SouthTuenMunGovernmentSecondary School
Biology Revision Note 2
Fluid mosaic model
Characteristics / FunctionsPhospholipid bilayer / makes the cell membrane permeable to fat-soluble substances, simple and small substances; but impermeable to water, ions and water-soluble substance
Protein (embedded half-way) / acts as enzymes
Channel protein
(penetrate through the bilayer) / makes the cell membrane permeable to certain ions, water and water-soluble substances
Carrier protein (penetrate through the bilayer) / carries out active transport
Glycoprotein (embedded half-way) / acts as receptors to substances in the blood e.g. hormones.
acts as recognition substances e.g. antigens for recognize foreign cells
Transport acrossthe membrane
Diffusion / the net movement of substances from a region of higher concentration to that of lower concentrationOsmosis / the net movement of water from a region of lower solute concentration/higher water potential to that of higher solute concentration/lower water potential through a semi-permeable membrane
Activetransport / the movement of substance through a membrane with the expenseof energy, this method can move substance againsta concentration gradient
Phagocytosis / large substance is engulfed, it is digestedand useful substances are absorbed; energy is required e.g. white blood cells kill bacteria
Osmosis and cells
In hypertonic solution, water movesout of a plant cell by osmosis, the plant cell becomesflaccid, this is known as plasmolysis and the cell is plasmolysed.
In hypertonic solution, water moves out of an animal cell by osmosis, the cell becomes crinkled.
In isotonicsolution (equal water potential) there is no net movement of water in or out of a cell.
In hypotonicsolution (higher water potential) – water moves in a plant cell by osmosis, the plant cell is turgid.
In hypotonic solution – water moves in an animal cell by osmosis, the cell will burst, this process is known as haemolysisand the cell is said to be haemolysed.
Enzyme
acts as a catalystto increase the speed of chemical reactionat 37oC
A + B C + D(A and B are substrates, C and D are products)
speed of chemical reaction can be measured by the rateof disappearance of substrate and / or the rate of making products
words endedwith –ase, e.g. catalase : catalyse the break down of hydrogen peroxide to formoxygen
enzyme is specific
enzyme is not used by the chemical reaction, it remains unchanged after a reaction
enzyme works best at 37oC, at low temperature, enzyme is inactive; at high temperature, enzyme (protein in nature)denatures and lose it function forever
different enzymes work best at different optimumpH, enzyme,not at its optimum pH, denatures
Lockand Keyhypothesis
Inhibitors
Competitive inhibitor has a similar shape to substrate. It competes with the substrate for the active site. When it binds with the enzyme, at the active site, the substrate cannot bind with enzyme. Thus the rate of reaction is lower. Under high concentration of substrate, the rate of reaction can be increased.
Non-competitiveinhibitor does not has a similar shape to substrate. It binds with the enzyme, not at the active site. It changes the shape of the active site. The substrate cannot bind at the active site. Thus the rate of reaction is lower. Under high concentration of substrate, the rate of reaction cannot be increased.
Application of enzymes in daily life
Biological washing powder : protease and lipase to remove protein (blood) stain and grease
Meat tenderizer : protease in fresh fruit (e.g. pineapple, papaya) is used to break down protein and makes meat soft