8. metabolic control & regulation Flashcards
1
Q
how do carbs, fat and protein compare in the amount of energy they produce?
A
[bomb calorimeter]
1g carbohydrate= 4.2 kcal
1g fat= 9.4 kcal
1g protein= 5.56 kcal
[metabolise in body]
carb= 4 kcal
lipid = 9 kcal
protein = 4 kcal
*we can’t utilise all the energy when we digest food
2
Q
BMR (kcal) calculation
A
men:
66+ (13.7xW) + (5xH) - (6.8xA)
women:
655 + (9.6xW) + (1.7xH) - (4.7xA)
W= weight in kg
H= height in cm
A= age in yrs
3
Q
energy balance
A
- energy balance is at the centre of major public health issues such as obesity and type 2 diabetes
- allows us to understand energy requirements of athletes/individuals
- there is a need to understand how the body uses fuel
- important that we can accurately measure EI and EE
4
Q
EI and EE
A
energy intake (calories eaten)
energy expenditure (calories burned)
5
Q
give a simplistic overview of metabolism
A
- eating food;
filled with energy, acter eating your bodys next tasks is to break down components - releases energy;
breaking down the sugar releases energy. furthermore, the cells of your body use this energy to perform their functions - digestive system;
complex protein molecules called digestive enzymes break carbohydrates into sugars (example, glucose), fats into fatty acids and proteins into amino acids - enzymes meet up;
inside your cells, more enzymes meet up with these compounds and undergo various chemical reactions - energy store;
reactions happen to release energy for immediate or future use. most of the energy is stored in your liver, skeletal muscles and body fat
6
Q
ATP component
A
ATP (adenosine triphosphate)
- nitrogenous base (adenine),
- five-carbon sugar (ribose),
- three phosphate groups
7
Q
what is released when ATP breaks down?
A
large amounts of ‘free energy’ released when ATP breaks down
(produces 7.3 kcal of free energy)
8
Q
ATP breakdown equation
A
ATP + H₂O → ADP + Pi + energy
(Pi = inorganic phosphate)
9
Q
examples of things ATP is used for
A
- digestion
- circulation
- muscle contraction
- tissue synthesis
- nerve conduction
- glandular excretion
10
Q
ATP and muscular contraction
A
Muscle contraction is a complex process that requires energy in the form of ATP (adenosine triphosphate). The cross-bridge cycle is the series of events that occurs during muscle contraction, in which myosin filaments interact with actin filaments within the muscle fiber. This interaction allows muscle fibers to shorten (contract), leading to movement. ATP plays a crucial role in this cycle by providing the energy required for the interactions between the actin and myosin filaments.
11
Q
how is ATP involved in the cross-bridge cycle (muscular contraction)?
A
- ATP hydrolysis provides the energy required to cock the myosin head (high-energy state).
- ATP binding to myosin is necessary for the detachment of the myosin head from actin.
- ATP hydrolysis after detachment allows the myosin head to re-cock, preparing it for another cross-bridge cycle.
- During prolonged muscle activity, ATP stores become depleted, and lactic acid build-up (from anaerobic metabolism) can lead to muscle fatigue
12
Q
comment of the limitations of ATP
A
- body stores about 80-100g of ATP
- at rest, average ATP consumption of 1.6kg/hr
- equivalent to 49kg of ATP/day
- ATP usage can rise 20-30fold in strenuous exercise (~0.5kg/min)
with limited supplies and high demand, ATP must continually be resynthesised (from ADP) to meet requirements
-> therefore the foods we eat and store provide energy to recharge ATP
13
Q
how much ATP does the body store?
A
80-100g
14
Q
What is the overall reaction for glucose metabolism in aerobic conditions?
A
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP (36).
15
Q
What is glycogenesis and how is it regulated?
A
Glycogenesis is the process of converting glucose into glycogen for storage. It is regulated by enzymes like glycogen synthase.
16
Q
What is the difference between glycolysis in aerobic and anaerobic conditions?
A
In aerobic conditions, pyruvate enters the Krebs cycle, while in anaerobic conditions, pyruvate is converted to lactate.
*Aerobic respiration, which uses oxygen, is the primary pathway for ATP production under normal conditions. Anaerobic glycolysis provides a rapid but less efficient alternative when the aerobic pathway is overwhelmed.
17
Q
How does the Cori cycle help recycle lactate produced during anaerobic exercise?
A
The Cori cycle converts lactate from muscles into glucose in the liver, which can then be reused by muscles for energy.
18
Q
What is the role of NADH and FADH₂ in the electron transport chain?
A
NADH and FADH₂ carry electrons to the electron transport chain, where they donate their electrons to create a proton gradient that drives ATP synthesis.
19
Q
What happens during oxidative phosphorylation?
A
During oxidative phosphorylation, a proton gradient is created by the electron transport chain, and ATP synthase uses this gradient to produce ATP.
20
Q
What is the fate of lactate produced during high-intensity exercise?
A
Lactate is released into the bloodstream and can be used by the liver for gluconeogenesis or by muscles for energy.
21
Q
How does exercise intensity affect lactate accumulation?
A
Higher intensity exercise leads to higher lactate production as oxygen becomes limited, leading to discomfort and fatigue.
22
Q
What is the primary function of glycogen in the body?
A
Glycogen serves as the storage form of glucose in the liver and muscles, providing a readily available source of energy when blood glucose levels drop.
23
Q
How is glucose converted to glycogen, and what enzyme plays a key role in this process?
A
Glucose is converted into glycogen via a process called glycogenesis. The enzyme glycogen synthase plays a key role in adding glucose molecules to the growing glycogen chain.
24
Q
Which enzyme is responsible for breaking down glycogen back into glucose-1-phosphate?
A
Glycogen phosphorylase is responsible for breaking down glycogen into glucose-1-phosphate during glycogenolysis.
25
What is the role of UDP-glucose in glycogenesis?
UDP-glucose provides the glucose molecule that is added to the glycogen chain during glycogenesis. It is an activated form of glucose.
26
What is the net ATP gain from glycolysis?
The net ATP gain from glycolysis is 2 ATP molecules, as 4 ATP are produced, but 2 ATP are consumed during the early stages.
27
Which enzyme regulates the rate of glycolysis, and why is it important?
Phosphofructokinase (PFK) is a key regulatory enzyme in glycolysis. It controls the rate at which glucose is metabolized by catalyzing the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate.
28
What happens to pyruvate after glycolysis in the presence of oxygen (aerobic conditions)?
In the presence of oxygen, pyruvate enters the Krebs cycle where it is further oxidized to produce CO₂, H₂O, and ATP.
29
What happens to pyruvate under anaerobic conditions (lack of oxygen)?
Under anaerobic conditions, pyruvate is converted into lactate in order to regenerate NAD⁺, which is necessary for glycolysis to continue.
30
What is the role of NADH in lactate formation?
NADH donates electrons to pyruvate, reducing it to lactate, which regenerates NAD⁺, enabling glycolysis to continue under anaerobic conditions.
31
At which exercise intensity does lactate start to accumulate in the blood?
High-intensity exercise causes lactate to accumulate in the blood as pyruvate production exceeds the rate at which it can be used in the Krebs cycle.
32
How does lactate contribute to muscle fatigue during intense exercise?
Accumulation of lactate leads to an increase in muscle acidity (lower pH), which impairs muscle function and contributes to fatigue during intense exercise.
33
What is the primary method of lactate removal during light exercise?
During light exercise, lactate is efficiently removed from the muscles and transferred to the bloodstream, where it can be taken up by other muscles or the liver for conversion back to glucose.
34
How does the Cori cycle help recycle lactate?
The Cori cycle transfers lactate produced in muscles to the liver, where it is converted back into glucose via gluconeogenesis, which can be reused by muscles for energy.
35
What percentage of lactate produced in muscles is used by the liver for gluconeogenesis?
Approximately 20-25% of lactate produced in muscles is used by the liver to produce glucose through gluconeogenesis.
36
What percentage of lactate formed is used directly by the muscles for energy?
Approximately 75-80% of lactate produced is used as an energy source by muscles during recovery or lower-intensity activity.
37
Explain the flow of lactate between muscle and liver during intense exercise.
During intense exercise, lactate is produced in the muscles and released into the bloodstream. The liver then takes up lactate and converts it into glucose, which can be sent back to the muscles to provide additional energy.
38
What are the products of the Krebs cycle for each molecule of pyruvate?
For each molecule of pyruvate, the Krebs cycle produces 2 CO₂, 4 H⁺ ions, and 1 ATP (via GTP). It also produces 3 NADH and 1 FADH₂.
39
How many molecules of ATP are generated from the complete oxidation of one molecule of glucose, including glycolysis, the Krebs cycle, and oxidative phosphorylation?
The complete oxidation of one glucose molecule generates a total of 36 ATP: 2 from glycolysis, 2 from the Krebs cycle, and approximately 32 from oxidative phosphorylation (electron transport chain).
40
What is the role of NADH and FADH₂ in the electron transport chain?
NADH and FADH₂ carry electrons to the electron transport chain, where they donate electrons to protein complexes, leading to the generation of a proton gradient across the mitochondrial membrane, which drives ATP production.
41
What is the final electron acceptor in the electron transport chain, and why is it important?
The final electron acceptor in the electron transport chain is oxygen (O₂), which combines with electrons and protons to form water (H₂O). This is essential for maintaining the flow of electrons through the chain.
42
What is oxidative phosphorylation, and how does it contribute to ATP production?
Oxidative phosphorylation refers to the process in which ATP is generated by the movement of protons across the mitochondrial membrane, driven by the electron transport chain. It accounts for over 90% of ATP produced in aerobic respiration.
43
How does the electron transport chain establish a proton gradient, and how does this lead to ATP synthesis?
The electron transport chain pumps protons (H⁺) across the inner mitochondrial membrane into the intermembrane space, creating a proton gradient. This gradient drives protons back into the mitochondrial matrix through ATP synthase, leading to ATP production.
44
Why is glucose the preferred fuel source for the body, especially during exercise?
Glucose is the preferred fuel source because it is readily available, can be metabolized both anaerobically (without oxygen) and aerobically (with oxygen), and provides a quick source of energy, particularly during high-intensity exercise.
45
What is the role of ATP in cellular metabolism?
ATP is the primary energy currency of the cell, used to power metabolic reactions, muscle contractions, and various cellular processes that require energy.
46
How does exercise intensity impact energy substrate utilization (glucose vs. fats)?
At low to moderate exercise intensity, fat is the primary fuel source. However, at high-intensity exercise, the body relies more on glucose (from muscle glycogen) for quick energy due to its faster availability.
47
What is the role of phosphocreatine (PCr) in energy production during exercise?
Phosphocreatine (PCr) helps resynthesize ATP rapidly during high-intensity exercise, allowing muscle contractions to continue. It lasts for about 50 meters in a 100-meter sprint.
48
How much more PCr is stored in muscles compared to ATP?
Muscle stores approximately 4 times more PCr than ATP.
49
What is the main energy source during the first few seconds of a sprint?
The phosphagen system (PCr) is the primary energy source for the first few seconds of a sprint.
50
How does creatine supplementation affect muscle performance?
Creatine supplementation increases muscle PCr levels, enhancing the resynthesis of ATP between bouts of high-intensity exercise, improving performance during repeated sprints.
51
What energy system is primarily used during a 200-400 meter race?
The phosphagen system initially provides energy, followed by anaerobic glycolysis as PCr stores are depleted.
52
What is the role of anaerobic glycolysis in energy provision for middle-distance events?
Anaerobic glycolysis contributes to ATP production by breaking down glucose/glycogen into lactate, especially after the initial energy from PCr runs out (typically after ~10 seconds).
53
How does the energy system change during a 1500-meter race?
A 1500-meter race utilizes phosphagen system initially, followed by anaerobic glycolysis to maintain speed, and aerobic glycolysis for sustained energy as oxygen delivery becomes more important.
54
How long do muscle phosphagens (PCr) last during high-intensity exercise?
Muscle phosphagens (PCr) provide energy for about 3-10 seconds of high-intensity exercise.
55
What is the benefit of creatine supplementation for team sports?
Creatine supplementation benefits team sports by enhancing performance in repeated high-intensity efforts (e.g., sprints) with short recovery periods between them.
56
In what type of exercise is anaerobic glycolysis the primary energy source?
Anaerobic glycolysis is the primary energy source during exercises lasting from 10 seconds to 2 minutes, such as middle-distance races or high-intensity intervals.
57
What is the source of energy after 4 minutes of exercise?
After 4 minutes of exercise, the body primarily relies on aerobic metabolism using muscle glycogen and fatty acids for energy.
*Aerobic respiration, which uses oxygen, is the primary pathway for ATP production under normal conditions. Anaerobic glycolysis provides a rapid but less efficient alternative when the aerobic pathway is overwhelmed
58
How does muscle fiber type influence energy use during exercise?
Slow-twitch fibers are more efficient for endurance (aerobic), while fast-twitch fibers are used for short bursts of high-intensity activity (anaerobic). Fiber type may shift with training, especially between fast-twitch subtypes.
59
How does genetics influence muscle fiber composition?
Genetics play a significant role in determining an individual's muscle fiber composition, influencing their ability to perform endurance vs. high-intensity activities.
60
What energy systems are active during a sprint (0-4 seconds)?
During the first 4 seconds of a sprint, anaerobic ATP from muscle stores is the primary energy source.
61
How long does muscle glycogen last during moderate exercise?
Muscle glycogen provides energy for 2-3 minutes of high-intensity exercise or up to 90 minutes of moderate-intensity exercise.----------------------------------------------------------------------------------------------------------------------------------------------
62
What is the role of phosphocreatine (PCr) in high-intensity exercise?
Phosphocreatine (PCr) helps regenerate ATP during high-intensity exercise, allowing muscles to continue contracting. It is used as an immediate energy source, especially for short bursts of activity.
63
How much PCr is stored in the muscles compared to ATP?
Muscles store about 4 times more phosphocreatine (PCr) than ATP.
64
How long do PCr stores last in high-intensity exercise?
Phosphocreatine lasts for about 50 meters during a 100-meter sprint, providing energy for the first few seconds of high-intensity activity.
65
What happens when PCr stores are depleted?
Once PCr stores are depleted, the body shifts to other energy systems, such as anaerobic glycolysis, to produce ATP.
66
What happens in the body after PCr is exhausted during exercise?
After PCr is depleted, the body switches to anaerobic glycolysis, where glucose or glycogen is broken down into pyruvate, and then lactate, producing ATP without the use of oxygen.
67
How long does anaerobic glycolysis provide energy during exercise?
Anaerobic glycolysis starts after about 5 seconds into high-intensity exercise and is maximal around 10-45 seconds.
68
What is the role of lactate in anaerobic glycolysis?
Lactate is produced when pyruvate is converted in the absence of oxygen. It helps in ATP production during high-intensity efforts but contributes to muscle fatigue if accumulated in large amounts.
69
How is anaerobic glycolysis used in middle-distance running (e.g., 200-400 meters)?
or 200-400 meter races, anaerobic glycolysis becomes the primary energy system as PCr stores are depleted, and the body requires rapid energy transfer.
70
What are the characteristics of slow-twitch muscle fibers?
Slow-twitch fibers are efficient for endurance activities, use oxygen for ATP production (aerobic), and are resistant to fatigue, making them ideal for long-duration activities.
71
What are the characteristics of fast-twitch muscle fibers?
Fast-twitch fibers are designed for explosive, high-intensity movements, using anaerobic pathways for ATP production. They tire quickly but generate high amounts of force.
72
Can muscle fibers shift types with training?
Studies show that muscle fiber shifts occur primarily between different fast-twitch subtypes, not between slow and fast-twitch fibers. However, exercise manipulation may potentially lead to fast-to-slow twitch shifts.
73
How does genetics influence muscle fiber composition?
Genetics determine an individual’s muscle fiber composition, affecting their natural predisposition to perform well in either endurance or high-intensity power activities.
74
Why is ATP resynthesis important in high-intensity exercise?
ATP is used as the primary energy source for muscle contractions, and its rapid depletion during exercise means it must be quickly resynthesized to sustain muscle performance, especially during intense activities like sprinting.
75
What is the role of creatine supplementation in energy production?
Creatine supplementation increases PCr levels in muscles, improving the ability to regenerate ATP quickly, which is particularly beneficial during repeated high-intensity efforts such as sprints.
76
What are the typical strategies for creatine supplementation?
Two common strategies:
Loading phase: 20g/day (4x5g doses) for 5 days, followed by a maintenance dose of 3-5g/day.
Slow release phase: 2-3g/day for a longer period (about 15 days), which can achieve similar results.
77
What are the benefits of creatine supplementation?
Creatine enhances PCr resynthesis, improving performance in repeated high-intensity sprints (lasting 6-30 seconds), but it has limited benefits for endurance-based activities.
78
Does creatine have any effects on endurance performance?
There is little evidence to support the benefit of creatine supplementation for endurance performance, but it can enhance short-duration, high-intensity efforts (e.g., sprints in team sports).
79
What is the primary energy system during a 100-meter sprint?
During a 100-meter sprint, the primary energy source is the phosphagen system, using ATP and PCr stored in the muscles.
80
What energy systems are used during a 200-400 meter race?
A 200-400 meter race starts with the phosphagen system (PCr) and transitions to anaerobic glycolysis as the PCr stores are depleted, with muscle glycogen becoming the primary energy source.
81
How does the body switch between energy systems during middle-distance running (e.g., 1500 meters)?
During a 1500-meter race, energy is initially supplied by the phosphagen system to accelerate, then shifts to anaerobic glycolysis to maintain speed, and finally to aerobic glycolysis for sustained energy as oxygen delivery increases.
82
How long do different energy systems last during exercise?
0-4 seconds: Anaerobic ATP from muscle stores.
4-10 seconds: Anaerobic ATP + CP.
10-45 seconds: Anaerobic ATP + CP + Muscle Glycogen.
45 seconds to 2 minutes: Muscle Glycogen (anaerobic lactic system).
2-4 minutes: Muscle Glycogen + Lactic Acid (anaerobic + aerobic systems).
4-10 minutes: Aerobic (muscle glycogen + fatty acids).
83
How long does muscle phosphagen (PCr) last during exercise?
Muscle phosphagen (PCr) lasts for 3-10 seconds during intense exercise.
84
How long does muscle glycogen provide energy for during exercise?
Muscle glycogen can provide energy for up to 2-3 minutes of high-intensity exercise or about 90 minutes for moderate-intensity exercise.
85
How long can blood glucose provide energy during exercise?
Blood glucose can provide energy for about 4 minutes, but muscle glycogen is the main source for sustained activity.
86
How long does fat (adipose tissue) provide energy during prolonged exercise?
Fat (adipose tissue) provides energy for prolonged exercise, lasting more than 120 minutes, with energy supply lasting up to 95 hours.
87
What happens to the energy systems during the first 10 seconds of high-intensity exercise?
During the first 10 seconds of high-intensity exercise, the body primarily uses anaerobic ATP (stored in muscles) and PCr.
88
What happens after 45 seconds to 2 minutes of high-intensity exercise?
After 45 seconds to 2 minutes, the body predominantly uses muscle glycogen in the anaerobic lactic system to continue generating ATP without oxygen.
89
How does the body maintain energy for long-duration events like marathons?
For long-duration events like marathons, the body relies on aerobic metabolism, using muscle glycogen and fatty acids as energy sources. This provides sustained ATP production over extended periods.
90
Why can't we rely solely on glycogen during long-duration exercise?
Glycogen stores are limited and eventually deplete, leading to fatigue.
91
What is beta-oxidation?
The process by which fatty acids are broken down to form Acetyl-CoA for the Krebs cycle.
92
What does "fats burn in a carbohydrate flame" mean?
Fat oxidation requires oxaloacetate, which is derived from carbohydrate metabolism.
93
What happens if muscle glycogen runs out?
Fatigue increases; fat oxidation alone is inefficient without carbohydrate-derived oxaloacetate.
94
What fuels dominate during an endurance event?
Initial sprints: anaerobic glycolysis; long steady phase: aerobic metabolism of fats and carbs.
95
What is a protein made of?
Amino acids linked by peptide bonds.
96
What makes amino acids unique?
Their side chain (R-group).
97
How many essential amino acids are there?
9 (8 in adults; 9 in infants).
98
Give examples of dietary sources of essential amino acids.
Eggs, soy, whitefish, sesame, peanuts, parmesan.
99
What is deamination?
Removal of the amino group from an amino acid, forming ammonia and a keto acid.
100
Where is urea excreted?
The kidneys, via urine.
101
Name three functions of protein in the body.
Structural support, enzyme production, hormone regulation.
102
What is nitrogen balance?
A measure of protein metabolism: intake vs output of nitrogen.
103
What does a positive nitrogen balance indicate?
Protein intake exceeds output – good for growth and recovery.
104
How is nitrogen intake calculated?
Protein intake × 0.16
105
Do athletes need more protein?
Yes, depending on intensity and training type.
106
Recommended intake for endurance athletes?
1.2–1.5 g/kg/day
107
Recommended intake for strength athletes?
1.4–1.7 g/kg/day
108
Is 2.5 g/kg/day necessary for athletes?
No scientific evidence supports such high intake.
109
Do protein supplements guarantee muscle gain?
Not necessarily; effectiveness depends on overall diet and training.
110
Can protein needs be met through diet alone?
Yes, with balanced and sufficient food intake.
111
What is glycogenolysis and where does it occur?
Glycogenolysis is the breakdown of glycogen into glucose-6-phosphate, primarily occurring in the liver and skeletal muscle.
112
What is the rate-limiting enzyme of glycolysis?
Phosphofructokinase-1 (PFK-1)
113
What are the main products of glycolysis per glucose molecule?
2 pyruvate, 2 ATP (net), 2 NADH
114
What happens to pyruvate under anaerobic conditions?
It is converted to lactate by lactate dehydrogenase.
115
Which enzyme converts pyruvate to acetyl-CoA?
Pyruvate dehydrogenase complex (PDC)
116
What is the process of breaking down triglycerides called?
Lipolysis
117
What enzyme initiates lipolysis?
Hormone-sensitive lipase (HSL)
118
What is β-oxidation?
The breakdown of fatty acids into acetyl-CoA in the mitochondria.
119
How are long-chain fatty acids transported into mitochondria?
Via the carnitine shuttle.
120
What molecule combines with acetyl-CoA to start the Krebs cycle?
Oxaloacetate
121
Where does the Krebs cycle occur?
Mitochondrial matrix
122
What are the main products of one turn of the Krebs cycle?
3 NADH, 1 FADH₂, 1 GTP, 2 CO₂
123
What is the final electron acceptor in the electron transport chain?
Oxygen (O₂)
124
How does oxidative phosphorylation produce ATP?
Proton gradient powers ATP synthase in the inner mitochondrial membrane.
125
Why does fat oxidation depend on carbohydrates?
Because oxaloacetate, needed for acetyl-CoA to enter the Krebs cycle, is derived from pyruvate (from carbohydrate metabolism).
126
What happens when carbohydrate availability is low?
Fat oxidation slows, and acetyl-CoA is diverted to ketone body production.
127
What makes proteins different from carbohydrates and fats?
Proteins contain nitrogen.
128
What is the basic structure of an amino acid?
A central carbon bonded to an amino group, carboxyl group, hydrogen, and an R side chain.
129
What type of bond joins amino acids?
Peptide bond
130
What is a polypeptide?
A chain of more than 3 and up to 100 amino acids.
131
Name three essential amino acids.
Leucine, lysine, methionine
(others: isoleucine, valine, histidine, threonine, tryptophan, phenylalanine)
132
What’s the difference between essential and non-essential amino acids?
Essential AAs must be obtained from the diet; non-essential can be synthesized by the body.
133
How many essential amino acids are there in adults?
8 (9 in infants)
134
What is transamination?
The transfer of an amino group from one amino acid to a keto acid.
135
What is the product of oxidative deamination?
Ammonia (NH₃) and a keto acid.
136
What happens to ammonia in the liver?
It enters the urea cycle and is excreted as urea.
137
What is the urea cycle's function?
To safely eliminate excess nitrogen.
138
Which amino acid is converted to pyruvate?
Alanine
139
Which amino acids are ketogenic (converted to acetyl-CoA)?
Leucine and lysine
140
Which amino acids are glucogenic (can be converted to glucose)?
Asparagine and aspartate (via oxaloacetate), others via pyruvate.
141
Which energy system dominates during short, intense activity (e.g., sprinting)?
Anaerobic glycolysis
142
What fuels long-duration, steady-state exercise?
Aerobic metabolism using carbohydrates and fat
143
What happens if muscle glycogen runs out during endurance exercise?
Performance drops significantly; fat oxidation becomes inefficient without carbohydrates.
144
What does a positive nitrogen balance indicate?
Muscle growth or tissue repair
145
What is the “free amino acid pool”?
Circulating and intracellular amino acids available for use in metabolism and synthesis.
146
What organs play a major role in protein metabolism?
Liver (processing & urea cycle), kidneys (excretion)
147
Which amino acids are important in the brain?
GABA, taurine, glycine, phenylalanine
