Biochemistry

Question 1

What enzymes does Lead inhibit?

Answer 1

• delt-aminolevulinate Dehydratase (delt-ALA buildup)

- Ferrochelatase (Protoporphyrin IX buildup)

Question 2

Porphyria Cutanea Tarda (PCT) – most common porphyria – is caused by a defect in which enzyme?

Answer 2

Uroporphyrinogen Decarboxylase

Question 3

Which vitamin deficiency takes several years of reduced dietary intake to develop, due to large hepatic stores of the vitamin?

Answer 3

Cobalamin (vitamin B12)

Question 4

Propionic Acidemia is caused by a deficiency in what enzyme?

Answer 4

Propionyl CoA carboxylase

• converts Propionyl CoA → Methylmalonyl CoA
• Requires Biotin as cofactor

Tx = Avoid diet w/ Methionine, Threonine, Valine, & Isoleucine b/c they are broken down into Propionyl CoA

Question 5

Methylmalonyl Acidemia is caused by a deficiency in what enzyme?

Answer 5

Methylmalonyl Coa Mutase

• converts Methylmalonyl CoA → Succinyl CoA
• requires vitamin B12 as cofactor (so deficiency of this could be another cause)

Tx = same as Propionic Acidemia

(this also causes Propionic Acidemia in addition to methylmalonyl acidemia)

Question 6

During fasting, Gluconeogenesis occurs. The initial committed step in this process is what?

Answer 6

Conversion of Pyruvate to Oxaloacetate in the mitochondria

& subsequent conversion of Oxaloacetate to PhosphoEnolPyruvate

Question 7

Key function of ApoA-I?

Answer 7

LCAT activation (cholesterol esterification)

Question 8

Key function of ApoB-48

Answer 8

Chylomicron assembly & secretion by the intestine

Question 9

Key function of ApoB-100?

Answer 9

LDL particle uptake by extra hepatic cells

Question 10

Key function of ApoC-II?

Answer 10

Lipoprotein Lipase activation

Question 11

Key function of ApoE-3 & 4?

Answer 11

VLDL & chylomicron remnant uptake by liver cells

Question 12

Hyperammonemia in hepatic encephalopathy causes depletion of ___a____ which results in inhibition of the TCA cycle.
Excess ammonia also depletes ___b___, an excitatory neurotransmitter, causing accumulation of ___c___, resulting in astrocyte swelling & dysfunction.

Answer 12

a) α-ketoglutarate
b) glutamate
c) glutamine

Question 13

Pompe’s Disease is caused by a deficiency in what enzyme?

Answer 13

Acid α-glucosidase

Question 14

In contrast to ___a___, which remove nucleotides from the end of a DNA molecule, ___b___ cut DNA at very specific DNA sequences w/in the molecule.

Answer 14

a) exonucleases

b) endonucleases

Question 15

Activity of which enzyme is the main cause of cataracts that occur in galactokinase deficiency?

Answer 15

Aldose reductase
(converts excess galactose to galactitol in retina cells)

Question 16

Tetrahydrobiopterin (BH4) is a cofactor for the enzymes involved in the synthesis of what molecules?

Answer 16

• Tyrosine
• DOPA (→melatonin) (→catecholamines)
• Serotonin (from Tryptophan)
• Nitric Oxide

Question 17

2 possible causes of Phenylketonuria?

Answer 17

1) Phenylalanine Hydroxylase lack of function (most common)

2) Dihydrobiopterin Reductase deficiency
this enzyme recycles BH2 → BH4 for use as Phenylalanine Hydroxylase cofactor

Question 18

RNA that contains nucleosides such as thymidine, pseudouridine, or dihydrouracil is what type of RNA?

Answer 18

tRNA

(Dihydrouracil = D arm)

(imp b/c have diff structures & I got a question about the structure of RNA w/ these nucleosides)

Question 19

What is the composition of the 3’ end of a tRNA molecule? 5’ end?

Answer 19

3’ end = CCA sequence used as a recognition sequence for the amino acid

5’ end = Terminal phosphate

Question 20

How do TNF-α, glucocorticoids, catecholamines, & glucagon increase insulin resistance?

Answer 20

They activate intracellular Serine Kinases, which phosphorylate Serine & Threonine residues on IRS-1.
This prevents tyrosine phosphorylation of IRS-1 by insulin (i.e. inhibits the Insulin receptor pathway)

Question 21

Orotic Aciduria - Tx?

Answer 21

Uridine supplementation

inhibits carbamoyl phosphate synthetase II

Question 22

Name the substrates that increase & decrease the activity of PFK-1

Answer 22

Increase = AMP & F-2,6-BP

Decrease = Acetyl CoA, Citrate, & ATP