ChemicalReactionsandEnzymes化學(xué)反應(yīng)和PPT課件

1、 Chemical rxns require an initial input of energy (activation energy) to get started usually supplied by kinetic energy (molecules collide and react) Most rxns occur more easily at higher temps第1頁(yè)/共10頁(yè)Enzymes Spontaneous rxns proceed too slowly to sustain life at body temp Enzymes act as biological

2、catalysts to speed up chemical rxns to solve this problemCatalyst a molecule that speeds up a rxn by lowering activation energy (catalyst is not used up in the rxn and remains unchanged)第2頁(yè)/共10頁(yè)Enzymes are substrate specificEnzymes are very specific and catalyze only a specific type of rxn (remember

3、, proteins have a very specific shape allowing them to function)Lock and Key Model specific shape of the enzyme allows them to bind to specific molecules and catalyze specific rxns第3頁(yè)/共10頁(yè)Induced Fit Model第4頁(yè)/共10頁(yè)Enzyme activity is affected by a cells physical and chemical environment1.Temperature a

4、s temperature increases, enzyme activity increases to a point extreme temps disrupt hydrogen bonds and ionic bonds holding enzymes shape and cause it to denature most human enzymes have an optimal temp of 35o to 40o C2.pH optimal pH range for most enzymes is pH 6 8 Extremes in pH will denature enzym

5、es3.Cofactors many enzymes require nonprotein helpers some bind to the active site permanently, others bind reversibly along with substrate (inorganic examples: zinc, iron, copper)Organic cofactors are called coenzymes most vitamins are coenzymes第5頁(yè)/共10頁(yè)4.Enzyme Inhibitors certain chemicals inhibit

6、the action of enzymesa.Competitive inhibitors inhibitors that resemble the shape of the normal substrate and compete for the active site and block itb.Noncompetitive inhibitors inhibitors that do not directly compete with substrate at active site bind to another part of enzyme causing it to change s

7、hape so active site cannot bind substrate第6頁(yè)/共10頁(yè)Metabolism can be controlled by regulating the activity of enzymesMany enzymes are controlled through allosteric regulation a regulatory molecule binds to an allosteric site on an enzyme (specific receptor site different from active site)1.Allosteric

8、enzymes have an active form (shape) and an inactive form2.Allosteric activators/inhibitors bind to allosteric site and change the shape of the enzyme to activate or inhibit the enzyme第7頁(yè)/共10頁(yè) Feedback inhibition switching off of a metabolic pathway by its end-product which acts as an inhibitor of an

9、 enzyme within the pathway (often by allosteric inhibition)第8頁(yè)/共10頁(yè)Industrial Uses of Enzymes Enzymes have long been used for industrial purposes Leather tanning proteases are used to soften hides and remove hair Brewing enzymes in barley grains at germination are used to convert stored starch to sugars that can be fermented by yeast Biotechnology enzymes are frequently used in genetic engineering Lactose-free milk some people are “l(fā)actose-intolerant” (do not produce lactase in pancreatic juices) cannot digest milk and mi