Cholesterol

Question 1

What is cholesterol

Answer 1

Insoluble molecule essential for life as a precursor and constituent of membranes and membrane components and precursor for steroid hormones

Question 2

What is the function of cholesterol in membranes

Answer 2

Moderates fluidity/stability

Question 3

What are glucocorticoids

Answer 3

Class of cholesterol derivatives hormones that are able to increase serum glucose via gluconeogenesis

Question 4

What are mineralocorticoids

Answer 4

Class of cholesterol derivatives hormones involved in water/salt balance

Question 5

What are androgens and estrogens

Answer 5

Class of cholesterol derivatives hormones involved in development/ sexuality

Question 6

What adds to the cholesterol pool

Answer 6

Dietary cholesterol
Cholesterol synthesis from all cells
Cholesterol synthesis and export to other cells by the liver

Question 7

What reduces the cholestrol pool

Answer 7

Removal of cholestrol from the body by the liver

Question 8

What is the only method of removal of cholestrol from the body

Answer 8

Via the liver

Question 9

What is familial hypercholestrolaemia (FHC)

Answer 9

Autosomal dominant genetic condition which results in elevated serum cholesterol and leads to cardiovascular disease

Question 10

Which form of FHC is treatable and develops later in life

Answer 10

Heterozygous

Question 11

Which form of FCH is likely to develop cardiovascular disease prematurely

Answer 11

Homozygous

Question 12

How is cholestrol transported

Answer 12

Exported from liver by VLDL and LDL to other cells

Question 13

Why is cholestrol transported to other cells

Answer 13

Increase cholestrol load in peripheral tissues

Question 14

How is cholestrol fed back to the liver from other tissue

Answer 14

HDLs

Question 15

Why do other tissues feedback to the liver using HDLs

Answer 15

Decreases cholestrol load in peripheral tissues

Question 16

What happens to excess cholesterol

Answer 16

Processed into bile acids or removed directly by exportation to gut

Question 17

Why is processing/ removal of excess cholesterol important

Answer 17

Aids solubilisation of lipid nutrients

Question 18

What is forward transport of cholestrol

Answer 18

Transport of ‘bad cholestrol’ using LDL from liver to cells (increases cell cholesterol)

Question 19

What is reverse transport of cholesterol

Answer 19

Transport of ‘good cholestrol’ from cells to liver via HDL (lowers cell cholesterol)

Question 20

Describe stage 1 of cholesterol synthesis

Answer 20

Synthesis of isopentenyl pyrophosphate

Question 21

Describe stage 2 of cholestrol synthesis

Answer 21

Condensate of 6 molecules of isopentenyl pyrophospahte to form squalene

Question 22

Describe stage 3 of cholestrol synthesis

Answer 22

Cyclisation of squalene and conversion into cholesterol

Question 23

What are all 27C atoms in cholesterol ultimately derived from

Answer 23

Acetyl CoA

Question 24

Where is the Acetyl CoA cholestrol is derived from produced

Answer 24

From glycolysis and TCA cycle via export of citrate and generation of acetyl CoA in cytoplasm

Question 25

What is the function of HMG-CoA reductive in cholesterol synthesis

Answer 25

Produces Melvalonate which is a committed step in cholesterol biosynthesis (used to produce isopentenyl pyrophosphate)

Question 26

Which drug targets HMG-CoA reductase

Answer 26

Statins

Question 27

What are the major sites of cholesterol synthesis

Answer 27

Cytosol and microsomes of liver and intestine

Question 28

What is the key to regulating cholesterol biosynthesis

Answer 28

HMG-CoA reductase control

Question 29

How is HMG-CoA reductase controlled

Answer 29

By amount and activity of enzyme

Question 30

Describe the processes involved in HMG-CoA reductase

Answer 30

Gene transcription Rate of mRNa translation Ubiquitination pathway (degrades protein) Phosphorylation (rate of activity/energy status of cell) Negative feedback fro, cholesterol in cell (allosteric inhibition)

Question 31

How do statins affect HMG-CoA reductase

Answer 31

Structural analogues of HMG-CoA reductase so reversible competitive inhibitor

Question 32

How is cholestrol disposed

Answer 32

Cannot be broken down so sterol nucleus must be removed before conversion to bile salts/removed via faeces to keep secreted cholesterol soluble

Question 33

How do gallstones form

Answer 33

Failure to produce enough bile so cholesterol is less soluble and precipitates into gallstones and cholelithiasis

Question 34

What is the most prominent role of vitamin D (cholestrol derived hormone)

Answer 34

Regulation of serum ca2+

Question 35

What converts 7-dehydrocholesterol to vitamin D

Answer 35

UV light

Question 36

Which 3 organs are involved in vitamin D synthesis

Answer 36

Skin, kidney and liver

Question 37

How does vitamin D maintain serum ca2+ levels

Answer 37

Released in response to low serum ca2+ and targets gut cells to increase ca2+ absorption from diet so more is available for bone synthesis

Question 38

What can cause ca2+ to be released from bone stores

Answer 38

Too much vitamin D