106: Lec 25

What 2 lipids do E. coli have (only these 2)?

Does each leaflet of the lipid membrane have different lipids?

Yes

Explain the numbering of lipids and how cell membrane leaflets are asymmetric

Cell membranes typically have 60 different lipid types. The composition differs between cell types and leaflets

In terms of proteins, what is the biological role of fatty acids, and what is this process called?

Upon addition to a protein, it anchors the protein to the membrane.Lipidation

How many polar parts does cholesterol have and what is it called (type of molecule)?

1, sterol

What is the core structure of all steroids and sterol?

Gonane, made of 4 rings (1 5C, 3 6C)

Describe the polarity and solubility of cholesterol

Weakly amphipathic, completely insoluble in water

Describe the structure of cholesterol

2 rings in chair conformation, makes it very bulky and rigid (not planar) and thus disrupts lipid membrane structure

What does cholesterol do to the membrane in terms of the gel and liquid crystal phase?

Lowers the temperature at which the membrane transitions from gel to liquid crystal

What are 3 important derivatives of cholesterol?

Vitamin D, bile salts, steroid hormones.

Explain what group vitamin D is in, what it does, and what the most important forms are

Where do we get vitamin D from and how do we activate it?

From lower layers of skin epidermis based on UV light. Activated by 2 hydroxylation steps, first in the liver second in kidneys

Bile salts:

How can we get cholesterol?

From diet, or make it (de novo)

What is the major site of cholesterol synthesis in mammals?

Liver hepatocytes

What is the number of carbon atoms we need to make cholesterol and where do we get these from?

27C, acetyl-CoA

What are the 3 stages of cholesterol synthesis?

2,3 happen in the endoplasmic reticulum

When and how do we make HMG CoA?

First step of stage 1 of cholesterol synthesis, acetyl CoA and acetoacetyl CoA come together to form it

What is the second step of stage 1 of cholesterol synthesis?

Reduction of HMG CoA to mevalonate. This uses 2 NADPH and catalysed by HMG CoA reductase.

What is the committed/RDS step in cholesterol synthesis?

HMG CoA —> mevalonate

How do we regulate HMG CoA reductase?

How do we transport cholesterol in blood/body?

Carried by lipoprotein particles as cholesterol esters (the particles emulsify the lipids for transport in the blood)

Structure of lipoprotein particles?

Their core is hydrophobic (oil drop) with a monolayer membrane

What are the protein components of lipoprotein particles called and what do they do?

What is a chylomicron remnant?

A lipoprotein particle that delivers dietary cholesterol esters to the liver

Functions of good and bad cholesterols and names?