B Transport across Membranes Flashcards
What type of substances can move through the phospholipid bilayer?
Non-polar, hydrophobic, uncharged, small substances.
What is the function of cholesterol?
A lipid that binds to the fatty acid tails of phospholipids and regulates fluidity of the membrane, by restricting movement of phospholipids/proteins to prevent water/ions from leaking out of the cell.
What is the function of glycolipids?
They are phospholipids that are attached to a carbohydrate, they act as cell markers (antigens) for cells, and allow cells to attach to one another to form tissues.
What are the two different types of proteins in the membrane?
- Extrinsic proteins: eg. surface proteins (provide mechanical support) and glycoproteins (act as recognition sites for foreign cells or specific chemicals).
- Intrinsic proteins: eg. transport proteins.
How does temperature affect membrane structure?
- A higher temperature will increase kinetic energy of phospholipids, causing the membrane to loose it’s structure and channel proteins to denature, as a result membrane permeability increases.
- If temperature gets too high, the membrane breaks down completely.
How do solvents eg. alcohols affect membrane structure?
- Non-polar solvents (or less polar than water) can dissolve the membrane and disrupt cells, increasing membrane permeability, and if the solvent is non-polar, the membrane breaks down completely.
What are the properties and functions of water?
- Polar, and forms hydrogen bonds.
- Solvent that readily dissolves ions and polar molecules, making it a good transport medium.
- Cohesion (attraction between water molecules) and adhesion (attraction between water molecules and other molecules) allow water molecules to form one continuous stream to transport substances.
- High latent heat of vaporisation - a large number of hydrogen bonds mean a lot of energy is needed to transform water into water vapour, allowing plants and animals to use this to cool down (sweat).
- High specific heat capacity - a large number of hydrogen bonds mean a lot of energy is needed to change the temperature of water, ensuring a stable environment for aquatic organisms (a buffer for temperature changes).
- Ice is less dense than water, meaning ice floats in water, creating a habitat for organisms.
- Cohesion creates surface tension of water, allowing pond skaters to walk on water.
What is water potential?
The pressure created by water molecules (in kPa).
What is osmosis?
The net movement of water from an area of higher water potential to an area of lower water potential, through a selectively permeable membrane.
What happens when cells have a lower water potential than the surrounding solution?
- Osmosis causes the cells to swell.
- In animal cells, this causes the cell to burst (cytolysis).
- In plant cells the cell wall prevents the protoplast inside the cell from bursting and the cell becomes turgid.
What happens when the cells have a higher water potential than the surrounding solution?
- Osmosis causes the cells to shrivel.
- In plant cells this is called plasmolysis.
- In animal cells this is called crenation.
What is a hypotonic environment?
The solution outside of the cell has a lower solute concentration (higher water potential) than inside the cell (causing cytolysis in animal cells).
What is an isotonic environment?
The solution outside of the cell has the same solute concentration as inside of the cell.
What is a hypertonic environment?
The solution outside of the cell has a higher solute concentration outside the cell than inside of the cell.
How do transport proteins control what diffuses in/out of the cell?
Transport proteins are often not always open, but remain closed until a chemical messenger binds to a binding site on the transport protein, changing the shape of the transport protein and allowing certain molecules to pass through.
