NUTR 2105 Lecture 7: Chapter 8 Metabolism
1 May 2018
School
Department
Course
Professor
Metabolism
Sum of all chemical reactions in the body
Chemical reactions follow metabolic pathways where compounds
are converted to new compounds
§
○
Energy is stored in the bonds that connect the molecules that make up
carbs, proteins, and fats
○
Energy is released when the bonds are broken. This occurs w/:
Aerobic (w/ oxygen) rx's
§
Anaerobic (w/o oxygen) rx's
§
Macronutrients need certain environments
§
○
To meet the body's constant energy supply, metabolism never stops
○
Metabolism processes adapt to meet individual needs and the
environment
○
Stages of metabolism
○
-
Metabolism Takes Places w/in Cells
Different cells perform diff metabolic functions
○
Each cell's structure is similar
Outside of cell
Plasma membrane: holds in the cell contents
□
§
Inside of cell is where metabolism occurs
Organelles
Mitochondria: powerhouse of the cell (generates most
of cell's energy from carb, protein, and fats)
®
Energy is generated by aerobic metabolism
®
□
Cytosol
Fluid portion of cell
®
Anaerobic metabolism
®
□
§
○
-
Liver Plays a Central Role in Metabolism (for mastering: most metabolically
active organ in the body)
Liver is the most metabolically active organ in the body
○
First organ to metabolize, store, and distribute nutrients after absorption
○
Converts monosaccharides, amino acids, glycerol, and fatty acids:
Into new compounds
§
Into energy
§
Or store them for future use
Triglycerides□
glycogen□
§
○
-
Metabolism Is a Series of Chemical Reactions
Metabolic pathways are sequences of reactions that convert compounds
from one form to another
○
Anabolic reactions: absorb energy/ make larger molecules
Glucose --> glycogen (gluconeogenesis)
§
Amino acids --> proteins
§
Fatty acids and glycerol --> triglycerides
§
○
Catabolic reactions: release energy/ break down molecules
glycogenolysis
§
○
-
Enzymes and Hormones Regulate Metabolism
Coenzymes assist enzymes
○
Hormones regulate anabolic and catabolic rx's
○
-
How does ATP Fuel Metabolism?
Before body can use energy from food, first has to disassemble
macronutrients into CO2and H2O while capturing released energy as
adenosine triphosphate (ATP)
Adenosine triphosphate (ATP): a high-energy molecule composed of
adenine, ribose, and 3 phosphate molecules
§
Any source of macronutrients can be used to generate ATP
§
ATP is the cell's direct energy source
§
Energy is stored in the bonds that connect the phosphate groups
§
The body must continually produce ATP to provide a constant
supply of energy
§
Adenosine diphosphate (ADP)
Formed □
§
○
ATP Can Be Regenerated from ADP and Creatine Phosphate
Regenerating ATP from ADP requires a source of phosphate
§
Sources
Inorganic phosphate produced from initial breakdown of ATP□
Inorganic phosphate in creatine phosphate (aka
phosphocreatine or PCr)
□
Both sources provide enough ATP to sustain a spring for 8 to
10 seconds
□
§
Creatine phosphate
High-energy compound in muscle cells when creatine
combines w/ phosphate
□
Phosphate molecule is released from ATP□
§
As creatine phosphate levels dwindle, the body switches to
anaerobic and aerobic metabolism to make ATP
§
Anaerobic metabolism
Produces more ATP per minute□
Only provides 1 to 1.5 mins of maximal activity□
Involved in high-intensity, short-duration activities, such as
sprinting and heavy weight lifting
□
§
Aerobic metabolism
Produce less ATP/ min□
Is able to produce ATP indefinitely□
Involved in low-intensity, long-duration activities□
When demand for ATP is greater than the rate of metabolism,
the activity slows down (this is the point/ key of training)
□
§
○
How Do the Macronutrients Provide ATP?
Carbs, fats, and proteins enter the metabolic pathways at some
point during the stages of metabolism
§
Major metabolic pathways
Glycolysis (stage 1)□
Pyruvate to acetyl CoA (stage 2)□
TCA stage (stage 3)□
Electron transport chain (stage 4)□
§
○
-
Glycolysis Transforms Glucose to Pyruvate
First step in forming ATP from glucose begins w/ glycolysis
○
Glucose metabolism is an essential energy source for all cells (remember
esp brain and red blood cells)
○
Glycolysis is a ten-step anaerobic catabolic pathway that takes place in
the cytosol of the cells
Begins w/ one six-carbon glucose molecule
§
Ends w/ 2 three-carbon molecules of pyruvate and 2 net molecules
of ATP
§
Glycolysis also generates 2 H+
§
Coenzyme NAD+ picks up hydrogen ions to form NADH
§
NADH carried hydrogen ions and electrons to the electron transport
chain
§
○
Other monosaccharides can also be used to produce ATP
○
Fructose and galactose
Just understand fed into glycolysis wherever needed
§
○
Pyruvate to lactate
Can happen anywhere in the body
§
During anaerobic metabolism, pyruvate reduced to lactate to
prevent buildup of excess H
§
Lactate diffuses out of cell and enters liver
§
Liver converts lactate to glucose via Cori cycle
§
2 different scenarios: do or don't have H
When burn, push a little further □
§
○
Cori cycle
Lactate converted to glucose in the liver
§
○
Glucogenic (can be used to make glucose) Amino Acids to Pyruvate
Glucogenic: anaerobically converted to glucose through
gluconeogenesis
□
Ketogenic: aerobically converted to glucose through acetyl
CoA when O is present
□
○
Glycerol to Pyruvate
Once glycerol portion of triglyceride is glucogenic, can be used to
make glucose
§
Glycerol produces v little energy compared w/ glucose, amino acids,
or fatty acids
§
○
Pyruvate is turned into Acetyl CoA when O is present
All energy-producing nutrients are transformed to acetyl CoA
before entering the TCA cycle
§
O must be present (occurs in the presence of O)
§
Two molecules of pyruvate cross the mitochondrial membrane and
enter the mitochondria
A carbon molecule and coenzyme A is added□
§
Acetyl CoA can enter 2 pathways
TCA cycle (if ATP is limited)□
Converted to fatty aid and stored as fat (ample ATP)□
§
2 molecules
§
○
Fatty Acids to Acetyl CoA
Hydrolyzed first from triglycerides by lipolysis before can be used
for energy
Hormone-sensitive lipase in adipose tissue catalyzes the rxn□
§
Fatty acids must be activated before they cross into the
mitochondria
§
The addition of coenzyme A to the carboxylic end of the fatty acid
chain activates the fatty acid
§
Once inside mitochondria, fatty acids are disassembled by beta-
oxidation
§
Beta-oxidation steps:
2 carbons at the end of the fatty acid are removed and joined
w/ CoA to form Acetyl CoA
□
This process continues until all carbon molecules are
converted
□
Hydrogen and electrons are released as each pair of carbon is
cleaved off
□
§
Fatty acids are ketogenic**
3 fatty acid chains and glycerol backbone□
Can be used to form ketone bodies□
§
and then fed into TCA cycle
§
○
Amino Acids to Acetyl CoA
Ketogenic amino acids
Leucine □
Lysine□
§
Both ketogenic and glucogenic amino acids
Isolecine□
Tryptophan□
Phenylanlanine□
Tyrosine□
§
Both ketogenic and glucogenic amino acids are transformed to
acetyl CoA before they enter the energy pathway**
§
○
-
Tricarboxylic Acid (TCA) Releases High-Energy Electrons and Hydrogen Ions
TCA cycle is the third stage for oxidation of acetyl CoA
○
Final stage in metabolism where then can make fatty acids
○
Location is in the mitochondria
○
These macronutrients enter the cycle as Acetyl CoA where most of the
energy in the OG molecule is now trapped
This stored energy is freed during the TCA cycle and is transferred
to two coenzyme hydrogen ion carriers to be released in the
electron transport chain
§
○
One molecule of acetyl CoA enters the TCA cycle at a time
○
For every acetyl CoA that enters the cycle, 2 carbons are lost as CO2
○
2NADH + H+and 1 FADH2are made during each turn of the cycle
Know first step need oxaloacetate (for TCA cycle to occur) and when
starving (especially depeletion of carbs) can't get this
§
○
-
Electron Transport Chain and Oxidative Phosphorylation Produces the Majority
of ATP
Comprised of a series of protein complexes located in the inner
mitochondrial membrane
○
Makes 90% of the ATP used by the body for energy, growth, and
maintenance
○
Electrons and transferred from one protein complex to another, resulting
in the formation of ATP and water
Protein complexes are called flavoproteins
Contain riboflavin and cytochromes□
Cytochromes contain iron and copper□
§
○
Though vitamins and minerals do not provide energy, they are essential
for energy production**
○
-
Overview of Metabolism
Absorptive v Postabsorptive states
Absorbptive (fed) state
Period w/in 4 hours following a meal in which anabolic
processes excess catabolic processes
□
§
Postabsorptive (fasted) state
Period of time usually more than 4 hours after eating□
Energy need are met by breakdown of stores□
§
Both are regulated by hormones
§
○
Carbs are stored as Glycogen
Red blood cells and CNS use prefer glucose but cannot store glucose
(so gotta store glycogen)
§
Liver and muscle convert glucose to glycogen w/ glycogenesis
§
Liver glycogen depleted 12 to 18 hours after eating
§
○
Excess carbs and amino acids stored as triglycerides
Excess glucose not stored as glycogen converted to triglycerides
25% of energy used for this conversion□
§
Excess amino acids not used by body converted to triglycerides
Amino acids undergo deamination and remaining carbons are
converted to acetyl CoA and then into fatty acids
□
§
○
Fatty acids stored as triglycerides
Excess cals in any form stored are triglyceride via lipogenesis
§
5% of energy converted to fatty acids to triglycerides
§
Dietary fat is easier to store as a triglyceride than dietary carb or
protein (that's why it's better to eat excess of other macronutrients
than fat b/c if eat extra fat will just go to fat but other
macronutrients can be used for other things)
§
Glucagon promotes lipolysis (break down of lipids [triglycerides] by
hydrolysis to release fatty acids and glycerol)
§
Insulin promotes fatty acid synthesis and inhibits lipolysis
§
○
During postabsorptive state, metabolism favors energy production
4 or more hours after eating, body meets energy needs from stored
energy
§
Stores are depleted during fasting
b/w meals and overnight
Energy via glycogen and fatty acids
®
□
After 18, the body adapts
Proteins, glycerol, pyruvate, and lactate are used to
make glucose
®
Lipolysis is increased
®
□
Prolonged fasting
Ketone bodies provide energy to brain
®
□
Severe fasting or starvation
Fat reserves are depleted
®
Muscle tissue is broken down to provide energy
®
□
§
○
Ketogenesis generates energy during prolonged fasting
Ketogenesis is the formation of ketone bodies
Occurs w/ the buildup of acetyl CoA□
Peaks after fasting or limited carb intake for 3 days□
Body uses this to slow down the body breaking down lean
body mass
□
§
As the fast continues the brain uses ketones for fuel
30% of fuel from ketones and 70% from blood glucose□
§
Ketoacidosis via excess accumulation of ketone bodies
Ketones are acidic□
Occurs w/ untreated type 1 diabetes□
Can lead to impaired heart activity, coma, and even death□
§
○
-
How does body metabolize alcohol?
7 cals/ g
○
Absorbed through stomach mucosa and intestinal lining
○
Metabolized by liver, about half oz/ 1.5 hours
○
Excess alc circulates throughout body until liver enzymes can break it
down
○
Excess alc is stored as fat
Fat metabolism is favored after alc consumption
§
Fewer fatty acids are used for energy when alc is consumed
§
Excess alc cals are stored as fatty acids in adipose tissue and liver
§
Alcoholics will have fat deposits in their liver
Can lead to cirrhosis□
Fat begins to accumulate after a single bout of drinking□
§
○
Enzymes that Metabolize Ethanol
Alcohol is metabolized through 3 distinct pathways
Alcohol dehydrogenase (ADH)
Present in the stomach and liver
®
Converts alcohol to acetyl CoA
Used to produce energy in TCA cycle
◊
Converted into fatty acids and stored as a
triglyceride
◊
®
□
Microsomal ethanol oxidizing system (MEOS)
Used during chronic alcohol consumption
®
Also metabolizes drugs
®
□
Brain
Catalase oxidizes alcohol to acetaldehyde
®
May be responsible for psychological effects
Reduced inhibitions
◊
®
□
§
○
-
Inborn Errors of Metabolism
Genetic conditions where lack enzyme that controls a specific metabolic
pathway
Results in the buildup of toxins
§
Cannot be cured
§
Cannot be controlled through diet
§
○
Phenylketonuria (PKU)
Unable to metabolize phenylalanine b/c enzyme phenylalanine
hydroxylase is lacking
§
Severe form
Can lead to behavior problems or mental retardation□
§
Mild to moderate conditions
Prevented by following a prescribed, controlled diet□
§
Treatment
Limited intake of phenylalanine□
Maintain adequate intake of tyrosine, energy, and protein□
Avoid foods and beverages w/ aspartame □
§
○
Maple syrup urine disease (MSUD)
Unable to metabolize branched-chain amino acids: leucine,
isoleucine, and valine
§
Untreated can lead to seizures, coma, and death
§
Treatment
Consume specifically designed formulas□
Avoid products like beef, chicken, fish, eggs, nuts, and
legumes
□
§
○
Homocystinuria
Unable to convert homocysteine to cystathione
§
Treatment
Diet low in amino acid methionine□
Supplement w/ B vitamins: folate, vitamin B6, and vitamin
B12
□
§
○
Galactosemia
Unable to convert galactose to glucose
§
Treatment
Avoid dietary lactose and galactose□
§
○
Glycogen storage disease
Unable to break down glycogen and provide glucose to muscle or
body
Treatment
Avoid foods w/ sucrose, lactose, galactose, and fructose
®
□
§
○
-
Chpt. 8 Metabolism
Monday, February 19, 2018
2:00 PM
Metabolism
Sum of all chemical reactions in the body
Chemical reactions follow metabolic pathways where compounds
are converted to new compounds
§
○
Energy is stored in the bonds that connect the molecules that make up
carbs, proteins, and fats
○
Energy is released when the bonds are broken. This occurs w/:
Aerobic (w/ oxygen) rx's
§
Anaerobic (w/o oxygen) rx's
§
Macronutrients need certain environments
§
○
To meet the body's constant energy supply, metabolism never stops
○
Metabolism processes adapt to meet individual needs and the
environment
○
Stages of metabolism
○
-
Metabolism Takes Places w/in Cells
Different cells perform diff metabolic functions
○
Each cell's structure is similar
Outside of cell
Plasma membrane: holds in the cell contents□
§
Inside of cell is where metabolism occurs
Organelles
Mitochondria: powerhouse of the cell (generates most
of cell's energy from carb, protein, and fats)
®
Energy is generated by aerobic metabolism
®
□
Cytosol
Fluid portion of cell
®
Anaerobic metabolism
®
□
§
○
-
Liver Plays a Central Role in Metabolism (for mastering: most metabolically
active organ in the body)
Liver is the most metabolically active organ in the body
○
First organ to metabolize, store, and distribute nutrients after absorption
○
Converts monosaccharides, amino acids, glycerol, and fatty acids:
Into new compounds
§
Into energy
§
Or store them for future use
Triglycerides
□
glycogen
□
§
○
-
Metabolism Is a Series of Chemical Reactions
Metabolic pathways are sequences of reactions that convert compounds
from one form to another
○
Anabolic reactions: absorb energy/ make larger molecules
Glucose --> glycogen (gluconeogenesis)
§
Amino acids --> proteins
§
Fatty acids and glycerol --> triglycerides
§
○
Catabolic reactions: release energy/ break down molecules
glycogenolysis
§
○
-
Enzymes and Hormones Regulate Metabolism
Coenzymes assist enzymes
○
Hormones regulate anabolic and catabolic rx's
○
-
How does ATP Fuel Metabolism?
Before body can use energy from food, first has to disassemble
macronutrients into CO2and H2O while capturing released energy as
adenosine triphosphate (ATP)
Adenosine triphosphate (ATP): a high-energy molecule composed of
adenine, ribose, and 3 phosphate molecules
§
Any source of macronutrients can be used to generate ATP
§
ATP is the cell's direct energy source
§
Energy is stored in the bonds that connect the phosphate groups
§
The body must continually produce ATP to provide a constant
supply of energy
§
Adenosine diphosphate (ADP)
Formed
□
§
○
ATP Can Be Regenerated from ADP and Creatine Phosphate
Regenerating ATP from ADP requires a source of phosphate
§
Sources
Inorganic phosphate produced from initial breakdown of ATP
□
Inorganic phosphate in creatine phosphate (aka
phosphocreatine or PCr)
□
Both sources provide enough ATP to sustain a spring for 8 to
10 seconds
□
§
Creatine phosphate
High-energy compound in muscle cells when creatine
combines w/ phosphate
□
Phosphate molecule is released from ATP□
§
As creatine phosphate levels dwindle, the body switches to
anaerobic and aerobic metabolism to make ATP
§
Anaerobic metabolism
Produces more ATP per minute□
Only provides 1 to 1.5 mins of maximal activity□
Involved in high-intensity, short-duration activities, such as
sprinting and heavy weight lifting
□
§
Aerobic metabolism
Produce less ATP/ min□
Is able to produce ATP indefinitely□
Involved in low-intensity, long-duration activities□
When demand for ATP is greater than the rate of metabolism,
the activity slows down (this is the point/ key of training)
□
§
○
How Do the Macronutrients Provide ATP?
Carbs, fats, and proteins enter the metabolic pathways at some
point during the stages of metabolism
§
Major metabolic pathways
Glycolysis (stage 1)□
Pyruvate to acetyl CoA (stage 2)□
TCA stage (stage 3)□
Electron transport chain (stage 4)□
§
○
-
Glycolysis Transforms Glucose to Pyruvate
First step in forming ATP from glucose begins w/ glycolysis
○
Glucose metabolism is an essential energy source for all cells (remember
esp brain and red blood cells)
○
Glycolysis is a ten-step anaerobic catabolic pathway that takes place in
the cytosol of the cells
Begins w/ one six-carbon glucose molecule
§
Ends w/ 2 three-carbon molecules of pyruvate and 2 net molecules
of ATP
§
Glycolysis also generates 2 H+
§
Coenzyme NAD+ picks up hydrogen ions to form NADH
§
NADH carried hydrogen ions and electrons to the electron transport
chain
§
○
Other monosaccharides can also be used to produce ATP
○
Fructose and galactose
Just understand fed into glycolysis wherever needed
§
○
Pyruvate to lactate
Can happen anywhere in the body
§
During anaerobic metabolism, pyruvate reduced to lactate to
prevent buildup of excess H
§
Lactate diffuses out of cell and enters liver
§
Liver converts lactate to glucose via Cori cycle
§
2 different scenarios: do or don't have H
When burn, push a little further □
§
○
Cori cycle
Lactate converted to glucose in the liver
§
○
Glucogenic (can be used to make glucose) Amino Acids to Pyruvate
Glucogenic: anaerobically converted to glucose through
gluconeogenesis
□
Ketogenic: aerobically converted to glucose through acetyl
CoA when O is present
□
○
Glycerol to Pyruvate
Once glycerol portion of triglyceride is glucogenic, can be used to
make glucose
§
Glycerol produces v little energy compared w/ glucose, amino acids,
or fatty acids
§
○
Pyruvate is turned into Acetyl CoA when O is present
All energy-producing nutrients are transformed to acetyl CoA
before entering the TCA cycle
§
O must be present (occurs in the presence of O)
§
Two molecules of pyruvate cross the mitochondrial membrane and
enter the mitochondria
A carbon molecule and coenzyme A is added□
§
Acetyl CoA can enter 2 pathways
TCA cycle (if ATP is limited)□
Converted to fatty aid and stored as fat (ample ATP)□
§
2 molecules
§
○
Fatty Acids to Acetyl CoA
Hydrolyzed first from triglycerides by lipolysis before can be used
for energy
Hormone-sensitive lipase in adipose tissue catalyzes the rxn□
§
Fatty acids must be activated before they cross into the
mitochondria
§
The addition of coenzyme A to the carboxylic end of the fatty acid
chain activates the fatty acid
§
Once inside mitochondria, fatty acids are disassembled by beta-
oxidation
§
Beta-oxidation steps:
2 carbons at the end of the fatty acid are removed and joined
w/ CoA to form Acetyl CoA
□
This process continues until all carbon molecules are
converted
□
Hydrogen and electrons are released as each pair of carbon is
cleaved off
□
§
Fatty acids are ketogenic**
3 fatty acid chains and glycerol backbone□
Can be used to form ketone bodies□
§
and then fed into TCA cycle
§
○
Amino Acids to Acetyl CoA
Ketogenic amino acids
Leucine □
Lysine□
§
Both ketogenic and glucogenic amino acids
Isolecine□
Tryptophan□
Phenylanlanine□
Tyrosine□
§
Both ketogenic and glucogenic amino acids are transformed to
acetyl CoA before they enter the energy pathway**
§
○
-
Tricarboxylic Acid (TCA) Releases High-Energy Electrons and Hydrogen Ions
TCA cycle is the third stage for oxidation of acetyl CoA
○
Final stage in metabolism where then can make fatty acids
○
Location is in the mitochondria
○
These macronutrients enter the cycle as Acetyl CoA where most of the
energy in the OG molecule is now trapped
This stored energy is freed during the TCA cycle and is transferred
to two coenzyme hydrogen ion carriers to be released in the
electron transport chain
§
○
One molecule of acetyl CoA enters the TCA cycle at a time
○
For every acetyl CoA that enters the cycle, 2 carbons are lost as CO2
○
2NADH + H+and 1 FADH2are made during each turn of the cycle
Know first step need oxaloacetate (for TCA cycle to occur) and when
starving (especially depeletion of carbs) can't get this
§
○
-
Electron Transport Chain and Oxidative Phosphorylation Produces the Majority
of ATP
Comprised of a series of protein complexes located in the inner
mitochondrial membrane
○
Makes 90% of the ATP used by the body for energy, growth, and
maintenance
○
Electrons and transferred from one protein complex to another, resulting
in the formation of ATP and water
Protein complexes are called flavoproteins
Contain riboflavin and cytochromes□
Cytochromes contain iron and copper□
§
○
Though vitamins and minerals do not provide energy, they are essential
for energy production**
○
-
Overview of Metabolism
Absorptive v Postabsorptive states
Absorbptive (fed) state
Period w/in 4 hours following a meal in which anabolic
processes excess catabolic processes
□
§
Postabsorptive (fasted) state
Period of time usually more than 4 hours after eating□
Energy need are met by breakdown of stores□
§
Both are regulated by hormones
§
○
Carbs are stored as Glycogen
Red blood cells and CNS use prefer glucose but cannot store glucose
(so gotta store glycogen)
§
Liver and muscle convert glucose to glycogen w/ glycogenesis
§
Liver glycogen depleted 12 to 18 hours after eating
§
○
Excess carbs and amino acids stored as triglycerides
Excess glucose not stored as glycogen converted to triglycerides
25% of energy used for this conversion□
§
Excess amino acids not used by body converted to triglycerides
Amino acids undergo deamination and remaining carbons are
converted to acetyl CoA and then into fatty acids
□
§
○
Fatty acids stored as triglycerides
Excess cals in any form stored are triglyceride via lipogenesis
§
5% of energy converted to fatty acids to triglycerides
§
Dietary fat is easier to store as a triglyceride than dietary carb or
protein (that's why it's better to eat excess of other macronutrients
than fat b/c if eat extra fat will just go to fat but other
macronutrients can be used for other things)
§
Glucagon promotes lipolysis (break down of lipids [triglycerides] by
hydrolysis to release fatty acids and glycerol)
§
Insulin promotes fatty acid synthesis and inhibits lipolysis
§
○
During postabsorptive state, metabolism favors energy production
4 or more hours after eating, body meets energy needs from stored
energy
§
Stores are depleted during fasting
b/w meals and overnight
Energy via glycogen and fatty acids
®
□
After 18, the body adapts
Proteins, glycerol, pyruvate, and lactate are used to
make glucose
®
Lipolysis is increased
®
□
Prolonged fasting
Ketone bodies provide energy to brain
®
□
Severe fasting or starvation
Fat reserves are depleted
®
Muscle tissue is broken down to provide energy
®
□
§
○
Ketogenesis generates energy during prolonged fasting
Ketogenesis is the formation of ketone bodies
Occurs w/ the buildup of acetyl CoA□
Peaks after fasting or limited carb intake for 3 days□
Body uses this to slow down the body breaking down lean
body mass
□
§
As the fast continues the brain uses ketones for fuel
30% of fuel from ketones and 70% from blood glucose□
§
Ketoacidosis via excess accumulation of ketone bodies
Ketones are acidic□
Occurs w/ untreated type 1 diabetes□
Can lead to impaired heart activity, coma, and even death□
§
○
-
How does body metabolize alcohol?
7 cals/ g
○
Absorbed through stomach mucosa and intestinal lining
○
Metabolized by liver, about half oz/ 1.5 hours
○
Excess alc circulates throughout body until liver enzymes can break it
down
○
Excess alc is stored as fat
Fat metabolism is favored after alc consumption
§
Fewer fatty acids are used for energy when alc is consumed
§
Excess alc cals are stored as fatty acids in adipose tissue and liver
§
Alcoholics will have fat deposits in their liver
Can lead to cirrhosis□
Fat begins to accumulate after a single bout of drinking□
§
○
Enzymes that Metabolize Ethanol
Alcohol is metabolized through 3 distinct pathways
Alcohol dehydrogenase (ADH)
Present in the stomach and liver
®
Converts alcohol to acetyl CoA
Used to produce energy in TCA cycle
◊
Converted into fatty acids and stored as a
triglyceride
◊
®
□
Microsomal ethanol oxidizing system (MEOS)
Used during chronic alcohol consumption
®
Also metabolizes drugs
®
□
Brain
Catalase oxidizes alcohol to acetaldehyde
®
May be responsible for psychological effects
Reduced inhibitions
◊
®
□
§
○
-
Inborn Errors of Metabolism
Genetic conditions where lack enzyme that controls a specific metabolic
pathway
Results in the buildup of toxins
§
Cannot be cured
§
Cannot be controlled through diet
§
○
Phenylketonuria (PKU)
Unable to metabolize phenylalanine b/c enzyme phenylalanine
hydroxylase is lacking
§
Severe form
Can lead to behavior problems or mental retardation□
§
Mild to moderate conditions
Prevented by following a prescribed, controlled diet□
§
Treatment
Limited intake of phenylalanine□
Maintain adequate intake of tyrosine, energy, and protein□
Avoid foods and beverages w/ aspartame □
§
○
Maple syrup urine disease (MSUD)
Unable to metabolize branched-chain amino acids: leucine,
isoleucine, and valine
§
Untreated can lead to seizures, coma, and death
§
Treatment
Consume specifically designed formulas□
Avoid products like beef, chicken, fish, eggs, nuts, and
legumes
□
§
○
Homocystinuria
Unable to convert homocysteine to cystathione
§
Treatment
Diet low in amino acid methionine□
Supplement w/ B vitamins: folate, vitamin B6, and vitamin
B12
□
§
○
Galactosemia
Unable to convert galactose to glucose
§
Treatment
Avoid dietary lactose and galactose□
§
○
Glycogen storage disease
Unable to break down glycogen and provide glucose to muscle or
body
Treatment
Avoid foods w/ sucrose, lactose, galactose, and fructose
®
□
§
○
-
Chpt. 8 Metabolism
Monday, February 19, 2018 2:00 PM
Metabolism
Sum of all chemical reactions in the body
Chemical reactions follow metabolic pathways where compounds
are converted to new compounds
§
○
Energy is stored in the bonds that connect the molecules that make up
carbs, proteins, and fats
○
Energy is released when the bonds are broken. This occurs w/:
Aerobic (w/ oxygen) rx's
§
Anaerobic (w/o oxygen) rx's
§
Macronutrients need certain environments
§
○
To meet the body's constant energy supply, metabolism never stops
○
Metabolism processes adapt to meet individual needs and the
environment
○
Stages of metabolism
○
-
Metabolism Takes Places w/in Cells
Different cells perform diff metabolic functions
○
Each cell's structure is similar
Outside of cell
Plasma membrane: holds in the cell contents□
§
Inside of cell is where metabolism occurs
Organelles
Mitochondria: powerhouse of the cell (generates most
of cell's energy from carb, protein, and fats)
®
Energy is generated by aerobic metabolism
®
□
Cytosol
Fluid portion of cell
®
Anaerobic metabolism
®
□
§
○
-
Liver Plays a Central Role in Metabolism (for mastering: most metabolically
active organ in the body)
Liver is the most metabolically active organ in the body
○
First organ to metabolize, store, and distribute nutrients after absorption
○
Converts monosaccharides, amino acids, glycerol, and fatty acids:
Into new compounds
§
Into energy
§
Or store them for future use
Triglycerides□
glycogen□
§
○
-
Metabolism Is a Series of Chemical Reactions
Metabolic pathways are sequences of reactions that convert compounds
from one form to another
○
Anabolic reactions: absorb energy/ make larger molecules
Glucose --> glycogen (gluconeogenesis)
§
Amino acids --> proteins
§
Fatty acids and glycerol --> triglycerides
§
○
Catabolic reactions: release energy/ break down molecules
glycogenolysis
§
○
-
Enzymes and Hormones Regulate Metabolism
Coenzymes assist enzymes
○
Hormones regulate anabolic and catabolic rx's
○
-
How does ATP Fuel Metabolism?
Before body can use energy from food, first has to disassemble
macronutrients into CO2and H2O while capturing released energy as
adenosine triphosphate (ATP)
Adenosine triphosphate (ATP): a high-energy molecule composed of
adenine, ribose, and 3 phosphate molecules
§
Any source of macronutrients can be used to generate ATP
§
ATP is the cell's direct energy source
§
Energy is stored in the bonds that connect the phosphate groups
§
The body must continually produce ATP to provide a constant
supply of energy
§
Adenosine diphosphate (ADP)
Formed □
§
○
ATP Can Be Regenerated from ADP and Creatine Phosphate
Regenerating ATP from ADP requires a source of phosphate
§
Sources
Inorganic phosphate produced from initial breakdown of ATP□
Inorganic phosphate in creatine phosphate (aka
phosphocreatine or PCr)
□
Both sources provide enough ATP to sustain a spring for 8 to
10 seconds
□
§
Creatine phosphate
High-energy compound in muscle cells when creatine
combines w/ phosphate
□
Phosphate molecule is released from ATP
□
§
As creatine phosphate levels dwindle, the body switches to
anaerobic and aerobic metabolism to make ATP
§
Anaerobic metabolism
Produces more ATP per minute
□
Only provides 1 to 1.5 mins of maximal activity
□
Involved in high-intensity, short-duration activities, such as
sprinting and heavy weight lifting
□
§
Aerobic metabolism
Produce less ATP/ min
□
Is able to produce ATP indefinitely
□
Involved in low-intensity, long-duration activities
□
When demand for ATP is greater than the rate of metabolism,
the activity slows down (this is the point/ key of training)
□
§
○
How Do the Macronutrients Provide ATP?
Carbs, fats, and proteins enter the metabolic pathways at some
point during the stages of metabolism
§
Major metabolic pathways
Glycolysis (stage 1)
□
Pyruvate to acetyl CoA (stage 2)
□
TCA stage (stage 3)
□
Electron transport chain (stage 4)
□
§
○
-
Glycolysis Transforms Glucose to Pyruvate
First step in forming ATP from glucose begins w/ glycolysis
○
Glucose metabolism is an essential energy source for all cells (remember
esp brain and red blood cells)
○
Glycolysis is a ten-step anaerobic catabolic pathway that takes place in
the cytosol of the cells
Begins w/ one six-carbon glucose molecule
§
Ends w/ 2 three-carbon molecules of pyruvate and 2 net molecules
of ATP
§
Glycolysis also generates 2 H+
§
Coenzyme NAD+ picks up hydrogen ions to form NADH
§
NADH carried hydrogen ions and electrons to the electron transport
chain
§
○
Other monosaccharides can also be used to produce ATP
○
Fructose and galactose
Just understand fed into glycolysis wherever needed
§
○
Pyruvate to lactate
Can happen anywhere in the body
§
During anaerobic metabolism, pyruvate reduced to lactate to
prevent buildup of excess H
§
Lactate diffuses out of cell and enters liver
§
Liver converts lactate to glucose via Cori cycle
§
2 different scenarios: do or don't have H
When burn, push a little further □
§
○
Cori cycle
Lactate converted to glucose in the liver
§
○
Glucogenic (can be used to make glucose) Amino Acids to Pyruvate
Glucogenic: anaerobically converted to glucose through
gluconeogenesis
□
Ketogenic: aerobically converted to glucose through acetyl
CoA when O is present
□
○
Glycerol to Pyruvate
Once glycerol portion of triglyceride is glucogenic, can be used to
make glucose
§
Glycerol produces v little energy compared w/ glucose, amino acids,
or fatty acids
§
○
Pyruvate is turned into Acetyl CoA when O is present
All energy-producing nutrients are transformed to acetyl CoA
before entering the TCA cycle
§
O must be present (occurs in the presence of O)
§
Two molecules of pyruvate cross the mitochondrial membrane and
enter the mitochondria
A carbon molecule and coenzyme A is added□
§
Acetyl CoA can enter 2 pathways
TCA cycle (if ATP is limited)□
Converted to fatty aid and stored as fat (ample ATP)□
§
2 molecules
§
○
Fatty Acids to Acetyl CoA
Hydrolyzed first from triglycerides by lipolysis before can be used
for energy
Hormone-sensitive lipase in adipose tissue catalyzes the rxn□
§
Fatty acids must be activated before they cross into the
mitochondria
§
The addition of coenzyme A to the carboxylic end of the fatty acid
chain activates the fatty acid
§
Once inside mitochondria, fatty acids are disassembled by beta-
oxidation
§
Beta-oxidation steps:
2 carbons at the end of the fatty acid are removed and joined
w/ CoA to form Acetyl CoA
□
This process continues until all carbon molecules are
converted
□
Hydrogen and electrons are released as each pair of carbon is
cleaved off
□
§
Fatty acids are ketogenic**
3 fatty acid chains and glycerol backbone□
Can be used to form ketone bodies□
§
and then fed into TCA cycle
§
○
Amino Acids to Acetyl CoA
Ketogenic amino acids
Leucine □
Lysine□
§
Both ketogenic and glucogenic amino acids
Isolecine□
Tryptophan□
Phenylanlanine□
Tyrosine□
§
Both ketogenic and glucogenic amino acids are transformed to
acetyl CoA before they enter the energy pathway**
§
○
-
Tricarboxylic Acid (TCA) Releases High-Energy Electrons and Hydrogen Ions
TCA cycle is the third stage for oxidation of acetyl CoA
○
Final stage in metabolism where then can make fatty acids
○
Location is in the mitochondria
○
These macronutrients enter the cycle as Acetyl CoA where most of the
energy in the OG molecule is now trapped
This stored energy is freed during the TCA cycle and is transferred
to two coenzyme hydrogen ion carriers to be released in the
electron transport chain
§
○
One molecule of acetyl CoA enters the TCA cycle at a time
○
For every acetyl CoA that enters the cycle, 2 carbons are lost as CO2
○
2NADH + H+and 1 FADH2are made during each turn of the cycle
Know first step need oxaloacetate (for TCA cycle to occur) and when
starving (especially depeletion of carbs) can't get this
§
○
-
Electron Transport Chain and Oxidative Phosphorylation Produces the Majority
of ATP
Comprised of a series of protein complexes located in the inner
mitochondrial membrane
○
Makes 90% of the ATP used by the body for energy, growth, and
maintenance
○
Electrons and transferred from one protein complex to another, resulting
in the formation of ATP and water
Protein complexes are called flavoproteins
Contain riboflavin and cytochromes□
Cytochromes contain iron and copper□
§
○
Though vitamins and minerals do not provide energy, they are essential
for energy production**
○
-
Overview of Metabolism
Absorptive v Postabsorptive states
Absorbptive (fed) state
Period w/in 4 hours following a meal in which anabolic
processes excess catabolic processes
□
§
Postabsorptive (fasted) state
Period of time usually more than 4 hours after eating□
Energy need are met by breakdown of stores□
§
Both are regulated by hormones
§
○
Carbs are stored as Glycogen
Red blood cells and CNS use prefer glucose but cannot store glucose
(so gotta store glycogen)
§
Liver and muscle convert glucose to glycogen w/ glycogenesis
§
Liver glycogen depleted 12 to 18 hours after eating
§
○
Excess carbs and amino acids stored as triglycerides
Excess glucose not stored as glycogen converted to triglycerides
25% of energy used for this conversion□
§
Excess amino acids not used by body converted to triglycerides
Amino acids undergo deamination and remaining carbons are
converted to acetyl CoA and then into fatty acids
□
§
○
Fatty acids stored as triglycerides
Excess cals in any form stored are triglyceride via lipogenesis
§
5% of energy converted to fatty acids to triglycerides
§
Dietary fat is easier to store as a triglyceride than dietary carb or
protein (that's why it's better to eat excess of other macronutrients
than fat b/c if eat extra fat will just go to fat but other
macronutrients can be used for other things)
§
Glucagon promotes lipolysis (break down of lipids [triglycerides] by
hydrolysis to release fatty acids and glycerol)
§
Insulin promotes fatty acid synthesis and inhibits lipolysis
§
○
During postabsorptive state, metabolism favors energy production
4 or more hours after eating, body meets energy needs from stored
energy
§
Stores are depleted during fasting
b/w meals and overnight
Energy via glycogen and fatty acids
®
□
After 18, the body adapts
Proteins, glycerol, pyruvate, and lactate are used to
make glucose
®
Lipolysis is increased
®
□
Prolonged fasting
Ketone bodies provide energy to brain
®
□
Severe fasting or starvation
Fat reserves are depleted
®
Muscle tissue is broken down to provide energy
®
□
§
○
Ketogenesis generates energy during prolonged fasting
Ketogenesis is the formation of ketone bodies
Occurs w/ the buildup of acetyl CoA□
Peaks after fasting or limited carb intake for 3 days□
Body uses this to slow down the body breaking down lean
body mass
□
§
As the fast continues the brain uses ketones for fuel
30% of fuel from ketones and 70% from blood glucose□
§
Ketoacidosis via excess accumulation of ketone bodies
Ketones are acidic□
Occurs w/ untreated type 1 diabetes□
Can lead to impaired heart activity, coma, and even death□
§
○
-
How does body metabolize alcohol?
7 cals/ g
○
Absorbed through stomach mucosa and intestinal lining
○
Metabolized by liver, about half oz/ 1.5 hours
○
Excess alc circulates throughout body until liver enzymes can break it
down
○
Excess alc is stored as fat
Fat metabolism is favored after alc consumption
§
Fewer fatty acids are used for energy when alc is consumed
§
Excess alc cals are stored as fatty acids in adipose tissue and liver
§
Alcoholics will have fat deposits in their liver
Can lead to cirrhosis□
Fat begins to accumulate after a single bout of drinking□
§
○
Enzymes that Metabolize Ethanol
Alcohol is metabolized through 3 distinct pathways
Alcohol dehydrogenase (ADH)
Present in the stomach and liver
®
Converts alcohol to acetyl CoA
Used to produce energy in TCA cycle
◊
Converted into fatty acids and stored as a
triglyceride
◊
®
□
Microsomal ethanol oxidizing system (MEOS)
Used during chronic alcohol consumption
®
Also metabolizes drugs
®
□
Brain
Catalase oxidizes alcohol to acetaldehyde
®
May be responsible for psychological effects
Reduced inhibitions
◊
®
□
§
○
-
Inborn Errors of Metabolism
Genetic conditions where lack enzyme that controls a specific metabolic
pathway
Results in the buildup of toxins
§
Cannot be cured
§
Cannot be controlled through diet
§
○
Phenylketonuria (PKU)
Unable to metabolize phenylalanine b/c enzyme phenylalanine
hydroxylase is lacking
§
Severe form
Can lead to behavior problems or mental retardation□
§
Mild to moderate conditions
Prevented by following a prescribed, controlled diet□
§
Treatment
Limited intake of phenylalanine□
Maintain adequate intake of tyrosine, energy, and protein□
Avoid foods and beverages w/ aspartame □
§
○
Maple syrup urine disease (MSUD)
Unable to metabolize branched-chain amino acids: leucine,
isoleucine, and valine
§
Untreated can lead to seizures, coma, and death
§
Treatment
Consume specifically designed formulas□
Avoid products like beef, chicken, fish, eggs, nuts, and
legumes
□
§
○
Homocystinuria
Unable to convert homocysteine to cystathione
§
Treatment
Diet low in amino acid methionine□
Supplement w/ B vitamins: folate, vitamin B6, and vitamin
B12
□
§
○
Galactosemia
Unable to convert galactose to glucose
§
Treatment
Avoid dietary lactose and galactose□
§
○
Glycogen storage disease
Unable to break down glycogen and provide glucose to muscle or
body
Treatment
Avoid foods w/ sucrose, lactose, galactose, and fructose
®
□
§
○
-
Chpt. 8 Metabolism
Monday, February 19, 2018 2:00 PM
Document Summary
Sum of all chemical reactions in the body. Chemical reactions follow metabolic pathways where compounds are converted to new compounds. Energy is stored in the bonds that connect the molecules that make up carbs, proteins, and fats. Energy is released when the bonds are broken. To meet the body"s constant energy supply, metabolism never stops. Metabolism processes adapt to meet individual needs and the environment. Mitochondria: powerhouse of the cell (generates most of cell"s energy from carb, protein, and fats) Liver plays a central role in metabolism (for mastering: most metabolically active organ in the body) Liver is the most metabolically active organ in the body. First organ to metabolize, store, and distribute nutrients after absorption. Converts monosaccharides, amino acids, glycerol, and fatty acids: Metabolic pathways are sequences of reactions that convert compounds from one form to another. Catabolic reactions: release energy/ break down molecules glycogenolysis.
