Complex lipids and cholesterol biochem

Question 1

1. Describe the sources and fates of cholesterol.

Answer 1

acetyl coa is source during fed state

steroids, membrane cholesterol, bile salts

Question 2

2. Describe in general the steps in the de novo synthesis of cholesterol.

Answer 2

2 acetyl coa–> becomes acetoacetyl coa.using hmg synthase it becomes HMG coa just like ketone bodies, but now we use hmg coa recuctase and NADPH this makes key intermediate mevalonate, we add some ATP and we get these wierd molecules geranyl pyrophoshate and then farnesyl pyrophosphate, in two more steps we get cholesterol

Question 3

3. Identify the key regulated step in cholesterol synthesis and describe how this step is regulated.

Answer 3

the key regulated step is of HMG coa reductase. Insulin up regulates it glucagon down res it, Cholesterol down regulates it by having scap bind SREBP and keeping it out of the nucleus, since SREBP also upregulates it.

Question 4

4. Describe the key features of the structures of glycerophospholipids, sphyngomyelin and glycerosphingolipids and the general aspects of their synthesis.

Answer 4

glycerophospholipids have a glycerol backbone with a polar head group on one of three spots

sphingolipids- have a sphingosine backbone with a fatty acid on one spot, and a polar head group, possibly a choline

glycosphingolipids- have a fatty acid and a sugar on the two binding sites

to make sphingomyelin we atrt with palmitoyl coa +serine to make sphinganine, add some reducers and get sphingosine (ceramide), add a phosphatiydl choline and u get sphingomyelin

Question 5

6. List the important functions of phosphatidylcholine, phosphatidylinositol and sphyngomyelin.

Answer 5

phosphotydyl inositol is cleaved from the membrane by phospholipase C to become IP3 and diacyl glycerol–> PKC IP3–>a second messenger to signal calcium influx

phosphotidyl choline helps make sphingomyelin, also a major constiuetn of pulmoanry surfactant

sphingomyelin-makes up part of myelin, apoptosis, signal transduction, lipid rafts

Question 6

7. Describe in general the synthesis of arachidonic acid and prostaglandins.

Answer 6

linoleic acid containing phospholipid is cleaved by phosphlipase A2 which make arachadonic acid. which then goes on to make PG’s through the COx’s or Leukotrienes