– They are biological protein catalysts that speed up the rate of a reaction by lowering the activation energy. This activation energy is the minimum energy for the reaction to proceed.
– Most enzymes are proteins and some include RNA molecules.
– Ribozymes (catalytic RNA) are substrate specific, they enhance the rate of a reaction and they are unchanged at the end of the reaction.
– Antibodies that have catalytic power are known as abzymes.
– For example sucrose is oxidized in the cell to produce carbon dioxide and water through respiration and with the aid of enzymes.
– The most important reaction in nature to sustain life is photosynthesis.
– In an energy profile diagram the transition state is when the atoms have the highest amount of energy between the intermediates of the reactants and products.
– The enzyme does not change the free energy of the reactants or products, hence, the equilibrium of the reaction does not change but is accelerates the rate at which the equilibrium is reached.
– Enzymes are versatile biochemical’s that can be distinguished by their catalytic power, specificity and regulation.
– Each second an enzyme can covert 100 to 1000 substrates to products. This is known as the turnover number or Kcat which is the number of molecules of substrate converted to product per enzyme molecule per second.
– Enzymes are classified into six major classes and they are given enzyme commission numbers. The six classes are:
– In order for enzymes to function properly they must be accompanied by cofactors. There are inorganic and organic cofactors. Organic can be sub divided to transiently and permanently cofactors.
– Holoenzyme is an active enzyme.
– Cofactor is a non protein part and an apoenzyme is an inactive protein part.
– An apoenzyme and a cofactor combine to form a holoenzyme.
– Inorganic catalysts are used to make ammonia (finely divided iron catalyst) in the Haber process and sulphuric acid (vanadium (v) oxide catalyst) in the Contact process.
– An enzyme interacts with its substrate through molecular recognition which is based on structural complmentarity.
– Substrate binds to the enzyme’s active site.
– Two different hypotheses were taught in class to explain the enzyme specificity and catalysis. They are Fisher’s lock and key and koshland’s induced fit hypothesis.
– There are four factors that affect the reaction velocity. Namely, [S], [E], temperature and pH.
– The graph of initial velocity vs. [S] hyperbolic curve is similar in shape to that of the oxygen – dissociation curve of myoglobin.
– Allosteric enzymes show a sigmodial curve which is similar to the shape of the oxygen-dissociation curve for hemoglobin.
– The assumptions of the Michaelis- Menten were relative concentrations of enzymes and substrates, steady-state assumption and the initial velocity.
– Conclusions about the Michealis- Menten kinetics were:
1) Km is numerically equal to the substrate concentration at which the reaction velocity is equal to ½ Vmax. Small Km has the higher affinity and large Km has the lower affinity of enzyme for the substrate.
2) The order of the reaction: when [S] is much less than Km , the velocity of the reaction is approximately proportional to the [S] and when the [S] is much greater than Km , the velocity is constant and equal to Vmax.
– The Line Weaver- Burk plot can also be used to calculate Km and Vmax.
– There are two types of inhibition on enzyme activity:
1) Irreversible: binds to enzymes through covalent bonds
2) Reversible: binds to enzymes through non- covalent bonds.
– In class we learnt about reversible inhibition. They include competitive, non-competitive, uncompetitive and mixed inhibition.
– Competitive inhibition: the Vmax is reversed by increasing the [S] and Km increases.
– Non- competitive inhibition: the Vmax is decreased and the Km is the same.
– Uncompetitive inhibition: both the Vmax and Km are reduced to the same amount.
– Mixed inhibition: the Vmax is always reduced and the Km may be increased or decreased.