2.1.5 - Biological Membranes

a) What is the role of membranes within a cell and surface of a cell?

• Separate chemical reactions within organelles

• Allows formation of concentration gradient

• Surrounds organelles

• Acts as a barrier

• Controls what enters and exits cell

b) What represents the biological membrane and what are the components?

Fluid Mosaic Model

Phospholipid: Contain hydrophobic tails that move away from aqueous solution and hydrophilic heads that move towards the aqueous solution - forms a bilayer

Extrinsic:

Glycolipids & Glycoproteins - help with cell recognition

Intrinsic:

Carrier - allows non polar molecules or non lipid soluble molecules to pass through using facilitated diffusion

Channel - allows lipid soluble and small molecules to pass through using simple diffusion

Cholesterol - maintains fluidity especially in high temperatures to reduce water loss

ci) What factors affect membrane structure and permeability?

Temperature:

• High temperatures cause proteins to denature

• Phospholipids have higher kinetic energy, forms larger gaps within the membrane which increases fluidity and permeability

pH:

• Too low will cause membrane proteins to denature - increasing membrane permeability

Solvent:

• Like alcohol can disrupt the bilayer and destroy the membrane

di) What are the different types of movement across membrane?

Simple Diffusion;

• Net movement from an area of low concentration to an area of high concentration down a concentration gradient

• Doesn’t require energy

Facilitated Diffusion:

• Similar to Diffusion however through a partially permeable membrane via the channel/ carrier proteins

ei) What is osmosis and the different type of solutions?

• Net movement of water molecules from an area of high concentration to an area of low concentration through a partially permeable membrane down the concentration gradient

Hypotonic:

• When there’s not much water within the cell so water moves in the cell making it turgid or to swells

Isotonic:

• Equal amount of water potential in and outside of the cell

Hypertonic:

• When there’s a lot of water inside the cell so water moves out causing the cell to crenate

What is active transport and 2 different types of bulk transports?

Net movement from an area of low to high concentration against concentration gradient

Bulk Transport

Endocytosis (large molecule moves into the cell):

• Cell membrane surrounds the molecule

• Encloses the molecule

• Material is pinched off in a vesicle

Exocytosis (large molecule moving out the cell):

• Vesicles moves through the cytoplasm to the membrane

• CSM fuses with the vesicle

• Then releases the material

What factors can affect rate of diffusion?

• Creating a steeper concentration gradient

• Increases Temperature - Increase Kinetic energy of particles diffusing