4.1 Structure of the cell-surface membrane Flashcards
Why are phospholipids important components of cell surface membranes?
The hydrophilic heads point to the outside of the cell surface membrane.
The hydrophobic tails point into the centre of the cell membrane
What is the function of a cell surface membrane?
It controls the movement of substances in and out of the cell.
What are the functions of phospholipids?
Allow lipid-soluble substances to enter and leave the cell.
Prevent water soluble substances from entering and leaving the cell.
Make the membrane flexible and self-sealing.
What is the function of proteins that occur on the surface of the bilayer?
They provide mechanical support.
They act as cell receptors for molecules eg hormones
What type of proteins span the phospholipid bilayer from one side to the other?
Protein channels
Carrier proteins
What are protein channels?
Water filled tubes that allow water-soluble ions to diffuse across the membrane.
What are carrier proteins?
They bind to ions or molecules, then change shape in order to move these molecules across the membrane.
What are the functions of cholesterol in the membrane?
Prevent leakage of water and dissolved ions from the cell.
Make the membrane less fluid at high temp.
Reduce lateral movement of other molecules
What is glycolipid?
A carbohydrate covalently bonded with a lipid.
What are the functions of glycolipids in the membrane?
Act as recognition sites.
Help maintain the stability of the membrane.
Helps cells to attach to one another.
What are the functions of a glycoprotein in the membrane?
Act as recognition sites.
Helps cells to attach to one another.
allows cells to recognise one another.
Why do most molecules not freely diffuse across the membrane?
Not lipid-soluble so cannot pass through the phospholipid bilayer.
Too large to pass through channels.
Are the same charge as the protein channel (repelled)
Electrically charged so it is hard to pass through the non polar tails.
