Chapter 9 Protein Regulation Part II

Question 1

What is the function of amino acids besides being the building blocks for peptides and proteins?

Answer 1

Amino acids may be oxidized for fuel.

Question 2

What is the cofactor we will explore in this chapter?

Answer 2

The pyridoxal phosphate.

Question 3

From what vitamin is the cofactor pyridoxal pyrophosphate derived?

Answer 3

Vitamin B6. Vitamin B6 is converted to the aldehyde and phosphorylated to form the cofactor pyridoxal pyrophosphate.

Question 4

How is the cofactor attached to the enzymes that require this cofactor?

Answer 4

Schiff base.

Question 5

Ammonotelic

Answer 5

excess ammonia directly flushed into the surrounding water.

Question 6

Ureotelic

Answer 6

organisms that convert ammonia to urea.

Question 7

Uricotelic

Answer 7

organisms that convert ammonia to uric acid.

Question 8

Why do we make urea?

Answer 8

ammonia within the body must be eliminated.

Question 9

What is the source of the nitrogen in urea biosynthesis?

Answer 9

amino acids.

Question 10

What are the central four amino acids of nitrogen metabolism?

Answer 10

glutamate

glutamine

alanine

aspartate

Question 11

What molecule forms when amino group is freed from glutamate?

Answer 11

alpha-ketoglutarate

Question 12

What molecule forms when amino group is freed from glutamine?

Answer 12

alpha-ketoglutarate

Question 13

What molecule forms when amino group is freed from alanine?

Answer 13

pyruvate

Question 14

What molecule forms when amino group is freed from aspartate?

Answer 14

oxaloacetate

Question 15

In what organ does amino acid catabolism take place?

Answer 15

Liver

Question 16

Chemical Mechanism for amino acid decarboxylation

Answer 16

refer to slides

Question 17

Chemical Mechanism for amino acid racemization

Answer 17

refer to slides.

Question 18

What is the role of the pyridoxal phosphate?

Answer 18

temporarily store these electrons through resonance stabilization.

Question 19

In what form is most of the nitrogen from skeletal muscle transferred to the liver?

Answer 19

alanine

Question 20

In what form is most of the nitrogen from some muscle and other metabolically active tissues transported to the liver?

Answer 20

glutamine

Question 21

Write mechanism of transamination

Answer 21

refer to slides.

Question 22

How are amino groups liberated from glutamate in the liver? What cofactor is required for this process?

Answer 22

through the enzyme L-glutamate dehydrogenase.

cofactor: NAD+ or NADP+

Question 23

What are allosteric regulators of L-glutamate dehydrogenase?

Answer 23

ADP positive allosteric modulator

GTP negative allosteric modulator

Question 24

What is the intercellular transport molecule that carries much of the excess ammonia from the tissues to the liver?

Answer 24

glutamine

Question 25

What is the mechanism for carrying excess ammonia from the muscle to the liver?

Answer 25

Phosphorylation of the side chain carboxyl in glutamate and glutamine creates a good leaving group. Nitrogen of ammonia acts a nucleophile to displace the inorganic phosphate.

Question 26

Which molecule provides the carbon for urea in the urea cycle?

Answer 26

bicarbonate.

Question 27

What is the origin of the first and second nitrogen atoms in the urea cycle?

Answer 27

First: ammonia Second: aspartic acid

Question 28

What is the origin of the oxygen?

Answer 28

water

Question 29

How is the balance of nitrogen maintained through both sides of the mitochondrial matrix?

Answer 29

Through the aspartate-glutamate antiporter, for every aspartate that is leaving glutamate carries new nitrogen to regenerate ammonia population.

Question 30

How is the balance of carbon maintained through both sides of the mitochondrial matrix?

Answer 30

Through the ornithine-citruline antiporter, for every citruline that leaves ornithine enters maintaining the carbon balance.

Question 31

What is the role of the first two ATP consumed in the urea cycle?

Answer 31

1. ATP activates bicarbonate. 2. ATP activates carbamide.

Question 32

What is the role of the third ATP?

Answer 32

Third ATP activates citruline forming citrullyl-AMP intermediate.

Question 33

Name the major allosteric regulator of the urea cycle.

Answer 33

N-acetyl glutamate.

Question 34

Explain what enzyme N-acetyl glutamate regulates and how?

Answer 34

N-acetyl glutamate regulates the carbomoyl phosphate synthase-I. N-acetyl glutamate is a positive allosteric regulator of the urea cycle.

Question 35

Explain what enzyme N-acetyl glutamate regulates and how?

Answer 35

N-acetyl glutamate regulates the carbomoyl phosphate synthase-I. N-acetyl glutamate is a positive allosteric regulator of the urea cycle. N-acetyl glutamate is produced from acetyl coA and glutamate. Therefore, when these compounds are abundant there is a need for the urea cycle.

Question 36

What are other ways in which the urea cycle is regulated?

Answer 36

substrate availability and enzyme synthesis turnover. More protein we eat more urea generated.

Question 37

How are urea cycle disorders treated?

Answer 37

Limiting protein intake.