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.