Cholesterol Biosynthesis

Question 1

cholesterol solubility in water

Answer 1

• low solubility in water

Question 2

cholesterol present in plasma bound to

Answer 2

• lipoproteins

Question 3

cholesterol esters are located where

Answer 3

• in the interior of lipoproteins

Question 4

free cholesterol is located where

Answer 4

• on the surface of lipoproteins

Question 5

cholesterol is a precursor for

Answer 5

• bile acids
• steroid hormones
• vitamin D

Question 6

result of defects in cholesterol synthesis in mice

Answer 6

• generally lethal

Question 7

most cholesterol synthesis occurs where?

Answer 7

• in the liver

- 80%

Question 8

what is cholesterol synthesized from

Answer 8

• HMG CoA in the cytosol

Question 9

rate limiting step of cholesterol synthesis

Answer 9

• HMG CoA reductase

Question 10

role of insulin in cholesterol synthesis

Answer 10

• positive regulator of HMG CoA reductase

Question 11

important intermediates in cholesterol synthesis

Answer 11

• geranyl diphosphate

- farnesyl diphosphate

Question 12

geranyl diphosphate goes on to to create

Answer 12

• geranylgeranyl disphosphate

Question 13

geranylgeranyl diphosphate goes on to create

Answer 13

• ubiquinone

- geranylgeranylated proteins (rho)

Question 14

ubiquionine important for

Answer 14

• oxidative phosphorylation

Question 15

geranylgeranylated proteins important for

Answer 15

• signal transduction

Question 16

fernesyl diphosphate goes on to create

Answer 16

• fernesylated proteins (Ras)

- dolichol phosphate

Question 17

dolichol phosphate important for

Answer 17

• synthesis of complex glycoproteins

Question 18

HMGCoA reductase expression and activity inhibited by

Answer 18

• oxysterols derived from intracellular free cholesterol

Question 19

LDL receptors are down regulated by

Answer 19

• free cholesterol

Question 20

fat and cholesterol are made in what state?

why

Answer 20

• in the fed state

- it takes 18 ATP to make them

Question 21

mechanisms to control cellular cholesterol levels

Answer 21

• biosynthesis
• uptake
• catabolism & excretion
• storage

Question 22

uptake

Answer 22

• LDL receptors on liver allow cholesterol to be taken up

Question 23

storage

Answer 23

• liver stores cholesterol using ACAT

Question 24

diet high in cholesterol result

Answer 24

• too much cholesterol in cell
• negative feedback on LDL receptors
• more cholesterol in the circulation

Question 25

diet high in saturated fats

Answer 25

- inhibit storage of cholesterol - more cholesterol in cell - down regulation of LDL receptors - more cholesterol in circulation

Question 26

result of saturated fatty acids

Answer 26

- reduce membrane fluidity | - reduce clustering and uptake of LDLR

Question 27

diet low in fiber

Answer 27

- not secreting bile acids out of system - higher level of cholesterol inside cell - down regulation of LDL receptors - up regulation of plasma LDL

Question 28

primary bile acids are synthesized where

Answer 28

- in the liver

Question 29

rate limiting step for bile acid synthesis

Answer 29

- 7 alpha hydroxylase

Question 30

which are the primary bile acids

Answer 30

- cholic and chenodeoxycholic acids

Question 31

deoxycholic and lithocholic acids are products of

Answer 31

- further metabolism in the intestine

Question 32

which are the must abundant primary bile acids?

Answer 32

- colic acids

Question 33

how do we convert bile acids to bile salts?

Answer 33

- add groups to make it more polar

Question 34

function of bile acids

Answer 34

- emulsify dietary fats for digestion and absorption - facilitate absorption of fat soluble vitamin - only significant mechanism for eliminating cholesterol from body - prevent precipitation of cholesterol out of solution in gall bladder so you don't get gall stones

Question 35

7 alpha hydroxylase activated by

Answer 35

- cholesterol

Question 36

7 alpha hydroxylase inhibited by

Answer 36

- bile acids

Question 37

importance of enterohepatic circulation of bile acids

Answer 37

- up to 99% of bile acids are reabsorbed, enter the portal circulation, and return to the liver