9. Protein and Amino Acid Metabolism

Question 1

Where does exopeptidase munch protiens?

What about endopeptidase?

Answer 1

Exo = outside (C or N terminus)

Endo = Inside (Somewhere in the middle; internal peptide bonds)

Question 2

What pathway is used for proteasomal degradation?

Answer 2

Ubiquitin pathway (Protiens are marked by ubiquitin for degradation by a proteosome)

Question 3

Where do the amino groups from protien breakdown go?

Answer 3

To the urea cycle!

Question 4

What happens to the carbon skeletons in protein degradation?

Answer 4

They are used for energy - either storage as glucose / glycogen / fatty acid synthesis or as cellular respiration products (TCA cycle)

Question 5

What is the job of enterokinase?

Answer 5

Extracellular proteolysis

It’s found in the small intestine, where it activates trypsin, which activates chymotrypsin.

Question 6

What amino acids are not Glucogenic?

Answer 6

Leucine / Lysine

(Gluconeogenesis is for winners and these AAs are L-osers)

Question 7

What amino acids can be either glucogenic or ketogenic?

Answer 7

Phenylalanine

Isoleucine

Tryptophan

Tyrosine

Threonine

(They have to do TWO jobs? That’s the PITTTs!)

Question 8

What important products come from Phenylalanine?

Answer 8

Tyrosine ⇒ Epinephrine, Thyroid Hormones, Dopamine

Question 9

What important coenzyme do transaminases require?

Answer 9

PLP (pyridoxyl-5’-phosphate)

-derived from pyridoxine-

Question 10

What are the clinically relevant transaminases, and what are they used for in the body?

What about a clinical setting?

Answer 10

ALT / AST - both used for Glutamate ⇔ alpha-ketoglutarate reactions

Used as liver funciton markers

Question 11

What kind of amino acids cannot be degraded in the liver?

Where are they degraded?

What specific amino acids are they?

Answer 11

Branch-Chain Amino Acids

Muscle, Kidney, Brain

Valine, Leucine, Isoleucine

Question 12

Other than transaminases, what important amino acid metabolic enzyme requires PLP?
What disease is associated with its deficiency?

Answer 12

cystathionine beta-synthase

It catalyzes homocystine ⇒ Cystathionine, and its deficiency causes homocystinuria.

Question 13

Maple Syrup Urine disease is caused by a buildup of what kind of amino acids?

What is the deficient enzyme?

Answer 13

Branched chain

Branched Chain alpha-ketoacid Dehydrogenase

Question 14

People who pay attention to Phenylketonurics labels might have a deficiency in which enzyme?

Answer 14

Phenylalanine Hydroxylase

Question 15

What amino acid is made into the following?

Epinephrine

Thyroid Hormones

Dopamine

Melanin

Answer 15

Tyrosine

Question 16

What amino acid is made into the following?

Serotonin

Melatonin

Niacin

Answer 16

Tryptophan

Question 17

What amino acid is made into Acetylcholine?

Answer 17

Serine

Question 18

What two amino acids are used to remove ammonia in the brain?

Answer 18

Glutamate / Glutamine

Question 19

What two amino acids are used to remove ammonia in the tissues (not the brain)?

Answer 19

Alanine / Glutamine

(The G bros are the ammonia pros, but the tissues can’t afford both - so they just get glutamine and this guy Al from off the street)

Question 20

What aspect of ammonia’s toxicity might be most important to Dr. Agbas?

Answer 20

Its ability to cause mitochondrial dysfunction.

It can also permeate membranes to get to the mitochondria.

Question 21

What three amino acids make Creatine?

Answer 21

Methionine

Arginine

Glycine

(MAGazine for storing energy)

Question 22

In regards to ALT

What two Ketoacid/Amino acid complexes are changed between?

Answer 22

ALT

Pyruvate + Glutamate -> alpha-ketoglutarate + Alanine

(ALT is ELITE so it gets Pyruvate, AL- in ALT stands for Alanine. Both use Glutamate / Alpha-KetoGlutarate)

Question 23

In regards to AST

What two Ketoacid / Amino Acid complexes are switched between?

Answer 23

AST

Oxaloacetate + Glutamate <-> Alpha-Ketoglutarate + Aspartate

(AST - A Second-rate Transaminase gets the last product of TCA on one end, and the ASS(partate) end of the amino acid deal on the other)

Question 24

The disease Alkaptonuria (Ochronosis) is caused by a deficiency of what enzyme?

Answer 24

Homogentisate Oxidase

Question 25

Heme can be derived from what Amino Acid?

Answer 25

Glycine

Question 26

What amino acid gives rise to Thyroid Hormones?