Amino Acid Catabolism

Question 1

In uncontrolled diabetes, or a tumor, what is the energy source?

Answer 1

• Glucose cannot be used efficiently

- Fat and, if not available, protein will be degraded

Question 2

Where are most amino acids metabolized?

Answer 2

In the liver

Question 3

What happens to the ammonia? What happens to the carbon skeleton?

Answer 3

• Ammonia: recycled or excreted

- Carbon skeleton: TCA cycle, gluconeogenesis, ketogenesis

Question 4

What happens to proteins in the stomach?

Answer 4

• Gastrin –> HCl

- Pepsinogen –> pepsin: protein degradation

Question 5

What happens to proteins in the duodenum?

Answer 5

• Acidity stimulatse secretin, which stimulates the pancreas to produce bicarbonate
• pH rises to 7

Question 6

What does the pancreas secrete for protein degradation?

Answer 6

Trypsin and chymotrypsin

Question 7

What is the general amino acceptor?

Answer 7

a-ketoglutarate

Question 8

Aminotransferases are _____ specific

Answer 8

amino acid

Question 9

What happens when a-ketoglutarate accepts an amino group? What is the amino acid that lost its amino group known as?

Answer 9

• Glutamate

- a-Keto acid

Question 10

PLP uses _______ as a cofactor in transamination reactions

Answer 10

Vitamin B6

Question 11

Vitamin B6 is a cofactor for _____ and ______

Answer 11

PLP

glycogen phosphorylase

Question 12

What happens in the liver in deamination reactions?

Answer 12

• Glutamate dehydrogenase removes the amino group from glutamate
• Re-creates a-ketoglutarate

Question 13

Where does deamination occur?

Answer 13

Mitochondria of liver cells

Question 14

What is the role of glutamine synthase?

Answer 14

• Uses energy to incorporate ammonia, and forms glutamine

- Glutamine is excreted into circulation

Question 15

What is the role of glutaminase?

Answer 15

• Once glutamine is incorporated into the liver mitochondria

- Converts glutamine to glutamate, which removes the ammonia that is then excreted as urea

Question 16

Pyruvate accepts an amino group from _____ to form _____

Answer 16

glutamate

alanine

Question 17

In the liver, alanine is degraded by removing an ______ to form ______

Answer 17

amino

pyruvate

Question 18

Pyruvate undergoes ________ to produce glucose

Answer 18

gluconeogenesis

Question 19

What are the steps to the glucose-alanine cycle?

Answer 19

• Glucose –> Pyruvate
• Pyruvate + Amino group from Glutamate –> Alanine
• Liver: Alanine – amino group –> Pyruvate
• Pyruvate –> gluconeogenesis = glucose
• Glucose can be used for exercise

Question 20

What are the sources of ammonia that contribute to glutamate in the mitochondria?

Answer 20

• Glutamine
• Alanine
• Glutamate

Question 21

Glutamate can donate its amino group to form what? How many ammonias does that produce?

Answer 21

• a-Ketoglutarate

- 1 ammonia

Question 22

Glutamine can donate its amino group to form what? How many ammonias does that produce

Answer 22

• Glutamate, which can donate its amino group to form a-Ketoglutarate
• So, 2 ammonias total

Question 23

Ammonia from the intestines arrives to the liver, and is combined with ____ to form ______ through the enzyme ___________, which utilizes ____ ATPs

Answer 23

HCO3
carbonoyl phosphate
carbonoyl phosphate synthetase 1
2

Question 24

Oxaloacetate uses the amino group from __________ to form __________, with the enzyme ___________

Answer 24

glutamate
aspartate
Aspartate amino transferase

Question 25

_____, like Glutamate, is an amino group donor

Answer 25

Aspartate

Question 26

What are the four cytosolic enzymes of the urea cycle?

Answer 26

1. Ornithine transcarbamylase 2. Arginosuccinate synthase 3. Arginosuccinase 4. Arginase

Question 27

How is citrilline synthesized? What enzyme? Where does it travel to?

Answer 27

- Enzyme: Ornithine transcarbamylase - Combining carbonyl-phosphate and ornithine - Travels to the cytosol

Question 28

How is arginosuccinate synthesized? What enzyme?

Answer 28

- Enzyme: Arginosuccinate synthase | - Citrilline and aspartate are combined

Question 29

How is arginine formed in the urea cycle? What enzyme?

Answer 29

- Enzyme: Arginosuccinase | - Fumarase is discarded from arginosuccinate, to form arginine

Question 30

How is ornithine synthesized in the urea cycle? Where does it travel to?

Answer 30

- Enzyme: Arginase | - Urea is removed from arginine to synthesize ornithine, which travels to the mitochondria

Question 31

Which enzymes of the TCA cycle contain both cytosolic and mitochondrial isoforms?

Answer 31

- Fumarase | - Malate dehydrogenase

Question 32

Which intermediate of the TCA cycle contributes to the formation of Aspartate?

Answer 32

Oxaloacetate

Question 33

Which intermediates link the TCA cycle and the urea cycle?

Answer 33

- Oxaloacetate - Fumarate - Aspartate - Malate

Question 34

What is the carbon skeleton converted to during amino acid catabolism?

Answer 34

Intermediates of the TCA cycle

Question 35

What do glucogenic amino acids create? What can that be incorporated into?

Answer 35

- Pyruvate | - Can be incorporated into gluconeogenesis

Question 36

What do ketogenic amino acids create?

Answer 36

- Acetyl-CoA | - Intermediates of ketone body synthesis

Question 37

Which amino acids are both ketogenic and glucogenic?

Answer 37

- Isoleucine - Phenylalanine - Threonine - Tryptophan - Tyrosine

Question 38

Which amino acids are exclusively ketogenic?

Answer 38

Lysine and Leucine

Question 39

Which amino acids are ketogenic?

Answer 39

- Leucine - Lysine - Phenylalanine - Tryptophan - Tyrosine - Isoleucine - Threonine

Question 40

What is glutamate dehydrogenase activated by?

Answer 40

ADP

Question 41

What is glutamate dehydrogenase inhibited by?

Answer 41

GTP

Question 42

What are the 4 enzymes of the urea cycle and carbamoyl phosphate synthase 1 regulated by?

Answer 42

Nutritional status

Question 43

What happens to the enzymes of the urea cycle when an individual is starving?

Answer 43

Enzymes are increased since you are metabolizing more amino acids

Question 44

What happens to the enzymes of the urea cycle when an individual is consuming a protein-rich diet?

Answer 44

- Surplus amino acids = more ammonia produced | - Enzymes are upregulated

Question 45

What is the high-energy used by the urea cycle offset by?

Answer 45

By the NADH (2.5 ATP) malate-oxaloacetate conversion reaction

Question 46

How many ATPs are utilized in the urea cycle? At which stage(s)?

Answer 46

- 3 ATPs are utilized in the urea cycle - 2 ATP at carbamoyl phosphate - 1 ATP at the stage of secondary reaction