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Flashcards in Biochem Deck (26):
1

Homocysteine can be converted into ________ or ______

methionine or cystathione

2

homocysteine to cystathione requres ______, _____ and _____.

Serine, B6 (pyridoxine) and cystathionine synthase

3

homocysteine to methionine requires what co-factors/enzymes?

homosysteine + 5 methyl THF + methylcobalumin ==> methionine + THF + B12

Enzyme = methionine synthase

4

What are the most serious serious consequences of homocystinuria?

hypercoagulability and thromboembolic occlusion ==> premature acute coronary syndrome (e.g. 12 yr old athlete with a heart attack in increased serum methionine levels)

5

What enzyme is likely eleveated in homocystinuria?

cystathionine synthase (B-6 cofactor; requires serine AA) catalyzeses conversion of homocysteine to cystathionine.

6

homocystinuria is associated with what clinical features?

ectopia lentis (ocular lens displacement)
intellectual disability
thrombosis/premature acute coronary syndrome

7

What amino acid is essential in pt. with homocystinuria?

cysteine! cannot convert homocystein to cyctathionine to cysteine

8

what amino acid is essential for rapidly deviding tumor cells?

asparagine (asparagine synthase converts aspartate to asparagine)

-tumor cells cannot produce asparagine quickly enough
-asparaginase chemothapy drug leads to lysis of rapidly growing cells

9

what enzyme is deficient in maple syrup urine disease?

defiiency in branched chain alpha-ketoacid dehydrogenase

-leads to buidup of

10

defiiency in branched chain alpha-ketoacid dehydrogenase causes _____, which manifests due to buildup of what AAs?

branched gain amino acids

Leucine, isoleucine, valine

11

what are the ketogenic aminio acids?

lysine,

12

What AA is essential in PKU?

tyrosine

PKU = pehnylalanine hyoxylase deficiency, which converts phenalalanine to tyrosine

13

what in addition to pehnylalanine hyoxylase deficiency can cause PKU?

deficiency in biosynthesis of tetrahydrobiopterin (BH4)

14

BH4 is a co-factor for conversion of phenylalanine to tyrosine and required for monoamine biosynthesis. What is another important role for BH4 that is unrelated to these processes?

co-factor in nitrous oxide production

15

What is the source of nitrogen for the formation of NO?

arginine

L -arginine + BH4 + nitrous oxide synthetase =>NO+ prod

16

symptoms of hyperamonemia are caused by depletion of what TCA intermediate?

alpha-ketoglutarate (shuts down TCA cycle)

used by rxn in liver tht leads to alanine (NH3) + alpha-ketoglutarate => pyruvate + glutamate (NH3)

17

what TCA/glycolytic rxns are most affected by thiamine deficiency?

pyruvate dehydrogenase (B1 cofactor)
alpha-ketoglutarate dehydrogenase (B1 co-factor)

also transketolase (PRshunt)

18

what TCA/glycolytic rxns are most affected by chronic alcohol consumption?

pyruvate dehydrogenase (B1 cofactor)
- NAD+ is depleted by alcohol dehydrogenase and acetaldehyde dehydrogenase resulting in INCREASED NADH/NAD+ ratio
- depletion of NAD+ impairs several dehydrogenase rxns including:

pyruvate dehydrogenase (B1 cofactor)

alpha-ketoglutarate dehydrogenase (B1 co-factor)

Malate dehydrogenase

isocitrate dehydrogenase

19

what enzyme converts phenylalanine to tyrasine?

phenylalanine hydroxylase

20

what enzyme converts tyrasine to L-dopa?

tyrasine hydroxylase

21

what enzyme is inhibited by carbadopa? what co-factor is required for this enzyme:?

dopamine decarboxylase (converts L-dopa to dopamine)

B6

22

what is homosystinuria caused by

autosomal recessive mutation of cystathionine beta synthase which leads to the inability to form cysteine from homocysteine and the buildup of methionine and homocystein

MAJOR CHARACTERISTICS THAT DISTINGUISH FROM MARFANS = INTELLECTUAL DISABILITY AND HYPERCOAGULABILITY - e.g. thombosis of the superior sagital sinus

23

insulin has what effect on phosphofructokinase-2 (PFK2)?

increases activity promoting the conversion of fructose-6-phosphate to fructose-2,6-bisphosphate

24

what is the effect of fructose-2,6-bisphosphate (F2,6BP) on phosphofructokinase-1 (PFK1) vs fructose-1,6-bisphosphatase (F1,6BPase)?

F2,6BP is increased under the presence of insulin and increases the activity of PFK1 (promoting conversion of F6P to F1,6,BP)

F2,6BP also decreases the activity of F1,6BPase (inhibiting the gluconeogenic conversion of F1,6,BP to F6P when in the fed state)

25

what is the effect of glucagon on fructose-2,6-bisphosphate? How does this lead to the formation of glucose?

glucagon activates fructose-2,6-bisphosphatase which converts fructose-2,6-bisphosphate (F2,6BP) to F6P

the function of this step is to eliminate the positive regulator of PFK1 (which under the influence of insulin and F2,6PB promote glycolysis) and remove the inhibition of F1,6BPase (to support gluconeogenisis)

activation of F1,6BPase promotes the conversion of F1,6BP to F6P

(allowing phosphoglucose isomerase to convert F6P into G6P and then glucose-6-phosphatase to convert G6P to glucose for gluconeogenesis)

26

what are the hydrophobic amino acids?

TTP VIP GAL

tyrosine
triptophan
phenyalanine

valine
isoleucine
proline

Glycine
Alanine
Leucine

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