Topic 1.3: Membrane Structure

Question 1

Components of a phospholipid

Answer 1

a) Polar head

b) Non-polar tails

Question 2

Component of polar head

Answer 2

a) Glycerol

b) Phosphate group

Question 3

Component of non-polar tails

Answer 3

Two chains of fatty acids

Question 4

Amphipathic

Answer 4

Containing both hydrophilic and hydrophobic regions

Question 5

Arrangement of phospholipis

Answer 5

Bilayer

a) Hydrophobic tails face inwards
b) Hydrophilic head face outwards

Question 6

Properties of the phospholipid bilayer

Answer 6

a) Held together by weak hydrophobic interactions between the tails.
b) Individual phospholipids can move within the bilayer (fluidity and flexibility)
c) Amphipatic properties restrict passage of certain substances.

Question 7

Components in animal cell membranes

Answer 7

a) Cholesterol
b) Proteins
c) Phospholipids

Question 8

Functions of cholesterol

Answer 8

a) Reduces fluidity by immobilising the outer membrane surface
b) Reduces permeability to some molecules
c) Prevents crystallization by separating phospholipid tails

Question 9

Integral proteins

Answer 9

a) Permanently attached to the membrane

b) Typically transmembrane

Question 10

Peripheral proteins

Answer 10

a) Temporarily attached

b) Associate with one surface of the membrane

Question 11

Functions of Membrane Proteins

Answer 11

a) Transport
b) Receptors
c) Anchorage
d) Cell recognition
e) Intercellular joinings
f) Enzymatic activity

Question 12

Transport

Answer 12

a) Protein channels

b) Protein pumps

Question 13

Receptors

Answer 13

Peptide-based hormones

Question 14

Anchorage

Answer 14

Cytoskeleton attachments

Question 15

Cell Recognition

Answer 15

MHC proteins and antigens

Question 16

Intercellular joinings

Answer 16

Tight junctions

Question 17

Enzymatic activity

Answer 17

Metabolic pathways

Question 18

Drawing of the fluid-mosaic model

Answer 18

a) Phospholipid bilayer
b) Glycoprotein
c) Carrier protein
d) Channel protein
e) Cholesterol

Question 19

Davson-Danielli model

Answer 19

a) Two layers of protein adjacent to the phospholipid bilayer
b) EMG showing two dark lines with a lighter band.

Question 20

Problems with Davson-Danielli model

Answer 20

a) Constant lipid-protein ratio and a uniform thickness
b) Permeability of certain substances such as H2O
c) Temperatures at which membranes solidified did not correlate with those expected.

Question 21

Falsification of Davson-Danielli model

Answer 21

a) Membrane proteins were discovered to be insoluble in H2O. Not able to form a uniform and continuous layer.
b) Fluorescent antibody tagging of membrane proteins showed they were mobile and not fixed
c) Freeze fracturing was used to split open the membrane and revealed irregular roguht surfaces within the membrane.

Question 22

Singer-Nicolson model

Answer 22

Proteins were embedded within the lipid bilayer rather than existing as separate layers