M2, C5 Plasma Membranes Flashcards
what is compartmentalisation
the formation of separate membrane-bound areas in a cell
define plasma membrane
the cell surface membrane that separates the cell from its external envrionment
what are membranes formed from
a phospholipid bilayer
hydrophilic phosphate heads form the inner and outer surface of a membrane
fatty acid tails are sandwiched inside to form the hydrophobic core
where do cells normally exist
aqueous environments
why are phospholipid bilayers suited for aqueous environments
the outer surfaces of the hydrophilic phosphate heads can interact with water
what is the fluid-mosaic model
shows how proteins occupy various positions in the membrane
phospholipids are free to move within the layer relative to each other
this gives the membrane flexibility
what are the components in a cell membrane
glycoprotein
glycolipid
cholesterol
hydrophilic heads of phospholipid molecules
Channel proteins
Carrier Proteins
hydrophobic tails of phospholipid molecules
what are the 2 types of membrane proteins
intrinsic and extrinsic
what are intrinsic proteins
transmembrane proteins that are embedded in both layers of the membrane
have amino acids and hydrophobic R groups on the external surfaces which interact with the hydrophobic core keeping them in place
what are channel proteins
channel proteins - provide a hydrophilic channel to allow passive movement of polar molecules and ions down a concentration gradient. this is held in place by the interactions between the hydrophobic core and the R groups on the outside of proteins
they are intrinsic
what are glycoproteins
Proteins with carbohydrates attached
they play a role in cell adhesion (when cells join together) and act as receptors for chemical signals
what are glycolipids
phospholipids with carbohydrates attached
antigens so the immune system recognises it as self or non-self
what is cell signalling
involves glycoproteins
when the chemical binds to the receptor on the glycoprotein, it elicits a response from the cell which can set off a cascade of events
what are extrinsic proteins
Extrinsic proteins: these are proteins which are found on the surface of the plasma membrane. They usually function as enzymes and catalyse chemical reactions inside the cell.
why is cholesterol in the plasma membrane
It is found between individual phospholipids preventing them from packing to closely together preventing the structure from crystallizing, as a result it regulates the fluidity and rigidity of the PLBL
what needs to happen for a chemical reaction to take place
all the organelles need to be in specific positions
what happens to phospholipids as temperature increases
they gain kinetic energy meaning they move more
the membrane becomes more fluid because it loses its structure
Carrier and Channel proteins denature and lose their shape increasing the permeability of the PLBL
what does the loss of structure in cell membranes mean
they become more permeable meaning particles can more easily cross it
what happens to carrier and channel proteins as temp increases
denature
increases membrane permeability further
why is water essential for the formation of the phospholipid bilayer
Because the non-polar tails of the phospholipids are orientated away from water which forms a bilayer with the hydrophobic core
the charged phosphate heads interact with water which keeps it intact
what are carrier proteins
carrier proteins - passive and active transport into cells. this often involves the proteins changing shape
they are intrinsic
how do organic solvents affect membranes
they dissolve membranes which disrupts cells= an increase in permeability
give a common example of an organic solvent
alcohol
why is alcohol in anti-septic wipes
the alcohols dissolve the membranes of bacteria in a wound, killing them and reducing the risk of infection
why are pure or very strong alcohol solutions dangerous
they are toxic
they destroy cells
the molecules can enter the membranes and disrupt the membrane because they lie between phospholipids
what happens when a membrane is disrupted
it becomes more fluid and more permeable
give an example of a cell that needs intact cell membranes to function
nerve cells
if neuronal membranes are disrupted then nerve impulses are no longer transmitted as normal, hence why people behave differently when they drink alcohol
suggest an experiment to investigate how temperature affects membrane permeability
- get 5 small pieces of beetroot, all equal sizes
- thoroughly wash under water
- place in 100ml of distilled water in a water bath
- increase the water bath by 10 degrees
- samples of water taken 5 mins after the water bath has increased by 10 degrees
- measure the absorbance of each sample using a colorimeter with a blue filter
- repeat 3 times
the results show that absorbance rapidly increases after 50 degrees hence suggesting that the membrane is disrupted between 40 and 50 degrees
what microscope would you see a detailed plasma membrane
electron microscope - you would see the double line which is 7-10 nm thick
(a light microscope you would see a single line)
how can polar and non-polar molecules pass through the membrane
Polar molecules require proteins to enable them to pass through the membrane
Non-polar molecules can diffuse directly through the phospholipid bilayer