Cell Membranes Flashcards
What are cell surface membranes?
- they act as barriers between the cell and its environment
- they control what entres and leaves
- they are partially permeable
What do cell surface membranes do?
- they divide the cell into different compartments
- they act as a barrier between the organelle and the cytoplasm
where are proteins situated in the fluid mosaic model?
- scattered throughout like a mosaic
- receptor proteins on the surface
- some protein are in fixed positions
- some proteins can move sideways through the bilayer
what makes up the fluid mosaic model?
- constantly moving phospholipids which form a bilayer
- cholesterol molecules
- glycoproteins
- glycolipids
what do phospholipids do in the cell membrane?
- they arrange themselves into a bilateral with their heads facing out on both sides
- the centre is hydrophobic so water soluble molecules (ions) can’t pass through
what does cholesterol do in the cell membrane?
- they fit between the phospholipids binding to the tails to pack everything close together this restricts movement making the membrane less fluid and more rigid
- helps maintain the shape of animal cells which is important in cells that have no support from other cells like red blood cells providing stability
what affects the permeability of a cell membrane?
- temperature
- solvent concentration
which experiment is used to investigate the permeability of a cell membrane?
how does temperature affect the amount of pigment that leeks out of beetroot cell membrane
(stage 1) investigating cell membrane permeability
- Use a scalpel to cut five equally sized pieces of beetroot on a cutting board
- rinse the pieces to remove any pigment released during cutting
(stage 2) investigating cell membrane permeability
- add 5cm3 of water to five test tubes using a measuring cylinder or pipette
- then add the five pieces to the test tubes
(stage 3) investigating cell membrane permeability
Place each test tube in a water bath at a different temperature for the same length of time measured using a stop watch
(stage 4) investigating cell membrane permeability
Remove the pieces of beetroot from the tubes leaving the coloured liquid
(stage 5) investigating cell membrane permeability
- Use a colorimeter to measure how much is absorbed
- the higher the absorbance the more pigment was released to the higher the membrane permeability
(stage 6) investigating cell membrane permeability
-connect the colorimeter to a computer collect data and produce a graph
how do temperatures below 0oc affect cell membrane permeability?
- the phospholipids don’t have much energy so don’t move very much
- they are packed closely and the membrane is rigid
- channel proteins in the membrane deform increasing the permeability of the membrane
- ice crystals may form and pierce the membrane making it highly permeable when it thaws
how do temperatures between 0oC and 45oC affect cell membrane permeability?
- the phospholipids can move around and aren’t packed as tightly together which makes the membrane partially permeable
- as the temperature rises the phospholipids move more since thy have more energy which increases the membranes permeability
how do temperatures above 45oC affect cell membrane permeability?
- the phospholipid bilayer starts to melt and the membrane becomes more permeable
- water inside the cell expands putting pressure on the membrane
- carrier proteins and channel proteins are put under pressure so cant control what enters or leaves the cell this means the permeability
what does partially permeable mean?
A membrane that is permeable to the small molecules of water and certain solutes but does not allow the passage of large solute molecules.
when was the fluid mosaic model suggested?
in 1972 it was suggested to describe the arrangement of molecules in the membrane
what is a glycoprotein?
a protein with a polysaccharide chain attached to it
what is a polysaccharide?
carbohydrates molecules which consist of sugar molecules
what are glycolipids?
lipids with an attached polysaccharide chain
What do receptor proteins do in the fluid mosaic model?
- allows the cell to detect chemicals released from other cells
- the chemicals signal the cell to respond
What does insulin do?
Th hormone insulin binds to receptor proteins on the liver which tells the cells to absorb glucose?
