Biological Membranes

Question 1

Roles of membrane

Answer 1

• partially membrane barrier bw cell+environment/bw cytoplasm+organelles
• sites of cell communication=cell signaling
• cell recognition=w antigens
• site of chemical reaction
• holding proteins/enzymes of metabolic pathways in place
• regulating transport of materials in/out of cells

Question 2

The fluid mosaic model (1972): Singer+Nicholson

Answer 2

• describes structure where various proteins are floating in the phospholipid bilayer
  role of components
• phospholipids=form basic structure+selectively permeable
• cholesterol=fits bw fatty acid tails+helps w membrane stability+makes membrane more of a barrier to water+ions
• channel proteins=allow movement of ions by facilitated diffusion
• carrier proteins=use ATP to move substances across the membrane/move large molecules by facilitated diffusion
• glycoproteins=cell recognition, hormone receptors+bind cells tgt
• glycolipids=cell recognition+hormone receptors

Question 3

Factors affecting membrane fluidity

Answer 3

• temp
  low temp=phospholipid x much Ek=packed closely tgt=rigid cell membrane=down permeability/fluidity
  medium temp=temp up=phospholipid more Ek=move faster+not closely packed=up permeability/fluidity
  high temp=phospholipid bilayer breaks down+channel/carrier proteins denature=x control what enters/leaves cell=up permeability/fluidity
• solvents
  In some solvents eg. Ethanol, phospholipids dissolve=more fluid membrane=disrupts membrane structure=more permeable
  Up conc. of solvent=up permeability cell membrane
• cholesterol
  high temp=phospholipid have more Ek=move further apart=cholesterol make it tightly packed=less fluidity
  low temp=phospholipids have less Ek=tightly packed=cholesterol creates space bw them=up fluidity

Question 4

Diffusion definition

Answer 4

Net movement of particles from a region of high concentration to a region of low concentration, down a conc gradient

Question 5

Types of diffusion

Answer 5

Simple
Facilitated

Question 6

Simple diffusion

Answer 6

Some molecules diffuse directly across cell membranes
- particles need to be small=pass through pores in bilayer+non-polar=dissolve through hydrophobic cell membrane core eg oxygen+CO2

Question 7

Facilitated diffusion

Answer 7

• transports large/polar molecules
• uses proteins=carrier/channel proteins=specific (allow 1/2 types of molecules)
• carrier proteins
  Large molecule attaches to carrier protein=carrier protein changes shape=carrier protein releases molecule on opposite side of membrane
• channel proteins
  Create pores in membrane which ions travel through