Metabolism III: Protein

Question 1

Can amino acids be synthesized de novo?

Answer 1

Yes, but nitrogen has to come from the environment

Question 2

Where are all AAs derived from?

Answer 2

intermediates in:
glycolysis
CAC
PPP-pyruvate

Question 3

Nitrogen enters the pathways by way of…

Answer 3

glutamate and glutamine

Question 4

How many AAs can plants and bacteria synthesize?

Answer 4

all of them

Question 5

How many AAs can mammals synthesize?

Answer 5

only about half of them

Question 6

What are the fates of carbon skeletons?

Answer 6

• ketogenic AAs
• Glycogenic AAs
• Gluco- and ketogenic AAs

Question 7

How can AAs be classified?

Answer 7

• essential vs nonessential
• fate of C skeleton
• hydrophobic vs hydrophilic

Question 8

AAs as a source of energy

Answer 8

humans derive a small fraction of their oxidative energy from the catabolism of AAs

Question 9

What are the three AA metabolic states?

Answer 9

• protein turnover
• dietary protein
• during starvation and uncontrolled diabetes

Question 10

What happens to AAs during protein turnover?

Answer 10

Was released from breakdown of cellular proteins

Question 11

What happens to AAs during dietary protein?

Answer 11

• Surplus AAs undergo oxidative degradation

- they cannot be stored

Question 12

What happens to AAs during starvation?

Answer 12

Muscle protein broken down to release AAs

Question 13

What happens to AAs in uncontrolled diabetes?

Answer 13

Carbohydrates are not properly utilized

Question 14

The AAs lose their amino groups to form what during metabolism?

Answer 14

a-keto acids (the carbon skeletons of AAs_

Question 15

What are the two metabolic fates of a-keto acids?

Answer 15

• undergo oxidation (Krebs) to CO2 and H2O

- provide 3 and 4 carbon units that can be converted by gluconeogenesis into glucose

Question 16

Where do the processes of AA degradation converge?

Answer 16

Krebs cycle

Question 17

What four AAs play a central role in AA metabolism?

Answer 17

• glutamate (a-KG)
• glutamine (a-KG)
• alanine (pyruvate)
• aspartate (oxaloacetate

Question 18

What are the two major biochemical processes that occur during AA catabolism?

Answer 18

• transamination

- deamination

Question 19

What is the enzyme involved in the process of alanine-glucose cycle?

Answer 19

alanine aminotransferase

Question 20

What is the enzyme involved in the process between a-KG and glutamate?

Answer 20

valine aminotransferase

Question 21

Where does transamination of alanine-glucose cycle occur?

Answer 21

• muscle

- Cytosol of liver

Question 22

What AA metabolism occurs during transamination in the muscle?

Answer 22

alanine- glucose cycle

Question 23

What is the reaction that occurs during alanine-glucose cycle?

Answer 23

Glutamate + pyruvate –> alanine + aKG (pyruvate)

Question 24

What does the alanine do in the alanine-glucose cycle?

Answer 24

• alanine transports ammonia from skeletal muscle to liver

Question 25

What is the alanine-glucose cycle in concert with?

Answer 25

Cori cycle

Question 26

What happens to pyruvate and lactate during the alanine-glucose cycle?

Answer 26

- transported to liver for gluconeogenesis - ammonia converted to urea in liver - energetic burden is imposed on liver and not muscle

Question 27

Where does deamination occur?

Answer 27

mitochondria of liver

Question 28

What is the reaction of deamination?

Answer 28

glutamate --> Ammonia + aKG

Question 29

Where does the ammonia in deamination go?

Answer 29

urea cycle

Question 30

Where does aKG go in deamination?

Answer 30

Krebs cycle | gluconeogenesis

Question 31

What enzyme is used in the conversion of glutamate + ammonia to glutamine?

Answer 31

Glutamin synthetase

Question 32

What is the enzyme used in the conversion of glutamine to glutamate?

Answer 32

Glutaminase

Question 33

What organ is more susceptible to ammonia toxicity?

Answer 33

Brain

Question 34

What occurs during the mechanisms of ammonia?

Answer 34

molecular mechanism is unclear

Question 35

What are the terminal states of ammonia intoxication in humans characterized by?

Answer 35

- comatose state - cerebral edema - increased cranial pressure

Question 36

What is the major acceptor of ammonia?

Answer 36

- glutamate (forms glutamine) | - this will deplete glutamate

Question 37

Glutamate and its derivative (gamma-aminobutyrate) are important ...

Answer 37

NTs

Question 38

What happens to the free ammonia produced in the extra-hepatic tissues?

Answer 38

converted to a non-toxic product

Question 39

What AA is affected in albinism

Answer 39

melanin synthesis from tyrosine

Question 40

What AA is affected in alkaptonuria?

Answer 40

Tyr degradation

Question 41

What AA is affected in maple syrup disease?

Answer 41

(branched chain ketoaciduria) | Iso, Leu, Val degradation

Question 42

What AA is affected in phenylketonuria?

Answer 42

conversion of Phe to Tyr