2. Transport Across Cell Membranes Flashcards
What forms a cell surface membrane?
Phospholipids
Proteins
Cholesterol
Glycolipids
Glycoproteins
What do phospholipids form?
A bilayer
How are phospholipids important?
Hydrophilic heads point outwards and attract water
Hydrophobic tails poing in the centre and repel water
What is the function of phospholipids?
Allow lipid soluble substances to enter and leave
Prevent water soluble substances to enter and leave
Make the membrane flexible
What is the function of proteins in the cell surface membrane?
Provide structural support
Act as channels
Act as receptors for hormones
What are the functions of cholesterol?
Reduce lateral movement of other molecules
Make the membrane less fluid at high temperatures
Prevent leakage of water
Strengthen the membrane
What is the function of glycolipids?
Act as recognition sites
Help maintain the stability of the membrane
Help cells to attach to one another
What is the function of glycoproteins?
Act as recognition sites
Allow cells to recognise one another
Why do most molecules not freely diffuse across the cell surface membrane?
Not soluble in lipids and cannot pass through the layer
Too large to pass through the channels
Of the same charge and so they are repelled
Why is it called the fluid mosaic model?
Fluid- the phospholipids can move to one another, flexible structure
Mosaic- the proteins are embedded in the bilayer
What is simple diffusion?
The net movement of molecules from a high concentration to a low concentration until evenly distributed
What types of protein are involved in facilitated diffusion?
Protein Channels
Carrier proteins
What is facilitated diffusion?
The movement of large polar molecules
What are protein channels?
Allow specific water soluble ions to pass through
If the ion is not present, the channel remains closed
The ion binds to the protein and changes the shape of it which allows it to open and close
What are carrier proteins?
When something is specific to the protein, it binds with it and causes the molecule to be release inside the membrane
What is osmosis?
The passage of water from a region where it has higher water potential to lower water potential through a selectively permeable membrane
What is pure water?
It has the water potential of 0
What would be examples of high water potential and low water potential?
High = -20ka
Low = -30ka
What happens when a cell becomes turgid?
Water enters the cell
Protoplast is pushed against cell wall
What happens when the call becomes plasmolysed?
Shrinks
Protoplast pulls away completely from the cell wall
What is active transport
The movement of molecules from a region of lower concentration to a region of higher concentration using ATP and carrier proteins
What is ATP used for?
To directly move molecules
How is it not a passive form of transport?
ATP is needed
Moved against a concentration gradient (lower to higher)
Carrier proteins which act as a pump are involved
Process is very selective
What is the sodium potassium pump?
Sodium ions are actively removed from the cell whilst potassium ions are taken in from the surroundings
