Molecule Transport And Cellular Signalling

The proteins in the cell membrane are used for

cell surface receptors

enzymes

surface antigens

transporters

POLAR molecules can not enter the cell

Membrane transport proteins transport polar molecules across the membrane

UNIPORTS - just move solutes from one side to another

COTRANSPORT SYSTEMS - work by simultaneously sending two solutes across the lipid bilayer

Two types of Co- Transport Systems

SYMPORT - solutes are all sent in the same direction

ANTIPORT - in which they are sent in different directions

THESE TRANSPORT PROTEINS DO NOT NEED ENERGY

E.G Channel proteins - allow solutes to pass if they are the correct size and charge

Carrier Proteins - bind to the solute and lead it through the bilayer

These are examples of PASSIVE TRANSPORT

Moves solutes agaisnt the natural concentration gradient

ATP energy required

Difference in ion concentration

Provides power to to molecular devices

Transmits signals by opening and closing channels

Allows the cell the control its membrane potential

Sodium/potassium/ATPase, uses the energy of hydrolysis to pump sodium out and potassium in

Creates a high concentration of potassium/low concentration outside.

Pottasium leak channel allows the potassium to leak out giving the cell a negative charge of the inside.

RELEASE of cellular substances

Packaged in vesicles

Membrane pinches

PINOCYTOTIC- small

PHAGOCYTOTIC- large

Specific receptor binding allow select/reject foreign molecules

Communication between cells

EITHER

Cells secrete chemical signals

OR

communication through physical contact

Local Chemical mediator are secreted chemicals in immediate surroundings

Hormones for distant cells

Neurotransmitters for neurons

Types of Hormones

Hydrophilic

bind to receptors of targets

may alter behaviour of cell OR stimulate/repress gene expression

Hydrophobic (easily difuse)

Nuclear proteins act as receptors 

Hormones binds to receptor.