Catalyst
Substance which speeds up chemical reaction by lowering activation energy without itself being chemically changed at the end of the reaction
Enzymes
ProteinFunctions as a biological catalystsAlters or speeds up chemical reactions by lowering activation energy without itself being chemically changed after the reaction
Activation energy
Energy required to make substances reactThe greater the activation energy, the slower the reaction at any particular tempIf activation energy of a reaction decreases, the rate of reaction increasesEnzymes provide an alternative pathway with lower activation energy required to start a reactionE.g. enzymes speed up breakdown of glucose and fats to CO2 and water at body temp
Why they are efficient in minute amounts
Since they remain chemically unchanged in the reactions they catalyse, the same amount of enzyme can catalyse a large number of chemical reactions
Process of enzyme-catalysed reactions
1. Binding of substrate to an enzyme to form enzyme-substrate complex2. Conversion of ES complex to enzyme-product complex3. Release of products from EP complex to yield free product and free enzyme
Metabolic pathway
series of enzyme-catalysed reactions in which the product from one reaction is the substrate for the next
What are some reactions that enzymes catalyse?
1. DigestionE.g. amylase digests starch to maltosemaltase digests maltose into glucoseprotease digests proteins into amino acidslipase digests lipids into fatty acids and glycerol2. Breakdown of complex substances/Catabolic pathwaysBreaks down complex molecules into smaller molecules, thereby generating a useful form of energy for the cell and some of the small molecules that the cell needs as building blocks (e.g. breakdown of glucose during respiration) - hydrolysis3. Building up of complex substances/Anabolic pathwaysUse energy harnessed by catabolism to drive the synthesis of many other molecules that form the cell (e.g. building proteins from amino acids) - condensation
How are enzymes classified?
Named according to the reactions they catalyseHydrolases: hydrolytic reactionsE.g. Carbohydrase: digest carbProtease: digest proteinsLipase: digest lipase/fats
Enzyme Specificity
- Enzymes are highly specific in their actions- It is specific due to its 3D conformation and active site- Active sites are regions of an enzyme into which a specific substrate can fit- The enzyme's active site is complementary in conformation to its substrate
Lock and Key Hypothesis
Enzyme: Lock, Substrate: Key1. An enzyme has a specific 3D conformation which contains an active site2. Only a substrate with a 3D conformation complementary to that of the active site can fit into the enzyme to form ES complex. Substrate fits into enzyme like a key fits into a lock3. Chemical reaction occurs, substrate is converted into products4. Products then detach from active site. The enzyme remains unchanged after the chemical reaction.
Induced Fit Hypothesis
Suggests that initial conformation of active site of an enzyme and the shape of the substrate molecule may not be complementaryHowever, binding of the substrate to active site induces a conformational change in the active site of the enzyme, enabling the substrate to fit more tightly into the active site.Amino acid side chains which make up the enzyme active site are moulded into a precise conformation which enables the enzyme to perform its catalytic functionThe active site has a 3D conformation complementary to that of the substrate only after the substrate is bound
Factors affecting rate of enzyme-catalysed reaction
Enzyme/substrate concentrationTemperaturepH
Enzyme/substrate concentration
As E/S conc increases, rate of enzyme-catalysed reactions increases linearlyFrequency of successful collisions between enzyme and substrate increases since there are more active sites/substrates availableMore ES complexes are formed per unit time resulting in more products formed per unit timeAt high E/S conc: As E/S conc increases, rate of reaction plateaus as all active sites are saturated
Temperature
At or near 0 deg:- Rate of reaction is 0 or very low- The KE of the enzymes and substrate molecules are very low- Rate of successful collisions between enzymes and substrate molecules is very low- Enzymes are inactivated (reversible)Between 0 deg and optimum temp:- Rate of reaction increases (doubles for every 10 deg)- As temp increases, KE of enzymes and substrate molecules increase- Frequency of successful collisions between enzyme and substrate molecules increases- More ES complex formed per unit time, resulting in more products formed per unit timeOptimum temp:- Frequency of successful collisions between enzymes and substrate molecules is highest- Most ES complexes are formed per unit time and hence most products formed per unit timeBeyond optimum temp:- Rate of reaction decreases- KE of enzymes and substrate molecules increases and frequency of unsuccessful collisions increase- Disrupts bonds maintaining 3D conformation of enzymes and leads to loss of 3D conformation of active sites as active sites are no longer complementary to substrates- Denaturation (irreversible)- Rate of reaction reaches 0 after all enzymes denature
pH
Amylase in saliva: 7, Pepsin in stomach: 2, Trypsin in small intestine: 8Extreme changed in acidity or alkalinity of solutions denature enzymesPoint M indicates maximum activity of (enzyme) at a pH of about *.As the solution's pH increases from * to * and decreases from to , its to solution's pH increases from * to * and decreases from * to *, its activity decreases. At pH and , (enzyme) is completely denatured