structure and transport Flashcards
what is simple diffusion?
- the net movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached
where does simple diffusion occur? what type of process is it?
- simple diffusion only occurs in liquids and gasses. This is because they possess kinetic energy already which is needed for them to constantly move as a fluid (not ATP)
- For molecules to diffuse across a membrane they must be small and lipid solubule
- is a passive process, so does not require ATP.
What is facilitated diffusion?
- The net movement of molecules from an area of high concentration to an area of low concentration across a partially permeable through protein channels or carriers
where does facilitated diffusion occur? what type of process is it?
- uses protiens embedded within the membrane to transport molecules from one side of the membrane to the other. Allows ions, polar molecules, and large molecules to move across a membrane.
- is a passive process (does not require ATP)
How does facilitated diffusion work with protein channels?
- protein channels are embedded all the way through the bilayer
- is a hollow tube, which fills with water
- this allows for water solubule ions to dissolve and pass through the membrane via the channel.
- it is a selective process because the channel proteins will only open in the prescence of certain ions (when binded to the protein)
how thick is the cell surface membrane?
7nm thick in total
what are the 5 components of a membrane?
- phospholipids, glycoproteins, glycolipids, proteins, cholesterol.
what are the components of a phospholipid?
draw a diagram and check in notes
- phosphate group
- glycerol molecule
- saturated fatty acid
- unsaturated fatty acid
how do phospholipids create a bilayer?
- align as a bilayer due to the hydrophillic, polar heads being attracted to water, and hydrophobic, nonpolar tails being repelled by it.
what are the properties of the head and tail of a phospholipid?
Head
- contains a phosphate group and a glycerol molecule
- has an overall negative charge, so is hydrophillic
Tail
- made of fatty acid chains
- fatty acid chains have no charge so are hydrphobic
what is the role of cholesterol within a cell membrane/phospholipid bilayer?
- is embedded between two phospholipids in the bilayer.
- it stabilises the membrane and controls its fluidity by restristing the lateral movement of other molecules.
- makes membranes less fluid and helps them to maintain integrity at high temps.
- prevents the membrane becoming too rigid/ maintains their fluidity in cold conditions.
why is the stabilisation of membranes at high temperatures a useful function of cholesterol?
- if membranes become too fluid, the gaps between phospholipids would be too big, and water and dissolved ions could leak out of the cell.
- this would cause dehyrdation, or for cells to burst.
what is the function of extrinsic/peripheral proteins?
- present in one side of the bilayer
- provides mechanical support
- cell recognition as receptors
- binds cytoskeleton to membrane
what is the function of intrinsic/transmembrane proteins?
- involved in the transport of molecules across a membrane
- e.g: channel proteins, carrier proteins, glycolipids
what is the structure and function of protein channels?
- hollow tubes that can fill with water
- provides a hydrophillic channel through the membrane
- this enables water soluble ions to dissolve and diffuse through the channel.
__________________ - allows for the passive movement of polar molecules and ions down the concentration gradient.
- each channel is specific to a particular molecule or ion
what is the structure and function of carrier proteins?
- allows either:
the passive movement of polar molecules/ions down the concentration gradient
OR the active transport of polar molecules/ions against their concentration gradient - will bind to other proteins or molecules in order to make them change shape, so that they can be transported to the other side of the membrane.
what is a glycoprotein?
- proteins with attatched carbohydrate chains of varying length and shape.
- plays a role in cell adhesion
- acts as a receptor for chemical signals
what is a glycolipid?
- lipids with attatched carbohydrate chains
- cell markers or antigens which work to recognise pathogens/forgeign things within the immune system (‘self/non self’?)
