2.3 Transport across cell membranes Flashcards
what is diffusion:
the net movement of a substance down a concentration gradient
DNA in prokaryotes vs eukaryotes
PRO
* circular w/ no free ends
* relatively short
* not bound to histones, doesnt exist as chromos
* no introns, only exons
EU
* linear DNA w/ 2 ends
* much longer
* tightly wrapped around histones, to form chromos
* has introns and exons
Function of cholesterol:
- cholesterol increases stability
- by reducing movement of other molecules in membrane
function of Extrinsic proteins
- receptor sites for hormones
- detect chemicals released from other cells
- cell recog.
Function of Glycolipid:
- for cell recog.
- carb chain can be metabolised to provide energy
Function of Glycoprotein?
- recognise type of cell
Cell signalling - act as receptors for hormones
- triggering changes in cell
Function of Intrinsic proteins:
- allows water soluble, large, charged molecules to pass through memb
- by facilitated diffusion or active transport
molecules that can only go through carrier or channel proteins?
polar, water soluble, large
* allows cell to control what goes in and out so there can be different concentrations on either side of membrane
Why is plasma mebrane described as Fluid Mosaic?
fluid - molecules within membrane able to move
mosaic - mixture of phospho. and proteins/ arrangement of proteins
describe homogenisation
- sample of tissue place in cold, isotonic, buffer solution
- solution homegenised using homogeniser (grinds up cells
- breaks plasma membrane of cells and releases organelles into homogenate
why does solution tissue is put in have to be ice cold?
ice cold to stop enzyme activity to prevent digestion of organelles.
why does solution tissue is put in have to be buffered?
so that pH is kept constant, so that proteins, enzymes are not denatured
describe filtration
- homogenate filtered through gauze
- to seperate large cell debris or tissue debris that wasn’t broken up
- leaving filtarte containing mixture of organelles
Describe centrifugation: (4)
(Just the actual centrifugation part)
- filtrate placed in tube into centrifuge and spun at low speed
- causes heaviest organelle to sink to botton and form pellet (nuclei)
- supernatatant drained, put in new tube and spun at higher speed
- new pellet forms (eg mitochondria)
order of mass of organelles
- nuclei
- chloroplast (if plant)
- mitochondria
- lysosomes
- endoplasmic reticulum
- ribosomes
examples of artefacts:
- dust
- fingerprints
explain how movement of substances across molecules is affected by membrane structure (5)
- phos. bilayer allows diffusion of non-polar, lipid soluble substances
- carrier/channel allow polar substances to cross bilayer
- no. of carrier/channel determines how much movement
- channel/carrier allow facilitated diffusion
- shape of carrier determines which substances move
- membrane SA determines how much movement
- cholesterol affects fluidity/permeability
centrifugation.
Why does solution have to be isotonic?
To prevent osmosis so that the organelles do not shrivel or burst.
What is ultracentrifugation? Describe what happens?
- used to separate very small things such as different lengths of DNA.
- sample put into tube.
- spun at a lower speed.
- the most dense organelle forms a pellet, at bottom of test tube.
- other organelles remain suspended in supernatant.
- supernatant removed and put into clean test tube and spun at higher speed.
- second most dense organelle forms sediment at bottom.
how do you find the sodium chloride solution with the same water potential as the potato using a graph
- plot a graph of concentration against ratio
- find the concentration where ratio is 1 (there is no mass change)
carrier proteins…
require energy
Compare and contrast the processes by which water and inorganic ions enter the cell. (3)
Compare
* Both move down concentration gradient.
* Both move through protein channels in membrane.
Contrast
* Ions can move against a concentration gradient by active transport.
