L21: AA Catabolism & Nitrogen Disposal (may)

Question 1

Why is removing the α-amino group so important?

Answer 1

1. Because that’s the first step in most AA degradation pathway
   * (or you can just say it’s the first step in aa catabolism)*
2. Because it is essential for energy production from AA carbon skeleton

Question 2

What is the fate of the AA nitrogen?

Answer 2

• It’s incorporated into other compounds
• Excess AA will be excreted as urea

Question 3

What are the 3 steps that produce urea?

Answer 3

1. Transamination
2. Oxidative Deamination
3. Urea cycle

Question 4

She9eer ib transamination blthab6?

Answer 4

It’s the first step in catabolism where il AA transfers its α-amino group wiya il α-ketoglutarate; this forms α-keto acid and glutamate.

Question 5

Il transfer elly y9eer ib transamination is catalyzed by what?

Answer 5

Transaminases (Aminotransferases)

Question 6

Where can transaminases be found?

Answer 6

in the mitichondria and cytosol

Question 7

What are the 4 characteristics of Transaminases?

Answer 7

1. Substrate specificity
2. Mechanism of action
3. Reaction equilibrium
4. Diagnostic value

Question 8

Alanine Aminotransferase (ALT) is in involved bas ib reactions involving Alanine & Aspartate Aminotransferase (AST) nafs il shay with Aspartate.

This is an example of what?

Answer 8

Substrate specifity in transamination

Question 9

All transamination reactions require?

Answer 9

the coenzyme pyridoxal phosphate (PLP)

Question 10

PLP (pyridoxal phosphate) is a derivative of?

Answer 10

Vitamin B6

Question 11

What is the equilibrium constant in transamination reactions? and why? and shnu faydat hal shay?

Answer 11

The equilibrium constant is near 1 because the reaction is bi directional, thus, have a role in both AA degradation AND synthesis pathways.

Question 12

what are indicators/diagnostic markers of most liver diseases, myocardial infarction, and muscle disorders?

Answer 12

High ALT & AST

Question 13

Where does oxidative deamination take place?

Answer 13

liver and kidney

Question 14

The liver and the kidneys have a specific dehydrogenase that carries out oxidative deamination of AA’s named what?

Answer 14

glutamate dehydrogenase

Question 15

Shesawee glutamate dehydrogenase blthab6?

Answer 15

it liberates the amine group as a free ammonia (NH3)

Question 16

What is the only AA that undergoes rapid oxidative deamination?

Answer 16

glutamate

Question 17

Shnu products il oxidative deamination? w laish nabeehum?

Answer 17

1. α-ketoglutarate: enters the central pathway of energy metabolism
2. Ammonia: source of Nitrogen for urea synthesis

Question 18

What is urea?

Answer 18

The major disposal form of amino groups derived from AAs

or just the end product of protein metabolism

Question 19

Urea accounts for?

Answer 19

about 90% of the nitrogen-containing components of urine

Question 20

What are the origins of urea molecules?

Answer 20

• One nitrogen from free ammonia
• The other nitrogen from aspartate
• The carbon and oxygen are derived from CO2

Question 21

Urea is produced by? Then transported to?

Answer 21

Produced by: the liver

Transported to: the kidneys for urinary excretion

Question 22

Describe the urea cycle

Answer 22

Question 23

What is the rate limiting step in the urea cycle?

Answer 23

Carbamoyl phosphate synthetase I

Question 24

What is an indicator of high levels of nitrogen in your body?

Answer 24

Arginine

Question 25

What will activate OR shut down the urea cycle?

Answer 25

Activate the urea cycle: HIGH levels of Nitrogen

Shut down the urea cycle: LOW levels of nitrogen

Question 26

What is an activator of N-Acetylglutamate (NAG) synthesis?

Answer 26

Arginine

Question 27

N-Acetylglutamate (NAG) is an essential what?

Answer 27

allosteric activator for carbomyl phosphate synthetase 1

(allosteric activator ya3ni it binds to an enzyme at a site other than the active site to enhance its activity)

Question 28

high levels of arginine enhances reaction shnu w shnu 3shan ya36eena NAG?

Answer 28

enhances il reaction between Glutamate & Acetyl CoA

Question 29

Describe she9eer laman you ingest a protein rich meal?

Answer 29

Ingestion of a protein-rich meal → ⬆️ [glutamate] (substrate & regulator of NAG synthesis) → ⬆️ [NAG] → ⬆️ CPSI activity → ⬆️ rate of urea synthesis.