Cholestrol Synthesis

Question 1

What is found in excess in the liver in both fasted and fed state?

Answer 1

Acetyl CoA

Question 2

What is the key enzyme in cholesterol synthesis?

Answer 2

HMG-CoA reductase

Question 3

What stimulates HMG-CoA reductase?

Answer 3

Insulin

Question 4

What inhibits HMG-CoA reductase?

Answer 4

AMPK (AMP-activated protein kinase)

Question 5

What stimulates AMPK?

Answer 5

AMP stimulates it large amounts of ATP breakdown creates AMP

Question 6

What inhibits AMPK?

Answer 6

Phosphocreatine

Question 7

What does a deficiency in liver kinase B cause?

Answer 7

Doesn’t uptake glucose leaving it in the bloodstream hyperglycemia

Question 8

What increases AMPK activity?

Answer 8

Leptin and adiponectin

Question 9

What does AMPK cause?

Answer 9

Energy producing processes and decreases energy consuming processes

Question 10

What breaks down HMG-CoA reductase?

Answer 10

Ubiquitin

Question 11

What inhibits HMG-CoA and why?

Answer 11

Glucagon and epinephrine so you do not waste energy on cholesterol during fight or flight or fasted states

Question 12

What does Insig do?

Answer 12

Holds SCAP-SREBP complex in ER in presence of sufficient cholesterol concentrations

Question 13

What occurs to the SCAP-SREBP complex once cholesterol levels decrease?

Answer 13

Insig releases it and it SCAP-SREBP continues to the Golgi

Question 14

What occurs to Insig once the SCAP-SREBP complex leaves the ER?

Answer 14

It is ubiquinated for proteolysis

Question 15

Once in the Golgi what occurs to the SCAP-SREBP complex?

Answer 15

SREBP is cleaved from SCAP by MBTPS1

Question 16

What occurs once SCAP is released from SREBP?

Answer 16

MBTPS2 cleaves it releasing the transcription factor

Question 17

What does ACAT do and why?

Answer 17

Esterifies cholesterol so that it can be transported and stays out of the membrane

Question 18

What occurs with a defect in ApoE?

Answer 18

IDL and chylomicrons remain in circulation too long causing hyperlipoproteinemia

Question 19

What does LCAT add to cholesterol?

Answer 19

Phosphatidylcholine instead of a fatty acid (ACAT fatty acid)

Question 20

Where does HDL get a fatty acid for esterification?

Answer 20

Its own membrane (no TAGs intracellularly)

Question 21

What receptor allows for LDL to be taken in by cells?

Answer 21

Apo B

Question 22

What occurs to LDL once inside the cell?

Answer 22

Transported to lysosomes to breakdown everything and receptor sent up to surface again

Question 23

What is the transcription of HMG-CoA reductase dependent on?

Answer 23

Intracellular cholesterol concentration

Question 24

What is the rate limiting step of steroid synthesis?

Answer 24

StAR

Question 25

What is StAR?

Answer 25

Protein responsible for transport of cholesterol into the mitochondria

Question 26

What is the first step in synthesis of all steroid hormones?

Answer 26

Cholesterol to progestagens

Question 27

What do progestagens get turned into?

Answer 27

Mineralocorticoids Glucocorticoids Androgens

Question 28

What do estrogens come from?

Answer 28

Androgens

Question 29

What enzyme is needed for androgens to turn to estrogens?

Answer 29

Aromatase

Question 30

Where are progestagens made?

Answer 30

Adrenal cortex, gonads, CNS

Question 31

Androgens are made:

Answer 31

Adrenal cortex and gonads

Question 32

Mineralocorticoids/glucocorticoids are made:

Answer 32

Adrenal cortex

Question 33

Estrogens are made:

Answer 33

Gonads

Question 34

When and where are estriols made?

Answer 34

Only in pregnancy by fetal adrenal glands, liver and placenta

Question 35

What is dihydrotestosterone?

Answer 35

5% of test is turned into this has a huge affect on secondary sex characteristics not primary characteristics

Question 36

What enzyme converts testosterone to dihydrotestosterone?

Answer 36

5 alpha-reductase

Question 37

What can 5 alpha-reductase deficiency lead to?

Answer 37

Male patterned baldness, benign prostatic hyperplasia, and prostate cancer

Question 38

What can aromatase deficiency lead to?

Answer 38

In males and females no secondary sex characteristics