Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Medical Biochemistry > Cholesterol and Steroid Metabolism > Flashcards

Cholesterol and Steroid Metabolism Flashcards

You may prefer our related Brainscape-certified flashcards:
USMLE® Step 1 flashcards
1
Q

What are the important functions of cholesterol?

A

1) Component of all cell membranes
2) Precursor of Bile Acids
3) Precursor of steroid hormones and Vitamin D

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Describe the structure of cholesterol.

A

4 carbon ring with a hydrocarbon tail and and OH group at other end.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Where is the site of attachment of fatty acids in cholesterol ester?

A

OH group on A chain on cholesterol.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is a cholesterol ester?

A

Cholesterol molecule with fatty acid attached to OH group end.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the main organ cholesterol metabolism takes place?

A

Liver

cholesterol pool

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

If cholesterol is completely cut out of the diet, why can high cholesterol levels persist? (in theory)

A

De Novo Synthesis in liver

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is required for cholesterol synthesis?

A

Acetyl CoA
NADPH
ATP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the rate limiting enzyme in cholesterol synthesis?

A

HMG CoA reductase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Where is the cell does cholesterol synthesis occur?

A

Occurs in the cytoplasm with enzymes in cytosol and ER

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Too much plasma cholesterol can lead to what?

A

Atherosclerosis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Too much cholesterol secretion causes formation of what?

A

Gall Stones

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are the two phases of cholesterol synthesis?

A

1) synthesis of mevalonic acid (mevalonate)

2) synthesis of cholesterol from mevalonate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How did the Acetyl CoA used in cholesterol synthesis get there?

A

From citrate, broken down by ATP-citrate lyase.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

In the first step of cholesterol synthesis, 2 Acetyl CoA are converted to what? By what enzyme?

A

Acetoacetyl CoA;

Thiolase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

During the second step of cholesterol synthesis, Acetoacetyl CoA is converted to what? By what enzyme?

A

HMG CoA;

HMG-CoA synthase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

HMG CoA is also known as what?

A

3-hydroxy-3-methylglutaryl CoA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

HMG CoA gets converted to what? By what enzyme?

A

Mevalonate;

HMG CoA Reductase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

HMG CoA reductase requires what reducing equivalents?

A

2 molecules of NADPH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

In stage 2 of cholesterol synthesis, Once mevalonate is made, what is formed next?

A

5-pyrophosphomevalonate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

During stage 2 of cholesterol synthesis, what is 5-pyrophosphomevalonate converted into in the 2nd step?

A

Isopentenyl pyrophosphate (IPP)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Isopentenyl pyrophosphate (IPP), besides beings converted into 3,3-dimethylallyl pyrophosphate (DPP), can also alternately be transformed into what?

A

Dolichol or ubiquinone

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

IPP plus DPP undergo condensation to form what?

A

Geranyl Pyrophosphate (GPP) -10 C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What gets added to Geranyl Pyrophosphate (GPP) to form Farnesyl Pyrophosphate (FPP -15 c)

A

IPP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

2 Farnesyl Pyrophosphate (FPP) molecules are joined to form what?

A

Squalene (30C)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Farnesyl Pyrophosphate (FPP) (15C) an important intermediate in cholesterol synthesis, can also be a precursor for what?

A

Dolichol

Ubiquinone

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Which two intermediates in cholesterol synthesis can be considered precursors for Dolichol or ubiquinone?

A 
Farnesyl Pyrophosphate (FPP)
Isopentenyl Pyrophosphate (IPP)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Is Squalene cyclic or non cyclic?

A

Non cyclic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Squalene undergoes cyclization to form what?

A

Lanosterol (30C)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

HMG CoA reductase is located where??

A

ER - cytosolic side

30
Q

AMP kinase ________ and therefore ______ HMG CoA reductase

A

Phosphorylates;

Inhibits

31
Q

How does cholesterol inhibit HMG CoA reductase?

A
  • Allosterically
  • regulating gene expression of enzyme
  • promoting degradation of enzyme
32
Q

AMP Kinase can be stimulated by what?

A

Glucagon or Epinephrine

33
Q

Glucagon __________ and therefore ________ HMG CoA reductase, decreasing cholesterol synthesis.

A

Phosphorylates (PKA Dependent);

Inactivates

34
Q

What are statins?

A
  • A class of drugs that cause enzyme upregulation (reversible inhibitors of HMG CoA reductase
  • long term regulation
35
Q

Which drugs (specifically) are statins?

A
  • Compactin
  • Simvastatin (Zocov)
  • Pravastatin (Pravacol)
  • Lovastatin (Mevacor)
  • all are structural analogs of Mevalonate.
36
Q

Low concentrations of intracellular cholesterol stimulates what?

A

SREBP = sterol regulatory element binding protein

- released from ER

37
Q

What is the function of SREBP?

A

Moves to a specific enhancer region (SRE= sterol responsive element) in the gene for HMG CoA reductase upregulation.

38
Q

Why does blocking HMG CoA reductase with statins cause an upregulation of the gene?

A

Cholesterol usually inhibits SCAP-SREBP (SREBP cleavage activating protein). Therefore, low levels of cholesterol cause SREBP cleavage (activation) leading to upregulation of HMG CoA gene.

Usually, giving a patient a large dose of statins accounts for any new HMG CoA synthesized

39
Q

________ concentrations of cholesterol and/or mevalonate leads to _____________ of the HMG CoA reductase enzyme.

A 
High concentrations;
Rapid degradation (proteolysis)
40
Q

When there is high levels of intracellular cholesterol, the ________ system in proteosomes leads to the degradation of ________

A

Ubiquitin;

HMG CoA Reductase

41
Q

What are the effects of low intracellular cholesterol on HMG-CoA reductase, LDL receptors, and serum cholesterol?

A
  • HMG CoA: upregulation
  • LDL receptor: upregulation
  • Increased uptake of LDL from serum
  • reduction in serum cholesterol
42
Q

Besides HMG CoA Reductase, intracellular cholesterol is a key regulator of?

A
  • LDL receptor endocytosis

- ACAT

43
Q

SLOS (Smith-Lemli-Optiz Syndrome) is a _________ defect of _________.

A

Autosomal recessive;

Cholesterol synthesis

44
Q

SLOS is relatively common and leads to what?

A
  • Microencephaly

- other embryonic malformations

45
Q

What enzyme is partially deficient in SLOS? What is this enzyme needed for?

A
  • 7-Dehydrocholesterol reductase

- needed for correct double bond formation in ring B

46
Q

What is major mechanism of elimination of cholesterol?

A

Cholesterol into bile acids –> excreted in feces

47
Q

Some cholesterol is modified by bacteria in the intestines to form what?

A

Cholestanol

Coprostanol

48
Q

What forms the bulk of fecal sterols?

A

Cholestanol
Coprostanol
Free cholesterol

49
Q

How do Coprostanol and Cholestanol differ?

A

Coprostanol: Hydrogen in B- orientation
Cholestanol: hydrogen in a-orientation

50
Q

What are the most abundant organic components of bile?

A

Phosphatidylcholine (lecithin) and bile salts

51
Q

What is another name for phosphatidylcholine?

A

Lecithin

52
Q

Bile enters the _____ through the _______ or is stored in the gall bladder.

A
  • Duodenum

- common bile duct

53
Q

What are the primary bile acids?

A

Cholic acid

Chenodeoxycholic acid

54
Q

What is the rate limiting enzyme in the synthesis of bile acids?

A

7-alpha-Hydroxylase

55
Q

What is the reaction 7-alpha-Hydroxylase catalyzes?

A

Catalyzes the addition of an OH group to carbon 7 on cholesterol. (making it into Cholic acid)

56
Q

How is 7-alpha-Hydroxylase regulated?

A

Inhibited by: Cholic acid

Stimulated by: cholesterol

57
Q

Bile acids that are conjugated with glycine form which bile salts before leaving the liver??

A
  • Glycocholic acid

- Glycochenodeoxycholic acid

58
Q

Bile acids that are conjugated with taurine form which bile salts before leaving the liver??

A
  • Taurocholic acid

- Taurochenodeoxycholic acid

59
Q

What is more effective at solubilizing lipids than bile acids?

A

Bile salts like:
Glycocholic acid
Taurochenodeoxycholic acid

60
Q

Other intestinal bacteria convert primary bile salts into ________ by removing ___________.

A

Secondary bile salts;

Hydroxyl groups

61
Q

Cholic acid, under the action of intestinal flora, becomes…

A

Deoxycholic acid

62
Q

Lithocholic acid, under the action of intestinal flora, becomes…

A

Chenodeoxycholic acid

63
Q

What is cholelithiasis?

A

Bile salt deficiency

64
Q

What are potential causes of Cholelithiasis?

A
  • Malabsorption of bile acids from intestine
  • Obstruction of the biliary tract
  • Interruption of the enterohepatic circulation
  • Decreased bile production (hepatic dysfunction)
  • Accelerated rate of bile recycling (excessive suppression of bile synthesis)
65
Q

What is Chenodeoxycholic acid used for?

A

Treatment of Cholelithiasis

66
Q

What is another name for chenodeoxycholic acid?

A

Chenodiol

67
Q

One of the four physiologically significant functions of bile acids/salts is that they facilitate ________ of dietary TAGS by acting as __________ that render fats accessible to __________.

A

Digestion;
emulsifying agents;
pancreatic lipases

68
Q

One of the four physiologically significant functions of bile acids/salts is that they facilitate the intestinal absorption of_________

A

Fat-soluble vitamins

69
Q

What is the significance of bile acids and phospholipids solubilizing cholesterol in the bile?

A

It prevents the precipitation of cholesterol in the gallbladder.

70
Q

Migrating gallstones that obstruct the ampulla of Vater can cause what?

A

Acute Pancreatitis

71
Q

Why is Pyrophosphate incorporated into cholesterol?

A

Without Pyrophosphate, compounds such as Squalene, Lanosterol all the downstream intermediates all the way up to cholesterol would be so hydrophobic, they would need carrier proteins to keep then soluble.

72
Q

What is Squalene cyclized with?

A

NADPH and O2

Medical Biochemistry (35 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions