AL Biology: Cell membrane

Made up of phospholipid bilayer, hydrophobic hydrocarbon chain face inward to each other----suit aqueous environment on both sides of the cell membrane and to accommodate the hydrophobic hydrocarbon chains.

it is in the form of fluid mosaic model----phospholipid and protein molecules can move side way within the bimolecular leaflet, movement is restricted by cholesterol but still in liquid form.
Function
Permeable to fat soluble substances
Carrier protein permeable to aqueous substance

The membrane protein:
outer or inner surface----peripheral protein(pp)
extended into leaflet----integral protein(ip)
penetrate both surface----transmembrane protein(tp)

type	location	function
enzymes	pp	[speeding up metabolic reactions]
recognition proteins	pp(outer)	[cell recognition(distinguishing foreign molecules from self molecules)]
receptor proteins	tp	[allowing the cell to recognize a signal and trigger corresponding reactions ]
channel proteins	tp	[forming channels through which small polar molecules may pass]
carrier proteins	tp	[for active transport and facilitated diffusion]

ERRCC

The surface carbohydrates:
mostly conjugated with membrane protein to form glycoprotein.

Differentiation in cell membrane:
Microvilli---- finger-liked projections which increases the surface area of the cell for absorption of material, facilitate absorption and secretion due to presence of contractile filament eg. intestine epithelial cell.
pseudopodia----foot-like membrane extensions found in cell capable of changing shape. It facilitate phagocytosis, pinocytosis or movement for itself.

Functions of the cell membrane
1. Maintains the integrity of the cell.
2.Controls the movement of material in and out of the cell by channel protein etc.
3.Protects the cell from harmful material outside such as hydrolytic enzyme
4.Recognition proteins perform cell recognition.
5.Receptor proteins allow the cell to recognize a signal and trigger corresponding reaction.
6.subcellular membranes divide the cell into compartments so that metabolic reactions can take place without interference.
7. Provides surface for attachment of enzyme
8. Provide electrical insulation(myelin sheath)
9. Enable movement, phagocytosis and pinocytosis.

resources from Advance level biology for Hong Kong