structure of cell surface membrane

plasma membrane

• controls how substances move in and out of the cell

• composed of two layers of phospholipids with proteins and carbohydrates within

what is the fluid mosaic model

• fluid- phospholipid molecules can move, membrane flexible so can change shape

• mosaic- proteins embedded in bilayer vary in shape, size and patterns

Describe how a lipid soluble substance will move into a cell differently to a water soluble substance

• lipid soluble moves through phospholipid bilayer by diffusion

• water soluble - intrinsic proteins act as channels allowing it to pass into and out of cell, by facilitated diffusion which is limited

what does cholesterol do

• provides strength and maintains membranes fluidity

describe why a phospholipid forms a bilayer

The hydrophilic phosphate head can hold at the surface of membranes to form phospholipid bilayer + tail

what can a phospholipid form

• bilayer

• liposome

• micelle

what are the functions of the phospholipid in the membrane?

• allow lipid soluble substances to enter and leave the cell

• prevent water soluble substances from entering and leaving the cell

• make the membrane flexible

give examples of membrane surrounded organelles

Mitochondria and chloroplast

what are intrinsic proteins

• Occur at the surface of the bilayer and extend only halfway through it

• provide mechanical support

• allow water soluble substances to pass into and out of cell

What are extrinsic proteins

• act throughout the whole bilayer

• protein channels- water soluble ions to diffuse

• carrier proteins- bind to molecules (glucose) and change shape to move molecules across the membrane

what are the functions of the protein in the membrane?

• structural support

• act as channels to transport water soluble ions across membrane

• help cells adhere together

• act as receptors for hormones

• cell recognition

features of cholesterol

• hydrophobic and prevent loss of water from the cell

• they also pull together the fatty acids tails of the phospholipid molecules limiting their movement

functions of cholesterol in membrane

• make membrane less fluid at high temperatures

• prevents leakage of water from cell

• reduce movement of other molecules

what is a glycolipid

• are made up of a carbohydrate covalently bonded with a lipid

where does the gycolipid extend to?

The watery environment outside the cell where it acts as a receptor for specific chemicals

functions of glycolipid

• Cell recognition

• stability

• cells attatch to one another and form tissues

where are carbohydrate chains attached to to form glycoprotein

extrinsic proteins on the outer surface of cell membrane

functions of glycoproteins

• recognition sites for hormones

• cells attach to one another and form tissues

• allows cells to recognise eachother

why does the cell surface membrane do not allow all molecules to freely diffuse across it

• not soluble in lipids and cannot pass through phospholipid bilayer

• too large to pass through channels of membrane

• same charge as charge on protein channels ( repelled)

• electrically charged (polar) so difficulty passing through non polar hydrophobic tails

functions of membranes within cells

• controls entry and exit of materials in cell

• provide surfaces on which reactions can occur

fluid mosaic model diagram

describe glycoprotein

• branching carbohydrate chain from protein which acts as a recognition site for hormones

Describe glycolipid

• acts as a recognition site