2.1.5 Biological membranes Flashcards
Function of cell surface membrane
Regulates the movement of substances into and out of the cell. It also has receptor molecules on it, which allow it to respond to chemicals like hormones.
What is the structure of the cell surface membrane?
Phospholipid bilayer
Phospholipid bilayer made up of:
Phospholipids
Cholesterol
Glycoproteins and glycolipids
Transport proteins
How do phospholipids form a bilayer?
Hydrophilic heads attract water and have hydrophobic trails which repel water. This means the molecules automatically arrange themselves into a bilayer
Function of cholesterol in cell surface membrane.
Increases fluidity of membrane at low temps and increases stability at high temps
How does cholesterol stop the membrane from being too rigid?
Stops phospholipid tails binding too closely together
How does cholesterol stop the membrane from being too fluid at high temperatures?
Binds to the tails.
What molecule makes up the chains attached to the surface of glycolipids and glycoproteins?
Carbohydrate.
What is the function of the carbohydrate chains attached to glycolipids and glycoproteins?
Allows them to act as receptor molecules.
Two types of transport proteins.
Channel and carrier proteins.
What is the permeability of cell membrane affected by?
Temperature and solvent concentration.
How does temperature impact the permeability of the cell membrane?
As temperature increases, lipids become more fluid and so it reduces the effectiveness of the membrane as a barrier.
How do very high temperatures impact the permeability of the cell membrane?
At very high temps proteins will denature which disrupts the membranes structure and so molecules can freely pass into the membrane. This is irreversible.
How does solvent concentration affect the permeability of the cell membrane?
Organic solvents can increase cell membrane permeability as they dissolve the lipids in the membrane.
Define diffusion
The net movement of molecules from an area of high concentration to an area of low concentration down a concentration gradient.
Factors affecting diffusion
Steepness of concentration gradient.
Temperature
Surface area
Size of molecules
How does the steepness of the concentration gradient affect the rate of diffusion?
The greater the concentration of gradient, the faster the rate of diffusion. If there are more molecules on one side of the membrane than the other,molecules will move across the membrane from that side
How does temperature affect the rate of diffusion?
The higher the temperature, the faster the rate of diffusion. This is because the particles have more kinetic energy so they move around faster.
How does surface area affect diffusion?
The greater the surface area, the greater the rate of diffusion. This is because more molecules and ions can cross it.
How does the size of molecules affect the rate of diffusion?
Large molecules will diffuse more slowly as they require more energy to move.
What are channel proteins?
Transport proteins that have a hydrophilic channel that certain molecules/ions use as a tunnel through the membrane.
What are carrier proteins?
transport proteins that bind to molecules and change shape to shuttle them across the membrane.
Define osmosis
The net movement of water molecules through a partially permeable membrane from a region of a high water potential to a region of a low water potential.
What is water potential?
The tendency of water to move out of a soloution.
