Biochemistry week 3

Question 1

What is the function of cholesterol

Answer 1

• Structural component for all cell membranes

Question 2

What is cholestorl a percursor for?

Answer 2

• Bile acids
  -Steroid hormones
  -Vitamin D

Question 3

Early cholesterol synthesis provides substrates important for what

Answer 3

• Cell proliferation
  -Electron transport–Combating oxidative stress

Question 4

What regulates cholesterol homeostasis

Answer 4

• The liver

Question 5

What does plasma cholestrol depend on

Answer 5

• Endogenous ( body made) synthesis
  -Dietary intake

Question 6

Explain the structure of cholesterol

Answer 6

• Very hydrophobic
  -Contains 4 fused hyrocarbon rings called steriod nucles
  -

Question 7

What does Ring A on cholesterol have

Answer 7

• Hydroxyl group at carbon 3

Question 8

What does Ring B on cholesterol have

Answer 8

-Has double boned between C5 and C6

Question 9

Where can cholesterol be synthesized

Answer 9

• Liver
  -Adrenal cortex
  -Intestine
  -Reproductive organs

Question 10

In cholestorl synthesis where do all the carbon atoms come from

Answer 10

acetyl coA`

Question 11

What provides the reducing power in cholesterol synthesis

Answer 11

• NADPH

Question 12

Where are the enzymes involved in cholesterol synthesis located in

Answer 12

• Cytosol
  -SER
  -Perioxisome

Question 13

To make 1 mol of cholestrol how much acetylcoA, ATP ans NADPH is used

Answer 13

• 18 moles of acetyl CoA

-36 moles of ATP

-16 moles of NADPH

Question 14

Name what regulates cholesterol synthesis

Answer 14

-Sterol-dependent regulation of gene expression
-Sterol independent phosphorylation/dephosphorylation
-Drug inhibition
-Hormonal regulation

Question 15

Name the proteins involed in Sterol-dependent regulation of gene expression

Answer 15

SREBP2
-SCAP

Question 16

Explain what happens in sterol-dependent regulation when cholesterol levels are LOW

Answer 16

• SREBP2, moves from ER to the golgi
  -Proteolysis activates SREBP
  -Then the active SREBP2 enters the nucles and promotes gene transcription for cholesterol synthesis

Question 17

Explain what happens in sterol-dependent regulation when cholesterol levels are HIGH

Answer 17

• Cholesterol binds to SCAP, causing a conformational change
  -SCAP binds to insig-1, keeping the SCAP complex in the ER
  -SREBP remains inactive so gene transcription is repressed

Question 18

In sterol independent regulation(phosphorylation/dephosphorylation):
- When is HMG CoA reductase inactive and active

Answer 18

• Inactive when phosphorylated
  -Active when dephosphorylated

Question 19

What is HMG CoA reductase controlled by + FUNCTION

In sterol independent regulation(phosphorylation/dephosphorylation)

Answer 19

• AMPK, which phosphorylates and inhibts the enzyme
  -Phosphoprotein phosphatase which dephosphorylates and activates the enzyme

Question 20

In sterol independent regulation(phosphorylation, dephosphorylation) WHAT DOES LOW ATP DO

Answer 20

• Activates AMPK , which reduces cholesterol

Question 21

Name a drug used in drug inhibition which is used to regulate cholesterol synthesis

Answer 21

• Statins

Question 22

Explain how statins work in drug inhibition

Answer 22

• They act as competitive inhibitors of HMG CoA reductase
  -They mimic HMG CoA

Question 23

How is cholesterol broken down

Answer 23

• It is converted to bile acids , secreted into bile and then into the feces

Question 24

During bile acid synthesis name the rate limiting enzyme

Answer 24

7a-hydroxylase

Question 25

Explain the structural changes to cholesterol that occurs during bile acid synthesis

Answer 25

- Insertion of OH groups into cholesterol -Reduction of double bonds in the B ring -Shortening of side chains by 3 carbons

Question 26

Explain how biles salts are formed

Answer 26

- Bile acids are conjugated with glycine or taurine, forming bile salts

Question 27

Exlain the function of intestinal flora on bile salts

Answer 27

- They can remove glycine and taurine from bile salts, regenerating bile acids

Question 28

What is gall stone disease caused by

Answer 28

- CAUSED BY choesterol precipitates when it exceeds the solubilizing capacity of bile

Question 29

What are other contributing factors to gallstone disease

Answer 29

- Excess cholesterol -Malabsorption of bile acids -Severe liver dysfunction

Question 30

What is familial hypercholesterolemia

Answer 30

High levels of cholesterol in the blood

Question 31

What is the cause of familial hypercholesteroemia

Answer 31

- Defective LDL receptors

Question 32

What is the inhertitance pattern of familial hypercholesterolemia

Answer 32

- Autosomal dominant