Plasma membranes Flashcards
Define compartmentalisation
the formation of separate membrane-bound areas in a cell
Why is compartmentalisation important to a cell?
- metabolism includes many different and often incompatible reactions
- containing reactions in separate parts of the cell allows the specific conditions required for cellular reactions (e.g. chemical gradients) to be maintained, and protects vital cell components
describe the structure of the phospholipid bilayer
made up of two layers of phospholipids
- hydrophilic phosphate heads form both the inner and outer surface of the membrane
- fatty acid tails are sandwiched in the middle of the membrane which form the hydrophobic core
describe the interaction of the membrane with the aqueous environment
- the outer surface of the membrane is formed from hydrohphilic phosphate heads which can interact with the water
Describe the fluid mosaic model
Fluid: the phospholipids are free to move within the layer relative to each other, giving the membrane flexibility
Mosaic: proteins embedded in the bilayer vary in shape, size and position
what are intrinsic proteins
transmembrane proteins that are embedded through both layers of a membrane
they contain amino acids with hydrophobic R groups on their external surfaces, which can interact with the hydrophobic core of the membrane, keeping them in place
describe channel proteins
- provides hydrophilic channel for passive movement of polar molecules/ions down a concentration gradient through membranes
- held in position by interactions between hydrophobic core and hydrophobic R groups on proteins
describe carrier proteins
- involves the shape of the protein changing
- both active and passive transport
describe glycoproteins
- intrinsic
- embedded in cell-surface membrane with attached carbohydrate chains
- cell adhesion
- receptors for chemical signals
what is cell adhesion
when cells join together to form tight junctions in certain tissues
how are glycoproteins receptors?
- chemical binds to receptors
- elicits response from the cell
- causes a direct response or a cascade of events inside the cell (cell communication/signalling)
some examples:
- receptors for neurotransmitters at nerve cell synapses- triggers or prevents impulses to next nerve
- receptors for peptide hormones which affect uptake/storage of glucose in cells
describe glycolipids
- lipids with attached carbohydrate chains
- they are cell markers/antigens which can be recognised by the immune system as self or non-self
describe cholesterol
- lipid with hydrophilic end and hydrophobic end
- regulates fluidity of membranes
- positioned between phospholipids in the membrane layer
- hydrophilic end interacting with the phospholipid heads, and hydrophobic end interacting with the phospholipid tails
- this pulls the phospholipids together without making them too rigid or too solid by stopping them from grouping too closely together and crystallising
describe extrinsic proteins
- present on one side of the bilayer
- hydrophilic R groups on their outer surfaces which interact with the polar heads of phopholipids or intrinsic proteins
- can be present in either layer, or move between them
effect of temperature on the membrane
- phospholipids are constantly moving
- if temp increases, phospholipids will have more K.E. so will move more
- membrane is more fluid and loses structure
- if temp continues to rise, cell will break down
- loss of structure increases permeability, making it easier for particles to cross
- carrier/channel proteins get denatured at higher temperatures
- these proteins are involved in transport across membrane so as they denature, membrane permeability will be affected
