Protein and AA metabolism

Question 1

Hartnup Disease

Answer 1

Defects in AA reabsorption -> Cystinuria

Question 2

Exopeptidase

Answer 2

attacks at C terminus or N terminus ends

Question 3

Endopeptidase

Answer 3

Attacks within the protein at a specific site

Question 4

Intracellular proteolytic control

Answer 4

via large proteasome that cleave polyubiquinated proteins.

Question 5

Extracellular proteolytic control

Answer 5

Proteolytic enzymes secreted as needed. First secreted as inactive zymogens, that are activated by proteolytic cleavage -> ex. inactive trypsinogen and chymotrypsinogen are released into the SI lumen. Trypsinogen is activated by enterokinase and then activated trypsin activates chymotrypsinogen into chymotrypsin.

Question 6

Essential AA

Answer 6

TIM HRKL VFWQ

Question 7

Ketogenic AA

Answer 7

Leu and Lys

Question 8

Ketogenic and Glucogenic

Answer 8

Ile, Trp, Phe, Tyr, Thr

Question 9

Glucogenic AA

Answer 9

His, Met, Gly, Val, Arg, Ala, Pro, Asn, Asp, Ser, Gln, Glu, and Cys

Question 10

Common precursors of AA

Answer 10

OAA -> D
Pyruvate -> A, V, L
Ribose 5 P -> H
3 -PG -> S
å KG -> E
PEP + Erythrose 4P -> F

Question 11

AA that can enter TCA cycle and where?

Answer 11

F, Y, D -> Fumarate
M, V, T, I -> Propionyl CoA -> Succinyl-CoA
Q, P, H, R -> E -> å ketoglutarate

Question 12

Function of transaminases and cofactor

Answer 12

transfer amino group from AA to an å-ketoacid and require pyridoxyl 5-P (B6)

Question 13

Removal of amino group from Glutamate generates å -KG via 3 mechanisms

Answer 13

1. ) oxidation deamination by glutamate dehydrogenase which releases ammonium ion
2. ) transfer of Amino group to pyruvate by ALT
3. ) transfer of amino group to OAA by AST

Question 14

Homocystinuria

Answer 14

Deficiency in cystathione B-synthase leads to buildup of homocysteine, which can accumulate and be excreted in urine.

Question 15

Where are BCAs degraded?

Answer 15

BCAs are not degraded in liver due to the absence of the required aminotransferase. Instead they are degraded mainly in muscle, kidney, and brain.

Question 16

Consequences of hyperhomocysteinemia and homocystinuria

Answer 16

Vitamin deficiencies of (B6, B12, and folic acid) or genetic defects in the enzyme cystathionine ß-synthase cause defective metabolism of homocysteine and can lead to heart disease and stroke, mental retardation.

Question 17

Maple syrup urine disease

Answer 17

AR disease resulting from deficient branched-chain å-keto acid dehydrogenase complex (BCKD). BCAs present in urine, which give hallmark of maple syrup smell. Higher in mennonite, amish, and jewish populations.

Question 18

Phenylketonuria (PKU)

Answer 18

deficiency in phenylalanine hydroxylase. Phe instead is converted to phenyllactate and phenylacetate, resulting in severe impairment of brain function.

Question 19

Trp derivatives
Ser derivatives
Tyr derivatives
Glu derivatives

Answer 19

Trp: serotonin -> melatonin and Niacin -> NAD
Ser: Acetlycholine
Tyr: Dopamine -> Norepi -> Epi., Thyroid hormones, Melanin
Glu: GABA

Question 20

Albinism and Tyrosinase

Answer 20

Albinism is due to lack of melanin. Conversion of tyrosine to melanin is via tyrosinase. Blocking of this enzyme results in partial or complete absence of pigmentation in skin.

Question 21

Thyroglobulin and Thyroid hormones

Answer 21

Thyroglobulin is made from thyroid and has over 120 tyrosine residues.

Question 22

Ammonia removal in brain vs ammonia removal in other tissues

Answer 22

Glu -> Gln in brain and then Gln -> Glu in liver and NH4+ enters urea cycle
Ala -> pyruvate with å KG -> Glu and NH4+ enters urea

Question 23

Hyperammonemia w/ Orotic aciduria

Answer 23

X-linked recessive defect of ornithine transcarbamoylase.

Question 24

Ammonia toxicity

Answer 24

excessive ammonia due to disorders in the urea cycle or liver failure can have highly toxic effects on the brain and CNS.

Question 25

Urea cycle and the high protein diet

Answer 25

urea production is increased by a high protein diet and decreased by high carb diet.

Question 26

Creatine is made from which 3 AA?

Answer 26

R, G, M