Cell Membranes Flashcards
ways substances can move across membranes (3)
osmosis
active transport
diffusion
cell surface/plasma membrane function (csm)
act as barrier between cell and enviro, controlling substances in + out cell
so are partially permeable
partially permeable definition
it lets some molecules through but not all
membranes inside cells function (3)
around organelles, dividing cell into different compartments
barrier between organelle + cytoplasm
control substances in + out organelle
3 substances making up membrane
lipids (mainly phospholipids)
proteins
carbohydrates
explain the fluid mosaic model
phospholipid bilayer - “fluid” as constantly moving
proteins scattered through bilayer
- carrier + channel allow large molecules + ions to pass through membrane
- receptor proteins
- some proteins fixed, others move sideways through bilayer
- glycoproteins (protein w carb attached)
- glycolipids
- cholesterol molecules
phospholipids in cms
form barrier to dissolved substances
hydrophilic head
hydrophobic tail
bilayer formed when arrange themselves, head face out towards h2o
bilayer center is hydrophobic - no water soluble substances can pass through eg ions + polar molecules
cholesterol function + where found
gives membrane stability
in all cell membranes but bacterial
what cholesterol does
type of lipid
binds to phospholipid tails in bilayer so pack closer
restricts movement - cm is more rigid
helps maintain shape of cell / organelle
has hydrophobic regions - further barrier
benefit of cholesterol in animal cells + blood cells
no cell wall, so helps maintain shape
membranes at below 0*C
phospholipids dont have much E so dont move much + pack close -> rigid
channel + carrier denature -> ↑ permeability
ice crystals? pierce membrane - more permeable when thaw
membranes at 0 - 45*C
phospholipids arent packed as close
partially permeable
as temp ↑ phospholipid movement ↑ since more E
- this ↑ permeability of membrane
membranes at over 45*C
bilayer breaks down, cm ↑ permeability
h2o in cell expands -> pressure on cm
channel + carrier denature, ↑ permeability since can’t control in + out
investigating cell membrane permeability practical 4
how temp affects beetroot membrane permeability
- use scalpel to cut 5 equal pieces of beetroot + rinse them to remove pigment released in cutting
- each piece in different test tube w 5cm^3 h2o
- each tube in h2o bath at different temps for same length of time
- remove pieces from tubes leaving coloured liquid
- turn on colorimeter + let stabilise for 5 mins
- pick blue colour filter (470 nm wavelength)
- put distilled h2o in curvette 3/4 full. make sure class isnt frosted or scratched where light will be passing through. calibrate to zero
- transfer some solution from test tube 1 to new curvette w pipette (3/4 full)
- put in colorimeter and read and record absorbance
- repeat 8 + 9
- ↑er absorbance reading, more pigment released, so ↑er permeability of cm
investigating effect of solvents practical
place pieces of beetroot in different solvents, eg alcohol
↑ conc of a solvent means ↑ permeability since it it dissolves the lipids in the membrane
process of diffusion
net movement of particles down a conc gradient from an area of high to low conc, they can diffuse both ways though but net movement is to low conc
continues till particles evenly distributed
factors affecting diffusion (3)
- ↑er the conc gradient, faster rate of diffusion
ROdiffusion slows over time until eqm reached - thinner exchange surface, less distance particles have to travel so quicker ROdiffusion
- larger surface area, faster ROdiffusion
factors affecting facilitated diffusion
- ↑er conc gradient, faster ROdiffusion , but rate levels off as eqm reached
- no. channel and carrier proteins, when all are in use, FD cant happen any faster, even if conc gradient was ↑
what is a conc gradient
the path from low to high conc
simple diffusion
when particles diffuse directly across a membrane
why is facilitated diffusion needed
- larger molecules eg amino acids and glucose would diffuse slowly through phospholipid bilayer due to size,
- charged paritcles eg polar molecules and ions diffuse slowly cuz water soluble and hydrophobic center of bilayer
is FD passive? ↑ or ↓ conc gradient?
↓ conc gradient
passive process
2 proteins used in FD
carrier proteins
channel proteins
carrier proteins
move large molecules
different proteins move different molecules
how do carrier proteins work in FD
large molecule attaches to protein in membrane
the protein then changes shape
this releases molecule on other side of membrane
channel proteins
form pores in membrane that charged particles diffuse through
different proteins facilitate diffusion of different charged particles
calculating ROdiffusion
find gradient of line on straight line graph
on curve, draw tangent
change y / change x
add units
what is osmosis
diffusion of h2o molecules across partially permeable membrane
area of ↑er water potential to ↓er (eg more/less h2o molecules
passive
what is water potential
potential / likelihood of h2o molecules to diffuse in or out of solution
more negative - stronger conc of solute in solution
what wp is pure water
0
decreases when solute added
define isotonic
cells in isotonic solution won’t lose / gain h2o
no net movement of h2o molecules since wps in cell outside and in the same
define hypotonic solution
solution w ↑er wp than in cell
define hypertonic solution
solution w ↓er wp than in cell
what happens if cell is in hypotonic solution
cell will swell as h2o moves in by osmosis
what happens if cell is in hypertonic solution
cell will shrink as h2o moves out by osmosis
factors affecting ROosmosis
- bigger wp gradient, faster rate. rate ↓ over time as wp difference gets smaller
- thinner exchange surface, faster rate
- larger SA, faster rate
active transport
movement of molecules/ions from low to high conc
uses carrier proteins and co-transporters
active process
carrier proteins in AT
same as facilitated diffusion but moves molecules from low to high conc and requires E
E usually from hydrolysis of ATP
co transporters + example
type of carrier p
bind 2 molecules at a time
one molecule being transported down its conc gradient, which transports a different molecule against its own
eg sodium and glucose co transporter
factors affecting AT
- speed of individual carrier proteins
- number of carrier proteins
- ROphotosynthesis + availability of ATP, no respiration = no AT
co transport and absorption of glucose
- Na+ ATed out epithelial cells in ileum to blood by Na/K pump creating conc gradient as ↑er conc Na+ ions in lumen of ileum than inside cell
- causes Na+ to diffuse from lumen of ileum to epithelial cells ↓ conc gradient via Na-glucoseco transporter
conc of glucose in cell ↑ - glucose diffuses out cell to blood, ↓ conc gradient through channel protein
investigating water potential 3 steps
- make serial dilutions
- measure change in mass
- produce calibration curve
what is a serial dilution
when you create a set of solutions that ↓ in conc by same factor each time
useful when making weak solutions as dont have to measure out v small vols
how to make a serial dilution
??
how to measure change in mass
- use cork borer to cut potatoes into identical chunks, 1cm diameter.
put into groups of 3 and measure w balance - put a group into a solution and leave for 20 mins
- take out of solution and pat dry gently w paper towel
- repeat w each group
- calc % change in mass for each group
how to produce calibration curve
use results of % mass change and plot graph against conc of solution
determine wp by looking at where it crosses at 0
