Chapter 3 - Cell membranes and transport Flashcards
(36 cards)
What is the cell membrane mostly made of?
Proteins and phospholipids.
Why are phospholipids important components of membranes?
- They form bi-layers
- This component allows lipid soluble molecules across, but not water soluble molecules.
What are the 2 ways proteins can be embedded in the membrane?
- Extrinsic proteins - on either surface of the bi-layer. (Structural support and form recognition sites).
- Intrinsic proteins - extend across both layers. (Carriers or form channels thus allowing active transport of ions).
What is the name given to the model of the membrane structure?
Fluid mosaic model.
What are the components of the fluid mosaic model?
- Intrinsic proteins (carrier proteins or channel proteins).
- Extrinsic proteins
- Glycoproteins/lipids
- Cholesterol
- Phospholipids (Hydrophilic phosphate head and hydrophobic fatty acid tail).
Why is the membrane model called the ‘fluid mosaic’ model?
- The individual phospholipids can move within a layer.
- The proteins vary in shape, size and pattern (mosaic).
What does the fluid mosaic model contain cholesterol and glycoproteins/lipids?
Cholesterol (animal cells) makes the membrane more rigid/stable.
Glyco have roles as hormone receptors or in cell-to-cell recognition.
How do lipid soluble and water soluble molecules move across the membrane?
Lipid-soluble - dissolve in the phospholipid and diffuse across the membrane.
Water-soluble - Must pass through intrinsic protein molecules which form water filled channels.
The cell surface membrane is selectively permeable to water and some solutes.
What is the definition of simple diffusion?
It is the movement of molecules/ions from a region where they’re in high concentration to a region of lower concentration. (Down a concentration gradient).
What is the rate of diffusion affected by?
- The concentration gradient
- Thickness of exchange surface/distance of travel over which diffusion takes place.
- The S.A. of the membrane.
- The size of the diffusing molecule.
- Temperature
Whats the definition of active transport?
The movement of molecules/ions across a membrane against a concentration gradient, using energy from the hydrolysis of ATP made by the cell in respiration.
The rate of active transport is limited by the number of what?
Carrier proteins
How does active transport happen?
- Molecule/ion combines with a specific carrier protein.
- ATP transfers a P group to the carrier protein (inside).
- Carrier protein changes shape and carries the molecule across the membrane.
- Molecule is then released into the membrane.
What is co-transport and how does it work?
A type of facilitated diffusion that brings molecules/ions into cells together on the same transport protein molecule. E.g. Sodium-glucose transport
- Glucose molecule and 2 Na ions attach to carrier.
- Carrier changes shape and deposits them inside the cell.
- They diffuse through the cell to the other membrane.
What is the definition of osmosis?
The net passive diffusion of water molecules across a partially permeable membrane from a region of high water potential to a region of lower water potential.
What is water potential?
It is the measure of the free energy of water molecules and is the tendency for water to move. Measured in kPa.
What two things you needs to know to calculate the water potential of a plant cell?
Solute potential - A measure of the osmotic strength of a solution.
Pressure potential - The pressure exerted by the cell contents on the cell wall.
What is it meant by hypotonic, hypertonic and isotonic?
Hypotonic - Water outside has a higher water potential.
Hypertonic - Water inside has a higher water potential.
Isotonic - Water potentials equal (No net movement).
What will decrease the water potential of a solution
?
The addition of a solute.
At incipient plasmolysis, what happens to the pressure potential of the cell?
Pressure potential = 0.
What is it called when a plant cell can take in m#n#mo more water?
The cell becomes turgid. (Provides support, maintains shape and holds them upright).
What happens to animal cells when they’re placed in a hypotonic/hypertonic solution?
They have no cell wall so…
In hypertonic- cell becomes crentated
In hypotonic - lysis occurs and the cell bursts.
How does the cell transport materials in bulk?
By Endocytosis - when material is engulfed by extensions of the plasma membrane and cytoplasm making a vesicle.(Phagocytosis -Solid material or Pinocytosis - Liquids)
Or Exocytosis - Substances leave the cell having been transported in a vesicle, which fuses with the cell membrane (digestive enzymes). Both require ATP.
What is the definition of facilitated diffusion?
The passive transfer of molecules or ions down a concentration gradient, across a membrane, by protein carrier molecules in the membrane.
