Lipid Membranes & Cells

Question 1

What is the overall function of lipids?

Answer 1

Lipids are the way that life make cells and compartments (organelles)

Question 2

What are the roles of lipids?

Answer 2

Lipids come together to form membranes

• provide structure
• allow selective transport
• inform communication between cells
• allow electrical conductance
• facilitate control mechanism

Question 3

What part of cells are a major drug target?

Answer 3

Membrane proteins are a major drug target

This is because although they are outside of the cell, they stimulate chemistry within

Question 4

What is a lipid?

Answer 4

They have both hydrophobic and hydrophilic character
Soluble in organic solvents and not so soluble in water
Hydrophobic greasy tail
Polar head group which is hydrophilic- water soluble

Question 5

What are examples of lipids?

Answer 5

Fatty acyl waters (phospholipids, glycolpids)
Steroids (cholesterol)
Waxes

Question 6

What are fatty acids?

Answer 6

They form fatty acyl esters
Hydrocarbon chains of varying lengths 
They can have different degrees of saturation
- no double bonds= saturated 
- double bonds = unsaturated

Question 7

What are membrane lipids?

Answer 7

These are phospholipids

They are abundant in all biological membranes

Question 8

What do phospholipids contain?

Answer 8

1) fatty acid
2) glycerol
3) phosphate
4) charged, polarised hydrophilic

Question 9

How do chemistry synthesise ester bonds?

Answer 9

1) add SoCl2 to change OH to Cl as Cl- is a better leaving group than water
- react with an alcohol to form an ester
(See mechanism)

Question 10

How does nature synthesise ester bonds?

Answer 10

It has Sc-OA ( acyl CoA) as it’s leaving group- good
React with alcohol
( see mechanism)

Sc-OA is natures good leaving group

Question 11

What are the two ways phospholipids can aggregate?

Answer 11

If there is 1 acyl chain- it forms a lipid micelle

If there are two acyl chains- it forms a phospholipid bilayer (most energetically favourable)

Question 12

What are the driving forces for bilayer formation?

Answer 12

(Self assembly in water)

1) hydrophobic effect- buried acyl chains (hydrophobic)
2) van der waals interactions between acyl chains
3) polar head groups interact with water
- electrostatic and hydrogen bonding

Question 13

What are membrane proteins?

Answer 13

Responsible for dynomic processes in membranes

Question 14

How do integral and peripheral proteins interact?

Answer 14

Integral proteins interact extensively with lipid hydrocarbons
Peripheral interact with hydrogen bonding and electrostatic interactions

Question 15

What is the fluid mosaic model?

Answer 15

The membrane is a fluid mosaic of proteins floating in a sea of lipids
Lipids can laterally diffuse within the membrane- so can proteins

Question 16

What does the fluid mosaic model contain?

Answer 16

Phospholipid bilayer
Intergalactic membrane protein
Cholesterol
Peripheral membrane protein

Question 17

What are examples of integral membrane proteins?

Answer 17

7 alpha helical bundle
Rhodopsin
Porins
Beta barrel

Question 18

What are the role of glycolipids?

Answer 18

Place sugars external
Allow communication within cell
Assymetric within a memebrane

Question 19

Describe the structure and position in the membrane of cholesterol

Answer 19

Polar head group and hydrophobic carbon tail
Steroid (25% of the membrane)
Sits within the membrane
Hydrophobic rail is embedded and has van der waals with other chains
Polar head forms H bonds to other phospholipid head groups

Question 20

Describe the role of cholesterol

Answer 20

Modulates membrane fluidity by disrupting the packing of lipids
Inert into bilayer and causes less regular interactions between phospholipids which causes fluidity

Question 21

What other parts of the membrane control fluidity

Answer 21

Unsaturated fatty acyl chains also make membrane more fluid

They prevent membrane rigidity which is important at low temperatures

Question 22

What is a LDL?

Answer 22

A low density lipoprotein (with cholesterol)
Transfers lipids around the body
Linked with atherosclerosis which is the thickening of arteries
High cholesterol causes heart disease

Question 23

How is cholesterol made?

Answer 23

Acetyl CoA to melvanoate (mediated by HmGCoA reductase) to squalene to cholesterol

Question 24

Describe the role of membrane drug targets

Answer 24

They are G protein coupled receptors GPCRs
Cell surface receptors
They transmit messages across the membrane (light, peptide, lipids or sugars)
Roles in vision, mood behaviour and smell
Sense molecule outside the cell- activates a signal transduction pathway

Question 25

How do beta1 and beta 2 ad renege in receptors act as drug targets?

Answer 25

Beta 1 receptor heart- controls cardiac output

Beta 2 receptor- lungs, controls muscle relaxation in lungs

Question 26

What is an antagonist and an agonist?

Answer 26

Antagonist is a receptor inhibitor

Agonist is a receptor activator