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Biochem II > Cholesterol > Flashcards

Cholesterol Flashcards

1
Q

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

A

Bile acids
Steroid Hormones
Vitamine D

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2
Q

Is Cholesterol hydrophobic or hydrophilic?

A

Hydrophobic

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3
Q

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

A

Blood plasma

Esterified form with a fatty acid attached at carbon 3

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4
Q

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

A

Acetate

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5
Q

What compound provides the reducing power for cholesterol synthesis?

A

NADPH

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6
Q

Where does synthesis of cholesterol occur in the body?

A

Cytosol of the cell and in the SER

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7
Q

What molecules are combined to form Acetoacetyl CoA?

A

Acetyl CoA - 2 of them

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8
Q

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

A

HMG-CoA

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9
Q

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

A

HMG-CoA Synthase

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10
Q

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

A

Ketone Bodies

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11
Q

What does the enzyme HMG-CoA reductase do?

A

Reduces HMG-CoA to Melavonate

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12
Q

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

A

Rate limiting and irreversible step in cholesterol synthesis!

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13
Q

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

A

SER

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14
Q

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

A

2

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15
Q

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

A

Sterol-dependent regulation of gene expression

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16
Q

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

A

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

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17
Q

Where in the cell do we find the SREBP?

A

Integral protein of the ER membrane

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18
Q

Name the other membrane protein that SREBP is associated with?

A

SCAP (SREBP cleavage activating protein)

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19
Q

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

A

Low sterol levels of the cell

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20
Q

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

A
  • 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
Q

This enzyme controls the HMG-CoA reductase covalently

A

Adenosine Monophosphate-activated protein kinase

22
Q

What form of the HMG-CoA is inactive?

A

Phosphorylated

23
Q

Dephosphorylation will affect the HMG-CoA how?

A

Activates the enzyme

24
Q

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

A

Insulin

Thyroxine

25
Q

How do glucagon and glucocorticoids effect cholesterol synthesis?

A

Down regulation of HMG-CoA reductase

26
Q

Why is it called a bile acid?

A

It has a terminal carboxyl group with a pKa of 6

27
Q

T or F

Bile Salts an amphipathic

A

True

28
Q

What makes bile salts amphipathic?

A

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

29
Q

What are the most common bile acids?

A

Cholic Acid

Chenodeoxycholic Acid

30
Q

Where are bile acids synthesized?

A

Liver

31
Q

What is the rate limiting step of bile acid synthesis?

A

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

32
Q

What will down regulate Cholesterol-7-alpha hydroxylase?

A

Cholic Acid

33
Q

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

A

They are conjugated with either glycine or taurine

34
Q

Only _____ _____ are found in bile.

A

Bile salts

35
Q

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

A

Bile Salts

36
Q

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

A

Bacteria in the intestine

37
Q

How are secondary bile acids formed?

A

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

38
Q

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

A

95%

39
Q

Where are bile acids primarily absorbed?

A

Ileum via Na+ bile salt co-transporter

40
Q

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

A

Phospholipids and bile salts

41
Q

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

A

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

42
Q

The fat soluble vitamins are?

A

ADEK

43
Q

Cholesterol is one of many _____________

A

Isoprenoids

44
Q

This vitamin is important for calcium homeostasis?

A

Vit D3

45
Q

This steroid hormone regulates the salt and water balance

A

Mineralocorticoids

46
Q

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

A

Glucocorticoids

47
Q

How many ATP are used to make squalene?

A

18

48
Q

The short term regulation of HMG-CoA reductase is?

A

Phosphorylation

Biochem II (3 decks)

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