Enzymes

biological catalysts speed up chemical reactions without being consumed usually proteins with tertiary or quaternary structure

Enzyme Action enzymes bind to specific reactants called substrates substrates bind to active sites on enzymes, forming the enzyme-substrate complex

Enzyme-Substrate Complex

Induced-Fit Model in the “induced-fit” model, the enzyme alters its shape to better “fit” substrate contrast with the “lock and key” hypothesis

Example: Sucrase

What reactions do these enzymes catalyze? lactase breaks down lactose (sugar found in milk) ATPase breaks off a phosphate group from ATP, resulting in ADP + an inorganic phosphate + energy amylase breaks down starch (in saliva & intestine)

What about this one? ATP synthase synthesizes ATP from ADP and inorganic phosphate

Cofactors and Coenzymes some enzymes require cofactors to function as catalysts cofactors are non-protein molecules or inorganic ions coenzymes are organic cofactors

Cofactors

Factors Affecting Rate of Enzyme Activity substrate concentration enzyme concentration temperature pH

Enzyme Regulation

Competitive Inhibition

competitive inhibitors have a similar structure to the substrate bind to the enzyme’s active site and block the substrate from binding

Irreversible Inhibitors Many drugs & pesticides act as irreversible inhibitors of enzymes cyanide (inhibits key enzyme in cellular respiration) antibiotics (inhibit bacterial enzymes)

Allosteric Regulation some enzymes have allosteric sites allosteric regulators either inhibit or stimulate an enzyme’s activity

Allosteric Regulation

allosteric activators promote the action of the enzyme allosteric inhibitors prevent the action of the enzyme (i.e. noncompetitive inhibition)

Feedback Inhibition often used to regulate multi-step metabolic pathways the product of a pathway usually acts as an allosteric inhibitor of the first enzyme of the pathway hill.com/sites/ /student_view0/chapter8/animations.html# hill.com/sites/ /student_view0/chapter8/animations.html#

Commercial Uses of Enzymes cheese lactose-free dairy products cheese corn & wheat syrup sweeteners etc.