Cell membranes Flashcards
Membranes in cells
There are many membranes surrounding the organelles within cells
Membranes in cells example:
Mitochondria
Nucleus
Chloroplasts
Cell membrane
Cell membrane forms a boundary around of the cell
Functions of cell membrane
1 substances move into & out of cell through cell membrane
2 All membranes act as barriers controlling what passes through them (partial permeability) & allowing the fluids either side of them to have different compositions
3 many chemical processes take place on membrane surfaces
4. The cell membrane is flexible allowing the cell shape to change
5 vesicles containing chemical secretions combine with cell membrane to release its content
The structure of membranes
Made up of two molecules:
1. Phospholipids
2. Proteins
The phospholipid bilayer: phospholipids
Hydrophilic head (polar) which is soluble in water
Hydrophobic tail (non polar) which is insoluble in water
If the molecules are tightly packed in water they from
Monolayer - hydrophilic head in water & hydrophobic tail in air
Micelles - hydrophilic heads point outwards water & all the hydrophobic tails are hidden inside
A monolayer may develop at a surface between air & water but this doesn’t happen in living cells where there is water based solution on either side of the membrane
With water on each side the phospholipid molecules form a bilayer with hydrophilic heads pointing into water while hydrophobic tails are protected in the middle
The fluid mosaic model: fluid
Fluid means that the molecules can change places within the membrane
The proportion of phospholipids containing unsaturated fatty acids seems to affect how freely proteins move within the membrane
The fluid mosaic model: mosaic
Mosaic means that proteins are randomly embedded into the phospholipid bilayer
The fluid mosaic model: Cholesterol
It makes membrane more stable & stronger making it harder for smaller molecules & ions to pass through the membrane
So it act as en effective barrier around the cell
