Amino Acid Metabolism; General Intro- Lecture 73

Question 1

What are essential amino acids?

Answer 1

amino acids that we cannot synthsize by us (an most mammals) and therefore have to be provided in the diet

Question 2

List all of the essential amino acids.

Answer 2

Phe Trp His
Val Ile Arg
Thr Met Lys
Leu

Question 3

How are non-essential amino acids synthesized?

Answer 3

mainly from carbohydrate precursors and a source of nitrogen (amonia or the alpha amino group of other amino acids)

Question 4

What is positive nitrogen balance?

Answer 4

dietary nitrogen > excreted nitrogen

normally found in conditions of growth and development (eg. children and body builders)

Question 5

What is negative nitrogen balance?

Answer 5

dietary nitrogen < excreted nitrogen

normally found in times of catabolic stress, illness, or infection

Question 6

What is nitrogen balance?

Answer 6

dietary nitrogen = excreted nitrogen

normally found in healthy adults

Question 7

What is the function of amino acids?

Answer 7

synthesis of new protein for growth and repair
replace damaged protein
to synthesize regulatory enzymes in response to metabolic conditions

Question 8

What is the function of transamination?

Answer 8

allow removal of alpha amino group from an aa
OR
allow transfer of alpha amino group from an aa to am alpha keto acceptor

Question 9

Describe the general transamination reaction.

Answer 9

amino acid 1 + alpha keto acid 1 < —- > alpha keto acid 2 + amino acid 2
via transaminase with a PLP cofactor

Question 10

What are the two key transaminase reactions?

Answer 10

GOT and GPT

Question 11

What is the GOT reaction?

Answer 11

Glutamate + OAA < – > alpha keto glutarate + Aspartate

via AST with a PLP cofactor

Question 12

What is the GPT reaction?

Answer 12

Glutamate + pyruvate < —- > alpha KG + Alanine

via ALT with a PLP cofactor

Question 13

____ reactions are involved in a typical transamination reaction.

Answer 13

Two half

Question 14

What happens in the first half reaction involved in transamination?

Answer 14

alpha amino group from donor amino acid is transferred to the PLP cofactor (present at the active site of the transaminase) and forms the alpha keto acid and the pyridoxamine P (Schiff base linkage)

Question 15

Descibe the second half reaction involved in transamination.

Answer 15

the first alpha keto acid product dissociates away from the active site and is replaced by a new alpha keto acid
the pyridoxamine cofactor transfers the amino group to the new alpha keto acid so that it it becomes the second amino acid product
the cofactor is regenerated
the second amino acid product dissociates

Question 16

What is a Schiff base linkage?

Answer 16

typical intermediate of reactions involving amino acid metabolism (transamination, decarboxylation, racemization, and modification of the side chains of amino acids)
can be broken at any of the linkages surrounding it depending on the reaction and the enzyme involved