WEEK 1

Question 1

What is the history of the plasma membrane?

Answer 1

1877 - Wilhelm Pfeffer studied osmotic pressure of plant cells and formulated the idea that protoplasm is surrounded by plasma membrane

1895 - Charles Ernest Overton study on osmotic properties of cells lead to the hypothesis that membranes have properties of oils

1917 - Irving Langmuir developed the method to spread molecular layers of lipids at air-water interface

1925 - Evert Gorter and Francois Grendel concluded that membranes are made of two opposite layers of lipids

Question 2

What model describes the phospholipid bilayer?

Answer 2

Fluid mosaic model

Question 3

What is the most common phospholipid in the cell membrane?

Answer 3

Phosphatidylcholine

Question 4

Describe the components of a phospholipid?

Answer 4

Polar head group
Glycerol backbone
Fatty acid chains

Question 5

What does the presence of cholesterol do in biological membranes?

Answer 5

• Reduces membrane fluidity by restricting movement of phospholipids (at high temp)
• Increases flexibility by disrupting the packing of hydrocarbon chains (at low temp)
• Reduces permeability of membranes to hydrophilic water soluble molecules
• Reduces segregation of different phospholipids which makes membrane lipid composition more heterogenous

Question 6

Phospholipids are constantly in motion at very ______ rates

Answer 6

fast

Question 7

What sort of movements are phospholipids constantly doing within the bilayer?

Answer 7

• Trans bilayer movement (flip-flop)
• Rapid rotation around a central axis
• Diffusion across monolayer
• Fatty acyl tails undergo constant flexion

Question 8

What is the difference between a hydrophilic molecule and a hydrophobic molecule?

Answer 8

A hydrophilic molecule attracts water whereas a hydrophobic molecule avoids water

Question 9

What lipids can be found in aqueous media?

Answer 9

Lipid
Micelles
Lipid bilayer
Inversed micelles

Question 10

What are the lipid phases with increasing temperature?

Answer 10

Lc phase - Crystalline lipid phase with three dimensional order of molecules
Lb phase - gell phase with lipid bilayer with tilted chains, angle depends on polar heads
Pb phase - Ripple/partially melted phase
La phase - Fluid phase where chains are disordered and heads ordering is lost

Question 11

What has a higher melting temperature, saturated lipids or unsaturated lipids?

Answer 11

Saturated chains

Question 12

What does an amino acid consist of around the central carbon atom?

Answer 12

Carboxyl group
Amine group
H atom
An “R” (variable) group

Question 13

Describe the secondary structure of proteins in B-pleated sheets

Answer 13

In B-pleated sheets the pleats are formed by hydrogen bonds between carbonyl and amino groups separated further on the backbone of polypeptide chain

Question 14

Describe the secondary structure of proteins in A-helix

Answer 14

a-helix is stabilised by hydrogen bonds between the oxygen atom in a carbonyl group of one amino acid and the hydrogen atom of the amino group that is four amino acid units farther along the chain

Question 15

What is the primary structure of protein?

Answer 15

Sequence of a chain of amino acids

Question 15

What is the primary structure of protein?

Answer 15

Sequence of a chain of amino acids

Question 16

What is the secondary protein structure?

Answer 16

Local folding of the polypeptide chain into helices or sheets

Question 17

What is the tertiary protein structure?

Answer 17

Three-dimensional folding pattern of a protein due to side chain interactions

Question 18

What is the quaternary protein structure?

Answer 18

Protein consisting of more than one amino acid chain

Question 19

What are the different functions of membrane proteins

Answer 19

Transporters
Anchors
Receptors
Enzymes

Question 20

How do the membrane proteins associate with the lipid bilayer?

Answer 20

• Transmembrane proteins (through the membrane)
• Monolayer-associated proteins
• Lipid linked proteins (Only lipid tail is linked to bilayer)
• Protein-attached protein

Question 21

What are the different molecular forces in biological molecules?

Answer 21

Coulomb potential
Image forces
Charge-dipole interaction
Induced dipoles
Dispersion forces
Hydrophobic forces
Hydration forces
Hydrogen bonds

Question 22

What are the different types of dipole interactions?

Answer 22

• Ion-induced dipole interactions
• Dipole induced dipole interactions
• Dispersion induced dipole interactions

Question 23

What are the different types of hydration forces?

Answer 23

• Ion-dipole (water becomes part of the structure)
• Hydrogen bonds
• Dipole-dipole

Question 24

How can we see hydrophobic and hydrophilic interactions on a macroscale?

Answer 24

When a water droplet is placed on a hydrophobic surface (e.g plastic) it forms a small interface with a droplet with greater height. When dropped on a hydrophilic surface (e.g glass) it forms a larger interface so the droplet is more spread out with reduced height.

Question 25

What is a key feature of water hydration?

Answer 25

It becomes part of the structure and so if disrupted through the removal or change of state between solid, liquid and gas the structure becomes compromised and destroyed

Question 26

What is the mattress model of the plasma membrane?

Answer 26

The plasma membrane is made up of many different types of phospholipids with different fatty acid tails that differ in saturation and length. The types of phospholipid varies throughout the membrane especially around peripheral and integral proteins

Question 27

How can you describe the structure and behaviour of cholesterol?

Answer 27

Cholesterol has a very small polar head and long non-polar tail. The head stays near the surface and the tail is embedded deep into the bilayer.

Question 28

How does the presence of cholesterol affect the permeability of the membrane?

Answer 28

Cholesterol regulates the membrane fluidity as well as the membrane’s permeability with more cholesterol causing a decrease in permeability of the membrane to hydrophilic water soluble molecules such as Na+ and H+