Cholesterol + Biological membranes

what is this?

cholesterol

What does cholesterol do?

• important to the membrane lipid

• cholesterol plays an important role in membranes because it is 20-25% of lipid mass in mammalian membranes

It increases membrane fluidity at low temps due to the structure, but the membrane responds less to high temp due to cholesterol rigidity

• Precursor to steroid hormones

Describe the role of lipoprotein particles in transporting cholesterol

• lipoprotein define any protein covalently linked to lipid groups.

HOWEVER: low density lipoprotein (LDL) and high density lipoprotein (HDL) are used for specific types of particles consisting of a phospholipid/protein coat, which carry lipids in their interior. These particles transport cholesterol and lipids in the bloodstream.

What is the composition of chylomicrons?

• mostly triacylgylcerols

What is the composition of LDL

• pretty even split between protein, free cholesterol and phosphollipids

What is the compositon of HDL

• the largest portion is protein

• HDL can function as a vesicle

• Smaller.

• Protein is greater than lipid conc, so it has a higher density.

• It has Apo A and Apo C → this is different than LDL’s Apo B-100, which is why they are taken up by cells differently!

What protein does LDL have

Apo B-100

What protein does HDL have?

Apo A and Apo C proteins

_________ transport triacylglyerols from intestines (diet) to the tissues

chylomicrons

What does low density lipoproteins do?

transport cholesterol from liver to peripheral tissues;

specific cell types bind the Apo B-100 of the LDL and take up the particles

What two deliver to the tissues?

LDL and chylomicron both deliver to the tissues, but they deliver different things. Chylomicron delivers triacylglycerol to the tissues from the intestines. LDL delivers cholesterol to peripheral tissues that have cells that can bind to Apo B-100.

What is the scavenger

HDL

What does HDL do?

collect cholesterol in the blood and transport it back

to the liver; cholesterol then converted to bile acid and excreted; HDLs are

cholesterol “scavengers”

So if a person is concerned about lowering cholesterol concentration in the

body, low ____ and high _____ in the blood is desirable; that should result in

lowering [cholesterol]

Low LDL and High HDL

Where is cholesterol synthesized?

In the liver! It is esterified and then transported to tissues by LDL.

The Apo B-100 protein targets the _____ to the ______; Apo A and Apo C proteins target ____ to the ____.

The Apo B-100 protein targets the LDL to the tissue; Apo A and Apo C proteins

target HDL to the liver

What is the cholesterol ratio

total cholesterol / HDL number

A “healthy” cholesterol ratio is ___; a higher ratio than this can result in

failure to adequately regulate cholesterol levels in the tissues.

3:5

Why is LDL considered bad

Most of the cholesterol found in the plaques has been delivered by

LDL particles. The foam cells possess LDL receptors and acquire their

cholesterol via LDL particles.

Atheromas is a progressive process in which macrophage cells fill with

cholesterol and cholesterol esters to form “foam cells”. Eventually

these calcify and protrude into the lumen of the artery to form

blockages. These deposits are plaques that block blood flow and can

result in heart attacks, strokes, and thromboses