Lipids and Membrane Structure

Question 1

What is meant by the fluid mosaic model

Answer 1

The idea that the phospholipids are flexible whilst the proteins are embedded inside, with different shapes and size

Question 2

How big is the phospholipid bilayer

Answer 2

4-5nm

Question 3

What is the phospholipid bilayer composed of

Answer 3

phospholipid
glycoproteins
proteins
Lipids–> phosph/coline , phosph/serine , Sphingomyel and cholesterol

NB the idea that different plasma membranes will have different compositions of the components and it is this which defines the membrane

Question 4

What are the functions of lipids

Answer 4

Energy stores - triaglycerol
Precursor for vitamins and hormones (steroids)
Bile acids eg Cholic acid
Membrane structure- phospholipid

Question 5

What are phospholipids composed of and describe it

Answer 5

phosphate group
glycerol backbone
fatty acid

• it is amphipathic

Question 6

Name the polar head groups which could attach onto the phosphate groups

Answer 6

inositol, serine ,choline, ethanoloamine

Question 7

What is phosphatidylcholine composed of?

Answer 7

phosphate group
glycerol backbone
fatty acid
choline

Question 8

What is sphingomyelin composed of?

Answer 8

Ceramide
phosphate head
choline

Question 9

Why are lipid bilayers asymmetrical

Answer 9

since two halves of the bilayer have different lipid composition
eg. phosphotidycholine and sphingomyelin face extracellular
phosphatidyserine and phosphotidyethanolamine face the cytosolic side

Question 10

Define the term fluidity means

Answer 10

The ese at which lipid molecules move about the plane of the bilayer
important in regulation of membrane function
(movement of proteins, signalling and exocytosis)

Lipid composition of the membrane defines the fluidity

Question 11

What determines fluidity?

Answer 11

Fatty acid length- the shorter chained fatty acids reduce the tendency of hydrocarbon chains to interact- increasing fluidity

Unsaturated fatty acid- The kinks in the unsaturated fatty acid results in less stable VdW with other lipids- increasing fluidity

High cholesterol- results in the random movement of polar heads by ordering the bilayer - decreasing fluidity

Question 12

Give an example of a disease caused by increased cholesterol

Answer 12

Increased cholesterol in the RBC cell membranes which is associated with Cirrhosis- this alters the shape which means the function is altered- this impairs the O2 transport and causes the destruction of RBC as well as Anaemia

Question 13

Give some examples of the classes of membrane proteins

Answer 13

Sructural, receptors, ion channels, transporters, enzymes

Question 14

Structural-

Answer 14

cell-cell contact, cytoskeletal organisation

eg. actin, spectrin, ankyrin

Question 15

Receptors-

Answer 15

signal recognition and transduction

eg. insulin receptor and glucagon receptor

Question 16

Ion channels-

Answer 16

maintenance of ionic gradients, transmission

eg. Acetlycholine, GABA

Question 17

Enzymes

Answer 17

Catalysis

eg. Andenlyl cyclase

Question 18

What are the three types of ways membrane proteins are organised?

Answer 18

Integral
Anchored
Peripheral

Question 19

Describe Integral Proteins

Answer 19

embedded into the lipid bilayer- most spanning the entire length of the bilayer
Transmembrane spanning domains can be alpha helix or beta plated sheets
eg. channel transporters

NB diagram about hydrophilic and hydrophobic areas

Question 20

Describe Anchored Proteins

Answer 20

anchored to the membrane by covelantly bound fatty acids
EITHER covalently linked to fatty acid chain ( signalling G protein called RAS) or onto the cell surface to glycolipid ( alkaline phosphotase)

Question 21

Describe peripheral proteins

Answer 21

attach to membrane surface by ionic interactions with integral proteins or with polar head group of phospholipid

eg. Spectrin- STRUCTURAL PORTIEIN on the cytoplasmic surface of erythrocytes interacting with ANKYRIN

Phospholipase A2 binds to the bilayer to cleave fatty acids from phospholipids.

Question 22

What removes integral proteins

Answer 22

detergent

Question 23

What removes anchored proteins

Answer 23

detergent and phospholipase

Question 24

what removes peripheral proteins

Answer 24

high salt, urea, detergent