Protein Turnover & Amino Acid Catabolism

Question 1

What type of amino acids must be obtained from the diet?

Answer 1

Essential amino acids

Question 2

What is protein turnover?

Answer 2

The degradation and re synthesis of proteins

Constantly occurs in cells

Question 3

What are the two main reasons for protein turnover?

Answer 3

• the switching off of cellular pathways
• the removal of damaged proteins

Question 4

How does a cell distinguish what protein is to be degraded?

Answer 4

Uses a molecular flag called ubiquitin

Question 5

What does ubiquitin signal for?

Answer 5

The destruction of the protein

Question 6

What is ubiquitin joined to?

Answer 6

Lysine residues in the proteins to be degraded

Is added to proteins using a series of 3 enzymes

Question 7

What three enzymes are involved in protein ubiquitination?

Answer 7

1) ubiquitin activating enzyme (E1)

2) ubiquitin conjugating enzyme (E2)

3) ubiquitin ligase (E3)

Question 8

What is the function of ubiquitin activating enzyme?

Answer 8

Transfers the activated ubiquitin to one of its own cysteine residues

Question 9

What is the function of the ubiquitin conjugating enzyme?

Answer 9

Takes the activated ubiquitin from E1 and transfers it to one of its own cysteine residues

Question 10

What is the function of ubiquitin ligase?

Answer 10

Transfers the ubiquitin to a lysine residue on the target protein

Question 11

How many ubiquitin molecules are required for the signalling of degradation to be effective?

Answer 11

4

Question 12

What is the 19s regulatory units 3 functions?

Answer 12

(1) binds specifically to polyubiquitinated proteins

(2) as isopeptidase in the unit removes ubiquitin so that it can be recycled

(3) it unfolds and directs the doomed protein into catalytic core

Question 13

What is the first step in amino acid degradation?

Answer 13

Removal of nitrogen

Question 14

The amino group of the amino acid is transferred to…

Answer 14

a-ketoglutarate

Question 15

What does amino acid degradation produce?

Answer 15

Glutamate

Question 16

What are the enzymes that do an amino acid group transfer called?

Answer 16

Aminotransferases

Question 17

Aspartate aminotranaferase catalyses the transfer of amino group from…

Answer 17

Aspartate

Question 18

Alanine aminotranaferase catalyses the transfer of amino group from…

Answer 18

Alanine

Question 19

Outline what oxidative deamination is?

Answer 19

The production of a free ammonium ion from glutamate catalysed by glutamate dehydrogenase

Question 20

What is the oxidative deamination reaction Sri en forward by?

Answer 20

Rapid removal of the ammonium ion

Question 21

Where is glutamate dehydrogenase found?

Answer 21

In the mitochondria of liver cells

Question 22

What is ammonium ion converted into?

Answer 22

Urea which is then excreted

Question 23

What are the 3 objectives of degradation of amino acid carbon skeletons;

Answer 23

(1) transform the carbon skeletons into major metabolic intermediates

(2) to be used to produce glucose or oxidised in the citric acid cycle

(3) only 7 molecules are ultimately produced

Question 24

How often does maple syrup urine disease occur?

Answer 24

1 in 180,000 births

Question 25

What can an individual with maple syrup urine disease not break down?

Answer 25

Amino acids

Isoleucine

Leucine

Valine

Question 26

How are the 4 components broke down in maple syrup urine disease?

Answer 26

By the process of oxidative decarboxylation

Question 27

How is phenylketonuria caused?

Answer 27

By an absence of phenylaline hydroxylsse

Question 28

How often does phenylketonuria occur?

Answer 28

1 in 200,000 births

Question 29

Mutations in the gene can either: (phenylketonuria)

Answer 29

• reduce activity of the enzyme
• target the defective enzyme towards the proteasome