Amino acid metabolism

Question 1

What is the concentration of free amino acids in plasma?

Question 2

Where do free amino acids come from?

Answer 2

Degradation of dietary protein
Synthesis of some proteins
Degradation of endogenous protein

Question 3

For what are free amino acids used?

Answer 3

For resynthesis of endogenous proteins
Energy production
As precursors for other biological pathways

Question 4

What happens in essential amino acid deficiency?

Answer 4

Since proteins require pretty much every amino acid, a missing or inadequate intake of a single amino acid can stunt growth in children or lead to protein breakdown in adults

Question 5

Two primary pathways for protein degradation

Answer 5

ATP-dependent ubiquitin-proteasome system and lysosomal pathway

Question 6

Relative breakdown time of regulatory proteins

Answer 6

Tend to be degraded and resynthesized faster than other proteins

Question 7

How much protein is lost every day and must be re-supplied by diet?

Answer 7

55 g

Question 8

What are examples of body states that would require positive nitrogen balance?

Answer 8

Growth in children, pregnancy, bodybuilding

Question 9

Major regulated step in the synthesis of urea

Answer 9

Synthesis of carbamoyl phosphate

Question 10

Where does urea biosynthesis occur?

Answer 10

In the liver

Question 11

Transamination

Answer 11

Transfer of the amino group to AKG to form glutamate

Question 12

Cofactor required for transaminases

Answer 12

Pyridoxal phosphate (derivative of B6)

Question 13

Alanine transaminase blood levels

Answer 13

Shows some sort of inflammation in the liver mostly, as well as some in the pancreas and kidney

Question 14

Aspartate transaminase blood levels

Answer 14

Shows inflammation/pathology somewhere.

Question 15

Aspartate transaminase

Answer 15

Glutamate that was just formed donates its nitrogen side chain to oxaloacetate, creating aspartate

Question 16

Glutamate dehydrogenase

Answer 16

NADP/NAD+ reduces glutamate to alphaketoglutarate and releases the nitrogen group to make ammonium

Question 17

Major regulated step in the synthesis of urea

Answer 17

Synthesis of carbamoyl phosphate

Question 18

What is absolutely required in the formation of carbamoyl phosphate?

Answer 18

N-acetylglutamate

Question 19

Overall reaction of the formation of urea

Answer 19

Aspartate + ammonia + CO2 + 3 ATP + 3 H2O -> urea + fumarate + 2 ADP + AMP + 4 Pi

Question 20

Where do things take place during urea formation?

Answer 20

Formation of carbamoyl phosphate and citrulline take place in the mitochondria. The others are in the cytosol.

Question 21

Control of the urea cycle

Answer 21

The amount of glutamate, which is higher postprandially, will lead to higher amounts of N-acetylglutamate and increase the activity of the urea cycle

Question 22

Main carriers of nitrogen to the liver

Answer 22

Alanine and glutamine

Question 23

Hyperammonemia

Answer 23

Too high of concentration of ammonia in the blood, which predisposes to coma

Question 24

Acquired hyperammonemia

Answer 24

Usually due to shunting of blood around the liver due to cirrhosis; ammonia produced from bacteria in the intestines is not converted to urea. Leads to “portal-systemic encephalopathy.”

Question 25

Ketogenic amino acids

Answer 25

Leucine and lysine

Question 26

Amino acids that are both ketogenic and glucogenic

Answer 26

Tyrosine
Tryptophan
Threonine
Isoleucine
Phenylalanine