Enzymes

1.7 & 3.3

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

Homework (p.57) #3

• What is the functional role of a coenzyme or a cofactor in an enzyme-induced reaction? Give an example of an enzyme that requires a cofactor or coenzyme.

Factors AffectingRate of Enzyme Activity

• substrate concentration

• enzyme concentration

• temperature

• pH

Homework (p.57) #5

• How does the rate of reaction change as a result of each of the following factors? (Support your answer with a graphic representation of the enzymatic rates.)

• enzyme concentration

• substrate concentration

• temperature

• pH

Homework (p.57) #10

• Why is it important for the human body to maintain a proper temperature and a proper pH at all times?

Enzyme Regulation

Competitive Inhibition

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 Regulation

Allosteric Regulation

• allosteric activators promote the action of the enzyme

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

Homework (p.57) #6, 8

• Describe noncompetitive inhibition. Provide an example to support your answer.

• Describe the different effects of an activator and an inhibitor on an allosterically regulated enzyme.

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

• http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter8/animations.html#

Commercial Uses of Enzymes

• cheese• lactose-free dairy

products• cheese• corn & wheat syrup

sweeteners• etc.

Homework (p.57) #11

• You are making a gelatin dessert, but the directions tell you not to use fresh pineapple because the gelatin will not solidify. Pineapple contains an enzyme, bromelain, which is a protease.– What effect does a protease have on a

protein like collagen?– Could you use cooked or canned pineapple

instead? Explain your answer.

Homework (p.57) #12

• Humans produce enzymes in the mouth, stomach, and small intestine that aid in the process of digestion. As we age, we tend to produce less of these enzymes. What effect could this have on digestion and nutrition?

Activation Energy (EA)

• all chemical reactions require an initial input of energy, called activation energy (EA)

Enzymes & Activation Energy

3.3

Enzymes and EA

Activation Energy

• enzymes increase the rate of a reaction by lowering the activation energy (EA)

• How?

How is Ea reduced?

• weak bonds form between substrate and enzyme

• enzyme provides proper orientation of substrate(s)

• enzyme puts strain on bonds of substrate(s), making them easier to break

Animation

• Activation Energy & Enzymes:

• http://www.sumanasinc.com/webcontent/animations/content/enzymes/enzymes.html