the cell membrane & transport through the cell membrane Flashcards
components of membranes, simple/facilitated diffusions, osmosis and active transport
why is the cell membrane called a fluid-mosaic model?
mixture + movement of phospholipids, proteins, glycoproteins & glycolipids
how do the molecules in a membrane affect its permeability?
- phospholipid bilayer allows diffusion of non-polar/ lipid-soluble substances
- membrane proteins allow polar/H2O-soluble substances to pass through bilayer (otherwise cant pass through)
- carrier proteins allow active transport
- channel/carrier proteins allow facilitated diffusion
- shapes of channels & proteins determine which molecules can pass through
- cholesterol affects fluidity & ,therefore, permeability of a membrane
phospholipids
- head has +ve charge bc of phosphate group โ> hydrophilic
- fatty acid tail is uncharged โ> hydrophobic
- align as bilayer
function of cholesterols in the bilayer
- restricts lateral movement of other molecules in membrane
- makes membrane less fluid at high temps
types of intrinsic proteins
- carrier proteins
- protein channels
function of carrier proteins in the bilayer
- binds to a molecule & changes shape to export it
- used in facilitated diffusion & active transport (passive process during fac. diffusion but active process during active transport)
function of protein channels in the bilayer
- form tubes that fill with water, allowing polar, H2O- soluble substances to diffuse across
- used in facilitated diffusion
function of extrinsic proteins in the bilayer
- provide mechanical support
- can connect to proteins/lipids, forming glycoproteins/glycolipids โ> act as receptors during cell recognition
simple diffusion
(type of transport)
= net movement of small, non-polar molecules down a conc. gradient until dynamic equilibrium is reached
> passive
Fickโs Law
rate of diffusion proportional to (S.A x conc. gradient)/thickness of exchange surface
facilitated diffusion
(type of transport)
= net movement of molecules down conc. gradient through carrier proteins/protein channels
>passive (doesnโt req. ATP)
osmosis
(type of transport)
= net movement of H2O molecules down water potential gradient through partially permeable membrane
> passive
define โwater potentialโ
= the pressure (KPa) created by H2O molecules & the ability of the sol. to give out H2O
โ> w.p doesnโt go above 0
โ> higher -ve no. = lower w.p
define โhypertonic solutionโ
HIGHpertonic solution ;)
= solution w higher water potential than cell
โ> water moves out solution, into cell
* animal cells โ> shrivelled
* plant cells โ> plasmolysed
define โisotonic solutionโ
= solution with same water potential as cell
* animal cells โ> remain same
* plant cells โ> flaccid
define โhypotonic solutionโ
hypOtonic solution
= solution with lower water potential than cell
โ> water moves into solution, out of cell
* animal cells โ> lysed (burst)
* plant cells โ> turgid
active transport
(type of transport)
= movement of molecules against a conc. gradient via a carrier protein using ATP
active process obviously
process of active transport
- certain molecules bind to receptor site on carrier proteins
- ATP binds to the carrier protein on inner membrane โ> hydrolysed into ADP + Pi
- causes protein to change shape, opening towards inner membrane
- molecules released โ> protein reverts to og. shape
nowhere near as complicated as u think lol, use ur brain
co - transport
(type of transport)
sodium potassium pump
- done via symport proteins
- eg. sodium - potassium pump
1. Na+ moves out cell โ> generates conc. gradient for Na+ from ileum into cell
2. Na+ moves into cell via facilitated diffusion, co-transporting glucose w it
name every type of transport
decribe how substances can cross a cell-surface membrane (5)
- simple diffusion down conc. gradient
- non-polar molecules pass via phospholipid bilayer but polar molecules go through proteins
- water moves by osmosis down water potential gradient
- active transport = movement of molecules against a conc. gradient via carrier proteins
- at req. ATP
- ref. to Na+/glucose transport
explain 3 features you would find in a cell specialised for absorption
- folded membrane/microvilli โ> larger S.A for absorption
- large no. of mitochondria โ> relaeases more energy for active transport
- large no. of carrier proteins โ> for active transport
describe two ways in which simple and facilitated diffusion are similar
- both passive
- down conc. gradient
give one way to ensure the temp remains constant in an exp.
use a thermometer to measure the water bath at specific time intervals
independant variable in osmosis req. prac
concentration of sugar solution
how to find water potential from values found from exp.
- plot calibration curve
- interpolate from ratio of 1
- change conc. into w.p