Adrenal Steroids

Question 1

What are the class of steroids called with 21 carbons? 19 carbons? 18 carbons?

Answer 1

21 carbons: pregnane 19: androstane 18: estrane

Question 2

Which enzyme regulates cholesterol biosynthesis?

Answer 2

HMG CoA Reductase

Question 3

What is the rate-limiting step of steroid synthesis?

Answer 3

StAR transport of cholesterol into mitochondria.

Question 4

What condition occurs in an individual with a mutation in StAR? It is associated with what symptoms and which two events?

Answer 4

*Congenital lipoid adrenal hyperplasia* -salt wasting/hyponatremia/hypovolemia -hyperkalemia -acidosis -death in infancy if untreated 1) Decreased steroidogenesis due to StAR mutation 2) Increased loss of steroidogenesis due to cellular damage from accumulating cholesterol esters.

Question 5

Describe the first step in steroid synthesis from cholesterol. It is catalyzed by which enzyme? Stimulated by which factors?

Answer 5

1) Cytochrome P450scc 2) Activated by ACTH, LH, and AII 3) Converts cholesterol to pregnenolone (21C) and isocaproaldehyde (6c)

Question 6

What is an example of an inhibitor of steroid synthesis? How does it work?

Answer 6

Aminoglutethemide inhibits P-450scc -works in adrenal, not very specific, inhibits aromatase & increases some steroid turnover

Question 7

Where in the cell does steroid synthesis occur?

Answer 7

Mitochondria or ER

Question 8

What 4 classes of enzyme are most important in steroid synthesis?

Answer 8

1) Hydroxylase 2) Dehydrogenase 3) Isomerase 4) Lyase

Question 9

How do target cells regulate which steroids they produce?

Answer 9

Expression of enzymes determines specificity of steroid synthesis.

Question 10

Which 3 steroid classes have 21 carbons? Which one has 19? 18?

Answer 10

21C pregnanes: progestins, glucocorticoids, mineralocorticoids 19 C androstanes: androgens 18C estranes: estrogens

Question 11

What are the 5 steps of steroid degradation?

Answer 11

1) Liver makes steroids hydrophilic 2) A ring double bond is reduced to dihydro derivative 3) The 3-ketone group is reduced to hydroxy derivative 4) Glucuronide or sulfate is conjugated to hydroxy groups 5) Hydrophilic; excreted rapidly

Question 12

Which form of steroids is the excreted degradation product?

Answer 12

Tetrahydro form

Question 13

What is the name of the steroid nucleus? How many carbons does it have?

Answer 13

Cyclopentanoperhydrophenanthrene (17C)

Question 14

Draw cholesterol

Answer 14