Cell membrane Flashcards
Cell surface membranes
A barrier between a cell and its environment which controls what enters and what leaves
Organelles membranes
A barrier which divides cell into different compartments and separates the organelles from cytoplasm
What model describes the structure of a cell membrane?
The fluid mosaic model
Why is the membrane described as ‘fluid’?
Because it is mainly composed of continuous double layer of phospholipid molecules (phospholipid bilayer)
These molecules constantly move as well as proteins which can move throughout membrane
Why is the membrane described as a mosaic?
Because scattered throughout the phospholipid bilayer are carrier proteins, channel proteins, receptor proteins, cholesterol, glycolipids ane glycoproteins
List of molecules that make up the membrane
Phospholipids
Intrinsic proteins (channel and carrier)
Extrinsic proteins (receptors)
Cholesterol
Glycolipid
Glycoprotein
Phospholipid bilayerstructure
A hydrophilic head facing outwards of the cell and into the cytoplasm to attract water
And hydrophobic tails centred in inside to repel water
What does the phospholipid bilayer allow to dissolve through?
Small non polar molecules due to non polar fatty acids in the centre eg o2 and co2
Water because it’s so small despite being polar
Channel proteins
For facilitated diffusion of large molecules such as glucose with a large pore to transport in/out of cell
Carrier proteins
For facilitated diffusion of largemolecules by changing the tertiary structure to release large molecules to other side once ion bonded to it
Extrinsic proteins
Act as receptors on surface of membrane to detect chemicals released from other cells to signal to cell to respond
What is cholesterol?
A type of lipid present in all cell membranes except bacteria cell membranes to provide stability
Role of cholesterol
Binds to hydrophobic fatty acids in phospholipids to pack them closer together and restrict movement = more rigid and maintains shape
Create further barrier to polar substances due to hydrophobic properties
Glycoproteins
A carbohydrate (glyco) bonded to a membrane protein
Glycolipid
A carbohydrate (glyco) bonded to a phospholipid (lipid)
What affects cell membrane’s permeability?
Temperature which affects movement of phospholipids thus affecting membrane structure and permeability
Effect of temperature on membrane permeability description of a graph
Below 0°c = very high permeability
0°c = rapidly decreased permeability
0°c to 45°c = begins increasing
Above 45°c = very high permeability
Why is below 0°c the permeability is very high?
Because at very cold temperatures the protein membranes have denatured causing increased permeability
Why is the permeability very low at 0°c?
Because the phospholipids have little energy so less fluid due to moving less so won’t allow molecules to enter
Why does the permeability begin to increase from 0°c to 45°c?
As temp increases, phospholipids move more due to having more energy so allow more molecules to enter
Why does the permeability increase rapidly above 45°c?
The membrane begins to break down due to increased energy of phospholipids
Proteins begin denaturing again so cannot control what leaves or enters (permeable)
