Review 8: Amino Acid Metabolism

Question 1

What are 3 sources of free amino acids

Answer 1

1) degradation of ingested protein
2) biosynthesis of amino acids
3) degradation of endogenous protein

Question 2

True or false: concentration of free amino acids is high

Answer 2

FALSE; conc is balanced so that utilization balances formation (<1mM in plasma)

Question 3

How is nitrogen excreted in the body?

Answer 3

urea

Question 4

What are the 2 steps in degrading amino acids?

Answer 4

1) removal of nitrogen to form urea (transamination)

2) degradation of carbon skeletons

Question 5

What are the 2 sources of nitrogen for the biosynthesis of urea?

Answer 5

1) aspartate

2) ammonia

Question 6

Where does urea synthesis occur?

Answer 6

liver

Question 7

What is the purpose of urea biosynthesis?

Answer 7

detoxification of ammonia

Question 8

What are ketogenic substrates?

Answer 8

1) acetoacetate

2) acetyl CoA

Question 9

What are glucogenic substrates?

Answer 9

1) pyruvate
2) alpha ketoglutarate
3) succinyl CoA
4) fumarate
5) oxaloacetate

Question 10

Define “nutritionally non-essential amino acids”

Answer 10

can be synthesized from precursor molecules

Question 11

Define “nutritionally essential” amino acids

Answer 11

need to be consumed in the diet

Question 12

What is the range of half lives for proteins in the body?

Answer 12

a few minutes - many days

Question 13

What percentage of total body protein is degraded and resynthesized every day in adults?

Answer 13

2-3%

Question 14

True or false: there is net accumulation of protein on a high protein diet

Answer 14

FALSE (excess amino acids are degraded, not stored)

Question 15

The body degrades ___g of protein every day

Answer 15

55

Question 16

What happens to the carbon skeletons of amino acids?

Answer 16

broken down and used immediately or stored as glycogen or fat

Question 17

What is the equation for nitrogen balance?

Answer 17

Nitrogen ingested (protein) - nitrogen excreted (urea)

Question 18

What are some examples where a POSITIVE nitrogen balance would be normal?

Answer 18

child growth, pregnancy, bodybuilding (ingest more than you excrete)

Question 19

When would you find NEGATIVE nitrogen balance?

Answer 19

starvation, trauma, infection, cancer, burn, sepsis

rate of protein synthesis is less than degradation so muscle mass decreases

Question 20

Urea biosynthesis occurs in the _________ and is excreted by the ___________

Answer 20

liver and kidney

Question 21

amino groups from amino acids are converted into what amino acid?

Answer 21

glutamate

Question 22

What is the pathway of nitrogen from an amino acid to urea?

Answer 22

NH2 group —-> glutamate ——> ammonia and aspartate —-> urea

Question 23

Define transamination

Answer 23

transfer of an amino group to alpha ketoglutarate to form glutamate

Question 24

True or false: there is just one transaminase

Answer 24

FALSE; there are multiple that act on specific amino acids

Question 25

What are the 2 transaminases that are important in clinical diagnosis?

Answer 25

1) Alanine transaminase
2) Asparate transaminase

both levels increase in the serum in times of liver failure

Question 26

What are the steps in urea synthesis?

Answer 26

1) transamination (move NH2 groups to glutamate)
2) production of aspartate and ammonia (formed from glutamate)
3) synthesis of urea from ammonia and aspartate

Question 27

Does urea synthesis consume or produce ATP?

Answer 27

consume

Question 28

Where in the cell does urea synthesis take place?

Answer 28

1) carbamoyl phosphate and citrulline synthase takes place in MITOCHONDRIA
2) all others in cytosol

Question 29

___________ enters the mitochondria and ___________ leaves it in the formation of urea

Answer 29

ornithine (IN); citrulline (OUT)

Question 30

increased levels of glutamate lead to increased ___ ____________ which activates the enzyme that makes carbomoyl phosphate

Answer 30

N-Acetylglutamate

Question 31

What are the two transporters of nitrogen to the liver?

Answer 31

1) alanine

2) glutamine

Question 32

What are the 2 ways to get hyperammonemia?

Answer 32

1) acquired (cirrhosis)

2) genetic (deficiency of enzyme in urea biosynthesis)

Question 33

Define glucogenic

Answer 33

yields TCA cycle intermediates or pyruvate that can be used for gluconeogenesis

Question 34

Define ketogenic

Answer 34

yields acetyl CoA, acetoacetyl CoA, or acetoacetate

Question 35

What are the only exclusively ketogenic amino acids?

Answer 35

lysine, leucine (two L amino acids)

Question 36

What amino acids are both ketogenic and glucogenic?

Answer 36

isoleucine
phenylalanine
threonine
tryptophan
tyrosine

(All the T’s –> think of T as plus sign. glucogenic + ketogenic)

Question 37

During an overnight fast, there is net protein ___________

Answer 37

degradation