Cholesterol Flashcards Preview

Biochem II > Cholesterol > Flashcards

Flashcards in Cholesterol Deck (48):
1

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

Bile acids
Steroid Hormones
Vitamine D

2

Is Cholesterol hydrophobic or hydrophilic?

Hydrophobic

3

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

Blood plasma
Esterified form with a fatty acid attached at carbon 3

4

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

Acetate

5

What compound provides the reducing power for cholesterol synthesis?

NADPH

6

Where does synthesis of cholesterol occur in the body?

Cytosol of the cell and in the SER

7

What molecules are combined to form Acetoacetyl CoA?

Acetyl CoA - 2 of them

8

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

HMG-CoA

9

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

HMG-CoA Synthase

10

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

Ketone Bodies

11

What does the enzyme HMG-CoA reductase do?

Reduces HMG-CoA to Melavonate

12

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

Rate limiting and irreversible step in cholesterol synthesis!

13

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

SER

14

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

2

15

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

Sterol-dependent regulation of gene expression

16

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

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

17

Where in the cell do we find the SREBP?

Integral protein of the ER membrane

18

Name the other membrane protein that SREBP is associated with?

SCAP (SREBP cleavage activating protein)

19

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

Low sterol levels of the cell

20

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

-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.

21

This enzyme controls the HMG-CoA reductase covalently

Adenosine Monophosphate-activated protein kinase

22

What form of the HMG-CoA is inactive?

Phosphorylated

23

Dephosphorylation will affect the HMG-CoA how?

Activates the enzyme

24

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

Insulin
Thyroxine

25

How do glucagon and glucocorticoids effect cholesterol synthesis?

Down regulation of HMG-CoA reductase

26

Why is it called a bile acid?

It has a terminal carboxyl group with a pKa of 6

27

T or F
Bile Salts an amphipathic

True

28

What makes bile salts amphipathic?

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

29

What are the most common bile acids?

Cholic Acid
Chenodeoxycholic Acid

30

Where are bile acids synthesized?

Liver

31

What is the rate limiting step of bile acid synthesis?

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

32

What will down regulate Cholesterol-7-alpha hydroxylase?

Cholic Acid

33

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

They are conjugated with either glycine or taurine

34

Only _____ _____ are found in bile.

Bile salts

35

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

Bile Salts

36

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

Bacteria in the intestine

37

How are secondary bile acids formed?

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

38

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

95%

39

Where are bile acids primarily absorbed?

Ileum via Na+ bile salt co-transporter

40

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

Phospholipids and bile salts

41

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

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

42

The fat soluble vitamins are?

ADEK

43

Cholesterol is one of many _____________

Isoprenoids

44

This vitamin is important for calcium homeostasis?

Vit D3

45

This steroid hormone regulates the salt and water balance

Mineralocorticoids

46

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

Glucocorticoids

47

How many ATP are used to make squalene?

18

48

The short term regulation of HMG-CoA reductase is?

Phosphorylation