Cholesterol Flashcards

1
Q

what are the sources of cholesterol

A

diet and de novo synthesis

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2
Q

what is cholesterol required for

A

synthesis of bile salts and vitamin D
synthesis of steroid hormones
appropriate myelination of nerves

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3
Q

what does de novo synthesis of cholesterol require

A

acetyl CoA
NADPH
ATP
carbon donor
reducing power
energy source

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4
Q

where does de novo synthesis occur

A

the cytosol but some enzymes are bound to membrane of the ER

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5
Q

how much does 1 mole of cholesterol require

A

18 moles of acetyl CoA
16 moles of NADPH
36 moles of ATP

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6
Q

what are the 4 phases of de novo synthesis called

A

synthesis of mevalonic acid
synthesis of farnesyl pyrophosphate
synthesis of squalene
synthesis of cholesterol

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7
Q

what is HMG CoA reductase (step 1)

A

rate limiting step in cholesterol biosynthesis

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8
Q

what does HMG CoA reductase do (step 1)

A

catalyzes the reduction of HMG CoA to mevalonate

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9
Q

what are statins

A

inhibitors of HMG CoA reductase

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10
Q

describe the cyclization of squalene (step 4)

A

cyclization of squalene to form the 4 sterol ring in the 30C lanosterol

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11
Q

what is lanosterol converted to

A

cholesterol (27C)

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12
Q

what does the conversion to cholesterol involve

A

the removal of 3 methyl groups and rearrangement of some double bonds that require the oxidation of NADPH

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13
Q

how is cholesterol biosynthesis regulated

A

-cholesterol inhibits HMG CoA reductase activity particularly in the liver
-cholesterol activates fatty acyl CoA : cholesterol acyltransferase (ACAT)

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14
Q

where is ACAT and what do they do

A

in the hepatocytes
promotes formation of cholesterol esters (accumulates in the liver)

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