3.2.3 TRANSPORT ACROSS MEMBRANES

Phospholipids in the membrane can move around freely a bit giving fluidity and many proteins are inserted in various areas like a mosaic

-Restricts the lateral movement of other molecules eg phospholipids
- Provides membrane stability/strength
- Controls fluidity.
- Prevents leakage of water/dissolved ions.

Transports molecules across membranes

- Provide mechanical strength
- Act as receptors
- For cell recognition and allow cells to attach to each other

-Act as recognition sites
-Help cells to attach to each other
- help maintain membrane stability(Gl)
- allows cell to recognise eachother (GP)

Separates the inside and outside of the cell
Controls movement of molecules
Enables cell recognition and signalling

Net movement of small/non polar molecules from high concentration to low concentration. Passive

Movement of large molecules /ions from high concentration to low concentration via usage of intrinsic proteins. Passive

Movement of water molecules from high water potential to low water potential across a partially permeable membrane.

the measure of pressure applied by water molecules
Pure water is 0kPa

Movement of molecules against the concentration gradient by using ATP and a carrier protein.

1) molecule binds to a receptor site in carrier protein
2) ATP binds to carrier protein and undergoes hydrolysis producing ADP + Pi
3) This causes protein to change shape, transporting the molecule to other side
4) Pi leaves and protein goes back to normal

1) Na+ is actively pumped out of epithelial cells into bloodstream and opposite for K
2) Na+ diffuses down from ileum to epithelial cell by a co transporter which also transports glucose against gradient.
3) Glucose then does facilitated diffusion from epithelial to bloodstream