotherms behaviourally avoid
environments where freezing conditions exist
!
Other animals can survive aquatic or terrestrial
sub-zero temperature by producing antifreeze
compounds
!
Properties of a solute that are due
solely to the concentration or
number of solute
particles/molecules
!
Ex. Glucose, glycerol, NaCl
!
Colligative
"
Properties of a solute that do not
relate to concentration but to the
chemical nature of the compound
!
Ex. AFP, AFGP
!
Non-colligative
"
AFP:
!
They bind along the face of the ice
crystal, where the protein forms weak
bonds with water molecules immobilized
in the ice crystal
"
Because ice growth is very orderly, the
presence of the bound protein prevents
ice crystal growth
"
Antifreeze protein bind to the surface of ice
crystals to prevent their growth
!
The freezing point decreases as the
plasma antifreeze concentration increases
(ex. In flounder)
"
Non-colligative Antifreeze Compounds:
!
Normal state = thermal hysteresis is zero
"
Antifreeze proteins cause the thermal
hysteresis gap to increase
"
Decreases freezing point
"
Thermal hysteresis is higher in spiders
and insects relative to fish
"
Thermal hysteresis is the difference between
freezing and melting temperatures
!
Freeze Avoidance 2.
EcothermsA)
Strategies for Cold Tolerance
Typically stay frozen all winter
!
Promote freezing in extracellular fluid by increasing ice
nucleating agents (INA)
!
Make glucose increase --> decrease freezing point and
stabilize macromolecules
!
Ex. Wood Frog
Produce ice nucleating agents (INA) to control where ice
forms (extracellular space)
1.
Extracellular ice formation is slow when controlled around
the site of an ice nucleating agent
2.
Increase concentration of organic osmolites (such as
glucose, trehalose, glycerol, sorbitol) -also colligative
solutes
3.
How do animals (such as woolly caterpillars) control ice
formation?
*convergent evolution of AFGP in Antarctic notothenoid fish and
Arctic cod
Woolly Caterpillar --> freeze tolerant
Arctic Cod --> freeze intolerant
Metabolism & Thermoregulation
#$%&'()*+, -./&%)&*, 0+,1203
0425,67
Write open-ended research questions leading to hypotheses1.
Explain how MR changes with body size2.
Draw graphs depicting relationship between environmental
and body temperatures
3.
Learning Outcomes:
First scientists weren't just looking for answers, they were
looking for good explanations
!
Logical
○
Not arbitrary
○
Internally consistent
○
Consistent with what we already know
○
Often able to make unexpected predictions
○
Good explanations are:
!
Aristotle
Ask a question --> come up with possible answers --> try to
disprove the answers
!
Where did like on Earth come from?
○
How can hibernating squirrels supercool without
freezing?
○
Why do some cold water fish species make antifreeze
proteins and other species do not?
○
Why is there variation in the length of time
amphibious fishes stay out of water?
○
Good questions are tough, open-ended questions
!
How does Science work?
Observe
!
Question
!
Hypothesis
!
Prediction(s)
!
Experiment(s)
!
Analyze & Conclude
!
Scientific Method:
Better: Why do deep sea animals have high
concentrations of organic osmolytes (e.g. TMAO) in
their blood and tissues?
○
Bad: What is the relationship between organic osmolytes
and water depth in ocean fishes?
!
Does it provide a satisfying possible answer to the
question asked?
○
Is it internally consistent?
○
Is it consistent with what we already know?
○
Does it pass the raised eyebrow test?
○
Quality Control for hypotheses and predictions:
!
Applying scientific method leads us to better and
better explanations
○
Scientific method was designed to help answer open-
ended questions
○
Hypotheses must explain the original observation
○
Predictions must be logical consequences of the
hypothesis and have the potential to disprove it
○
Imagination and creativity drive good science
○
Key points:
!
Applying the Scientific Method to these questions that don't
demand an explanation usually results in confusion.
What stages of development are shortened by an
increase in temperature during incubation?
○
Why can geckos that hatch later (incubated at lower
temperatures) withstand greater range of
temperature?
○
*How does temperature impact performance during
early development?
○
Possible Research Questions:
!
Activity: Gecko youngsters more at risk after incubating during a
heat wave
What is 'known', summarize previous findings that led to
current study
!
What is 'unknown', experiments are often based on
unanswered questions generated by earlier studies
!
Dissect each figure before reading text describing that
figure, use your own words (this helps you to interpret the
data independent of author's interpretation)
!
*see worksheet to prepare for assignment
Arctic animals face many challenges during the long, cold
dark winter months
!
Many different strategies have evolved to cope with low
temperature and/or lack of food during winter
!
Muskox, arctic fox, ground squirrels, ptarmigan, arctic cod,
and woolly caterpillars are some of the animals that survive
in the Canadian arctic
!
How do very cold temperatures impact these organisms?
!
What strategies are employed to survive arctic winter?
!
Metabolism & Thermoregulation
Endotherm: own production of metabolic heat used to
regulate body temperature
!
Ectotherm: environment influences body temperature
!
Homeotherm: thermoregulates by physiological means
!
Poikilothem: variable body temperature with environmental
change
!
Heterothem: regional/temporal (ex. Hibernating mammal)
!
Review:
Ex. A rhino that is 6x larger than a vole,
does not eat 6x less
"
NOT proportional --> more complex
relationship
!
Log -Log Plot
"
Y axis = mass-specific metabolic rate
"
Note:
!
Metabolic rate (e.g. O2 consumption) decreases with
increasing body mass (in vertebrates)
○
logMR = log a + b*logW
!
Advantage of a log-log plot is that one can
have a big range of numbers all on one graph
!
Weight specific MR = a*Weight(b-1) *a power
function relation
○
Surface 'law' stated that MR is
proportional to body-surface area and
related to maintaining a 37C body temp
(in mammals)
"
As animal gets bigger, ratio
decreases
!
Therefore, a smaller animal loses
heat faster than a larger animal
!
SA/volume is not proportional
"
*does not explain relationship between
metabolic rate and body mass in
ectotherms
"
Max Rubner (1900s)
!
All organisms show allometric relationship, not
just mammals
!
Has now been some-what
discredited
!
Fractal theory -related to transporting
material to/from cells
"
Multiple-causes theory -there are many
underlying processes
"
Other theories:
!
The explanation for allometric metabolism-weight
relations remains unknown
○
Body SizeA)
Body temperature also increases
"
Metabolic rate or oxygen uptake increases as
they digest food (and then declines post-
digestion)
!
*see slide
!
SDA = specific dynamic action
○
Food Intake & DigestionB)
Metabolic rate is affected by many factors:
02/06/18
Draw graphs depicting changes in MR with temperature1.
Explain the mechanisms that endotherms use to generate
heat in detail
2.
Write the results section for a graph on early development
of thermogenesis, draw a conclusion
3.
Learning Outcomes:
Allometry: pattern of change in a parameter (e.g. MR) with
change in body size
!
a,b = constants
○
W = weights
○
Allometric Equation: MR = a*Wb
!
O2 uptake or O2 consumption (mL O2/hr)
○
Heat produced (e.g. J/hr or kcal/hr)
○
Metabolic Rate:
!
Log-log plot
!
As body size increases, the amount of oxygen
consumption (per gram of tissue) decreases
!
Weight specific MR has a negative slop with body
mass
○
Weight-specific Metabolic Rate: amount of O2 consumed
or heat produced per gram or kilogram of body mass (e.g.
mL O1/hr/g or J/h/kg)
!
Terms:
Melting of ice --> heat produced
!
=direct calorimetry (oxygen uptake would be indirect
calorimetry)
!
Note: metabolic rate was first measured by putting animal within
a chamber covered in ice
Relationship is observed in all organisms
(unicellular/mutlicellular, ectotherm/endotherm)
!
*see slide
!
Log-log plot
!
Metabolic rate vs. body mass has a positive slop (~0.75)
Not a log-log plot
!
*see slide
!
Weight-specific metabolic rate vs. body mass has negative
hyperbolic? slope
Factor Change Impact on MR
Body Mass Increase Increases (but is not
proportional)
Food Increase Increases (SDA)
Activity Level Increase Increases
Temperature Increase Increases (in
ectotherms)
Age Increase Decreases (in
humans)
Reproductive State Active Increases
Hormones Increase (ex.
Thyroid)
Increases
Hypoxic
Environment
Low O2 Decreases
Time of Day
(circadian rhythms)
Becoming
more active
Increases
Metabolic Rate is impacted by many factors:
Arctic animals expend less energy to thermoregulate at cold
ambient temperatures, and can thermoregulate at lower
temperatures
!
Tropical species increase their metabolic rate more rapidly
in response to colder temperatures (sharper slope)
!
*see slide
!
Major adaptation: insulation
!
Note: animals have evolved to cope with temperature in different
parts of the planet
Allows them to generate heat
effectively
!
In newborns, BAT is found in discrete
regions
"
Brown adipose tissue (BAT) or brown fat is the
tissue involved in non-shivering thermogenesis
!
BAT is more vascularized to
deliver more O2 and help carry the
heat away
!
Vascularization
"
BAT contain more mitochondria
that tend to be larger --> more ATP
hydrolysis and heat produced
!
Mitochondria
"
Smaller in BAT
!
Size lipid droplet
"
Discrete deposits of BAT (usually
around neck, abdomen)
!
WAT is usually subcutaneous (in
abdomen)
!
Location
"
Brown colouration of BAT is due
to pigment
!
Yellowish colouration in WAT
!
Colour
"
WAT -diet
!
Acclimation to cold
increases content (in
mammals)
◊
Through development, BAT
content decreases with age
(in most mammals)
◊
Seasonal: hibernators
increase BAT content
◊
BAT
!
Change
"
Brown (vs. White) Adipose Tissue
!
ATP -energy currency of cell
"
*see figure on slide
"
Normal Cell: movement of H+ through ATP
synthase creates energy captured by ADP +
P --> ATP
!
Fat deposits --> free fatty acids + O2 (via
lipase)
"
O2 triggers movement of H+ across
mitochondrial membrane in oxidative
phosphorylation
"
Does not create ATP but creates
energy as heat when H+ lose their
charge through UCP
!
Mitochondrial membrane have
uncoupling protein or thermogenin (not
in normal cell) to move H+ into the cell
that creates HEAT
"
ATP synthase is present but is not used?
"
Generates 10x more heat than a normal
cell
"
BAT cells: heavily innervated from
sympathetic nervous system with
norepinephrine (bind to beta receptors on BAT
cell membrane)
!
BAT oxidative phosphorylation can be used for
hibernating arousal
!
*see figure
"
As the age of the reindeer
increases, the % change in O2
consumption with norepinephrine
decreases
!
Results:
"
Norepinephrine stimulates BAT
and increases the metabolic rate
!
Older animals show a decreased
response to norepinephrine
because non-shivering
thermogenesis and BAT decrease
with age
!
Conclusion:
"
Maximum change in rate of O2 consumption
(%) elicited by norepinephrine decreases
(hyperbolically) as reindeer age (0 days -30
days)
!
Non-shivering thermogenesis -futile cyclinga.
Involuntary contractions
!
High frequency with little net movement
!
Shivering*b.
Voluntary contractions
!
Inefficient reactions for heat is produced
!
Physical activity (movement)*c.
Digestion (SDA)d.
*these only last for a period of time (will become less
effective at generating heat; costly, burning through
fuel that is mostly muscle glycogen stores)
Increase Thermogenesis (heat produced)1.
Increase insulationa.
Huddlingb.
Counter-current heat exchangerc.
Peripheral vasoconstrictiond.
Drop in metabolic rate (in hibernators)e.
Decrease Heat Loss 2.
Strategies for Cold Tolerance in Endotherms
Will increase circulation to peripheral blood vessels to
increase heat loss while swimming
!
*seal has very thick layer of blubber
02/13/18
Asking a research question, then write a hypothesis and
prediction
1.
Explain multiple factors affecting heat loss in endotherms2.
Calculate Q10 or predict metabolic rate from Q10 data in
ectotherms
3.
Learning Outcomes:
Resting metabolic rate is significantly lower in
winter (vs. summer)
!
Steeper slope in metabolic rate in
summer at temperatures below the LCT
relative to winter
"
More constant metabolic rate in the winter
(decreases due to increasing air temperature
during the summer)
!
LCT is higher in the summer (~ 5C) than in the
winter (~ -30C)
!
Results:
○
Because the fur thickness is greater in the
winter, the animal is better insulated
!
Therefore, thermoregulation is more
energetically costly in the summer reindeer
!
Conclusion:
○
*See Figure 11.2
!
Question: Why does it require less energy to
thermoregulate in reindeers at 14 days relative to 1
days?
○
Hypothesis: Thermoregulation is more challenging in
newborn reindeer because they have less insulation
relative to older stages.
○
If so, then older individuals will have more
insulation (fur, fat), than newborns.
!
If so, then adding insulation (fur coat) to
newborns will lower the LCT and steepness of
the slope of the metabolic rate response.
!
Prediction:
○
*See resting MR vs. Air Temperature in the early life of
reindeer
!
Reindeer increase the thickness of their fur (--> guard hairs)
during winter to increase their insulation
Design an experiment to test this hypothesis
○
Start by writing a prediction
○
Explain your experimental design (How many
animals? Treatments? Protocol? Measurements?_
○
Expected result: draw a graph and label axes if
evidence for prediction
○
Penguins exposed to Antarctic winter temperatures (-30
to -40C) and high winds huddle to decrease heat loss
!
Possible Exam Question:
Colder blood in extremities --> smaller temperature
gradient between blood and environment so the
organism loses less heat
○
The arteries and veins are close together to allow
countercurrent heat exchange to occur
○
Therefore, the temperature of venous blood rises as
blood travels towards the body
○
Note: has to be followed by episodes of vasodilation
so tissues do not die by prevention of blood flow
(oscillating)
○
*see slide
!
Have red muscle (oxidative, used for swimming) into
the core of muscle body (usually in periphery)
○
Red muscle is generating heat
○
Usually this heat would be lost to environment
○
Venous blood carries this heat away and is then
transferred to arterial blood coming in
○
All heat is then captured in the muscle
○
Allows them to swim very fast for predatory
purposes
○
= regional heterothermy
○
Ex. Counter-current heat exchange in tuna muscle
!
Counter-current heat exchange permits restriction of heat flow to
appendages
When blood travels close to the surface of the animal, heat
is lost across the skin
!
When temperatures are cold, blood is diverted from the
skin through arteriovenous (AV) shunts = artiovenous
anastomes --> reducing heat loss
!
When an animal is in a hot environment, shunts are
constricted and blood moves through the vessels closer to
the skin surface, enhancing heat loss
!
Peripheral Vasoconstriction
*see figures on slide
!
Hummingbirds enter torpor at night
!
High MR relative to body size (increase SA:V) -->
lose heat faster than larger animals
○
Low air temperatures
○
Availability of food
○
Why do some small mammals hibernate/torpor? What are
the challenges in winter or overnight?
!
Body temp increases rapidly with arousal
○
While the groundhog was in hibernation, its body
temperature was almost equal to the ambient temperature
!
Temperature of soil in hibernaculum decreases over
time
○
Arousals -reboots brain
○
Brown fat is used for arousal --> increases body
temperature very quickly
○
Only conscious for 12 days during whole winter
○
Active Hibernati
ng
Body
Temp.
37C -3.0C
(supercoo
ling)
Can
supercool
Heart Rate 250 bpm 6 bpm 42 fold
decrease
Respiration
Frequency
100
breaths/m
in
6
breaths/m
in
17 fold
decrease
Metabolic
Rate
100% 4% 25 fold
decrease
Fluctuate between short and long arousals
○
Arctic ground squirrels have periodic arousals over
hibernation
!
Do not thermal conform -some regulation occurs
○
When ambient temperature is far below 0C,
metabolic rate production is elevated to keep body
temperature from falling close to the ambient
temperature
○
When the ambient temperature is above 0C,
metabolic rate is minimal, and the body temperature
virtually matches the ambient temperature (if in
TNZ)
○
*See slide: Metabolic Rate & Body Temperature vs.
Ambient Temperature
!
Hibernation and Daily Torpor
The Arctic woolly caterpillar will freeze completely for
years and thaw when ambient temperatures increase
!
O2 uptake (metabolic rate) increases linearly with ambient
temperature = thermo-conformer
!
Heart rate
!
Respiration rate
!
Enzyme activity rate
!
Aka how much change is observed in metabolic rate
with 10C temperature change
○
Q10 = Rate at T / Rate at T-10
○
*note Q10 ~ 2 is normal (will be larger if animals
hibernate or enter torpor)
○
Temperature coefficient = Q10
!
Metabolic rate at 15C = 8 mL O2/hour
!
Metabolic rate at 5C = 2 mL O2/hour
!
Q10 = 8/2 = 4
!
What is the Q10 of the woolly caterpillar?
○
3.0 = x / 100
!
Therefore, metabolic rate at 20C is 300
mL O2/g/hr
"
X = 3*100 = 300 mL O2/g/h
!
If the tiger moth caterpillar has a Q10 of 3.0 and
metabolic rate at 10C is 100 mL O2/g/h, then what is
the metabolic rate at 20C?
○
Questions:
!
Ectotherms:
Behavioural thermoregulation
!
Regional heterothermy
!
Ectotherms conform to environmental temperatures (generally),
however there are a few exceptions:
Kinetic energy increases with
temperature
"
Weak bonds (H-H) change, temperature
changes ionization state of water
"
Active site (amino acids with charges)
can change with temperature -->
substrate binding may change
"
Conformational changes requires
flexibility in molecule (temperature
changes can alter flexibility of protein or
enzyme)
"
Temperature changes enzymes kinetics
because:
!
Enzymes
○
Lipids
○
Temperature affects molecules, macromolecules, cells,
tissues
!
Ectotherms can experience temperature changes, resulting in big
physiological changes
02/15/18
Describe the influence of temperature change on enzymes
and cell membrane lipids
1.
Provide examples of animals that are freeze tolerant vs
intolerant and discuss strategies for survival in sub-zero
temperatures
2.
Learning Outcomes:
Goes through freeze-thaw winter-summer cycle
!
Enzymes need to function properly in short summer so they
can eat, grow and reproduce
!
Lipids in cell membranes are strongly influenced by
temperature changes
○
Cell membranes must also have integrity across a range of
temperatures
!
Ex. Woolly Caterpillar
Pyruvate (substrate) ---> lactate (product) via LDH
(NADH --> NAD+)
!
Conformational change occurs when it binds NADH and
pyruvate in the activate site
!
His193 and Arg-171 form weak bonds with pyruvate in
active site
!
Temperature can affect the active site and how things bind
!
Lactate Dehydrogenase (LDH)
Ectotherms have similar affinities at the temperature
of the environment where they usually reside
○
Enzyme-substrate affinity decreases with increasing
temperature in individual organisms
!
They have evolved different forms of LDH
(homologs)
○
How do animals maintain the affinity (Km) of LDH for the
substrate at different temperatures?
!
Alter the expression of different homologs
!
Change concentration of enzyme (gene
transcription changes that lead to changes in
protein translation --> new proteins)
!
Phenotypic plasticity --> acclimatization responses
between seasons
○
How do animals maintain the activity (Vmax) of LDH at
different temperatures?
!
Enzyme-substrate affinity (Km) is kept ~constant at the body
temperature of the natural habitat
*see slide
!
Polar heads on outside with non-polar fatty acid chains
inside
!
Acute decrease in temperature --> rigid membrane
with decreased fluidity (gel state)
○
Change head group
!
More double bonds, less packing, more space
(increase unsaturation)
!
Shorter FA tails, more mobile
!
Acclimation to colder temperature to increase
fluidity:
○
**remember we are talking about cell membranes
mostly of ectotherms, but some endotherms also have
decreased body temperature (heterothermy) and the
same processes would occur
○
Maintenance of a relative constant membrane fluidity
regardless of tissue temperature is called homeoviscous
adaptation
!
Lipid bilayer membrane fluidity is approximately the same
at natural body temp (is conserved)
!
Lipid bilayer membrane of cells:
Freezing point of seawater = -1.6 C
"
Freezing point of freshwater = 0C
!
If water is cooled to less than freezing point
with agitation, seed crystals, nucleators it is
said to be: supercooled
!
As ice forms, osmotic pressure increases
in the extracellular fluid
"
Protects against further freezing by
decreasing the freezing point
"
As water leaves down the osmotic
pressure gradient (cell--> ECF) there will
be an increase in the osmotic pressure of
the intracellular fluid, which also protects
against freezing by lowering the freezing
point
"
*see process of extracellular freezing in a
tissue
!
Intracellular ice formation almost always
kills the cell, and is therefore most often
fatal for animals
"
Extracellular ice formation can be
tolerated if the formation is controlled
"
Nucleating proteins lower freezing point
"
Ice nucleating agents (INA) = dissolved or
undissolved substance that promotes freezing
(e.g. macromolecules, calcium salts, membrane
components, microbes)
!
Freeze Tolerance1.
Ex. Turtles below the ice
"
Many ectotherms behaviourally avoid
environments where freezing conditions exist
!
Other animals can survive aquatic or terrestrial
sub-zero temperature by producing antifreeze
compounds
!
Properties of a solute that are due
solely to the concentration or
number of solute
particles/molecules
!
Ex. Glucose, glycerol, NaCl
!
Colligative
"
Properties of a solute that do not
relate to concentration but to the
chemical nature of the compound
!
Ex. AFP, AFGP
!
Non-colligative
"
AFP:
!
They bind along the face of the ice
crystal, where the protein forms weak
bonds with water molecules immobilized
in the ice crystal
"
Because ice growth is very orderly, the
presence of the bound protein prevents
ice crystal growth
"
Antifreeze protein bind to the surface of ice
crystals to prevent their growth
!
The freezing point decreases as the
plasma antifreeze concentration increases
(ex. In flounder)
"
Non-colligative Antifreeze Compounds:
!
Normal state = thermal hysteresis is zero
"
Antifreeze proteins cause the thermal
hysteresis gap to increase
"
Decreases freezing point
"
Thermal hysteresis is higher in spiders
and insects relative to fish
"
Thermal hysteresis is the difference between
freezing and melting temperatures
!
Freeze Avoidance 2.
EcothermsA)
Strategies for Cold Tolerance
Typically stay frozen all winter
!
Promote freezing in extracellular fluid by increasing ice
nucleating agents (INA)
!
Make glucose increase --> decrease freezing point and
stabilize macromolecules
!
Ex. Wood Frog
Produce ice nucleating agents (INA) to control where ice
forms (extracellular space)
1.
Extracellular ice formation is slow when controlled around
the site of an ice nucleating agent
2.
Increase concentration of organic osmolites (such as
glucose, trehalose, glycerol, sorbitol) -also colligative
solutes
3.
How do animals (such as woolly caterpillars) control ice
formation?
*convergent evolution of AFGP in Antarctic notothenoid fish and
Arctic cod
Woolly Caterpillar --> freeze tolerant
Arctic Cod --> freeze intolerant
Metabolism & Thermoregulation
#$%&'()*+, -./&%)&*, 0+,1203 0425,67
Write open-ended research questions leading to hypotheses1.
Explain how MR changes with body size2.
Draw graphs depicting relationship between environmental
and body temperatures
3.
Learning Outcomes:
First scientists weren't just looking for answers, they were
looking for good explanations
!
Logical
○
Not arbitrary
○
Internally consistent
○
Consistent with what we already know
○
Often able to make unexpected predictions
○
Good explanations are:
!
Aristotle
Ask a question --> come up with possible answers --> try to
disprove the answers
!
Where did like on Earth come from?
○
How can hibernating squirrels supercool without
freezing?
○
Why do some cold water fish species make antifreeze
proteins and other species do not?
○
Why is there variation in the length of time
amphibious fishes stay out of water?
○
Good questions are tough, open-ended questions
!
How does Science work?
Observe
!
Question
!
Hypothesis
!
Prediction(s)
!
Experiment(s)
!
Analyze & Conclude
!
Scientific Method:
Better: Why do deep sea animals have high
concentrations of organic osmolytes (e.g. TMAO) in
their blood and tissues?
○
Bad: What is the relationship between organic osmolytes
and water depth in ocean fishes?
!
Does it provide a satisfying possible answer to the
question asked?
○
Is it internally consistent?
○
Is it consistent with what we already know?
○
Does it pass the raised eyebrow test?
○
Quality Control for hypotheses and predictions:
!
Applying scientific method leads us to better and
better explanations
○
Scientific method was designed to help answer open-
ended questions
○
Hypotheses must explain the original observation
○
Predictions must be logical consequences of the
hypothesis and have the potential to disprove it
○
Imagination and creativity drive good science
○
Key points:
!
Applying the Scientific Method to these questions that don't
demand an explanation usually results in confusion.
What stages of development are shortened by an
increase in temperature during incubation?
○
Why can geckos that hatch later (incubated at lower
temperatures) withstand greater range of
temperature?
○
*How does temperature impact performance during
early development?
○
Possible Research Questions:
!
Activity: Gecko youngsters more at risk after incubating during a
heat wave
What is 'known', summarize previous findings that led to
current study
!
What is 'unknown', experiments are often based on
unanswered questions generated by earlier studies
!
Dissect each figure before reading text describing that
figure, use your own words (this helps you to interpret the
data independent of author's interpretation)
!
*see worksheet to prepare for assignment
Arctic animals face many challenges during the long, cold
dark winter months
!
Many different strategies have evolved to cope with low
temperature and/or lack of food during winter
!
Muskox, arctic fox, ground squirrels, ptarmigan, arctic cod,
and woolly caterpillars are some of the animals that survive
in the Canadian arctic
!
How do very cold temperatures impact these organisms?
!
What strategies are employed to survive arctic winter?
!
Metabolism & Thermoregulation
Endotherm: own production of metabolic heat used to
regulate body temperature
!
Ectotherm: environment influences body temperature
!
Homeotherm: thermoregulates by physiological means
!
Poikilothem: variable body temperature with environmental
change
!
Heterothem: regional/temporal (ex. Hibernating mammal)
!
Review:
Ex. A rhino that is 6x larger than a vole,
does not eat 6x less
"
NOT proportional --> more complex
relationship
!
Log -Log Plot
"
Y axis = mass-specific metabolic rate
"
Note:
!
Metabolic rate (e.g. O2 consumption) decreases with
increasing body mass (in vertebrates)
○
logMR = log a + b*logW
!
Advantage of a log-log plot is that one can
have a big range of numbers all on one graph
!
Weight specific MR = a*Weight(b-1) *a power
function relation
○
Surface 'law' stated that MR is
proportional to body-surface area and
related to maintaining a 37C body temp
(in mammals)
"
As animal gets bigger, ratio
decreases
!
Therefore, a smaller animal loses
heat faster than a larger animal
!
SA/volume is not proportional
"
*does not explain relationship between
metabolic rate and body mass in
ectotherms
"
Max Rubner (1900s)
!
All organisms show allometric relationship, not
just mammals
!
Has now been some-what
discredited
!
Fractal theory -related to transporting
material to/from cells
"
Multiple-causes theory -there are many
underlying processes
"
Other theories:
!
The explanation for allometric metabolism-weight
relations remains unknown
○
Body Size
A)
Body temperature also increases
"
Metabolic rate or oxygen uptake increases as
they digest food (and then declines post-
digestion)
!
*see slide
!
SDA = specific dynamic action
○
Food Intake & DigestionB)
Metabolic rate is affected by many factors:
02/06/18
Draw graphs depicting changes in MR with temperature1.
Explain the mechanisms that endotherms use to generate
heat in detail
2.
Write the results section for a graph on early development
of thermogenesis, draw a conclusion
3.
Learning Outcomes:
Allometry: pattern of change in a parameter (e.g. MR) with
change in body size
!
a,b = constants
○
W = weights
○
Allometric Equation: MR = a*Wb
!
O2 uptake or O2 consumption (mL O2/hr)
○
Heat produced (e.g. J/hr or kcal/hr)
○
Metabolic Rate:
!
Log-log plot
!
As body size increases, the amount of oxygen
consumption (per gram of tissue) decreases
!
Weight specific MR has a negative slop with body
mass
○
Weight-specific Metabolic Rate: amount of O2 consumed
or heat produced per gram or kilogram of body mass (e.g.
mL O1/hr/g or J/h/kg)
!
Terms:
Melting of ice --> heat produced
!
=direct calorimetry (oxygen uptake would be indirect
calorimetry)
!
Note: metabolic rate was first measured by putting animal within
a chamber covered in ice
Relationship is observed in all organisms
(unicellular/mutlicellular, ectotherm/endotherm)
!
*see slide
!
Log-log plot
!
Metabolic rate vs. body mass has a positive slop (~0.75)
Not a log-log plot
!
*see slide
!
Weight-specific metabolic rate vs. body mass has negative
hyperbolic? slope
Factor Change Impact on MR
Body Mass Increase Increases (but is not
proportional)
Food Increase Increases (SDA)
Activity Level Increase Increases
Temperature Increase Increases (in
ectotherms)
Age Increase Decreases (in
humans)
Reproductive State Active Increases
Hormones Increase (ex.
Thyroid)
Increases
Hypoxic
Environment
Low O2 Decreases
Time of Day
(circadian rhythms)
Becoming
more active
Increases
Metabolic Rate is impacted by many factors:
Arctic animals expend less energy to thermoregulate at cold
ambient temperatures, and can thermoregulate at lower
temperatures
!
Tropical species increase their metabolic rate more rapidly
in response to colder temperatures (sharper slope)
!
*see slide
!
Major adaptation: insulation
!
Note: animals have evolved to cope with temperature in different
parts of the planet
Allows them to generate heat
effectively
!
In newborns, BAT is found in discrete
regions
"
Brown adipose tissue (BAT) or brown fat is the
tissue involved in non-shivering thermogenesis
!
BAT is more vascularized to
deliver more O2 and help carry the
heat away
!
Vascularization
"
BAT contain more mitochondria
that tend to be larger --> more ATP
hydrolysis and heat produced
!
Mitochondria
"
Smaller in BAT
!
Size lipid droplet
"
Discrete deposits of BAT (usually
around neck, abdomen)
!
WAT is usually subcutaneous (in
abdomen)
!
Location
"
Brown colouration of BAT is due
to pigment
!
Yellowish colouration in WAT
!
Colour
"
WAT -diet
!
Acclimation to cold
increases content (in
mammals)
◊
Through development, BAT
content decreases with age
(in most mammals)
◊
Seasonal: hibernators
increase BAT content
◊
BAT
!
Change
"
Brown (vs. White) Adipose Tissue
!
ATP -energy currency of cell
"
*see figure on slide
"
Normal Cell: movement of H+ through ATP
synthase creates energy captured by ADP +
P --> ATP
!
Fat deposits --> free fatty acids + O2 (via
lipase)
"
O2 triggers movement of H+ across
mitochondrial membrane in oxidative
phosphorylation
"
Does not create ATP but creates
energy as heat when H+ lose their
charge through UCP
!
Mitochondrial membrane have
uncoupling protein or thermogenin (not
in normal cell) to move H+ into the cell
that creates HEAT
"
ATP synthase is present but is not used?
"
Generates 10x more heat than a normal
cell
"
BAT cells: heavily innervated from
sympathetic nervous system with
norepinephrine (bind to beta receptors on BAT
cell membrane)
!
BAT oxidative phosphorylation can be used for
hibernating arousal
!
*see figure
"
As the age of the reindeer
increases, the % change in O2
consumption with norepinephrine
decreases
!
Results:
"
Norepinephrine stimulates BAT
and increases the metabolic rate
!
Older animals show a decreased
response to norepinephrine
because non-shivering
thermogenesis and BAT decrease
with age
!
Conclusion:
"
Maximum change in rate of O2 consumption
(%) elicited by norepinephrine decreases
(hyperbolically) as reindeer age (0 days -30
days)
!
Non-shivering thermogenesis -futile cyclinga.
Involuntary contractions
!
High frequency with little net movement
!
Shivering*b.
Voluntary contractions
!
Inefficient reactions for heat is produced
!
Physical activity (movement)*c.
Digestion (SDA)d.
*these only last for a period of time (will become less
effective at generating heat; costly, burning through
fuel that is mostly muscle glycogen stores)
Increase Thermogenesis (heat produced)1.
Increase insulationa.
Huddlingb.
Counter-current heat exchangerc.
Peripheral vasoconstrictiond.
Drop in metabolic rate (in hibernators)e.
Decrease Heat Loss 2.
Strategies for Cold Tolerance in Endotherms
Will increase circulation to peripheral blood vessels to
increase heat loss while swimming
!
*seal has very thick layer of blubber
02/13/18
Asking a research question, then write a hypothesis and
prediction
1.
Explain multiple factors affecting heat loss in endotherms2.
Calculate Q10 or predict metabolic rate from Q10 data in
ectotherms
3.
Learning Outcomes:
Resting metabolic rate is significantly lower in
winter (vs. summer)
!
Steeper slope in metabolic rate in
summer at temperatures below the LCT
relative to winter
"
More constant metabolic rate in the winter
(decreases due to increasing air temperature
during the summer)
!
LCT is higher in the summer (~ 5C) than in the
winter (~ -30C)
!
Results:
○
Because the fur thickness is greater in the
winter, the animal is better insulated
!
Therefore, thermoregulation is more
energetically costly in the summer reindeer
!
Conclusion:
○
*See Figure 11.2
!
Question: Why does it require less energy to
thermoregulate in reindeers at 14 days relative to 1
days?
○
Hypothesis: Thermoregulation is more challenging in
newborn reindeer because they have less insulation
relative to older stages.
○
If so, then older individuals will have more
insulation (fur, fat), than newborns.
!
If so, then adding insulation (fur coat) to
newborns will lower the LCT and steepness of
the slope of the metabolic rate response.
!
Prediction:
○
*See resting MR vs. Air Temperature in the early life of
reindeer
!
Reindeer increase the thickness of their fur (--> guard hairs)
during winter to increase their insulation
Design an experiment to test this hypothesis
○
Start by writing a prediction
○
Explain your experimental design (How many
animals? Treatments? Protocol? Measurements?_
○
Expected result: draw a graph and label axes if
evidence for prediction
○
Penguins exposed to Antarctic winter temperatures (-30
to -40C) and high winds huddle to decrease heat loss
!
Possible Exam Question:
Colder blood in extremities --> smaller temperature
gradient between blood and environment so the
organism loses less heat
○
The arteries and veins are close together to allow
countercurrent heat exchange to occur
○
Therefore, the temperature of venous blood rises as
blood travels towards the body
○
Note: has to be followed by episodes of vasodilation
so tissues do not die by prevention of blood flow
(oscillating)
○
*see slide
!
Have red muscle (oxidative, used for swimming) into
the core of muscle body (usually in periphery)
○
Red muscle is generating heat
○
Usually this heat would be lost to environment
○
Venous blood carries this heat away and is then
transferred to arterial blood coming in
○
All heat is then captured in the muscle
○
Allows them to swim very fast for predatory
purposes
○
= regional heterothermy
○
Ex. Counter-current heat exchange in tuna muscle
!
Counter-current heat exchange permits restriction of heat flow to
appendages
When blood travels close to the surface of the animal, heat
is lost across the skin
!
When temperatures are cold, blood is diverted from the
skin through arteriovenous (AV) shunts = artiovenous
anastomes --> reducing heat loss
!
When an animal is in a hot environment, shunts are
constricted and blood moves through the vessels closer to
the skin surface, enhancing heat loss
!
Peripheral Vasoconstriction
*see figures on slide
!
Hummingbirds enter torpor at night
!
High MR relative to body size (increase SA:V) -->
lose heat faster than larger animals
○
Low air temperatures
○
Availability of food
○
Why do some small mammals hibernate/torpor? What are
the challenges in winter or overnight?
!
Body temp increases rapidly with arousal
○
While the groundhog was in hibernation, its body
temperature was almost equal to the ambient temperature
!
Temperature of soil in hibernaculum decreases over
time
○
Arousals -reboots brain
○
Brown fat is used for arousal --> increases body
temperature very quickly
○
Only conscious for 12 days during whole winter
○
Active Hibernati
ng
Body
Temp.
37C -3.0C
(supercoo
ling)
Can
supercool
Heart Rate 250 bpm 6 bpm 42 fold
decrease
Respiration
Frequency
100
breaths/m
in
6
breaths/m
in
17 fold
decrease
Metabolic
Rate
100% 4% 25 fold
decrease
Fluctuate between short and long arousals
○
Arctic ground squirrels have periodic arousals over
hibernation
!
Do not thermal conform -some regulation occurs
○
When ambient temperature is far below 0C,
metabolic rate production is elevated to keep body
temperature from falling close to the ambient
temperature
○
When the ambient temperature is above 0C,
metabolic rate is minimal, and the body temperature
virtually matches the ambient temperature (if in
TNZ)
○
*See slide: Metabolic Rate & Body Temperature vs.
Ambient Temperature
!
Hibernation and Daily Torpor
The Arctic woolly caterpillar will freeze completely for
years and thaw when ambient temperatures increase
!
O2 uptake (metabolic rate) increases linearly with ambient
temperature = thermo-conformer
!
Heart rate
!
Respiration rate
!
Enzyme activity rate
!
Aka how much change is observed in metabolic rate
with 10C temperature change
○
Q10 = Rate at T / Rate at T-10
○
*note Q10 ~ 2 is normal (will be larger if animals
hibernate or enter torpor)
○
Temperature coefficient = Q10
!
Metabolic rate at 15C = 8 mL O2/hour
!
Metabolic rate at 5C = 2 mL O2/hour
!
Q10 = 8/2 = 4
!
What is the Q10 of the woolly caterpillar?
○
3.0 = x / 100
!
Therefore, metabolic rate at 20C is 300
mL O2/g/hr
"
X = 3*100 = 300 mL O2/g/h
!
If the tiger moth caterpillar has a Q10 of 3.0 and
metabolic rate at 10C is 100 mL O2/g/h, then what is
the metabolic rate at 20C?
○
Questions:
!
Ectotherms:
Behavioural thermoregulation
!
Regional heterothermy
!
Ectotherms conform to environmental temperatures (generally),
however there are a few exceptions:
Kinetic energy increases with
temperature
"
Weak bonds (H-H) change, temperature
changes ionization state of water
"
Active site (amino acids with charges)
can change with temperature -->
substrate binding may change
"
Conformational changes requires
flexibility in molecule (temperature
changes can alter flexibility of protein or
enzyme)
"
Temperature changes enzymes kinetics
because:
!
Enzymes
○
Lipids
○
Temperature affects molecules, macromolecules, cells,
tissues
!
Ectotherms can experience temperature changes, resulting in big
physiological changes
02/15/18
Describe the influence of temperature change on enzymes
and cell membrane lipids
1.
Provide examples of animals that are freeze tolerant vs
intolerant and discuss strategies for survival in sub-zero
temperatures
2.
Learning Outcomes:
Goes through freeze-thaw winter-summer cycle
!
Enzymes need to function properly in short summer so they
can eat, grow and reproduce
!
Lipids in cell membranes are strongly influenced by
temperature changes
○
Cell membranes must also have integrity across a range of
temperatures
!
Ex. Woolly Caterpillar
Pyruvate (substrate) ---> lactate (product) via LDH
(NADH --> NAD+)
!
Conformational change occurs when it binds NADH and
pyruvate in the activate site
!
His193 and Arg-171 form weak bonds with pyruvate in
active site
!
Temperature can affect the active site and how things bind
!
Lactate Dehydrogenase (LDH)
Ectotherms have similar affinities at the temperature
of the environment where they usually reside
○
Enzyme-substrate affinity decreases with increasing
temperature in individual organisms
!
They have evolved different forms of LDH
(homologs)
○
How do animals maintain the affinity (Km) of LDH for the
substrate at different temperatures?
!
Alter the expression of different homologs
!
Change concentration of enzyme (gene
transcription changes that lead to changes in
protein translation --> new proteins)
!
Phenotypic plasticity --> acclimatization responses
between seasons
○
How do animals maintain the activity (Vmax) of LDH at
different temperatures?
!
Enzyme-substrate affinity (Km) is kept ~constant at the body
temperature of the natural habitat
*see slide
!
Polar heads on outside with non-polar fatty acid chains
inside
!
Acute decrease in temperature --> rigid membrane
with decreased fluidity (gel state)
○
Change head group
!
More double bonds, less packing, more space
(increase unsaturation)
!
Shorter FA tails, more mobile
!
Acclimation to colder temperature to increase
fluidity:
○
**remember we are talking about cell membranes
mostly of ectotherms, but some endotherms also have
decreased body temperature (heterothermy) and the
same processes would occur
○
Maintenance of a relative constant membrane fluidity
regardless of tissue temperature is called homeoviscous
adaptation
!
Lipid bilayer membrane fluidity is approximately the same
at natural body temp (is conserved)
!
Lipid bilayer membrane of cells:
Freezing point of seawater = -1.6 C
"
Freezing point of freshwater = 0C
!
If water is cooled to less than freezing point
with agitation, seed crystals, nucleators it is
said to be: supercooled
!
As ice forms, osmotic pressure increases
in the extracellular fluid
"
Protects against further freezing by
decreasing the freezing point
"
As water leaves down the osmotic
pressure gradient (cell--> ECF) there will
be an increase in the osmotic pressure of
the intracellular fluid, which also protects
against freezing by lowering the freezing
point
"
*see process of extracellular freezing in a
tissue
!
Intracellular ice formation almost always
kills the cell, and is therefore most often
fatal for animals
"
Extracellular ice formation can be
tolerated if the formation is controlled
"
Nucleating proteins lower freezing point
"
Ice nucleating agents (INA) = dissolved or
undissolved substance that promotes freezing
(e.g. macromolecules, calcium salts, membrane
components, microbes)
!
Freeze Tolerance1.
Ex. Turtles below the ice
"
Many ectotherms behaviourally avoid
environments where freezing conditions exist
!
Other animals can survive aquatic or terrestrial
sub-zero temperature by producing antifreeze
compounds
!
Properties of a solute that are due
solely to the concentration or
number of solute
particles/molecules
!
Ex. Glucose, glycerol, NaCl
!
Colligative
"
Properties of a solute that do not
relate to concentration but to the
chemical nature of the compound
!
Ex. AFP, AFGP
!
Non-colligative
"
AFP:
!
They bind along the face of the ice
crystal, where the protein forms weak
bonds with water molecules immobilized
in the ice crystal
"
Because ice growth is very orderly, the
presence of the bound protein prevents
ice crystal growth
"
Antifreeze protein bind to the surface of ice
crystals to prevent their growth
!
The freezing point decreases as the
plasma antifreeze concentration increases
(ex. In flounder)
"
Non-colligative Antifreeze Compounds:
!
Normal state = thermal hysteresis is zero
"
Antifreeze proteins cause the thermal
hysteresis gap to increase
"
Decreases freezing point
"
Thermal hysteresis is higher in spiders
and insects relative to fish
"
Thermal hysteresis is the difference between
freezing and melting temperatures
!
Freeze Avoidance 2.
EcothermsA)
Strategies for Cold Tolerance
Typically stay frozen all winter
!
Promote freezing in extracellular fluid by increasing ice
nucleating agents (INA)
!
Make glucose increase --> decrease freezing point and
stabilize macromolecules
!
Ex. Wood Frog
Produce ice nucleating agents (INA) to control where ice
forms (extracellular space)
1.
Extracellular ice formation is slow when controlled around
the site of an ice nucleating agent
2.
Increase concentration of organic osmolites (such as
glucose, trehalose, glycerol, sorbitol) -also colligative
solutes
3.
How do animals (such as woolly caterpillars) control ice
formation?
*convergent evolution of AFGP in Antarctic notothenoid fish and
Arctic cod
Woolly Caterpillar --> freeze tolerant
Arctic Cod --> freeze intolerant
Metabolism & Thermoregulation
#$%&'()*+, -./&%)&*, 0+,1203 0425,67
Document Summary
Draw graphs depicting relationship between environmental and body temperatures. First scientists weren"t just looking for answers, they were looking for good explanations. Ask a question --> come up with possible answers --> try to disprove the answers. Applying the scientific method to these questions that don"t demand an explanation usually results in confusion. Applying scientific method leads us to better and better explanations. Scientific method was designed to help answer open- ended questions. Predictions must be logical consequences of the hypothesis and have the potential to disprove it. Activity: gecko youngsters more at risk after incubating during a heat wave. What is "known", summarize previous findings that led to current study. What is "unknown", experiments are often based on unanswered questions generated by earlier studies. Dissect each figure before reading text describing that figure, use your own words (this helps you to interpret the figure, use your own words (this helps you to interpret the data independent of author"s interpretation)