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Transcript of End Show Slide 1 of 34 Copyright Pearson Prentice Hall Lecture :ch2–sec4 Chemical Reactions &...
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Slide 1 of 34
Copyright Pearson Prentice Hall
Lecture :ch2–sec4 Chemical Reactions & Enzymes
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2–4 Chemical Reactions and Enzymes
Slide 2 of 34
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Chemical Reactions
Chemical Reactions
A chemical reaction is a process that changes one set of chemicals into another set of chemicals.
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2–4 Chemical Reactions and Enzymes
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Chemical Reactions
Chemical reactions always involve changes in the chemical bonds that join atoms in compounds.
–Breaking bonds releases energy
–Forming bonds stores energy
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2–4 Chemical Reactions and Enzymes
Slide 4 of 34
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Energy in Reactions
•In order to stay alive, organisms need to carry out reactions that require energy.
•Because matter and energy are conserved in chemical reactions, every organism must have a source of energy to carry out chemical reactions.
•Plants get their energy from the sun.
•Animals get their energy from eating plants or other animals.
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2–4 Chemical Reactions and Enzymes
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Energy in Reactions
Activation Energy
●Chemical reactions that release energy do not always occur spontaneously.
●Chemists call the energy that is needed to get a reaction started the activation energy.
Jumping bean analogyJumping bean analogy
Reactants
Products
Activation Energy Barrier
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2–4 Chemical Reactions and Enzymes
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Energy in Reactions
Activation energy is a factor in whether the overall chemical reaction releases energy or absorbs energy.
Ex: PhotosynthesisEx: Photosynthesis Ex: Cellular respirationEx: Cellular respiration
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2–4 Chemical Reactions and Enzymes
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Enzymes
Why are enzymes important to living things?
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2–4 Chemical Reactions and Enzymes
Slide 8 of 34
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Enzymes
Enzymes
●Some chemical reactions that make life possible are too slow or have activation energies that are too high to make them practical for living tissue.
●These chemical reactions are made possible by catalysts (biological catalysts are Enzymes).
How: Lower Activation energy
Result: Speed up rate of reaction
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2–4 Chemical Reactions and Enzymes
Slide 9 of 34
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An enzyme can decrease the energy of activation which speeds up the how fast the products are produced
Figure 5.5A
Reactants
Products
EnzymeEA
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2–4 Chemical Reactions and Enzymes
Slide 10 of 34
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Enzymes
Lowering the activation energy has a dramatic effect on how quickly the reaction is completed.
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2–4 Chemical Reactions and Enzymes
Slide 11 of 34
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Enzymes
Enzymes are very specific, generally catalyzing only one chemical reaction.
For this reason, part of an enzyme’s name is usually derived from the reaction it catalyzes.
• Ex: Amylase breaks down amylose ( as type of starch found in flour)
• Amylose (starch) lots of glucoseamylaseamylase
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2–4 Chemical Reactions and Enzymes
Slide 12 of 34
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Enzymes
• Ex: sucrase breaks down sucrose (table sugar)
SubstrateSubstrate
ProductsProducts
EnzymeEnzyme
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2–4 Chemical Reactions and Enzymes
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Enzymes
• Exception: Catalase breaks down Hydrogen peroxide
Oxygen gas – O2
2 Hydrogen peroxide 2 water + oxygen + heat energy
Catalase
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2–4 Chemical Reactions and Enzymes
Slide 14 of 34
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Enzyme Action
Enzyme Action
●For a chemical reaction to take place, the reactants must collide with enough energy so that existing bonds will be broken and new bonds will be formed.
●If reactants do not have enough energy, no reaction will take place.
Reactants
Products
Activation Energy Barrier
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2–4 Chemical Reactions and Enzymes
Slide 15 of 34
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Enzyme Action
The Enzyme-Substrate Complex
Enzymes provide a site where reactants can be brought together to react, reducing the energy needed for reaction.
The reactants of enzyme-catalyzed reactions are known as substrates.
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2–4 Chemical Reactions and Enzymes
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Enzyme Action
The substrates glucose and ATP bind to the active site on the enzyme, hexokinase, forming an enzyme-substrate complex.
The fit is so precise that the active site and substrates are often compared to a lock and key.
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2–4 Chemical Reactions and Enzymes
Slide 17 of 34
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Enzyme Action
The enzyme and substrates remain bound together until the reaction is done and the substrates are converted to products.
The products of the reaction are released and the enzyme is free to start the process again.
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2–4 Chemical Reactions and Enzymes
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Enzyme Action
An Enzyme-Catalyzed Reaction
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2–4 Chemical Reactions and Enzymes
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Enzyme Action
Regulation of Enzyme Activity
Enzymes can be affected by any variable that influences a chemical reaction.
●Many enzymes are affected by changes in temperature.
●Enzymes work best at certain pH values.
●Enzymes work best at certain ionic (salt) concentrations
1 2 3 4 5 6 7 8 9 10pH
Enzymatic
Activity
pepsin trypsin
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2–4 Chemical Reactions and Enzymes
Slide 20 of 34
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Enzyme Action
Regulation of Enzyme Activity
Temperature is a measurement of the average amount of heat/ movement a group of molecules has
–Too Cold: molecules move too slow decrease reaction rate
●Ex: enzyme responsible for producing key tomato flavor molecule stops working below 55 deg. F
–Too Hot: weak bonds between amino acids of the enzyme break denatured enzyme!!!
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2–4 Chemical Reactions and Enzymes
Slide 21 of 34
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Enzyme Action
Regulation of Enzyme Activity
pH measures how acidic or basic the environment is
Basic: pH greater than 7 -14 [Less H+]
neutral: pH 7 (pure water and most cells) [H+ = OH-]
Acidic: pH less than 7 [more H+]
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2–4 Chemical Reactions and Enzymes
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Enzyme Action
Regulation of Enzyme Activity
Altered concentration of H+ interfere with amino acid chain folding of the enzyme (remember enzymes are proteins!)
H+H+H+H+
H+H+
H+H+H+H+
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2–4 Chemical Reactions and Enzymes
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Enzyme Action
Regulation of Enzyme Activity
Enzymes work best at certain ionic (salt) concentrations
Ex: Increased Na+ Cl- (table salt)
Na+Na+Na+Na+
Na+Na+
Cl-Cl-
Cl-Cl-
Cl-Cl-
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2–4 Chemical Reactions and Enzymes
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Enzymes
Cells can regulate the activities of enzymes.
•Most cells contain proteins that help to turn key enzymes “on” and “off” at critical stages in the life of the cell.
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2–4 Chemical Reactions and Enzymes
Slide 25 of 34
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Enzymes
Enzymes play essential roles in:regulating chemical pathways.
making material that cells need.
• Many antibiotics interfere with bacteria running necessary chemical pathways including stopping the enzymes that bacteria use to make their protective cell walls.
releasing energy.
• Carbon monoxide poisoning stops cell’s enzymes from getting energy out of glucose
transferring information.
• Pesticides stop enzymes that run insects nervous system
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