Chapter 7- Proteins and Amino Acids (Oct 25)

Question 1

the ____ is the primary site of uptake of amino acids after a meal

Answer 1

liver

Question 2

20% of the AA in the liver as used for

Answer 2

synthesis of proteins and N-compounds

Question 3

What are the steps of catabolism for amino acids that aren’t used for the synthesis of proteins or N-containing compounds?

Answer 3

1. removal of alpha-amino group
2. excretion of nitrogen
3. use of C-skeleton

Question 4

describe step 1 of catabolism for amino acids that aren’t used for the synthesis of proteins or N-containing compounds

Answer 4

removal of the alpha-amino group

• transamination = the transfer of amino group to alpha-ketoglutarate
• amino acid + alpha-ketoglutarate = alpha-keto acid + glutamate
• deamination of glutamate regenerates alpha-ketoglutamate

Question 5

describe step 2 of catabolism for amino acids that aren’t used for the synthesis of proteins or N-containing compounds

Answer 5

excretion of nitrogen
(urea in mammals)
(ammonia in fish)
(uric acid in birds and land reptiles)

Question 6

describe step 3 of catabolism for alpha-keto amino acids that aren’t used for the synthesis of proteins or N-containing compounds

Answer 6

alpha keto acid + amino group = amino acid

• precursors of glucose, fatty acids, ketone bodies

Question 7

describe step 3 of catabolism for glucogenic amino acids that aren’t used for the synthesis of proteins or N-containing compounds

Answer 7

C-skeletons degraded to:

• pyruvate or one of the 4C or 5C intermediates of the citric acid cycle
• major C source for gluconeogenesis
• catabolized for energy
• converted to glycogen or fatty acids

Question 8

describe step 3 of catabolism for ketogenic amino acids that aren’t used for the synthesis of proteins or N-containing compounds

Answer 8

• C-skeletons degraded to Acetyl CoA
• no net synthesis of glucose b/c Acetyl CoA (2C) enters citric acid cycle, lost as CO2
• converted to fatty acids or ketone bodies (no net synthesis of glucose)
• catabolized for energy

Question 9

what makes an amino acid indispensable?

Answer 9

the animal can’t make the carbon skeleton

Question 10

Can ammonium be used by animals to make amino acids? Explain

Answer 10

Yes, but only from the ammonium arising from amino acid catabolism (NOT from dietary supply in monogastrics)
- In ruminants: from microbial amino acid synthesis

Question 11

describe how dispensable amino acids are synthesized by the animal

Answer 11

transamination rxns

- amino group transferred from an existing amino acid to the alpha-carbon of an alpha-keto acid

Question 12

essential amino acids must be provided in the ____.
They can be broken down into:
1.
2,

Answer 12

diet

1. amino nitrogen
   - used to make a non-essential amino acid or excreted
2. C skeleton
   - metabolic pathway intermediates
   - oxidized for energy
   - converted and stored as fat

Question 13

non-essential amino acids ___ be provided in the diet and are used __ __
The can be broken down into:
1.
2.

Answer 13

can
as is

1. amino nitrogen
   - make a non-essential amino acid or excreted
2. carbon skeleton
   - metabolic pathway intermediates
   - oxidized for energy
   - converted and stored as fat