Structure of cell membrane

Phospholipids

The hydrophilic phosphate head faces outwards and the hydrophobic tails face inwards

Forms a barrier to dissolved substances. The centre is hydrophobic so water soluble molecules cannot pass. However, only small, non-polar and lipid soluble molecules can diffuse through by simple diffusion. (CO2, O2 and Water)

The fluid-mosaic model

Fluid - Because the phospholipids are constantly moving and sliding over eachother Mosaic - Because the proteins scattered through the bilayer are like tiles in a mosaic

*Allow lipid soluble substances to enter and leave the cell *Prevent water soluble substances from entering and leaving the cell *Make membrane flexible and self-sealiong

Scattered in between the tails

Reduces movement of phospholipids reducing the fluidity of the membrane and provides strength They are also very hydrophobic so prevent the leakage of water and dissolved ions preventing permeability

Extrinsic proteins, Intrinsic proteins and glycoproteins

Protein channel and carrier protein

Contains water in the middle and allows water soluble molecules to pass through the cell membrane by dissolving them down the middle and letting them through by facciliated diffusion

Performs facilitated diffusion to large or polar molecules that need to get through the cell membrane

These are proteins partially embedded in the cell membrane and they provide mechanical support and act as cell receptors for hormones

Lipids and extrinsic proteins with a carbohydrate group attached to them

Extends into tissue fluid outside of the cell Acts as receptor sites Maintain stability of membrane Helps cell attach to eachother to form tissue

Cell surface receptor for hormones and neurotransmitters Act as recognition sites Help cells attach to one another Allow cells to recognise one another

*Control the entry and exit of materials in discrete organelle (Mitochondria , Chloroplast etc) *Separates organelles from cytoplasm so that specific metabolic reactions can take place inside of them *Provides an internal transport system e.g the ER *Isolates enzymes that might damage the cell *Provides surfaces on which reactions can occur