ZOO 3200 Lecture 2: Membranes
2 May 2018
School
Department
Course
Professor
Overview of membrane structure -comparative aspects
•
Temperature and membrane fluidity
•
Metabolic rate and membranes
•
Diet and exercise and membranes
•
Other factors affecting membranes
•
Outline:
Chapter 2 (pages 31-40)
•
Chapter 6 (pages 132-133)
•
Chapter 10 (page 246)
•
Chapter 28 (pages 719, 738-739)
•
Reading:
All animals have a lipid bilayer membrane that separates the
intracellular from the extracellular fluid
•
The membranes contain peripheral and integral membrane proteins
•
Myelin sheath: 81% lipid and 20% protein *used mostly as an
insulator
○
Mitochondrial membranes: 20-50% lipid and 50-80% protein
*have larger protein
○
The % lipid: protein ratio and protein composition varies according to
function
•
The membrane is a fluid mosaic
•
Plasma membrane
A)
Mitochondrial inner and outer membranes
B)
Nuclear membrane
C)
Endoplasmic reticulum (rough and smooth)
D)
Golgi
E)
Lysosome
F)
Peroxisome
G)
Types of membranes:
•
Intercellular joinings
○
Enzymatic activity
○
Transport (active/passive)
○
Cell-cell recognition
○
Anchorage/attachment
○
Signal transduction
○
Types of membrane protein functions:
•
E.g. phospholipid cardiolipin (CDL) binds to cytochrome oxidase
○
Some membrane proteins require certain phospholipids for activity
•
Amphipathic molecules
!
Polar head (choline + phosphate) -Glycerol
Residue -Nonpolar tails (2 FA)
□
E.g. Phosphatidyl Choline:
!
DOPC = dioleoylphosphatidyl choline
□
DSPC = distearoylphosphatidyl choline
□
DPPC = dipalmitoyl phosphatidyl choline
□
There may be different charger on headgroups and different
acyl chains
!
This allows considerable flexibility in designing
different membranes for different functions under
various environmental conditions
□
*thousands of combinations are possible
Phospholipids
○
Has complex membrane properties
!
Interaction of cholesterol with polar head fills the gaps
(between polar heads) causing membrane permeability (for
small molecules like water/urea) to decrease
!
Cholesterol
○
Lipids in membranes:
•
Lipid rafts are regions that accumulate cholesterol and glycolipids
○
These regions are more rigid and preferentially recruit specific
proteins that are involved in signaling pathways
○
Occurs in the plasma membrane, Golgi apparatus and
lysosomes
!
Lipid rafts readily move in the plasma membrane
○
Membrane rafts:
•
Lipid composition varies across the two leaflets of the same
membrane
○
Changes in distribution have biological consequences
○
Phosphatidylserine exposure also act as a marker for
programmed cell death
!
Platelet is able to play its role in clot formation only when
phosphatidylserine moves to the outer leaflet
○
Membrane Asymmetry:
•
Temperature
○
Metabolic rate
○
Diet
○
Exercise
○
Factors that affect/correlate with the lipid composition of membranes:
•
Overview of Membranes
Warm temperatures make the phospholipid bilayer more fluid
(liquid crystalline state)
○
Cold temperatures make the phospholipid molecules more rigid (gel
state)
•
The liquid crystalline state is the norm at physiological temperatures
•
Ex. Although the gills of tuna and icefish play the same basic
functions, they must function at very different temperatures
○
The membranes are maintained at various fluidity at different
temperatures
○
As environmental temperature varies, homeostatic changes to the
phospholipids of cell membranes are needed to allow membranes to
retain their fluidity (homeoviscous adaptation)
•
Widespread through various vertebrates
○
Fluidity is kept relatively constant at the respective ordinary body
temperatures of the species by evolution of different membrane
phospholipid compositions
○
Homeoviscous adaptation of membranes:
•
Acyl chain length
○
Number of double bonds in acyl chains
○
Position of double bonds in acyl chains
○
Phospholipid head groups
○
Cholesterol content
○
Membrane melting temperature is a function of:
•
Shortening fatty acid chain length (rare)
○
Un-saturating fatty acid chain length
○
Changing the polar head group: phosphatidylcholine (PC) -
phosphatidylethanolamine (PE)
○
Acclimatizing membrane to cold temperatures (increasing fluidity):
•
Cholesterol decreases fluidity (increases order) in the liquid-
crystalline phase
○
Rigid steroid ring system limits motions of FA chains
○
Cholesterol increases fluidity (decreases order) in the gel phase
○
Changes to membrane fluidity:
•
% of unsaturated hydrocarbon tails are higher in antarctic species
compared to tropical species
○
*note: phosphatidylethanoamines have a higher % compared to
phosphatidylcholines
○
The degree of unsaturation of the hydrocarbon tails of brain
phospholipids in fish varies with habitat temperature
•
Temperature & Membrane Fluidity
Mammals have higher metabolic rates compared to amphibians and
reptiles
•
There are fewer pumps that are more effective (higher
molecular activity)
!
Higher Na pump activity in mammals compared to amphibians
(in both kidney and brain)
○
Suggests that lipids are different and may be partly
responsible for differences in the activity of the sodium
pump
!
Amphibian membranes have more saturated fatty acids
(compared to mammals) at the same temperature
○
Decrease in molecular activity in the sodium pump (in
kidney and brain) for rat
!
Increase in molecular activity in the sodium pump for toad
!
Lipid swapping experiment:
○
*Therefore, membrane phospholipids have influences on the
activity of the membrane pump
A substantial part of resting metabolic rate is due to the sodium pump
(22%) via ATPase
•
E.g. with binding of ATP
○
Conformational changes will occur more slowly in colder
temperatures
○
Membrane proteins can undergo conformational changes
•
Membranes & Metabolism
The rate of myocardial infarction in Greenland Inuit was much lower
than that in Denmark even though the fat intake and serum cholesterol
levels were comparable or higher (increased bleeding time by 70%)
•
n3=omega3='w'3
○
n3&n6 = plants and bacteria
○
n9 = plants, bacteria and animal
○
Fatty acid desaturation:
•
Danes: low omega 3, high omega 6 (lower cholesterol)
○
Innuits: high omega 3, low omega 6 (higher cholesterol)
•
Higher n3 intake (eicosapentenoic acid) --> decreased
cardiovascular mortality
○
Higher n6 intake (arachidonic acid) --> increased cardiovascular
mortality
•
Mechanism of action of omega 3 & 6 fatty acids:
•
Slower clotting time in Inuits
○
•
Dietary omega-3 FA correlate with HDL levels and inversely
correlate with fasting plasma insulin levels, insulin resistance,
postprandial glucose levels, plasma TG levels and diastolic BP
○
Omega 3 --> decreased inflammation --> decreased oxidative
stress --> increased insulin sensitivity
○
Alaskan Inuit have a lower prevalence of insulin resistance, metabolic
syndrome and type 2 diabetes than western populations
•
Diet and Membrane Proteins
Eats Corophium volutator before migration (in refueling stop)
with 31% omega 3 as EPA (20:5) and 14% omega 3 as DHA
(22:6)
○
They are incorporating these FA as muscle rather than fat
○
Fluidity
!
Permeability
!
n3/n6 ratio
!
Local protein environment
!
Affects membrane:
○
*this activates key membrane-bound enzymes of oxidative
metabolism
Semipalmated sandpiper (longest non-stop flight; 4500km in 3 days)
•
Diet & Migration (exercise)
Membranes allow partitioning of molecules in different compartments
and affect the function of membrane functions
•
Membranes are dynamic structures that change in response to various
factors
•
Summary:
Membranes
Tuesday,+ September+ 12,+2017
1:02+PM
Overview of membrane structure -comparative aspects
•
Temperature and membrane fluidity
•
Metabolic rate and membranes
•
Diet and exercise and membranes
•
Other factors affecting membranes
•
Outline:
Chapter 2 (pages 31-40)
•
Chapter 6 (pages 132-133)
•
Chapter 10 (page 246)
•
Chapter 28 (pages 719, 738-739)
•
Reading:
All animals have a lipid bilayer membrane that separates the
intracellular from the extracellular fluid
•
The membranes contain peripheral and integral membrane proteins
•
Myelin sheath: 81% lipid and 20% protein *used mostly as an
insulator
○
Mitochondrial membranes: 20-50% lipid and 50-80% protein
*have larger protein
○
The % lipid: protein ratio and protein composition varies according to
function
•
The membrane is a fluid mosaic
•
Plasma membraneA)
Mitochondrial inner and outer membranesB)
Nuclear membraneC)
Endoplasmic reticulum (rough and smooth)D)
GolgiE)
LysosomeF)
Peroxisome G)
Types of membranes:
•
Intercellular joinings
○
Enzymatic activity
○
Transport (active/passive)
○
Cell-cell recognition
○
Anchorage/attachment
○
Signal transduction
○
Types of membrane protein functions:
•
E.g. phospholipid cardiolipin (CDL) binds to cytochrome oxidase
○
Some membrane proteins require certain phospholipids for activity
•
Amphipathic molecules
!
Polar head (choline + phosphate) -Glycerol
Residue -Nonpolar tails (2 FA)
□
E.g. Phosphatidyl Choline:
!
DOPC = dioleoylphosphatidyl choline
□
DSPC = distearoylphosphatidyl choline
□
DPPC = dipalmitoyl phosphatidyl choline
□
There may be different charger on headgroups and different
acyl chains
!
This allows considerable flexibility in designing
different membranes for different functions under
various environmental conditions
□
*thousands of combinations are possible
Phospholipids
○
Has complex membrane properties
!
Interaction of cholesterol with polar head fills the gaps
(between polar heads) causing membrane permeability (for
small molecules like water/urea) to decrease
!
Cholesterol
○
Lipids in membranes:
•
Lipid rafts are regions that accumulate cholesterol and glycolipids
○
These regions are more rigid and preferentially recruit specific
proteins that are involved in signaling pathways
○
Occurs in the plasma membrane, Golgi apparatus and
lysosomes
!
Lipid rafts readily move in the plasma membrane
○
Membrane rafts:
•
Lipid composition varies across the two leaflets of the same
membrane
○
Changes in distribution have biological consequences
○
Phosphatidylserine exposure also act as a marker for
programmed cell death
!
Platelet is able to play its role in clot formation only when
phosphatidylserine moves to the outer leaflet
○
Membrane Asymmetry:
•
Temperature
○
Metabolic rate
○
Diet
○
Exercise
○
Factors that affect/correlate with the lipid composition of membranes:
•
Overview of Membranes
Warm temperatures make the phospholipid bilayer more fluid
(liquid crystalline state)
○
Cold temperatures make the phospholipid molecules more rigid (gel
state)
•
The liquid crystalline state is the norm at physiological temperatures
•
Ex. Although the gills of tuna and icefish play the same basic
functions, they must function at very different temperatures
○
The membranes are maintained at various fluidity at different
temperatures
○
As environmental temperature varies, homeostatic changes to the
phospholipids of cell membranes are needed to allow membranes to
retain their fluidity (homeoviscous adaptation)
•
Widespread through various vertebrates
○
Fluidity is kept relatively constant at the respective ordinary body
temperatures of the species by evolution of different membrane
phospholipid compositions
○
Homeoviscous adaptation of membranes:
•
Acyl chain length
○
Number of double bonds in acyl chains
○
Position of double bonds in acyl chains
○
Phospholipid head groups
○
Cholesterol content
○
Membrane melting temperature is a function of:
•
Shortening fatty acid chain length (rare)
○
Un-saturating fatty acid chain length
○
Changing the polar head group: phosphatidylcholine (PC) -
phosphatidylethanolamine (PE)
○
Acclimatizing membrane to cold temperatures (increasing fluidity):
•
Cholesterol decreases fluidity (increases order) in the liquid-
crystalline phase
○
Rigid steroid ring system limits motions of FA chains
○
Cholesterol increases fluidity (decreases order) in the gel phase
○
Changes to membrane fluidity:
•
% of unsaturated hydrocarbon tails are higher in antarctic species
compared to tropical species
○
*note: phosphatidylethanoamines have a higher % compared to
phosphatidylcholines
○
The degree of unsaturation of the hydrocarbon tails of brain
phospholipids in fish varies with habitat temperature
•
Temperature & Membrane Fluidity
Mammals have higher metabolic rates compared to amphibians and
reptiles
•
There are fewer pumps that are more effective (higher
molecular activity)
!
Higher Na pump activity in mammals compared to amphibians
(in both kidney and brain)
○
Suggests that lipids are different and may be partly
responsible for differences in the activity of the sodium
pump
!
Amphibian membranes have more saturated fatty acids
(compared to mammals) at the same temperature
○
Decrease in molecular activity in the sodium pump (in
kidney and brain) for rat
!
Increase in molecular activity in the sodium pump for toad
!
Lipid swapping experiment:
○
*Therefore, membrane phospholipids have influences on the
activity of the membrane pump
A substantial part of resting metabolic rate is due to the sodium pump
(22%) via ATPase
•
E.g. with binding of ATP
○
Conformational changes will occur more slowly in colder
temperatures
○
Membrane proteins can undergo conformational changes
•
Membranes & Metabolism
The rate of myocardial infarction in Greenland Inuit was much lower
than that in Denmark even though the fat intake and serum cholesterol
levels were comparable or higher (increased bleeding time by 70%)
•
n3=omega3='w'3
○
n3&n6 = plants and bacteria
○
n9 = plants, bacteria and animal
○
Fatty acid desaturation:
•
Danes: low omega 3, high omega 6 (lower cholesterol)
○
Innuits: high omega 3, low omega 6 (higher cholesterol)
•
Higher n3 intake (eicosapentenoic acid) --> decreased
cardiovascular mortality
○
Higher n6 intake (arachidonic acid) --> increased cardiovascular
mortality
•
Mechanism of action of omega 3 & 6 fatty acids:
•
Slower clotting time in Inuits
○
•
Dietary omega-3 FA correlate with HDL levels and inversely
correlate with fasting plasma insulin levels, insulin resistance,
postprandial glucose levels, plasma TG levels and diastolic BP
○
Omega 3 --> decreased inflammation --> decreased oxidative
stress --> increased insulin sensitivity
○
Alaskan Inuit have a lower prevalence of insulin resistance, metabolic
syndrome and type 2 diabetes than western populations
•
Diet and Membrane Proteins
Eats Corophium volutator before migration (in refueling stop)
with 31% omega 3 as EPA (20:5) and 14% omega 3 as DHA
(22:6)
○
They are incorporating these FA as muscle rather than fat
○
Fluidity
!
Permeability
!
n3/n6 ratio
!
Local protein environment
!
Affects membrane:
○
*this activates key membrane-bound enzymes of oxidative
metabolism
Semipalmated sandpiper (longest non-stop flight; 4500km in 3 days)
•
Diet & Migration (exercise)
Membranes allow partitioning of molecules in different compartments
and affect the function of membrane functions
•
Membranes are dynamic structures that change in response to various
factors
•
Summary:
Membranes
Tuesday,+ September+ 12,+2017 1:02+PM
Document Summary
All animals have a lipid bilayer membrane that separates the intracellular from the extracellular fluid. The membranes contain peripheral and integral membrane proteins. The % lipid: protein ratio and protein composition varies according to function. Myelin sheath: 81% lipid and 20% protein *used mostly as an insulator. Some membrane proteins require certain phospholipids for activity. E. g. phospholipid cardiolipin (cdl) binds to cytochrome oxidase. There may be different charger on headgroups and different acyl chains. This allows considerable flexibility in designing different membranes for different functions under various environmental conditions. Interaction of cholesterol with polar head fills the gaps (between polar heads) causing membrane permeability (for small molecules like water/urea) to decrease. Lipid rafts are regions that accumulate cholesterol and glycolipids. These regions are more rigid and preferentially recruit specific proteins that are involved in signaling pathways. Lipid rafts readily move in the plasma membrane. Occurs in the plasma membrane, golgi apparatus and lysosomes.
