Lec 1 Cell Membrane Physiology

Question 1

Cell membrane’s General Structure Components:

Answer 1

• phosphilipids - in bilayer
• integral membrane proteins (transmembrane)
• glycoprotein - protein w/ carbo attached
• glycolipid - lipid with glycoprotein
• (BOTH for signalling)
• channel proteins - transport
• cholesterol - fluidity

Question 2

Lipid Components (3)

Answer 2

glycerophospholipids
cholesterol
sphingolipids

Question 3

Glycerophosphoipid Components:

Answer 3

fatty acid “tail” 16-18C
* hydrophobic

Glycerol backbone (ester linked to FA tail)
* hydrohpilic

Phosphate ‘head’
* hydrophilic
* Choline (most common), ethanolamine, glycerol, inositol

Question 4

Cholesterol Components

Answer 4

Steroid

Intercalates between phospholipids - OH to aqueous interface

Impacts membrane fluidity
* small - stiff - decreases fluidity
* larger - increases fluidity

Question 5

Spingolipid Componets

Answer 5

sphingosine backbone
often sugar residues serving a number of functions

Question 6

What 2 main structures classes can lipids fit into?

Answer 6

1) fatty acids
2) isoprenoid (make up cholesterol)

Question 7

Structure of Phospholipid:

Answer 7

1) hydrocarbon chain (hydrophobic fatty acid tails)
2) backbone
* Glycerol (phosphoglycerides)
* ceramide (sphingomyelin)

3) Phosphate-alcohol head group

Question 8

2 types of phosphoglycerides:

Answer 8

Phosphodiate
* both fatty acids linked by ester link
* more commonly found in cell membrane

Plasmogen
* one fatty acid linked by ester link, other linked by ether link

Question 9

phosphatidylethanolamine, phosphatidylserine, phosphatidylcholine

Answer 9

• 3 common phosphoglycerides in the cell mambrane
• named based on the functional group attached to the polar phosphate head group! (serine, choline, etc)

Question 10

Sphingomyelin?

Answer 10

• common phospholipid in membrane
• contains ceramide backbone (why not called phospholipid)
• specific head group - choline

Question 11

where can glycerol-3-phosphate be derived from?

Answer 11

1. addition of phosphate to glycerol (in liver)
2. conversion of G3P from DHAP

Question 12

What step in phosphate synthesis is this?
2 fatty acyl CoA’s added to glycerol-3-phosphate forming phosphatidic acid
Often, fatty acid C1 is saturated and fatty acid C2 is unsaturated

Answer 12

Steps 1 and 2

Question 13

What step is this in phospholipid synthesis?
Addition of head group (hydroxul first activated by attachment of cytosine diphosphate (CDP))

Answer 13

Step 3

Question 14

What step is this in phospholipid synthesis?
Modification/Alteration of Head group
(phosphatidylserine and phosphatidylethanolamine - interconvert in reversibel head-group exchange reaction)

Answer 14

Step 4

Question 15

Phosphatidylinositol?

Answer 15

• less common in membrane
• important in cell signaling

Question 16

Where does phospholipid syntehsis occur?

Answer 16

primarily on luminal surface of smooth ER and inner mitochondrial membrane

Question 17

How do newly synthesized phospholipids leave the ER?

Answer 17

• enzyme - flippase
• translocated phospholipids accross ER to cytosolic side

Question 18

What are steroids?

Answer 18

complex molecules mode from 6 isoprene units
4 fused rings with various substituents

Question 19

What do you call a steroid with a OH group at C3?

Answer 19

a STEROL
ex. cholesterol

Question 20

What are the 4 steps in cholesterol synthesis?

Answer 20

1. Condensation -** 3 acetyl CoA** into mevalonate
2. Formation of isopentenyl pyrophosphate
3. Creation of squalene
4. Cyclization into cholesterol

Question 21

What is rate limiting step in cholesterol synthesis?

Answer 21

Step 1 when 3 acetyl CoA’s and condensed into mevalonate - catalyzed by HMG CoA reductase!

Question 22

How do Statin medications lower cholesterol?

Answer 22

• bloack enzyme HMG CoA reductase - stops cholesterol synthesis

Question 23

What role does NADH play in cholesterol synthesis?

Answer 23

• is a coenzyme from vitB3 generated in pentose-phosphate shunt

Question 24

How does Step 2 - conversion of mevalonate to active isoprene isopentenyl pyrophosphate occur?

Answer 24

Addition of 3 phosphates (generated from using 3 ATP)

Question 25

How many acetyl CoA’s are required to make squalene?

Answer 25

3 acetyl CoA’s in 1 isoprene unit
6 isoprene units in squalene therefore, total 18 are NEEDED

Question 26

What do Step 3&4 of cholesterol synthesis both require?

Answer 26

NADH

Question 27

How is cholesterol synthesis regulated?

Answer 27

Through the inhibition of HMG CoA reductase of high intracellular levels of cholesterol
* This is genetic regulation - it blocks the transcription of HMG CoA reductase gene

Reversible covalent modification
* glucagon promotes phosphorylation of HMG CoA reductase - inhibiting it
* (insulin de-phosphorylates it activating the enzyme)