2.4 - fluid mosaic model

function of phospholipid

forms a bilayer which acts as a barrier between cytoplasm and aqueous surroundings

function of channel proteins/carrier proteins

they allow the passage of specific ions and molecules across the membrane

function of enzymes

they catalyse reactions

function of receptors

they have specific binding sites, allowing chemical messengers (e.g. hormones) to bind to the protein, resulting in the relay of message to the inside of the cell

function of glycoproteins

they play a role in cell to cell recognition and cell adhesion.

they consist of carbohydrate chains covalently bonded to proteins.

they are found on the side of the membrane facing the exterior of the cell

function of glycolipids

they consist of carbohydrate molecules covalently bonded to phospholipid molecules.

the carbohydrate molecules are attached to the side of the membrane facing the exterior of the cell, they are involved in cell recognition

function of cholesterol

it plays a role in reducing fluidity of the cell membrane

membrane fluidity increases…

1. higher temperature

2. presence of unsaturated fatty acids in the phospholipids (saturated - decreease)

3. cholesterol increases membrane fluidity at low temperatures and decreases at high temperatures

define fluid mosaic

fluid - phospholipids and protein molecules are able to move freely and laterally within the phospholipid bilayer

mosaic - protein molecules are randomly embedded and scattered among the phospholipids

osmosis (no concentration gradient, only water potential)

water molecules pass through the channel by osmosis, there is a net movement of water molecules from a regino of higher water potential to a region of lower water potential through the partially permeable cell surface membrane

simple diffusion

said molecules are able to pass directly through the hydrophobic core of the cell surface membrane by simple diffusion down the concentration gradient from a region of high concentration to a region of lower concentration

facilitated diffusion

channel proteins provide a hydrophilic passage to allow specific hydrophilic molecules and ion to move across the hydrophobic core of the membrane

binding to the binding site of carrier proteins result in a change in shape of the carrier protein and said molecule is transport across the cell surface membrane

protein channel - aquaporins

facilitate the movement of water molecules across the membrane into or out of the cell

active transport

said molecules move up the concentration gradient from a region of lower concentration to a region of higher concentration, carrier proteins change shape to transport the said molecules across the cell surface membrane and this energy comes from the hydrolysis of ATP