Steroid Biosynthesis

Question 1

Describe the structure of cholesterol?

Answer 1

• 4 rings (3 6 membered, 1 5 membered)
• 1st ring has an OH group
• 2nd has a double bond
• 4th ring has an 8-carbon aliphatic side chain
• The 4 rings make up what is called a cyclopentanoperhydrophenanthrene nucleus

Question 2

Where is cholesterol found?

Answer 2

Both inner and outer leaflets of the plasma membrane

• OH group exterior
• Ring structure and aliphatic chain buries into lipid enviroment along with phospholipids

Question 3

What happens to cholesterol in warm blooded mammals?

Answer 3

Tends to reduce fluidity of membrane, helps stop phospholipd tails from moving around (does opposite in cold-blooded)

Question 4

What proteins is cholesterol associated with?

Answer 4

Lipoproteins - made up of apoproteins, triglycerols, phospholipids

Question 5

What cells contain cholesterol as cholesterol esters?

Answer 5

Steroid-secreting endocrine cells. They take of OH group

Question 6

What organ synthesises cholesterol?

Answer 6

Liver

Question 7

What does cholesterol inhibit in the cholesterol biosynthesis pathway (negative feedback inhibition)?

Answer 7

HMG-CoA reductase which converts HMG CoA to mevalonate, this eventually becomes cholesterol

Question 8

What lipoproteins have the highest percentage of cholesterol esters?

Answer 8

IDL: 30%
LDL: 35-40%

Question 9

What plasma lipoprotein takes lipids from the gut to the liver?

Answer 9

Chylomicrons

Question 10

What is an increased plasma lipoprotein density due to?

Answer 10

More protein associated and lower lipid content

Question 11

What lipoprotein takes lipids from the liver to around the body?

Answer 11

VLDL

Question 12

What cells make chylomicrons?

Answer 12

Epithelial cells of the gut

Question 13

What do lipoprotein lipases do?

Answer 13

Break down tiacyglycerols that are in chylomicrons and release free fatty acids and glycerol.