biological membranes 2.1.5 Flashcards
what are examples of membranes ?
cell surface membrane, tonoplast, outer mitochondrial membrane, inner mitochondrial membrane , outer chloroplast membrane, nuclear envelope
what are the roles of membranes?
1 partially permeable barriers between the cell and its environment or organelles in the cytoplasm
2 site of chemical reactions
3 site of cell communication
explain in more detail how membranes are barriers
the cells surface membrane creates an enclosed space separating the internal environment from the external.
there are also intercellular membranes and they control the exchange of materials through them.
why are membranes the site for chemical reactions?
membranes are folded to increase their surface area making chemical reactions more efficient
why are membranes the site for communication?
cell signalling allows for multicellular organisms to control and coordinate their bodies and to respond to their environment. CSM are important in signalling pathways as they control what enters and exits the cell.
signalling molecules are small and
describe the structure of phospholipids ?
the phosphate head is connected to the glycerol by a phosoester bond. the glycerol is connected to the fatty acids by the ester bonds
what is the fluid mosaic model ?
proteins distributed throughput the protein in a mosaic pattern
membrane is fluid ( movement of proteins and phosolipids )
what type of molecules can move through a membrane ?
small, non polar like oxygen and CO2
small polar molecules like water and urea are hard to move through
and molecules that ae charged like ions cant move through
what does cholesterol do ?
affects membrane fluidity as they pack the phosolipids closer together
making it less permeable
what are glycoproteins ?
cell membrane proteins that have a carbohydrate chain attached on the extracellular side
what are glycolipids ?
lipids with carbohydrate chains attached ,located on the outer surface of cell membranes. this enables them to act as receptors
what are types of receptor ?
signalling receptors ( bind to hormones and neurotransmitters )
involved in endocytosis
involved in call adhesion and stabilisation
can act as antigens for cell identifications
what are the two type of membrane proteins ?
intrinsic - inside the membrane , eg. carrier and channel proteins
extrinsic - partially embedded or lying on the surface of the membrane eg. glycoproteins
what effects the permeability of cell membranes ?
temperature
solvent concentration
what happens to membranes at high temperatures ?
diffusion occurs at a higher speed
phosolipids gain kinetic energy and move more
increased fluidity creates gaps providing pathways through which substances pass
reduced effectiveness as a barrier to polar molecules = more permeable
reversable
what happens to membranes at very high temperature ?
membrane layer breaks down completely
proteins denature around 40 degrees
no longer a barrier and is fully permeable
irreversible
what happens to membranes at low temperatures ?
membrane permeability initially decreases, less fluid membrane
phosolipids are packed closer together, less gaps
protein channels remain in place but carrier proteins don’t work as well
slower rate of respiration as less ATP for active transport ( because enzymes are needed )
molecules and ions move slower
what happens to membranes at very low temperature ?
below 0 , the water is cytosol freezes and expands which punctures or damages the membrane
increased permeability once they have defrosted
how does water effect membrane permeability ?
because its polar is doesn’t disrupt the cell membrane as the phosolipids don’t dissolve in it
the hydrophobic tails orient away from water forming a bilayer with hydrophobic core, the charge phosphate heads interact with water to keep the layer intact
how do less polar solvents effect membranes ?
eg. ethanol and benzene
cause membrane permeability to increase as phosolipids dissolve in it
ethanol causes membrane disintegration as cholesterol becomes dissolved in it leaving large gaps
what 4 factors effect the rate of diffusion ?
temperature
surface area
concentration gradient
distance
what is simple diffusion ?
diffusion where there is no barrier/membrane
what factors effect simple diffusion ?
