ENZYMES A protein with catalytic properties due to its power of specific activation Modified by J Pritchard from © 2007 Paul Billiet ODWS

Understandings  Enzymes have an active site to which specific substrates bind.  Enzyme catalysis involves molecular motion and the collision of substrates with the active site.  Temperature, pH and substrate concentration affect the rate of activity of enzymes.  Enzymes can be denatured.  Immobilized enzymes are widely used in industry. Modified by J Pritchard from © 2007 Paul Billiet ODWS

Enzyme structure  Enzymes are proteins  They have a globular shape  A complex 3-D structure  Must contain an active site (area where substrate will bind) Human pancreatic amylase © Dr. Anjuman BegumDr. Anjuman Begum Modified by J Pritchard from © 2007 Paul Billiet ODWS

The substrate  The substrate of an enzyme are the reactants that are activated by the enzyme  Enzymes are specific to their substrates  The specificity is determined by the active site Modified by J Pritchard from © 2007 Paul Billiet ODWS

The active site  One part of an enzyme, the active site, is particularly important  The shape and the chemical environment inside the active site permits a chemical reaction to proceed more easily © H.PELLETIER, M.R.SAWAYA ProNuC Database ProNuC Database Modified by J Pritchard from © 2007 Paul Billiet ODWS

Cofactors  An additional non- protein molecule that is needed by some enzymes to help the reaction  Tightly bound cofactors are called prosthetic groups  Cofactors that are bound and released easily are called coenzymes  Many vitamins are coenzymes Nitrogenase enzyme with Fe, Mo and ADP cofactors Jmol from a RCSB PDB file © 2007 Steve Cook H.SCHINDELIN, C.KISKER, J.L.SCHLESSMAN, J.B.HOWARD, D.C.REES2007 Steve Cook STRUCTURE OF ADP X ALF4(-)-STABILIZED NITROGENASE COMPLEX AND ITS IMPLICATIONS FOR SIGNAL TRANSDUCTION; NATURE 387:370 (1997) Modified by J Pritchard from © 2007 Paul Billiet ODWS

The Lock and Key Hypothesis  Fit between the substrate and the active site of the enzyme is exact  Like a key fits into a lock very precisely  The key is analagous to the substrate and the lock is analagous to the enzyme’s active site.  Temporary structure called the enzyme-substrate complex formed  Products have a different shape from the substrate  Once formed, they are released from the active site  Leaving it free to become attached to another substrate Modified by J Pritchard from © 2007 Paul Billiet ODWS

The Lock and Key Hypothesis Enzyme may be used again Enzyme- substrate complex E S P E E P Reaction coordinate Modified by J Pritchard from © 2007 Paul Billiet ODWS Enzymes are NOT used up in a reaction

The Lock and Key Hypothesis  Substrate enters with a minimum rate of motion – enough to start the reaction  Enzyme will lower the amount of energy required.  This explains enzyme specificity  This explains the loss of activity when enzymes denature Modified by J Pritchard from © 2007 Paul Billiet ODWS

Chemical reactions  Chemical reactions need an initial input of energy = THE ACTIVATION ENERGY  During this part of the reaction the molecules are said to be in a transition state. Modified by J Pritchard from © 2007 Paul Billiet ODWS

Reaction pathway Modified by J Pritchard from © 2007 Paul Billiet ODWS

Making reactions go faster  Increasing the temperature make molecules move faster  Biological systems are very sensitive to temperature changes.  Enzymes can increase the rate of reactions without increasing the temperature.  They do this by lowering the activation energy.  They create a new reaction pathway “a short cut” Modified by J Pritchard from © 2007 Paul Billiet ODWS

An enzyme controlled pathway  Enzyme controlled reactions proceed 108 to 1011 times faster than corresponding non-enzymic reactions. Modified by J Pritchard from © 2007 Paul Billiet ODWS

Factoring affecting enzyme-catalysed reactions  Temperature  pH  Substrate concentration Modified by J Pritchard from © 2007 Paul Billiet ODWS

The effect of temperature  Fluids with higher temperatures have faster moving molecules.  Reactions that use enzymes have upper limits.  That temperature is based on when the enzymes will lose their shape because bonds are stressed & broken.  Change shape = denaturing Modified by J Pritchard from © 2007 Paul Billiet ODWS

The effect of temperature Temperature / °C Enzyme activity Denaturation Modified by J Pritchard from © 2007 Paul Billiet ODWS Increase in molecular collisions

The effect of temperature  For most enzymes the optimum temperature is about 30°C  Many are a lot lower, cold water fish will die at 30°C because their enzymes denature  A few bacteria have enzymes that can withstand very high temperatures up to 100°C  Most enzymes however are fully denatured at 70°C Modified by J Pritchard from © 2007 Paul Billiet ODWS

Temperature & Enzymes  Thermolabile enzymes, such as those responsible for the color distribution in Siamese cats and color camouflage of the Arctic fox. Siamese cats: coat colours on the tips of the nose, ears and paws are darker colours at the tips of their bodies, where the temperature is slightly cooler, and the enzymes will thus only be active in these regions. Arctic Fox: in summer, the enzymes for white coat colour are denatured, then as the weather gets colder, the enzymes begin working and produce a white coat. Modified by J Pritchard from © 2007 Paul Billiet ODWS

The effect of pH  Extreme pH levels will produce denaturation  The structure of the enzyme is changed  The active site is distorted and the substrate molecules will no longer fit in it  The negative and positive areas of a substrate must match the opposite charge when the substrate is in the active site of an enzyme.  This change in ionisation will affect the binding of the substrate with the active site. Modified by J Pritchard from © 2007 Paul Billiet ODWS

The effect of pH Optimum pH values Enzyme activity Trypsin Pepsin pH Modified by J Pritchard from © 2007 Paul Billiet ODWS

Effect of substrate concentration  Constant amount of enzyme As concentration of a substrate increases, the rate of reaction will increase. Modified by J Pritchard from © 2007 Paul Billiet ODWS

Substrate concentration: Non-enzymic reactions  The increase in velocity is proportional to the substrate concentration Reaction velocity Substrate concentration Modified by J Pritchard from © 2007 Paul Billiet ODWS

Substrate concentration: Enzymic reactions  Faster reaction but it reaches a saturation point when all the enzyme molecules are occupied.  If you alter the concentration of the enzyme then V max will change too. Reaction velocity Substrate concentration V max Modified by J Pritchard from © 2007 Paul Billiet ODWS

Use of Enzymes in Industry  Food production, cleaning laundry, textiles  Problems must be overcome Purifying enzymes are required Purifying enzymes is expensive Enzymes will need to be reused Have to trap them & prevent them from being washed out with the product Modified by J Pritchard from © 2007 Paul Billiet ODWS

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Previous test question  qk qk Modified by J Pritchard from © 2007 Paul Billiet ODWS

Metabolism - Understandings  Metabolic pathways consist of chains and cycles of enzyme-catalysed reactions  Enzymes lower the activation energy of the chemical reactions that they catalyse  Enzyme inhibitors can be competitive or non- competitive  Metabolic pathways can be controlled by end- product inhibition Modified by J Pritchard from © 2007 Paul Billiet ODWS

Metabolism  Sum of all chemical reactions that occur within you Modified by J Pritchard from © 2007 Paul Billiet ODWS

Anabolic ReactionsCatabolic Reactions Build complex moleculesBreak down complex molecules Are endergonicAre exergonic Are biosyntheticAre degradative Example: photosynthesisExample: cellular respiration

Metabolic Pathways  Many occur in a specific sequence  Can be metabolic or biochemical  The product of one reaction is the reactant in the next Modified by J Pritchard from © 2007 Paul Billiet ODWS

Cyclic Metabolism Modified by J Pritchard from © 2007 Paul Billiet ODWS

The Induced Fit Hypothesis  Modified from the lock and key hypothesis  Some proteins can change their shape (conformation) Changes in the R-group  When a substrate combines with an enzyme, it induces a change in the enzyme’s conformation  The active site is then moulded into a precise conformation  Making the chemical environment suitable for the reaction  The bonds of the substrate are stretched to make the reaction easier (lowers activation energy) Modified by J Pritchard from © 2007 Paul Billiet ODWS

Comparing the two Modified by J Pritchard from © 2007 Paul Billiet ODWS

The Induced Fit Hypothesis  This explains the enzymes that can react with a range of substrates of similar types Hexokinase (a) without (b) with glucose substrate Modified by J Pritchard from © 2007 Paul Billiet ODWS

Inhibitors  Inhibitors are chemicals that reduce the rate of enzymic reactions.  The are usually specific and they work at low concentrations.  They block the enzyme but they do not usually destroy it.  Many drugs and poisons are inhibitors of enzymes in the nervous system. Modified by J Pritchard from © 2007 Paul Billiet ODWS

The difference between competitive and non-competitive inhibition Modified by J Pritchard from © 2007 Paul Billiet ODWS

The effect of enzyme inhibition  Competitive: These compete with the substrate molecules for the active site.  Rate of reaction will decrease Modified by J Pritchard from © 2007 Paul Billiet ODWS Folic acid is essential to bacteria as a coenzyme

Competitive inhibition can be…. Reversible Irreversible Modified by J Pritchard from © 2007 Paul Billiet ODWS

The effect of enzyme inhibition  Irreversible inhibitors: Combine with the functional groups of the amino acids in the active site, irreversibly. Examples: nerve gases and pesticides, containing organophosphorus, combine with serine residues in the enzyme acetylcholine esterase. Modified by J Pritchard from © 2007 Paul Billiet ODWS

The effect of enzyme inhibition  Reversible inhibitors: These can be washed out of the solution of enzyme by dialysis. Modified by J Pritchard from © 2007 Paul Billiet ODWS

The effect of enzyme inhibition  Non-competitive: These are not influenced by the concentration of the substrate. It inhibits by binding irreversibly to the enzyme but not at the active site.  Known as allosteric inhibition  Causes a change in the shape of the enzyme’s active site  Cana be reversible or irreversible Modified by J Pritchard from © 2007 Paul Billiet ODWS

Non-competitive inhibition Examples  Cyanide combines with the Iron in the enzymes cytochrome oxidase.  Heavy metals, Ag or Hg, combine with –SH groups. These can be removed by using a chelating agent such as EDTA. Modified by J Pritchard from © 2007 Paul Billiet ODWS

Applications of inhibitors  Negative feedback: end point or end product inhibition  Poisons snake bite, plant alkaloids and nerve gases.  Medicine antibiotics, sulphonamides, sedatives and stimulants Modified by J Pritchard from © 2007 Paul Billiet ODWS

End-Product Inhibition  Prevents a cell from wasting chemical resources and energy  Recall that some metabolic pathways are linear  If there is enough end product the 1 st enzyme action is shut down  When the existing end product is used up, the 1 st enzyme is reactivated Modified by J Pritchard from © 2007 Paul Billiet ODWS

Bozeman Enzyme review Modified by J Pritchard from © 2007 Paul Billiet ODWS