Cholesterol

Question 1

How does cholesterol effect fatty acid chains?

Answer 1

it inserts itself between fatty acid chains and prevents their crystalisation

Question 2

what enzyme synthesises cholesterol?

Answer 2

Acetyl Coenzyme A

Question 3

how is cholesterol transported in the blood?

Answer 3

by low density lipoproteins

Question 4

what are some importnat derivatives of cholesterol?

Answer 4

bile salts and steroid hormones

Question 5

all 27 carbon atoms of cholesterol are derived from what molecule?

Answer 5

acetyl CoA

Question 6

What are the three steps to cholesterol synthesis?

Answer 6

1. synthesis of isopentenyl pyrophosphate
2. condensation fo 6 molecules of isopentenyl pyrophosphate to form squalene
3. squalene cyclizes and the tetracyclic product is converted to cholesterol

Question 7

whats the normal cholesterol level in adult humans?

Answer 7

140 g

Question 8

why is a high cholesterol dangerous?

Answer 8

normal levels are essential to life, however deposition in arteries is associated with cardiovascular disease and stroke

Question 9

regulation of cholesterol biosynthesis is via what system?

Answer 9

it is controlled by a negative feedback mechanism mediated primarily by changes in the amount and activity of 3 hydroxy 3 methylglutaryl CoA reductase

AKA

HMG CoA reductase

which is inhibited by statins

Question 10

how do we control the rate of synthesis of HMG CoA reductase?

Answer 10

controlled by SREBP (sterol regulatory element binding protein) -

when cholesterol levels are down, this transcription factor induces transcription of HMG CoA reductase

Question 11

how is rate of HMG CoA reductase translation controlled?

Answer 11

rate of translation is inhibited by nonsterol metabolites derived from mevalonate and dietary cholesterol

Question 12

how is degredation of HMG CoA reductase controlled?

Answer 12

in response to increasing levels of cholesterol, the enzyme undergoes proteolysis

Question 13

how can we control phosphorylation of HMG CoA reductase?

Answer 13

phosphorylation decreases the activity of the reductase and occurs in response to low levels of ATP

Question 14

what is the main site of cholesterol synthesis?

Answer 14

in the liver -

Question 15

cholesterol in ecess of the liver’s own needs is exported in the blood in what form?

Answer 15

in the form of very low density lipoproteins ( VLDLs)

Question 16

how do statins work?

Answer 16

statins inhibit the synthesis of HMG CoA reductase in the liver

Question 17

what pharmacological agent can we give that reduces absorption of exogenous cholesterol?

Answer 17

we can give cholestyramine colestipol - which sequesters bile acids in the intestine and reduces the absorption of exogenous cholesterol and increases the metabolism of endogenous cholesterol into bile acids

Question 18

what is the purpose of bile salt as it relates to cholesterol?

Answer 18

eliminates cholesterol from the body (cholesterol is a bile salt precursor)

Question 19

how do we turn bile acids into bile salts?

Answer 19

conjugating bile acids with either glycine or taurine

Question 21

how can an increased cholesterol lead to gall stones?

Answer 21

not enough bile salts being secreted to handle the amount of cholesterol being secreted

• due to malabsorption of bile acids, biliary tract obstruction, hepatic dysfunction, reduced bile acid synthesis, lack of melatonin-

Question 22

cholesterol is the precursor to which 5 major classes of steroid hormones?

Answer 22

progestagens, glucocorticoids, mineralocorticoids, androgens and estrogens

Question 23

what can vitamin D deficiency in children lead to?

Answer 23

rickets - a disease characterised by inadequate calcification of cartilage and bone