Cholesterol Metabolism

Question 1

Cholesterol is a precursor of which substances

Answer 1

Bile acids (in liver) 
Steroid hormones (adrenal cortex, gonads) 
Vitamin D (skin)

Question 2

Major tissue sites of cholesterol metabolism

Answer 2

Liver, intestine, adrenal cortex, ovaries, testes, placenta

Question 3

Where in cells does cholesterol metabolism occur

Answer 3

cytosol and SER

Question 4

Which molecule are all the carbons for cholesterol metabolism derived

Answer 4

Acetyl CoA

Question 5

During cholesterol synthesis, which is the first sterol to be produced

Answer 5

Lanosterol (30C)

Question 6

Cholesterol has how many carbons

Answer 6

27

Question 7

Which sterol in cholesterol metabolism is needed for viitamin D3 production

Answer 7

7-dehydrocholesterol (27C)

Question 8

Which enzyme converts 7-dehydrocholesterol to cholesterol

Answer 8

7-dehydrocholesterol 7-reductase

Question 9

Which enzyme controls the rate-limiting step of cholesterol synthesis

Answer 9

HMG CoA reductase

Question 10

What are the four regulatory steps in cholesterol synthhesis

Answer 10

1. Sterol-dependent regulation of gene expression
2. Sterol accelerated enzyme degradation
3. Covalent modification (phosphorylationdephosphorylation)
4. Hormonal regulation

Question 11

The regulatory mechanisms in cholesterol metabolism act on which enzyme

Answer 11

HMG CoA synthase

Question 12

Which transcription factor controls expression of the gene for HMG CoA reductase

Answer 12

SREBP-2 (sterol regulatory element-binding protein-2)

Question 13

Sterol regulatory element-binding protein-2 is an integral protein in which organelle membrane

Answer 13

ER membrane

Question 14

Sterols bind to which protein when cholesterol levels are high to inhibit cholesterol synthesis

Answer 14

SCAP (SREBP Clevage Activating Protein)

Question 15

SCAP binds to which protein in the ER membrane when cholesterol levels are high retain SREBP in the ER

Answer 15

Insig proteins (Insulin induced gene products)

Question 16

What does the SREBP-1 protein do

Answer 16

upregulates expression of genes involved in fatty acid synthesis in response to insulin

Question 17

Which molecule can covalently inactivate HMG CoA reductase

Answer 17

AMP-activated protein kinase

Question 18

Which molecule can covalently activate HMG CoA reductase

Answer 18

Protein phosphatase

Question 19

Two hormones that induce the gene for HMG CoA reductase

Answer 19

insulin and thyroxine

Question 20

Two hormones that repress the gene for HMG CoA reductase

Answer 20

Glucagon and glucocorticoids

Question 21

Drugs that are competitive inhibitors of which enzyme are used to treat hypercholesterolemia

Answer 21

HMG CoA reductase

Question 22

Dietary cholesterol (Exogenous): Transported as _____________ from the intestine to the liver and EHT

Answer 22

chylomicrons

Question 23

De novo synthesis cholesterol (Endogenous):Transported as ______ and ________ from the liver to the EHT

Answer 23

VLDL and LDL

Question 24

Reverse Transport of cholesterol: Transported as _________ from the EHT to the liver

Answer 24

HDL

Question 25

What is the name of the molecule that cholesterol is stored as

Answer 25

cholesteryl esters

Question 26

what is the enzyme needed to convert cholesterol to cholesteryl esters

Answer 26

ACAT (acyl coA cholesterol acyl transferase) Cholesterol + Acyl CoA ---> cholesteryl ester + CoA

Question 27

Two way in which cholesterol is excreted

Answer 27

It is converted into bile acid and salts it is secreted into bile and excreted in feces

Question 28

What are neutral fecal sterols

Answer 28

coprostanol & cholestanol together with cholesterol

Question 29

Smith-Lemli-Opitz syndrome (SLOSI is due to a partial deficiency in which enzyme

Answer 29

7-dehydrocholesterol-7-reductase

Question 30

What clinical presentation can result from a deficiency in 7-dehydrocholesterol-7-reductase

Answer 30

Multisystem embryonic malformations * microencephaly, short nasal root, high arched palate, cleft palate * CNS defects, polydactyly * Severe mental & growth retardation

Question 31

What are four causes of hyperchlesterolemia

Answer 31

1. Diabetes mellitus 2. Familial disorders (Lipoprotein metabolism) 3. Hypothyroidism 4. Nephrotic syndrome

Question 32

Where does the synthesis of bile acids occur

Answer 32

liver

Question 33

What is the starting molecule for bile acid synthesis

Answer 33

cholesterol

Question 34

Which enzyme is needed for synthesis of bile acids

Answer 34

7 alpha-hydroxylase

Question 35

Addition of which two molecules convert Cholic acid and Chenodeoxycholic acid to conjugated bile salts

Answer 35

Glycine and Taurine

Question 36

In which organ is bile concentrated

Answer 36

gall bladder

Question 37

Which vitamin is needed during bile acid synthesis

Answer 37

vitamin C

Question 38

What are the functions of bile acids/salts

Answer 38

1. help in lipid emulsification during lipid digestion and absorption 2. solubilize dietary lipids 3. facilities action of pancreatic lipases 4. lipids are more readily absorbed by the intestine 5. Solubilizes cholesterol present in the bile

Question 39

What two processes do bile acids undergo in the intestine are they have been used

Answer 39

Deconjugation and dehydroxylation

Question 40

What are the two main secondary bile salts

Answer 40

deoxy cholic acid and lithocholic acid

Question 41

What are the two causes of cholelithiasis

Answer 41

increased excretion of cholesterol in bile decreased availability of bile salt in the bile