________________________ with catalytic properties ENZYMES ________________________ with catalytic properties © 2017 Paul Billiet ODWS

Chemical reactions Chemical reactions need an initial input of energy = THE ________________________________________________________ ________________________________________________________ During this part of the reaction the molecules are said to be in a ________________________________________________________ ________________________________________________________ © 2017 Paul Billiet ODWS

Reaction pathway (exothermic) © 2017 Paul Billiet ODWS

An endothermic reaction Activation energy Reactants Products Free energy Reaction coordinate Transition state © 2017 Paul Billiet ODWS

Making reactions go faster Increasing the temperature makes molecules move __________________________________________ Biological systems are very sensitive to ___________________________________________ __________________can ____________________ the rate of reactions without the need to increase the temperature They do this by lowering the _________________________________________ They create a new reaction pathway “a short cut” . © 2017 Paul Billiet ODWS

An enzyme controlled pathway Enzyme controlled reactions proceed 108 to 1011 times faster than corresponding non-enzymic reactions. © 2017 Paul Billiet ODWS

Enzyme structure Enzymes are proteins They have a globular shape A complex 3-D structure http://www.chem.ubc.ca/personnel/faculty/withers/group/group/b egum/Human%2520Pancreati%2520Amylase% © 2017 Paul Billiet ODWS Human pancreatic amylase

The active site The _________________and the _________________________ _______________________ inside the active site permits a chemical reaction to proceed more easily. DNA ploymerase © 2017 Paul Billiet ODWS

Cofactors An additional non-protein molecule needed by some enzymes to help the reaction Tightly bound ______________________ are called prosthetic groups Cofactors that are bound and released easily are called ________________________ Many vitamins are coenzymes. © 2017 Paul Billiet ODWS Nitrogenase enzyme with Fe, Mo and ADP cofactors

The substrate The substrates of enzymes are the ___________________________ that are activated by the enzymes Enzymes are _______________________to their substrates The specificity is determined by the _______________________________________________. © 2017 Paul Billiet ODWS

The Lock and Key Hypothesis Enzyme may be used again Enzyme-substrate complex P E Reaction © 2017 Paul Billiet ODWS

The Lock and Key Hypothesis Fit between the substrate and the active site of the enzyme is exact __________________________________________________________ ___________________________________________very precisely ________________________________________________formed ________________________________________ from the substrate Products are released from the active site Leaving it free for another substrate molecule. © 2017 Paul Billiet ODWS

The Lock and Key Hypothesis This explains ______________________________________________ This explains the loss of activity when enzymes ________________________ © 2017 Paul Billiet ODWS

The Induced Fit Hypothesis Some proteins can change their shape (conformation) Substrate + enzyme, induces a change in the enzyme’s conformation Active site moulded to a precise conformation The chemical environment is now suitable for the reaction The bonds of the substrate are stretched to make reaction easier (lowers activation energy). © 2017 Paul Billiet ODWS

The Induced Fit Hypothesis Hexokinase (a) without (b) with glucose substrate This also how some enzymes can react with a range of substrates of similar types. © 2017 Paul Billiet ODWS

Factors affecting Enzymes substrate concentration pH temperature inhibitors. © 2017 Paul Billiet ODWS

Substrate concentration: Non-enzymic reactions Reaction velocity Substrate concentration The increase in velocity is proportional to the substrate concentration. © 2017 Paul Billiet ODWS

Substrate concentration: Enzymic reactions Reaction velocity Substrate concentration Vmax Faster reaction but it reaches a ____________________________when all the enzyme molecules are occupied Alter the concentration of the enzyme then Vmax will change too. © 2017 Paul Billiet ODWS

The effect of pH Optimum pH values Enzyme activity Trypsin Pepsin 1 3 5 7 9 11 © 2017 Paul Billiet ODWS

The effect of pH Extreme pH levels will produce ______________________________ The structure of the enzyme is changed The active site is distorted and the substrate molecules will no longer fit in it At pH values slightly different from the enzyme’s optimum value, small changes in the charges on the enzyme and it’s substrate molecules will occur This change will affect the binding of the substrate with the active site. © 2017 Paul Billiet ODWS

The effect of temperature Q10 (the temperature coefficient) = the increase in reaction rate with a 10°C rise in temperature For chemical reactions the Q10 = 2 to 3 Enzyme-controlled reactions follow this rule as they are chemical reactions BUT at high temperatures proteins _____________________ The ________________________for an enzyme controlled reaction will be a balance between the Q10 and denaturation. © 2017 Paul Billiet ODWS

The effect of temperature Temperature / °C Enzyme activity 10 20 30 40 50 Optimum Increasing number of collisions (Q10) Denaturation © 2017 Paul Billiet ODWS

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. © 2017 Paul Billiet ODWS