structure of cell surface membrane Flashcards
What is a phospholipid and what is the layer called
They have a hydrophilic head on the outside and hydrophobic tails on the inside and it’s a lipid bilayer which means there two phospholipids
Why is it good that phospholipids are lipid soluble
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 embedded in the phospholipid bilayer
Some proteins occur in the surface of the bilayer and never extended completely across it. They act either to give mechanical support to the membrane or, in conjunction with glycolipids, as cell receptors for molecules such as hormones.
Other proteins completely span the phospholipid bilayer from one side to the other. Some are Channel proteins which form water filled tubes to allow water soluble ions 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 the proteins
Provide structural support
Act as channels transporting water soluble 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 for example hormones
What does Cholesterol do and function does it have for the lipid bilayer
They add strengthen to the bilayer and are hydrophobic so they help to stop water loss they also pull together the fatty acid tails of the phospholipid molecules, limiting their movement and that of other molecules but without making the membrane as a whole too rigid
The functions are too reduce lateral movement of other molecules including phospholipids
Make the membrane less fluid at high temperatures
Prevent leakage of water and dissolved ions from the cell
Why are glycolipids and what are the functions
There are made up of carbs covalently binder with a lipid. The carbohydrate portion extends from the phospholipid bilayer into the watery environment outside the cell where is acts as a cell surface receptor for specific chemicals
What are the functions
Act as recognition site
Help maintain the stability of the membrane
Help cells to attach to one another and so form tissues
What is a glycoprotein and what is the function
Carbohydrate chains are attached to many extrinsic proteins on the outer surface of the cell membrane these also act as cell surface receptors
The functions are
Act as recognition sites
Helps cells to attach to one another and so form tissues
Allows cells to recognise one another for example lymphocytes can refinish an organisms own cells
Why is the cell surface permeable
The cell surface membrane controls the movement of substances into and out of the cell.I’m general most molecules do not freely diffuse across it becomes many are:
Not soluble in lipids and therefore cannot pass through the phospholipid layer
Too large to pass through the Chanels 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
Electronically charged and therefore have difficulty passing through the non polar hydrophobic tails in the phospholipid bilayer
What is the fluid mosaic model of the cell surface membrane
It’s the way in which all the various molecules are combined into the structure of the cell surface membrane this is because:
Fluid the individual phospholipid molecules can move relative to one another. This gives the membrane a flexible structure that is constantly changing in shape.
Mosaic because the proteins that are embedded in the bilayer vary in shape size and pattern in the same way as the stones or tiles of a mosaic
