Chapter 5 Flashcards
IDETNIFY FIVE ROLES OF SURFACE MEMBRANES AT THE SURFACE OF CELL.
Separates cells from external environment.
Has antigens, so body’s immune system can recognise it as self.
Controls what goes into and out of the cell.
Communicates with other cells with hormone receptors etc. Site of chemical reactions.
May contain enzymes involved in specific metabolic pathways.
WHAT IS THE ROLE OF PLASMA MEMBRANES WITHIN CELLS?
REFER TO MITOCHONDRIA AND CHLROPLASTS.
Compartmentalisation.
In mitochondria, the inner membrane is called the cristae. This increases the surface area for respiration.
In chloroplasts the thylakoid membrane stores chlorophyll for photosynthesis.
WHAT IS THE FLUID MOSAIC MODEL?
This describes the structure of the plasma membrane as a mosaic of components
WHAT ARE EXTRINSIC MEMBRANE PROTEINS?
Peripheral proteins present in one side of the bilayer.
Have hydrophilic R-groups that interact with the polar heads of the phospholipids or with intrinsic proteins.
This can be in either layer and some can move between layers.
WHAT ARE INTRINSIC MEMBRANE PROTEINS?
Contain amino acids with hydrophobic R-groups on external surfaces which interact with the hydrophobic core keeping them in place.
WHAT ARE CHANNEL PROTEINS
Provide a hydrophilic channel that allows diffusion of polar molecules and ions.
WHAT ARE CARRIER PROTEINS
Facilitate both passive and active transport. This can change shape using ATP to allow the molecule to pass.
WHAT ARE GLYCOPROTEINS?
Embedded in the membrane with carbohydrate chains. Allows cell adhesion.
Acts as a receptor for chemical signals.
WHAT ARE GLYCOLIPIDS
Lipids with attached carbohydrate chains. These are antigens and allows cell recognition.
WHAT IS THE PURPOSE OF CHOLESTEROL IN THE BILAYER?
Regulates the fluidity of membranes.
It adds stability without making them too rigid.
Prevents the lipid solidifying by stopping the phospholipid from grouping too closely and crystallising.
HOW DOES DIFFUSION ACROSS MEMBRANES OCCUR?
HOW IS EQULIBRIUM MAINTAINED?
Passive process which takes advantage of the particles’ natural kinetic energy. Particles move down a concentration gradient and eventually are all equally spread out, equilibrium is reached.
The equilibrium is maintained, when molecules enter the cell they move to their required place so the flow is kept constant. E.g. water moves to the mitochondria to start respiration.
HOW DOES SIMPLE DIFFUSION OCCUR FOR LIPIDS AND MSLL POLAR MOLECULES.
- NON-POLAR MOLECULES: travel down freely
- LIPIDS SOLUBLE: dissolve in the bilayer and can travel freely across.
- POLAR MOLECULES: repelled by hydrophobic interior.
WATER: an exception. It is so abundant that some water can travel down by diffusion. But it’s quite slow.
HOW DOES FACILIATED DIFFUSION WORK?
Polar molecules cannot pass by simple diffusion. They need facilitated diffusion to help them pass. They go through protein channels. This is still a passive process but requires the use of channels which provide a path by which the molecules can pass.
WHAT ARE 5 FACTORS AFFECTING DIFFUION RATE?
- TEMPERATURE:
- DIFFUSION DISTANCE:
- SURFACE AREA:
- SIZE OF DIFFUSING MOLECULE:
- CONCERTATION GRADIENT:
HOW DOES OSMOSIS WORK?
The net diffusion of water from an area of high water potential to an area of low water potential down a water potential gradient.
When solute is added to water the water potential is lowered because the molecule binds to the water, less water molecules are ‘free’.
