Chapter 26 Cholesterol

Front 1

where is cholesterol synthesized?

Back 1

liver (some in small intestine)

Front 2

what is the committed step in cholesterol synthesis?

Back 2

HMG-CoA--->mevalonate; catalyzed by HMG-CoA reductase

Front 3

describe the progression of Acetyl-CoA to isopentenyl pyrophosphate

Back 3

1) acetyl CoA--->HMG-CoA
2) HMG-CoA--->mevalonate
3) mevalonate-->isopentenyl pyrophosphate

Front 4

what is isopentenyl pyrophosphate?

Back 4

activated isoprene unit

Front 5

all carbon atoms in cholesterol are derived from what?

Back 5

acetyl CoA

Front 6

regulation of HMG-CoA reductase at the level of transcription

Back 6

low levels of cholesterol enhance gene transcription

Front 7

regulation of HMG-CoA reductase at the level of translation

Back 7

high levels of metabolites derived from mevalonate and dietary cholesterol inhibit translation of reductase mRNA

Front 8

regulation of HMG-CoA reductase at the level of degradation of reductase protein

Back 8

high levels of cholesterol and other sterols increase degradation of HMG-CoA

Front 9

regulation of HMG-CoA reductase at the level of enzymatic activity

Back 9

AMP-activated protein kinase phosphorylates and inhibits HMG-CoA

Front 10

how is dietary fat transported to the liver?

Back 10

by chylomicrons

Front 11

4 transporters of endogenous cholesterol

Back 11

very low density lipoproteins
intermediate-density lipoproteins
low-density lipoproteins (to tissues)
high-density lipoproteins (back to liver)

Front 12

what are the 4 components of low density lipoproteins?

Back 12

unesterified cholesteral and phospholipids on outside
core of cholesterol molecules esterified to fatty acids
apoproteins (target LDL to tissues that need it)

Front 13

describe process of LDL uptake into cells

Back 13

receptor-mediated endocytosis
1) apoprotein of LDL binds to LDL receptor
2) receptor-LDL complex is internalized and fuses with lysosomes
3) receptor returns to plasma membrane
4) contents of LDL is hydrolyzed to cholesterol and amino acids

Front 14

cholesterol inside cells suppress what?

Back 14

LDL receptor synthesis

Front 15

foam cells

Back 15

formed when LDL are oxidized and taken up by macrophages, can be trapped in walls of blood vessels, forming atherosclerotic plaques

Front 16

2 ways to treat high cholesterol

Back 16

bile salt sequestrants--bile salts are synthesized from cholesterol--sequestrants join with bile salts and are excreted so more bile salts are created from cholesterol
statins--competitive inhibitors of HMG-CoA reductase

Front 17

how are steroid hormones derived from cholesterol?

Back 17

removal of side chain and series of hydroxylations/oxidations

Front 18

cytochrome P450 mono-oxygenases

Back 18

-catalyze hydroxylation reactions--use NADPH and O2--one O atom forms OH group and other is reduced to water
-has heme group

Front 19

isoprene derivatives
(name 5 examples)

Back 19

chlorophyll, vit K, A, and E, coenzyme Q
many plant products and fragrances are isoprene derivatives (lemon oil, rubber trees, menthol, etc)