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(J) Biochemistry Test 3 > Lecture 31 - Amino Acid Catabolism > Flashcards

Lecture 31 - Amino Acid Catabolism Flashcards

1
Q

How are amino acids absorbed by the body?

L31 S5

A

Absorbed as single AAs, dipeptides, or tripeptides

Broken down using different enzymes such as:

  • pepsin
  • enteropeptidase
  • aminopeptidase (N-terminus)
  • dipeptidase
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2
Q

What are the main structures that degrade proteins in the cell?

L31 S6

A
  • proteasome

- lysosome

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3
Q

Describe the structure and function of the proteasome.

L31 S9

A

Structure:

  • two 19S regulatory end pieces
  • one 20S catalytic center piece

Function:

  • regulatory units bind and recognize ubiquitinated proteins
  • regulatory unit cleaves ubiquitin to be recycled
  • ATPase activity
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4
Q

What are the possible outcomes of AAs produced from proteolysis?

L31 S11

A
  • can be reduced and nitrogen disposed of
  • reused to make new proteins
  • carbon skeletons can but used to generate other substances
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5
Q

How are amino acids deaminated?

L31 S12

A

Most AAs use both (indirect deamination):

  • aminotransferase (unique to AA)
  • glutamate dehydrogenase (general)

Serine and threonine (direct deamination):
-only dehydratase (unique to AA)

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6
Q

What is the coenzyme for deamination and what is it derived from?

L31 S12

A

Pyridoxal phosphate (PLP)

Derived from pyridoxine (vitamin B6)

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7
Q

How does direct deamination occur?

L31 S13

A

Only occurs with serine and threonine (hydroxyl group attached to proximal carbon of AA)

Procedure:

  • AA is dehydrated resulting in double bond formation
  • water is then added back and amine group leaves (replaced by carbonyl)
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8
Q

How does indirect deamination occur?

L31 S15

A

Process:

  • amine group is transferred from AA to α-ketoglutarate to make glutamate (aminotransferase)
  • amine is removed from glutamate by glutamate dehydrogenase (used NAD+/NADP+)
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9
Q

What are the two special aminotransferases and what reaction do they catalyze?
Why are these reactions important?

L31 S16

A

Aspartate aminotransferase (AST)/serum glutamate-oxaloacetate transaminase (SGOT):

  • aspartate + α-ketoglutarate -> oxaloacetate + glutamate
  • interconverts aspartate and oxaloacetate

Alanine aminotransferase (ALT)/serum glutamate-pyruvate transaminase (SGPT):

  • alanine + α-ketoglutarate -> pyruvate + glutamate
  • interconverts alanine and pyruvate
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10
Q

What are the 4 molecules that contribute atoms to urea?

L31 S21

A
  • NH4+ (through carbamoyl phosphate)
  • CO2 (through carbamoyl phosphate)
  • H2O (contributes carbonyl)
  • aspartate (contributes NH2-)
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11
Q

What is the reaction catalyzed by carbamoyl phosphate synthase I?
What is special about this reaction?

L31 22

A

-CO2 + NH3 + 2ATP -> carbamoyl phosphate + ADP

Committing step of urea cycle

Activated by N-acetylglutamate (NAG)

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12
Q

What step of the urea cycle follows synthesis of carbamoyl phosphate?
What is special about this?

L31 S21

A

Carbamoyl phosphate + ornithine -> citrulline + Pi

This reaction takes place in the mitochondria and ornithine must be imported

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13
Q

What step of the urea cycle follows synthesis of citrulline?
What is special about this?

L31 S21

A

Citrulline + aspartate + ATP -> argininosuccinate + AMP + PPi

Reaction occurs in the cytoplasm. Both citrulline and aspartate must be exported from the mitochondria.

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14
Q

What step of the urea cycle follows synthesis of argininosuccinate?
What is special about this?

L31 S24

A

Argininosuccinate -> arginine + fumarate

Fumarate is imported into the mitochondria and recycled back into aspartate

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15
Q

What enzyme is used to convert oxaloacetate (intermediate of fumarate conversion) to aspartate?

L31 S25

A

Serum glutamate-OXALOACETATE transaminase (SGOT)/ASPARTATE aminotransferase (AST)

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16
Q

What step of the urea cycle follows synthesis of arginine?
What is special about this?

L31 S26

A

Arginine + H20 -> urea + ornithine

17
Q

What molecules are amino acid skeletons used to make? (7)

L31 S29-33

A
  • pyruvate
  • oxaloacetate
  • α-ketoglutarate
  • succinyl-CoA
  • fumarate
  • acetyl-CoA
  • acetoacetate
18
Q

What amino acids carbon skeletons are used to make pyruvate?

L31 S29

A
  • serine
  • threonine
  • glycine
  • alanine
  • cysteine
19
Q

What amino acids carbon skeletons are used to make oxaloacetate?

L31 S30

A
  • asparagine

- aspartate (using SGOT/AST)

20
Q

What amino acids carbon skeletons are used to make α-ketoglutrate?

L31 S31

A
  • glutamine
  • proline
  • arginine
  • histidine
  • glutamate (glutamate dehydrogenase)
21
Q

What amino acids carbon skeletons are used to make succinyl-CoA?

L31 S33

A
  • methionine
  • valine
  • isoleucine
22
Q

What are the ketogenic only AAs?

L31 S34

A
  • leucine

- lysine

23
Q

What AA’s are both glucogenic and ketogenic?

L31 S34

A
  • isoleucine
  • phenylalanine
  • threonine
  • tryptophan
  • tyrosine

(J) Biochemistry Test 3 (10 decks)

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