Lecture 6: Membranes

Question 1

What is the membrane permeable, hardly permeable to and in impermeable to?

Answer 1

Permeable: to small molecules 
Eg non polar (O2 and CO2), and polar molecules eg H2O (much slower)
Hardly permeable: to larger molecules 
Eg glucose 
Impermeable: to ions 
eg Na+, K+, Cl-

Question 2

What are the main components of a membrane?

Answer 2

Membrane type: protein %: lipid %: carbohydrate %
Nerve : 19. : 79. : 3
Red blood cell. : 49. : 43. : 8
Mitochondria : 78. : 22. : 0
(Inner membrane)

1. Lipids: main components are phospholipids, glycolipids, and sterols (eg cholesterol)
   -phospholipids consist of a polar head (hydrophilic) - phosphate and alcohol and a non-polar tail (hydrophobic) -consists of fatty acids
2. Proteins: integral (in membrane) peripheral and lipid anchored
3. Carbohydrates: cell identification tags, can be attached onto
   Proteins- glycoproteins
   Lipids- glycolipids

Question 3

What is the difference between saturated fats and unsaturated fats

Answer 3

Saturated fats lack double bonds, and are solid at room temp
Unsaturated fats contain double bond and are liquid at room temp

Question 4

The specific nature of the protein composition of membranes account for: 4 things, what are they and explain

Answer 4

1. Cell recognition: specific reaggregation of mixed cells, graft rejection, blood type (transfusion specificity), and contact inhibition is related to it also. Close contact of another cell inhibits further cell division
2. Signal recognition: responsiveness of a specific cell to a particular hormone depends on the presence of a specific receptor protein. Many of these receptors are membrane associated
3. Energy generation:
   a) energy conservation: mitochondria- electron transport chain and oxidative phosphorylation takes place on inner mitochondrial membrane
   b) photosynthesis: light driven ATP production takes place on membrane of chloroplasts
4. Transport- will go into another flash card for this baby!

Question 5

What are the 3 different types of transport, explain each of them

Answer 5

A) passive diffusion: for the molecules that can penetrate the nuclear membrane The rate is proportional to the concentration gradient and is dependant on the permeability coefficient (which is a measure of the ability of that molecule to traverse the membrane). Diffusion of ions is also effected by the electrical gradient

B) facilitated or carrier mediated diffusion: involves a carrier protein within the membrane and transports the molecule whose rate of entry would otherwise be to slow. Some of the properties are:

• nett movement from high concentration to low concentration (uniport)
• accelerated
• selective
• can be subject to competition and inhibition
• temperature sensitive
• subject to saturation

C) active transport: is similar to facilitated diffusion in that it has a carrier protein. However it differs in that

• molecules move from a high concentration to low (against)
• it requires an input of energy (direct or indirect)
  
  • direct active transport: transports molecules using the energy derived from ATP
  • indirect active transport: transport of a molecule using the energy stored in an electrochemical ion gradient. Such transport may be:
    
    • symport: transported molecules and co-transported ion move in the same direction
    • antiport: transported molecule and co-transported ion move in opposite directions