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Leaving Certificate Biology (Enzymes) Note on Enzymes, created by eimearkelly3 on 08/08/2013.

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Created by eimearkelly3 over 5 years ago
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MetabolismMetabolism is the sum of all the chemical reactions that take place within an organism. e.g. growth, movement, maintenance of a constant internal state, repair, response to stimuli, and reproduction.The most important controllers of cellular reactions are enzymes.Sources of energySolar energy : sunlight e.g. absorption of sunlight by chlorophyll --> photosynthesisCellular energy : sources of energy that are capable of being released by reaction within a cell.

EnzymesEnzymes are protein catalysts made by the cell.A catalyst is a substance that speeds up a reaction without itself being used up in the reaction.Enzymes are therefore biological catalysts (not all proteins are enzymes but all enzymes are proteins)Enzymes are proteins that speed up a reaction without being used up in the reaction.Metabolic reactions controlled by enzymes Photosynthesis Respiration Digestion Protein synthesis Cell division

Enzymes are folded into globular shapes that will fit neatly and react only with a substance of a shape that matches the enzyme (complex 3D shape)Anything that changes the shape of an enzyme will reduce its efficiency to speed up a reaction.SUBSTRATE : The substance with which an enzyme reactsPRODUCT : The substance(s) the enzyme forms.

Catabolic enzymes Break down large molecules into simpler molecules e.g. amylase (breaks starch down into maltose) amylase is produced by the salivary glands in the mouth and also by the pancreas. Amylase is also found in germinating seeds

Anabolic enzymesConvert simple molecules into more complex molecules e.g. DNA polymerase (plants + animals) This is an enzyme found in the vast majority of living organisms, its function is to form and repair DNA. The enzymes involved in photosynthesis are also anabolic, their function is to convert water and carbon dioxide in to glucose

Denatured : The specific 3D shape has been altered and will therefore no longer fit the substrate. GENERALLY IRREVERSIBLE

Factors affecting enzyme activityTemperature....At very low temperatures (0 degrees for water) ice forms. The cell contents become solid and enzymes cannot work.As the temperature increases from 0 degrees the rate of molecular movement increases. This causes the substrate molecules and enzymes to 'bump' into each other more often --> rate of reaction increases.Human enzymes are designed to work at 37 degrees while most plant enzymes prefer 20-30 degrees.Above a certain temperature, enzymes begin to lose their 3D shape. Consequently, the rate of reaction falls.When the shape of an enzyme is fully lost (above 50 degrees) the enzyme is said to be denatured (has lost its ability to function).PHEnymes work over a very narrow PH range. For most enzymes this is PH 6-8. (optimum 7) *Pepsin in the stomach has an optimum PH of 2.Enzyme activity is also affected by the enzyme-substrate concentration.

Active siteThe active site is the part of the enzyme that combines with the substrate (was referred to as the lock and key hypothesis as the active site was believed to be rigid in structure).It is now known that when the substrate enters the active site, the active site changes shape slightly to form a more precise fit around the substrate. This is referred to as the INDUCED FIT MODEL of enzyme action.

Immobilised enzymes are enzymes that are attached to, or fixed to, each other or an inert material.Immobilised enzymes are not free in solution.

BIOPROCESSINGThe use of enzyme-controlled reactions to produce a product.Industrial bioprocessing use immobilised enzymes. They may be held in a bead of soft permeable gel, or coat the internal surface of a porous solid.Bioprocessing can also be desccribed as the use of biological materials (organisms, cells, organelles, enzymes) to manufacture commercial products or treatment procedures of commercial, medical, or scientific interest. e.g. drugs, vaccines, antibioticsImmobilised enzymes are used in urine testing for illegal drugs and other chemicals.Example of bioprocessing with enzymes --> production of glucose and fructose from sucrose using sucrase 

BIOREACTORA bioreactor is a stainless steel vessel used to produce useful substances from the activiies of biological agents.

Methods of immobilising enzymesImmobilised enzymes may be attached to each other, to insoluble supports or enclosed within a membrane or gel. A range of different immobilisation techniques are used:PHYSICAL METHODS:AdsorptionEnclosed by a membraneTrapped in a gelCHEMICAL METHODS:Bonded to  supportBonded to each other

Adsorption - enzymes are physically attached to inactive supports such as glass beads, ceramics, cellulose particles or artificial polymers such as gels (all insoluble)Sodium alginate is commonly used as a gel for immobilisation. This gel is permeable to the entry of the substrate and the exit of the product. The gel prevents the exit of the enzyme

Advantages of immobilised enzymes: can be reused - cheaper can be recovered from the reaction vessel at the end of the process - rapidly purified immobilisation often stabilises the enzyme - reduces the amount needed cheaper than using free enzymes but just as efficient

Uses of immobilised enzymes: penicillin acylase --> alters the structure of penicillin to produce a wider spectrum antibiotic. glucose isomerase --> converts glucose to fructose which is used to sweeten soft drinks. lactose --> used to convert lactose into sweeter tasting sugars (glucose + galactose). These products are used to replace condensed milk in the manufacture of soft toffee and caramel.


Immobilised enzymes