• Created by: caprice
  • Created on: 26-11-13 16:52


an enzyme is a protein. factors that affect enzyme reactins are:

  • Temperature
  • PH
  • Enzyme concerntration
  • substrate concerntration
  • surface area

enzymes work so fast that in a few secons a factor become limiting. there are two parts to an enzyme graph. in section a temeratur ewill be the limiting factor. at part b the other factors will be limiting.

to start a chemical reaction bonds need to be broken this can be done by adding a catalyst or increasing temperature.

activation energy is the energy needed to start areaction. enzymes can lower the activation rate by making and breaking binds. or creating a OH within the ative site which makes the reaction more likely

an enzyme needs to have a complemntary shape to the substrat ( INDUCED FIT)

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mutation is a change in the arrangement of bases in an induvisula gene or in the structure of the chromosome. 

if a single codon is changed or misread during the process, then the ammini acids for which it codes may be different and so the poly peptide chain and th efinal protein may be altered. this is called mutation.

some mutations can be caused  by the misopying of just one or a small number of nuclotides.

chromosomal mutation - invlve changes in the positions of genes within the chromosomes.

whole chromosomal mutations - where an entire chromosome is either lost during meosis or duplicated in one cell by errors in the process. 

most mutations are neutral, they can happen to any cell at any time. but most commonly occour when DNA  is copied for cell division.

exposure to mutagens such as x-rays, ionising radiation increase the rate at whcoh mutations occour.

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Cardiac Cycle

(diastole)Blood at a low pressure in the veins flows into the atria. This increases the pressure inside the empty atria as they fill. Some of the blood trickles through the open atrioventricular valves into the relaxed ventricles below.

When the atria are full, they go into atrial systole, their walls contract and blood is pushed through the valves into the ventricles. The pressure in the atria is increased due to the contractions and the pressure is increasing in the ventricles as they fill with blood.

When the atria contract, blood cannot flow back into the veins because the pressure of the blood pushes on the valves in the veins to shut them.

After a short delay the ventricles contract from the apex (base) upwards. The pressure inside the ventricles increases due to the ventricular systole. As the pressure increases to a higher level than the pressure in the atria, blood pushes against the atrioventricular valves, shutting them (the first heart sound) and preventing backflow.

The semilunar valves open under the pressure and blood leaves the heart.

The ventricles relax - ventricular diastole - and the semilunar valves snap shut behind the blood (the second heart sound).

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Meselson and Stahls experiment

  • meselson and stahl grew bactira over several generations on a medium containing a heavy isotope of nitrogen ( 15N) the DNA cells therefore contained heavy (15N) Nitrogen.
  • the cells were then transferred to a new medium containing the normal ligher isotope (14N). at varioius time after the transfer samples of the bacteria were collected
  • The DNA was then extracted and dissolved in a solution of cesium chloride
  • the samples were then spun rapidly in a centrifuge. this creates a concerntration graditen in the tube.
  • DNA molecules move in the gradient until they reach a place where their density equals that of the cesium
  • DNA containing 14N moved to a position in the gradient determined by its density. DNA containing 15N is denser that 14N so it sank to a lower position in the cesium gradient
  • After One generation in 14N, the bacteria yeilded a single band of DNA with a density between 14N and 15N. indicating only one strand of each duplex contained 15N
  • after two generations in 14N, two bands were obtained, one of intermediate density( one strand contained 15N) and one low density(in which niether strand contained 15N)
  • meselson and stahl concluded that the replcarion of DNA duplex involves building new molecules by seperating parent strands and then adding new nucleotides to form the complentary strand on each of these templates. 

this experiment provides evidence for semi conservative replcation of the DNA molecule where two parent strands serve as the template for synthesis of the new strand.

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carbohydrates area group of substances used as both energy sources and structual materials in organisms

all carbohydrates contain carbon, hydrogen, and oxygen with the general formula Cx(H2O)y

monosaccharides - these are double sugars with the formula (CH2O)n where n can be 3-7

disaccharides- these are double sugars, formed wheb two monosaccarides meet

polysaccharides - these are large molecules formed from may monosacchrides.


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starch from different plants have different relative amounts of amylose and amylopectin. however it is generally between 70%-80%


  • 1-4 glycosidic bonds
  • unbranched chains
  • helical structure


  • 1-4 and 1-6 glycosidic bonds
  • highly branched chains

animals do not store carbohydrates as starch but as gylcogen.

gylcogen has a similare structure to amylopectin, containing many alpha 1-6 gylocidic bonds that produce aneven more branched structure.whereas gylcogen is stored as small granules, particully in muscule and liver. gylcogen is less densed and more solube that starch and is broken down rapidly  - higher metabolism.

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Lipids are a diverse group of compund that are insoluble in water but soluble in organic solvent such as ethanol.

lipid contail carbon hydrogen and oxygen.

triglyerides are formed when one glycerol reacts with 3 fatty acids


unsaturated fats differ from saturated fats because they  have a single bond whereas saturdate fats have a double bond.

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Protein Synthesis

protein syntheseis happens in two stages. the first stage is transcription. 


  • the DNA unwinds and hydrogen bonds betweens the bases split to seperat the two strands
  • only one strand is used in the formation oF mRNA  ( Template strand) 
  • ribonucleotides are paired with their complementay base pairs  (Uracil pairs with adenine instead of thymine) 
  • the ribonucleotides are then joined up by RNA Polymerase to form a strand of mRNA

the secons stage is translation


  • The mRNA carries the genetic message
  • transfer RNA (TRNA) translates the base sequence on the mRNA into the protein amino acid sequence
  • each tRNA molecule carries an amino acid to the mRNA, where the amino acids joins others carried by other tRNA to build  a Polypeptide.
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Blood Clotting

Blood Clotting Mechanism

  • clot formation is stimulated when there is damage ti a blood vessle
  • damage exposes collagen fibres to which platelets attach
  • the platelets releast thromboplastion
  • in the presenece of calcium ions and vitamin K, thromboplastin converts inactive prothrombin into active thrombin.
  • this in turn converts the soluble fribinogen into insolunoe fibrin
  • which forms a network of fibres, trapping cells and debris to make a clot
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  • damage to endothelial lining of arterty ( e.g by smoking, high blood pressure)
  • inflammatory response - white blood cells move into the artery wall
  • cholesterol builds up, leading to formation of atheroma
  • build up of calcium, salts and fibres leading to plaque formation
  • narrowing of the artery
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Treatment of CVD

risk of CVD can be reduced by lifestyle changes:

  • stopping smoking
  • moderate exercise serveral timea a week
  • stopping over consumption of alchol
  • dietry changes, lowering cholesterol

medical treatment that can help is

  • reducimg high blood pressure 
  • reduction of cholesterol e.g. statins
  • anticoagulants
  • platelet inhibitors
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mode of action

lower cholesterol level in the blood by blocking the liver enzyme that makes cholesterol

risk/side affect

muscle aches, nausea, constipation and diarrhoea, liver faliure, 

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Diffusion - Single Celled Organisms

organism need subatances toenter and leave the body in sufficent quantities. in very small organsism simple diffusion is fast enough to supply their needs. big organism have much smaller surface area to volume. so there is not enough surface to serve needs of the large volume inside by diffusion.

to overcome limitations of diffusion larged organisms have special organs, like lungs to increase surface area for exchange. A mass transport system e.g heart and circulation. move the exchanged materials around the body.

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water is the medium of transort in all living organism because it is an excellent solvent. the solven ability comes from the fact that water molecules have uneve charge distribution. 

ionic substances such as sodium chloride dissolve easily in water because the positivley and negatively charges ions are seperated due to dipole nature of water. 

hydrogen bonds form between molecules due to their dipole nature , holding molecules together. 

h bonding creates cohesion.

h bonding means it takes a lot of energy yo warm the water up  and also turn it into gas. so temperature fluctuations in living things are small. also transpiration and sweating take energy from the body and cool it down.

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Daphnia Experiment

it is difficult to study the human heart of human so we used living organism as a model.

a daphnia is an invertrebrate which is suitabke for testing this because;

  • it is abudent and easily obtained
  • is transperent
  • has a very simple nervous system and will not usffer stress as much mammals might. which makes it ethicllay more appropiate

thing that need to be done to make a successful experiment

  • immobilise the daphnia
  • control the variables - temp and daphina size 
  • accurate measurements
  • repeat
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mRNA & tRNA Structures


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Protein folding & the 3D structure of proteins/enz


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