Lecture 8 - Amino Acid Catabolism

Question 1

Which enzymes cleave peptide bonds?

Answer 1

Proteases

Question 2

Are amino acids stored?

Answer 2

Nope

Question 3

What is the purpose of amino acid metabolism?

Answer 3

To get the nitrogen out of the amino acid and into urea for excretion

Question 4

In general terms, what is the first step of amino acid catabolism?

Answer 4

Removal of the amino group from the carbon skeleton by transamination and deamination

Question 5

What happens to the amino group of an amino acid in the liver?

Answer 5

Amino groups are transferred to alpha-ketoglutarate, which converts the amino acid to a ketoacid and the alpha-ketoglutarate to glutamate

Question 6

_____ and _____ are converted to glutamate in the liver

Answer 6

Alanine and glutamine

Question 7

Where are alanine and glutamine degraded?

Answer 7

Muscle and other tissues

Question 8

Define transamination

Answer 8

Transferring the NH3 group from an amino acid to a ketoacid

Question 9

What does transamination require?

Answer 9

Pyridoxal phosphate (PLP)

Question 10

Define deamination

Answer 10

Removal of the NH3 group, generating free NH3

Question 11

What accompanies deamination?

Answer 11

Redox reaction using NAD or NADP

Question 12

Which molecules are always involved in transamination reactions?

Answer 12

Glutamate and alpha-ketoglutarate

Question 13

What is the enzyme that is used in transamination reactions?

Answer 13

(Name of amino acid being converted) transaminase

Question 14

What is the delta G value of transaminase reactions and what does this mean?

Answer 14

• delta G = 0

- They are fully reversible

Question 15

What is significant about the structure of pyridoxal phosphate?

Answer 15

The pyridine ring allows for movement of electrons from NH+

Question 16

Where is pyridoxal phosphate attached to the enzyme and when is it released?

Answer 16

• Attached at lysine

- Released for reaction to occur

Question 17

Which amino acid is most commonly deaminated?

Answer 17

Glutamate

Question 18

Which enzyme is involved in the deamination of glutamate?

Answer 18

Glutamate dehydrogenase

Question 19

Which cofactors are needed for the deamination of glutamate?

Answer 19

NAD+ + H2O -> NADH + H+

Question 20

What is produced in the deamination of glutamate?

Answer 20

Alpha-ketoglutarate

Question 21

Is the deamination of glutamate reversible?

Answer 21

Yes

Question 22

Which enzyme is involved in the deamination of alanine?

Answer 22

Alanine dehydrogenase

Question 23

Which cofactors are needed for the deamination of alanine?

Answer 23

NAD+ + H2O -> NADH + H+

Question 24

What is produced in the deamination of alanine?

Answer 24

Pyruvate and NH3

Question 25

What is involved in an amino acid oxidase?

Answer 25

Amino acid is converted to an alpha-ketoacid

Question 26

What are the cofactors needed in an amino acid oxidase reaction?

Answer 26

O2 + H2O -> NH3 + H2O2

Question 27

What occurs in the most common deamination route?

Answer 27

Transamination is used to generate glutamate, and then glutamate undergoes deamination

Question 28

Describe the deamination of aspartate

Answer 28

- Non-oxidative - Enzyme used is asparate alpha-deaminase - Produces fumarate and NH3

Question 29

Describe the deamination of serine

Answer 29

- Non-oxidative - Enzyme used if serine dehydratase - Produces pyruvate and NH3

Question 30

What is produced from oxidative deamination in muscle?

Answer 30

Ammonia

Question 31

What does transamination of amino acids in muscle cause?

Answer 31

Buildup of glutamate

Question 32

What is the function of glutamine in the blood?

Answer 32

Principle carrier of excess NH4

Question 33

How is glutamate converted to glutamine?

Answer 33

- Enzyme is glutamine synthetase | - Cofactors are NH3 in and ATP -> ADP + Pi

Question 34

How is glutamine converted to glutamate?

Answer 34

- Enzyme is glutaminase | - Cofactor is H2O -> NH4+

Question 35

What happens to the released NH4?

Answer 35

Enters the urea cycle

Question 36

_____ is the main route for the removal of NH4 from glutamate

Answer 36

Glutamate dehydrogenase

Question 37

____ is a secondary NH4 carrier

Answer 37

Alanine

Question 38

Where does alanine transport NH4?

Answer 38

From muscle to liver

Question 39

_____ is the main route for the removal of NH4 from alanine

Answer 39

Alanine dehydrogenase

Question 40

What happens to excess NH3?

Answer 40

Converted to urea and excreted

Question 41

Why is NH3 harmful?

Answer 41

High [NH3] activates glutamate dehydrogenase/glutamine synthetase, producing glutamate and glutamine, which uses up ATP/NADH and can be damaging to the brain