Cholesterol

Question 1

Cholesterol is a structural component of cell membranes and a precursor for these important things in our body?

Answer 1

Bile acids
Steroid Hormones
Vitamine D

Question 2

Is Cholesterol hydrophobic or hydrophilic?

Answer 2

Hydrophobic

Question 3

Cholesterol is found where in the body and in what form?

Answer 3

Blood plasma

Esterified form with a fatty acid attached at carbon 3

Question 4

All the carbons for cholesterol synthesis are produced from what biochemical compound?

Answer 4

Acetate

Question 5

What compound provides the reducing power for cholesterol synthesis?

Answer 5

NADPH

Question 6

Where does synthesis of cholesterol occur in the body?

Answer 6

Cytosol of the cell and in the SER

Question 7

What molecules are combined to form Acetoacetyl CoA?

Answer 7

Acetyl CoA - 2 of them

Question 8

When we add a third Acetyl CoA to acetoacetyl the produced formed is called?

Answer 8

HMG-CoA

Question 9

What enzyme is responsible for the synthesis of the HMG-CoA?

Answer 9

HMG-CoA Synthase

Question 10

When HMG-CoA synthase is in the mitochondria it is used to make?

Answer 10

Ketone Bodies

Question 11

What does the enzyme HMG-CoA reductase do?

Answer 11

Reduces HMG-CoA to Melavonate

Question 12

What is unique about the reduction step of HMG-CoA?

Answer 12

Rate limiting and irreversible step in cholesterol synthesis!

Question 13

Where in the cell do we find the HMG-CoA reductase enzyme?

Answer 13

SER

Question 14

How many NADPH is used to form melavonate from HMG-CoA?

Answer 14

2

Question 15

What is a big player in the regulation of Choleseterol Synthesis?

Answer 15

Sterol-dependent regulation of gene expression

Question 16

In the sterol-dependent regulation of cholesterol the expression of the gene for HMG CoA reductase is controlled by:

Answer 16

The transcription factor SREBP (sterol regulatory element-binding protein-2)

Question 17

Where in the cell do we find the SREBP?

Answer 17

Integral protein of the ER membrane

Question 18

Name the other membrane protein that SREBP is associated with?

Answer 18

SCAP (SREBP cleavage activating protein)

Question 19

What would cause the SREBP-SCAP complex to be sent out of the ER to the Golgi?

Answer 19

Low sterol levels of the cell

Question 20

What happens to the SREBP-SCAP complex once in the Golgi?

Answer 20

• 2 proteases cleave the SREBP from SCAP
• SREBP moves to the nucleus and binds the SRE
• This binding up regulates the synthesis of HMG-CoA reductase.

Question 21

This enzyme controls the HMG-CoA reductase covalently

Answer 21

Adenosine Monophosphate-activated protein kinase

Question 22

What form of the HMG-CoA is inactive?

Answer 22

Phosphorylated

Question 23

Dephosphorylation will affect the HMG-CoA how?

Answer 23

Activates the enzyme

Question 24

An increase in these hormones will favour the up regulation of HMg-CoA reductase:

Answer 24

Insulin

Thyroxine

Question 25

How do glucagon and glucocorticoids effect cholesterol synthesis?

Answer 25

Down regulation of HMG-CoA reductase

Question 26

Why is it called a bile acid?

Answer 26

It has a terminal carboxyl group with a pKa of 6

Question 27

T or F | Bile Salts an amphipathic

Answer 27

True

Question 28

What makes bile salts amphipathic?

Answer 28

Hydroxyl group lies beneath the plane of the molecule while the methyl group lie above the plane of the molecule

Question 29

What are the most common bile acids?

Answer 29

Cholic Acid | Chenodeoxycholic Acid

Question 30

Where are bile acids synthesized?

Answer 30

Liver

Question 31

What is the rate limiting step of bile acid synthesis?

Answer 31

The introduction of a hydroxyl group at carbon 7 of the steroid nucleus by the enzyme cholesterol-7-alpha-hydoxylase

Question 32

What will down regulate Cholesterol-7-alpha hydroxylase?

Answer 32

Cholic Acid

Question 33

What happens to the bile acids before they leave the liver?

Answer 33

They are conjugated with either glycine or taurine

Question 34

Only _____ _____ are found in bile.

Answer 34

Bile salts

Question 35

What is the only effective mechanism for the excretion of cholesterol in the body?

Answer 35

Bile Salts

Question 36

How can the taurine and glycine be removed from the bile salts when the body wants to recycle?

Answer 36

Bacteria in the intestine

Question 37

How are secondary bile acids formed?

Answer 37

The bacteria in the intestine will remove the hydroxyl group of the bile acid producing deoxycholic and lilocholic acid from chenodeoxycholic acid.

Question 38

This percent of bile acids secreted in the intestine will be absorbed?

Answer 38

95%

Question 39

Where are bile acids primarily absorbed?

Answer 39

Ileum via Na+ bile salt co-transporter

Question 40

Cholesterol secretion into the bile must be accompanied by the secretion of these two compounds too

Answer 40

Phospholipids and bile salts

Question 41

What happens if the cholesterol secretion process is disrupted and more cholesterol is secreted?

Answer 41

The cholesterol may precipitate in the gallbladder leading to gallstone disease - cholelithiases

Question 42

The fat soluble vitamins are?

Answer 42

ADEK

Question 43

Cholesterol is one of many _____________

Answer 43

Isoprenoids

Question 44

This vitamin is important for calcium homeostasis?

Answer 44

Vit D3

Question 45

This steroid hormone regulates the salt and water balance

Answer 45

Mineralocorticoids

Question 46

This steroid hormone has a big role in regulation of metabolism...

Answer 46

Glucocorticoids

Question 47

How many ATP are used to make squalene?

Answer 47

18

Question 48

The short term regulation of HMG-CoA reductase is?

Answer 48

Phosphorylation