Cell Surface Membrane Structure Flashcards
What does a cell surface membrane do?
Controls the movement in and out of the cell.
What does the cell surface membrane form a boundary between?
The cytoplasm and environment
What is the bilayer made up of?
Phospholipids with hydrophilic phosphate heads on both sides as they are attracted by water and hydrophobic tails in the centre of the membrane which are repelled by water.
What are the 3 functions of the phospholipid bilayer?
- Allow lipid soluble substances to enter and leave the cell
- Prevent water soluble substances entering and leaving the cell
- Makes the membrane flexible and self sealing
What are found embedded in the phospholipid bilayer throughout the membrane?
Proteins
What do proteins do that never cross it?
Provide mechanical support or act as receptors
What are the two types of proteins called that span the whole membrane?
Channel or carrier proteins
What are channel proteins?
Water filled tubes that allow water soluble ions to diffuse across.
What are carrier proteins?
Bind to larger molecules like glucose and amino acids then change their shape in order to move them across the membrane.
What are the 5 functions of proteins?
- Structural support
- Act as channels allowing water soluble molecules through
- Carrier proteins allow active transport across membranes
- Act as receptors to identify cells
- Help cells adhere together
What molecules add strength to the membrane?
Cholesterol
How does cholesterol add strength to the membrane?
- Very hydrophobic prevents water and dissolved ions being lost
- Pulls together fatty acid tails limiting movement
What are the 3 functions of cholesterol?
- Reduce lateral movement of phospholipid molecules
- Makes membranes less fluid at high temperatures
- Prevent leakage of water and dissolved ions frok the cell
What are glycolipids made up of?
A carbohydrate covalently bonded with a lipid
What do glycolipids do?
Carbohydrate part extends from the phospholipid bilayer into watery environment outside where it acts as a cell-surface receptor