Exam 3 Biochem-Lecture 29

Example of Phospholipid is
Dipalmitoylphosphatidylcholine (DPCC)  or dipalmitoyllecithin
Dipalmitoylphosphatidylcholine (DPCC) or dipalmitoyllecithin

  • is the major component of surfactant in the lungs (80%).
  • It is produced by type II epithelial cells and prevents atelectasis

  • Decreases surface tension of the fluid layer of the lung.
  • Surfactant also contains: PG, PI and 2 surfactant proteins.

 

Phosphatidylethanolamine Synthesis occur in

  • liver
  • brain

 

Phosphatidylethanolamine-N-methyltransferase

occurs in liver only

 

Phospholipase A1

  •  inhibited by  glucocorticoid
  • can remove fatty acids selectively from carbon 1 of the glycerol backbone.

 

Phospholipase  A2can

remove fatty acids selectively from carbon 2 of the glycerol backbone.

 

Roles of Cholesterol:

  • Membrane structure
  • A precursor for the synthesis of the steroid hormones and bile acids.

Both dietary cholesterol and that synthesized de novo are transported through the circulation in ….?

lipoprotein particles
The form in which cholesterol is stored in cells
cholesteryl esters,

 

The synthesis and utilization of cholesterol must be tightly regulated in order to prevent:

  • over-accumulation
  • abnormal deposition within the body.

The abnormal deposition of cholesterol and cholesterol-rich lipoproteins in the coronary arteries cause:
Atherosclerosis
Most plasma cholesterol is in a/an
 esterified form

Most plasma cholesterol is in an esterified form, with a fatty acid attached at….?

This makes it even more hydrophobic then free cholesterol.

 C-3

 

All carbon atoms of cholesterol are derived from ?

acetate

 

In Cholesterol Biosynthesis, reducing power in the form of NADPH is provided mainly by glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase of the ……….pathway????

pentose phosphate pathway

In Cholesterol Biosynthesis, reducing power in the form of ………… is provided mainly by glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase of the pentose phosphate pathway????

NADPH
Cholesterol Biosynthesis has ….major steps
5

 

 

All the reduction reactions of cholesterol biosynthesis use ……..as a cofactor.

NADPH

In Cholesterol Biosynthesis, Acetyl-CoA units are converted to mevalonate by a series of reactions that begins with the formation of …..?

HMG-CoA.
In Cholesterol Biosynthesis, HMG-CoA is converted to mevalonate by ….?
HMG-CoA reductase
What is the rate limiting step of cholesterol biosynthesis???
The reaction catalyzed by HMG-CoA reductase
HMG-CoA reductase is most active in
in the dephosphorylated state

 

•What activates HMG-CoA reductase activity??

Insulin

 

Statins

competitive inhibitors of HMG-CoA Reductase.

 

Drug Therapy for Dyslipidemia

 

Simvastatin
Pravastatin
Lovastatin

Statins exert their major effect by
reduce LDL levels
Statins affect blood cholesterol levels by

  1. inhibiting cholesterogenesis in the liver
  2.  which results in increased expression of the LDL receptor gene
  3. The greater number of LDL receptors on the surface of hepatocytes results in increased removal of LDL from the blood thereby lowering LDL-C levels

The greater number of LDL receptors on the surface of hepatocytes results in

  1. increased removal of LDL from the blood
  2. thereby lowering LDL-C levels

 

The most abundant bile acids in human bile are

  • chenodeoxycholic acid (45%)
  • cholic acid (31%).

chenodeoxycholic acid (45%) and cholic acid (31%) are
primary bile acids

 

Within the intestines the primary bile acids are acted upon by bacteria and converted to

the secondary bile acids
Primary bile acid is converted to secondary bile acid

  • deoxycholate (from cholate
  • lithocholate (from chenodeoxycholate).

 

In liver the carboxyl group of primary and secondary bile acids is conjugated via ……….bond to either glycine or taurine before their being resecreted into the bile canaliculi.

an amide bond
Bile acids perform 4 physiologically significant functions:

1. Eliminate of excess cholesterol.

2. Solubilize cholesterol in the bile, thereby preventing the precipitation of cholesterol in the gallbladder.

3. Facilitate the digestion of dietary triacylglycerols

4. Facilitate the intestinal absorption of fat-soluble vitamins.

Dietary cholesterol is transported from the small intestine to the liver within….?
chylomicrons
Cholesterol synthesized by the liver, and excess dietary cholesterol in the liver are  transported in the serum within ….?
LDLs
cholesterol is excreted in the bile as………  or as ………….following conversion to bile acids in the liver.

  • free cholesterol
  • bile salts

 

 

Reverse cholesterol transport allows peripheral cholesterol to be returned to the liver in …..?

HDLs
Cholesterol found in plasma membranes can be extracted by …….. and esterified by the …………..

  • HDLs
  • HDL-associated enzyme LCAT

 

The liver synthesizes ………. and these are converted to ……….. through the action of endothelial cell-associated lipoprotein lipase.

  • VLDLs
  • LDLs