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Biochem Finals > Lipid Metab -1b > Flashcards

Lipid Metab -1b Flashcards

0
Q

Cholesterol is the precursor of:

A 
vit D (skin)
Bile acids (liver)
Steroid hormones (adrenals and glands)
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1
Q

Important component of membranes and outer layer of lipoproteins

A

Cholesterol

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2
Q

Protects gallbladder membrane from harmful effects of bile salts

A

Cholesterol

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3
Q

Organ that have the greatest capacity to synthesize cholesterol

A 
Iiver
Intestine
Adrenal cortex
Gonads 
Placenta
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4
Q

All carbon atoms of cholesterol are derived from

A

Acetyl-CoA

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5
Q

Cholesterol synthesis takes place in the ——–

A

Cytosol and ER

700mg/day

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6
Q

How many ATPs do you need to synthesize cholesterol?

A

18 ATP/cholesterol

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7
Q

Five steps in the synthesis of cholesterol

A
  1. Biosynthesis of mevalonate (rate-limiting)
  2. Formation of isoprenoid units/ isopentenyl pyrophosphate
  3. Formation of squalene
  4. Cyclization of squalene to lanosterol
  5. Conversion of lanosterol to cholesterol
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8
Q

Rate limiting step in the synthesis of cholesterol

A
  1. Biosynthesis/formation of MEVALONATE
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9
Q

Committed enzyme in the rate limiting step in synthesis of cholesterol

A

HMG-CoA reductase

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10
Q

An intrinsic membrane protein of the ER and its active site extnds to the cytosol

A

HMG-CoA reductase

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11
Q

Hormone that Stimulates HMG-CoA reductase

A

Insulin

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12
Q

Hormone that Inhibits HMG-CoA reductase

A

Glucagon

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13
Q

Cholesterol inhibits HMG-CoA reductase by what mechanism?

A

Feedback inhibition

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14
Q

Drugs that inhibit HMG-CoA reductase

A

“Statins”

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15
Q

Sequential phosphorylation of mevalonate by kinases utilizing ATP;
Takes place several times; most expensive

A

Step 2 of cholesterol synthesis

Formation of isoprenoid units/isopentenyl phosphate

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16
Q

How many isoprenoid units does it take to make 1 cholesterol?

A

6 isoprenoid units

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17
Q

1 mevalonate to 1 isop unit = ? ATP

A

3 ATPs

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18
Q

6 isoprenoid units to 1 cholesterol = ? ATP

A

18 ATPs

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19
Q

Involves initial ismoerization & then condensation of isopentenyl pyrophosphate (c-5)

A

Step 3 of cholesterol synthesis

Formation of squalene

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20
Q

(2) two isopentenyl-PP condenses to form

A

Geranyl pyrophosphate (c-10)

21
Q

(1) one gernayl pyrophosphate condenses wt (1) one IPP to form

A

Farnesyl pyrophosphate (c-15)

22
Q

(2) two farnesyl PP condenses to form

A

Squalene (c-30)

23
Q

Enzyme responsible for the cyclization of squalene to lanosterol

A

ER-bound squalene oxidocyclase

24
Q

2 enzymatic activities of squalene oxidocyclase

A
  • epoxidase (monooxygenase)

- cyclase (oxidosqualene : lanosterol cyclase)

25
Q

Major route from lanosterol to cholesterol

A

Lanosterol -> 7-dehydrocholesterol -> cholesterol

26
Q

Alt route from lanosterol to cholesterol

A

Lanosterol -> zymosterol -> desmosterol -> cholesterol

27
Q

Hydrolysis of stored TAG in adipose tissue; mobilization of fatty accids from TAG stored in adipose tissue

A

Lipolysis

28
Q

Key enzyme involved in lipolysis

A

Hormone-sensitive TAG lipase

29
Q

Covalently modulated regulatory enzyme

A

Hormone-sensitive TAG lipase

30
Q

Hormone-sensitive TAG lipase is regulated by ——–

A

Hormones acting thru cAMP

31
Q

Hormone-sensitive TAG lipase is activated thru ——-

A

Phosphorylation reaction catalyzed by protein kinase

32
Q

Principal means by whc FAs are oxidized to generate enery (ATP)

A

Beta oxidation

33
Q

Where does beta oxidation take place?

A

Mitochondria

34
Q

Involves removal of 2 carbon atoms at a time starting from the carboxyl end of the fatty acid

A

Beta oxidation

35
Q

Major end product of beta-oxidation

A

Acetyl-CoA

36
Q

Steps in beta oxidation

A
  1. Activation of free fatty acids to fatty acyl CoA
  2. Carnitine transport*
  3. Oxidative phase
  4. Thiolysis
37
Q

Mandatory step in beta oxidation which takes place in the cytosol

A
  1. Activation of free FA to fattyl acyl CoA
38
Q

Activation of free FA to fatty acyl CoA is catalyzed by

A

Thiokinase or Acyl CoA synthetase

39
Q

Rate limiting/ committed step in beta oxidation; takes place in the inner mitochondrial membrane

A
  1. Carnitine transport
40
Q

Carnitine transport is catalyzed by ? (Committed enzyme)

A

Carnitine Acyl CoA transferase I

41
Q

Carnitine acyl CoA transferase I is inhibited by an intermediate metabolite of lipogenesis called ——-

A

Malonyl CoA

42
Q

Transfers the carnitine-fatty acyl complex into the mitochondrial matrix

A

Translocase

43
Q

A carrier molecule; from lysine and methionine

A

Carnitine

44
Q

Step in beta oxidation that has two substeps and occurs in the mitochondrial matrix

A

Oxidative phase

45
Q

1st oxidative phase
Enzyme: ?
Coenzyme: ?
ATP: ?

A

Acyl CoA dehydrogenase
FAD
2 ATP

46
Q

2nd oxidative step
Enzyme: ?
Coenzyme: ?
ATP: ?

A

B-hydroxyacyl CoA DH
NAD
3 ATP

47
Q

Oxidation-hydration-oxidation

A

B-oxidation

48
Q

How many ATP per cycle are produced during beta-oxidation

A

5ATP

49
Q

Thiolysis is catalyzed by

A

Ketothiolase

50
Q

What happens during thiolysis?

A

B-ketoacyl CoA -> (B-ketoacyl CoA DH/CoASH)-> fatty acyl CoA + Acetyl CoA

Biochem Finals (11 decks)

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