Enzymes

1.7

Enzymes

• proteins produced by cells

• biological catalysts• speed up chemical

reactions without being consumed

Activation Energy (EA)

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

Enzymes and EA

Activation Energy

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

• How?

What are enzymes?

• enzymes are globular proteins that act on substrates (reactants)

• substrates bind to specific sites (active sites) on enzymes, creating the enzyme-substrate complex

Enzyme-Substrate Complex

Induced-Fit Model

• in the “induced-fit” model, the enzyme alters shape to better “fit” substrate

• “lock and key” model

And then what?

• 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

Example: SucraseImage from: http://awesomebiology.wikispaces.com/Enzymes

What do these enzymes do?

• 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

Animation

• Activation Energy & Enzymes:

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

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 AffectingRate of Enzyme Activity

• substrate concentration

• enzyme concentration

• temperature

• pH

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

Allosteric Regulation

• some enzymes have allosteric sites (receptor sites away from the active site)

• allosteric sites can bind substances that 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. non-competitive inhibition)

Feedback Inhibition(Image from: http://classes.midlandstech.edu/carterp/Courses/bio225/chap05/ss2.htm)

• can be used to regulate multi-step metabolic pathways

• the end product of a pathway acts as an allosteric inhibitor of the first enzyme of the pathway

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

Homework (p.57) #1

• What is a substrate and active site? How are they related?

• Why is an enzyme considered a biological catalyst?

Homework (p.57) #2,3

• Describe the induced-fit hypothesis of enzyme-substrate interaction.

• 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.

Homework (p.57) #5

• How does the rate of a 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) #8,9

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

• Describe how feedback inhibition reduces the waste of cellular resources.

Homework (p.57) #10

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

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.

Commercial Uses of Enzymes(Image from: http://housewares.hardwarestore.com/35-176-laundry-detergents.aspx)

• cheese• lactose-free dairy

products• cheese• corn & wheat syrup

sweeteners• etc.