Biology 1.4 and 1.5 revision

enzymes, immobolised enzymes and biosensors 

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AS Biology 1.4 Enzymes and Metabolism
Most enzymes are proteins, which are capable of catalysing (speeding up) biochemical reactions and
are therefore called biological catalysts. Enzymes act on one or more compounds (called the
substrate) they may break a single substrate molecule down into simpler substances, or join two or
more substrate molecules chemically together. The enzyme itself is unchanged in the reaction ­ its
presence merely allows the reaction to take place more rapidly. When the substrate attains the
required activation energy to enable it to change into the product, there is a 50% chance that it will
proceed forward to form the product, otherwise it reverts back to a stable form of the reactant
again. The part of the enzyme's surface into which the substrate is bound and undergoes reaction is
known as the active site. This is made of different parts of polypeptide chain folded in a specific
shape so they are closer together. The substrate fits into the cleft and locks into position. For some
enzymes, the complexity of the binding sites can be very precise, allowing only a single kind of
substrate to bind to it. Some other enzymes have low specificity and will accept a wide range of
substrates of the same general type (e.g. lipases bind to fatty acid chain length of lipid). This is
because the enzyme is specific for the type of chemical bond involved and not an exact substrate.
An enzyme is called a biological catalyst because it speeds up biochemical reactions and are not used
A substrate is the molecule that the enzyme acts on.
The active sites are the points that attract the substrate to the enzyme. They are all specified to a
certain substrate.
Metabolism is all the chemical activities of life by which we obtain energy, grow and heal. They are
complex and needed to maintain the organism.
Catabolism is the reaction when chemical bonds are broken to break apart and become two separate
molecules such as digestion which is the breakdown of food absorbed into the body and blood.
Anabolism is the chemical reaction when two substrates are bound together to form one single
molecule such as photosynthesis which is when carbon dioxide and water join together to create
energy (glucose).
If the gene that codes the enzyme was altered by a mutation it could affect the functioning of an
enzyme by having no affect, shape could be changed and the active site could be changed.

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Lock and Key theory
Induced Fit
Substrate forces itself into the active site. When the products leave, the active site returns to normal.
The Turnover Number is the amount of reactions an enzyme can catalyse in a certain amount of time.
The Activation energy is the energy needed to start a chemical reaction.
Enzymes can be denatured by heat.
Factors affecting enzyme action
1. Temperature
1- Collision activity increasing and energy.
2- Optimum temperature= faster rate.…read more

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Different enzymes work the best at different pHs, called the optimum pH. E.g. pepsin has
optimum Ph around 2.
Small changes in pH can alter enzyme activity. Large changes in pH prevent enzyme activity.
3. Substrate Concentration
1. Substrate concentration is proportional to rate of
reaction, the more substrates the more reactions
2. Enzyme concentration is limiting all enzymes working at
maximum rate. All active sites are full.
Inhibitors slow down enzyme catalysed reactions. Some inhibitors control pathways naturally in cells.…read more

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E.g. cyanide is a non ­ competitive inhibitor of
cytochrome oxidase.
Increasing substrate concentration has no affect on the rate of reaction. This is because the inhibitor
binds to a different site to the substrate. E.g. cyanide as a non competitive inhibitor of cytochrome
A buffer is a chemical that can act as bases and acids. Keep a pH constant prevent it becoming to
acidic or too alkaline.
Immobilised Enzymes
Enzymes that is entrapped or adsorbed onto an inert material or matrix.…read more

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The reading on the display is proportional to the oxygen taken up and the glucose concentration.
When a reaction occurs the electrodes pick up slight electrical changes and convert this to an electric
current. This is then amplified and displayed.…read more


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