Protein Turnover And Amino Acid Catabolism(Week 4)

Question 1

Give three sources of amino acids.

Answer 1

Ingested in the diet
Turnover of endogenous proteins
De novo biosynthesis

Question 2

Give three uses of amino acids

Answer 2

Protein synthesis
Nitrogen and carbon source of general and special product biosynthesis
Energy source

Question 3

What types of organisms oxidise amino acids to give energy

Answer 3

Carnivores. Not herbivores or plants

Question 4

What are the three circumstances where amino acids undergo oxidative degradation.

Answer 4

Normal synthesis and degradation of excess cellular proteins.
When a protein rich diet exceeds the body’s need for protein, the surplus is stored as glucose, glycogen or fats as amino acids cannot be stored
During starvation or uncontrolled diabetes.

Question 5

Where does amino acids catabolism occur?

Answer 5

The liver

Question 6

What happens in the liver with regards to amino acid catabolism

Answer 6

Excess amino groups are transferred to alphaketoglutarate to form glutamate.

Question 7

What happens in skeletal muscles with regards to amino acid catabolism

Answer 7

Excess amino groups are transferred to pyruvate to form alanine, which is then converted to glutamate.

Question 8

What happens in all other tissues with regards to amino acid catabolism

Answer 8

Excess amino groups are transferred to the R-group of glutamine then converted to glutamate

Question 9

Why are glutamate and glutamine important for nitrogen metabolism

Answer 9

They act as a general collection point for amino groups

Question 10

Essential amino acids cannot be synthesised and need to be obtained in the diet. What are the 9 essential amino acids?

Answer 10

Histidine 
Isoleucine 
Leucine 
Methionine 
Phenylalanine 
Threonine 
Valine

Question 11

What causes acute pancreatitis?

Answer 11

The zymogens of the proteolutic enzyme are converted to the active forms prematurely, attacking the pancreatic tissue.

Question 12

Protein turnover needs to be tightly regulated. What is the protein which tags other proteins for distraction?

Answer 12

Ubiquitin

Question 13

Give an overview of how ubiquitin attaches to the protein.

Answer 13

Attach AMP
Attach E1
Attach E2
Bind to E3 and get close to the target
Attach to target

Question 14

What can a defective E3 enzyme cause?

Answer 14

Protein aggregation

Question 15

What is the specific amino acid sequence called which determines the half life of proteins?

Answer 15

Degrons

Question 16

What is the role of theE3 enzyme?

Answer 16

To read the N-terminal residues.

Question 17

What machine causes the ‘death’ of proteins, and what is its structure?

Answer 17

The 20S proteasome. It is comprised of 28 homologous subunits arranged on four rings of seven subunits each.

Question 18

What are the functions of the 19S complex?

Answer 18

Detect ubiquitin
Cleave off intact UBQ
Unfold the ‘doomed’ protein

Question 19

What is the first step in amino acid degredation

Answer 19

Transamination reaction.

This form glutamate and a carbon skeleton.

Question 20

What is the second step in amino acid degradation?

Answer 20

Oxidative deamination of glutamate. This forms ammonium ions.
Glutamate dehydrogenase, releases NH4+. Glutamate dehydrogenase uses NAD+ or NADP+. This sequesters a free ammonium ion which is toxic.

Question 21

What happens to the NH4+ ions?

Answer 21

The peripheral tissues transport nitrogen to the liver.
NH4+ + glutamate + ATP = glutamine + ADP + Pi.
This uses the glutamine synthesise enzyme.

Question 22

What cycle allows branches amino acids to be broken down in the muscle?

Answer 22

The glucose adenine cycle.

Question 23

What do the enzymes aminotransferases do?

Answer 23

Use transaminition reactions to make glutamate.

Question 24

What does the enzyme glutamate dehydrogenase do and where is it found?

Answer 24

In the liver.

Used to make ammonium and NAD(P)H, as well as regenerating alpha-ketoglutarate.

Question 25

What are the products of the urea cycle?

Answer 25

Urea and fumarate.

Question 26

What products can urea go on to create?

Answer 26

Glucose or aspartate.

Question 27

The presence of what in the blood indicates liver damage?

Answer 27

Alanine and aspartate aminotransferase

Question 28

How are the carbon skeletons processed?

Answer 28

Carbon skeletons are metabolised to seven major matabolic intermediates.
Amino acids metabolised to Acetyl CoA and acetoacetyl CoA are ketogenic amino acids because they form fats but not glucose, the only amino acids that are ketogenic are leucine and lysine.
The rest are. Allied glucogenic amino acids.