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GOATED POM > Cholesterol > Flashcards

Cholesterol Flashcards

1
Q

How many carbon atoms compose cholesterol?

A

27 carbon atoms

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2
Q

What is the structure of cholesterol?

A

27 carbon atoms, consists of cyclic rings with a hydrophobic tail steroid ring
Carbon and hydrogen,
C3 hydroxyl group

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3
Q

Why is cholesterol important?

A

Fluid dynamics within phospholipid bilayer, enables mechanical stability & fluidity

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4
Q

How does cholesterol maintain fluid stability within the phospholipid bilayer?

A

The cholesterol ring system interferes with motions of the fatty acid side chains

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5
Q

What is the first step of cholesterol synthesis?

A

Isopentenyl pyrophosphate- activated isoprene synthesis

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6
Q

What is the second stage of cholesterol synthesis?

A

Condensation of 6 molecules of isopentenyl pyrophosphate to form squalene (cytoplasmic reactions)

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7
Q

What is the fate of squalene?

A

Squalene undergoes demethylation and cyclisation to give cholesterol by monooxygenases

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8
Q

How is isopententyl pp formed (stage 1 &2)?

A

Two molecules of acetyl-CoA condense to form four carbon acetyoacyl-CoA

This is added to acetyl-CoA

Forms 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA)

Converted into isopentenyl

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9
Q

What happens to HMG-CoA?

A

HMG-CoA reductase reduces HMG-CoA into Mevalonate

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10
Q

Which molecule provides the reducing power for the reduction of HMG-CoA into Mevalonate?

A

NADP+

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11
Q

Where does reduction HMG-CoA occur within a cell?

A

Within the cytoplasm

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12
Q

What is the fate of mevalonate?

A

Undergoes sequential phosphorylation at hydroxyl groups attached to c3 and c5 by kinase; decarboxylated into Isopenenyl-PP

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13
Q

What molecule is consumed for the phosphorylation of mevalonate?

A

ATP

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14
Q

What is the first step of squalene formation after isopentyl-PP is formed?

A

2 molecules of isopentenyl-PP condense to form dimethylallyl-pp

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15
Q

What happens to dimethylallyl-pp?

A

Addition of isopentenyl to form 15 carbon species

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16
Q

What enzyme catalyses the farnesyl-pp reaction?

A

Geranyl transferase

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17
Q

What is the term for the 15 carbon compound formed from 3 isopentenyl-pp?

A

Farnesylpp

18
Q

How is squalene formed?

A

2 molecules of Farnesyl-pp condense, by squalene synthetase

19
Q

Where does demethylation and cyclisation of squalene occur?

A

Endoplasmic reticulum

20
Q

What is the fate of squalene?

A

Reduced in the presence of oxygen and NADPH, forms squalene epoxide

21
Q

How is cholesterol formed from squalene?

A

Squalene –> squalene epoxide –> lanosterol –> cholesterol

22
Q

What does cholesterol decompose into?

A

Glycocholate, taurocholate

23
Q

What are steroid hormones derived from?

A

Cholesterol

24
Q

What 5 classes of steroid hormones derive from cholesterol?

A 
Oestrogens
Androgens
Corticosteroids
Mineralcorticoids
Progesterones
25
Q

What is the role of cholesterol in vitamin-D synthesis?

A

7-dehydrodcholesterol within epidermis –> provitamin-d3 –> Vitamin-d3 –> calcitriol

26
Q

What is familial hypercholesteroaemia?

A

Monogenic dominant trait, cholesterol transportation is defective

27
Q

What type of mutation is FH?

A

Loss of function in the LDL-receptor gene

28
Q

How can FH be controlled?

A

Inhibition of de no cholesterol synthesis in the liver

Reduction of dietary cholesterol absorption

29
Q

What drug can reduce cholesterol synthesis?

A

HMG-CoA-Reductase inhibitors (Statins)
Resins(Sequestration of bile acid complexes)

30
Q

What is lovastatin?

A

Statins are a competitive inhibitor of HMG-CoA reductase, resembles 3-HMG, thus mevalonate cannot be synthesised

31
Q

What are resins (cholestryamine) ?

A

Bind or sequester bile-acid cholesterol complexes, prevents their reabsorption by the intestine

32
Q

Orlistat function?

A

Inhibition of pancreatic and gastric lipases

33
Q

How do chylomicrons enter the bloodstream?

A

Lacteals of the intestine to the thoracic duct and to the left subclavian vein where they enter the bloodstream

34
Q

How are chylomicrons incorporated into tissues?

A

Lipoprotein lipase

35
Q

What are the 3 major steps of cholesterol synthesis?

A
  1. Synthesis of isopentenyl pyrophosphate, an activated isoprene unit which serves as a key building block (cytoplasm).
  2. Condensation of six molecules of isopentenyl pyrophosphate to form squalene (cytoplasm).
  3. Cyclisation and demethylation of squalene by monooxygenases to give cholsterol (ER).
36
Q

How is cholesterol transported in LPs?

A

As cholesterol esters

37
Q

Life cycle of VLDLs, LDLs, IDLs and HDLs

A
38
Q

How do serum cholesterol levels vary with different types of FH?

A

Heterozygous: 2-3x - Atherosclerosis in mid age

Homozygous: 5x - Atherosclerosis in adolescence

39
Q

How is LDL endocytosed?

A
  1. Binding to LDLR
  2. Endocytosis
  3. Clathrin coat is uncloated
  4. Fusion with endosome
  5. Transfer to lysosome
  6. Budding off to transport vesicles
  7. Return of LDL to membrane+exocytosis
40
Q

What is HMG CoA inhibited by?

A

Statins, mevalonate, cholesterol, bile salts

41
Q

What are the 5 major classes of FH?

A
42
Q

What is the purpose of LCAT?

A

Creating cholesterol esters

GOATED POM (39 decks)

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