Simmon's-Amino Acid Metabolism

Question 1

Where can free amino acids be derived from?

Answer 1

1. Degradation of ingested protein
2. Bio-synthesis of amino acids (non essential ones)
3. Degradation of endogenous protein

Question 2

What can amino acids be degraded to?

Answer 2

Carbon Skeletons–> glucogenic (pyruvate and parts of CAC) and ketogenic (acetoacetate, acetyl coA)
-can be used immediately for energy or stored as glycogen or fat for future energy production
Nitrogen–> urea

Question 3

What are amino acids used for?

Answer 3

1. re-synthesis of endogenous protein
2. precursors for synthesis of other biomolecules (Purines, Pyrimidines, Porphyrins, Others)
3. for energy production (amino group is excreted as urea in the process)

Question 4

Which enzymes are the most rapidly degraded?

Answer 4

the rate limiting enzymes

Question 5

How much of the ingested protein is degraded?

Answer 5

All of it-cant increase muscle mass by ingesting more protein?

Question 6

If you don’t ingest enough protein do you still degrade protein?

Answer 6

Yes degradation is required

Question 7

What is the nitrogen balance?
Positive Balance
Negative Balance

Answer 7

Nitrogen balance=nitrogen ingested-nitrogen excreted

Positive balance= synthesis>degradation

e. g. growth in children, pregnancy, and bodybuilding
- proteins synthesis occurs at a slightly higher rate than protein degradation

Negative balance=
protein synthesis< degradation
e.g. starvation, protein malnutrition, trauma, infection, cancer, burn injury, sepsis, surgery
(rate of protein degradation can be accelerated in case of disease)

Question 8

Where is urea synthesized?

Answer 8

liver

Question 9

What is urea excreted by?

Answer 9

kidney

Question 10

What are the two steps from amino acids to urea?

Answer 10

1. glutamate

2. ammonia or aspartate

Question 11

What happens if children have a deficiency in an essential amino acid, what about an adult?

Answer 11

children: retard in growth
adult: loss of body protein

Question 12

What are the two primary pathways for protein degradation?

Answer 12

ATP dependent ubiquitin

lysosomal pathway

Question 13

What is the range of half lives?

Answer 13

few minutes to many days

regulatory proteins tend to be degraded and resynthesized at faster rates

Question 14

Adults degrade and resynthesize how much of their total body protein everyday? how much loss

Answer 14

300 g
2-3%

55g loss (loss must be replaced by dietary protein)

Question 15

Transamination

Answer 15

Step in the degradation of most amino acids
transfer of the amino group to alpha-ketoglutarate to from glutamate

amino group+ alpha ketoglutarate–>glutamate

(enzyme….transaminase, eg. alanine transaminase)

Question 16

What cofactor is required for transaminases?

Answer 16

pyridoxal phosphate (active derivative of vitamin B6)

Question 17

During tissue damage cells necrose and release transaminases, what does an increase in alanine transaminase mean, what about aspartate transaminase?

Answer 17

ALT: hepatitis, cirrhosis, liver metastases, obstructive jaundice, infectious mononucleosis, pancreatitis, renal disease, alcohol ingestion

AST: liver disease, heart failure, myocarditis, pericarditis, myositis, muscular dystrophy, trauma, pancreatitis, renal infarct, eclampsia, neoplasia, cerebral damage, seizures, hemolysis, alcohol ingestion

Question 18

How is glutamate made into aspartate?

Answer 18

Glutamate+Oxaloacetate–>alpha ketoglutarate+ aspartate

enzyme: aspartate transaminase

Question 19

How is glutamate made into ammonia?

Answer 19

glutamate + NAD(P)+ H20–> NH4 + alpha-ketoglutarate + NAD(P)H

enzyme: glutamate dehyrogenase

Question 20

What is the major regulated step in urea formation? What is its allosteric activator?

Answer 20

Formation of carbamoyl phosphate

enzyme: carbamoyl phosphate synthetase 1)

Question 21

When enzyme changes arginine to urea in the last step of urea formation?

Answer 21

arginase

Question 22

What is its allosteric activator of carbamoyl phophate synthetase 1?

Answer 22

Activator: N-Acetylglutamate

–>increased levels of glutamate lead to increased levels of N-acetylglutamate

Question 23

What does a long-term exposure to high protein diet or a high rate of protein degradation do to levels of urea cycle enzymes?

Answer 23

increased

Question 24

What part of the urea cycle take place in the mitochondria

Answer 24

synthesis of carbamoyl phosphate

citrulline leaves
ornithine enters

Question 25

What two amino acids carry nitrogen to the liver?

Answer 25

Alanine (via alanine-glucose cycle)

Glutamine

Question 26

What is the function of urea biosynthesis?

Answer 26

detoxification of ammonia

Question 27

What happens if ammonia concentration gets too high

Answer 27

hyperammonenia –>predisposes to coma
–>hepatic coma results from decreased capacity of liver to remove ammonia

–>acquired hyperammonemia: portal systemic shunting
ammonia produced by bacteria in intestine is absorbed but not converted to urea in the liver–> “portal-systemic encephalopathy”

–>genetic

Question 28

Glucogenic

Answer 28

yields TCA cycle intermediates or pyruvate that can be used for gluconeogenesis

Question 29

Ketogenic

Answer 29

yields acetyl CoA, acetoacetyl CoA, or acetoacetate

Ex: lysine and leucine

Question 30

What amino acids are both glucogenic and ketogenic?

Answer 30

Isoleucine, Phenylalanine, Threonine, Tryptophan, Tyrosine

Question 31

In muscle transient storage after a meal is caused by what?

Answer 31

stimulation of protein synthesis (by aa and insulin)

inhibition of protein degradation (insulin)

Question 32

During an overnight fast, the decrease in what leads to net degradation and release of amino acids for gluconeogeneis in the liver?

Answer 32

• the decrease in plasma aa and insulin

- increase in glucagon