Structure Of The Cell Surface Membrane Flashcards
Why are phospholipids important in the cell surface membrane
The hydrophilic heads of both phospholipid layers point to the outside of the cell surface membrane attracted by water on both sides
The hydrophilic tails of both phospholipid layers point into the centre of the cell membrane, repelled by the water on both sides
What are the functions of the phospholipid in the membrane
Allow lipid soluble substances to enter and leave the cell
Prevent water soluble substances entering and leaving the cell
Make the membrane flexible and self sealing
How are proteins imbedded in the phospholipid bilayer
Some proteins occur in the surface of the bilayer and never extend completely across it - act to give mechanical support, or in conjunction with glycolipids as cell receptors
Some are protein channels, which form water filled tubes to allow water soluble joke to diffuse across the membrane. Others are carrier proteins that bind to ions or molecules like glucose and amino acids, then change shape in order to move these molecules across the membrane
What are the functions of proteins in the membrane
Provide structural support
Act as channels transporting water soluble substances across the membrane
Allow active transport across the membrane through carrier proteins
Form cell surface receptors for identifying cells
Help cells adhere together
Act as receptors
What do cholesterol molecules do in the phospholipid bilayer
They add strength to the membranes
Very hydrophobic and therefore ply an important role in prevent water loss and dissolved ions form the cell
What are the functions of cholesterol in the membrane
Reduce lateral movement of other molecules including phospholipids
Make the membrane less fluid at high temps
Prevent leakage of water and dissolved ions from the cell
What are glycolipids
Made up of carbohydrates 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 attach to one another and so form tissues
What are glycoproteins
Carbohydrate chains are attached to many extrinsic proteins on the outer surface of the cell membrane
Why are the functions of me of glycoproteins in the membrane
Acts as recognition sites
Help cells to attach to one another and so form tissues
Allows cells to recognise one another
Why can most molecules not freely diffuse pass the cell surface membrane
Many are :
Not soluble in lipids and cannot pass through the phospholipid layer
Too large to pass through the channels in the membrane
Of the same charge as the charge on the protein channels and so even if they are small enough to pass through they are repelled
Electrically charged and therefore difficult to pass through non polar hydrophobic tails in the phospholipid bilayer
Why’s it called the fluid mosaic model
Fluid - as the individual phospholipid molecules can move relative to one another. This gives the membrane a flexible structure that is constantly changing shape
Mosaic - as the proteins that are embedded in the phospholipid bilayer vary in shape, size and pattern in the same way as the stones of tiles
