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Chemical Reactions and Enzymes
Specialized Proteins
10/5/2011
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Key question: What happens to chemical bonds during chemical
reactions?
•Answer: Chemical reactions involve changes in the chemical bonds that join atoms together.–Some bonds are broken;
–Other, new bonds, are formed
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Key question: How do energy changes affect whether a chemical reaction will
occur?• Energy is released or absorbed whenever
chemical bonds are formed or broken–This means chemical reactions also
involve changes in energy• Answer: Chemical reactions that
release energy often occur on their own, or spontaneously. Chemical reactions that absorb energy will not occur with a source of energy.
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Where do living things get the energy they need for chemical
reactions?•Plants and other photosynthetic organisms transform sunlight energy into glucose
•Animals get their energy by consuming other organisms
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Activation Energy
•The energy needed to get a reaction started is called
the activation energy
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Key question: What role do enzymes play in living things and what affects
their function?•Answer (part 1): Enzymes speed up
biochemical reactions that place in cells
• Enzymes are called catalysts: substances that speed up chemical reactions
• Catalysts work by lowering the activation energy of chemical reactions, so the reaction gets started faster
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How do enzymes work?
• Enzymes provide a site (called active site) where reactants can react, lowering the activation energy needed
• The reactants of enzyme-catalyzed reactions are called substrates
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• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html
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Enzymes are Specific & Reusable
• Only certain substrates fit within an enzyme’s active site– Each biochemical reaction has a specific
enzyme which catalyzes it• Enzymes are not “used” or “transformed”
while performing their functions– After catalyzing the reaction, the products are
released from the unchanged enzyme– The enzyme’s active site is now open to
catalyze the reaction again
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Key question: What role do enzymes play in living things and
what affects their function?
• Answer (part II): Temperature, pH, and regulatory molecules can affect the activity of enzymes
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Temperature and pH
•The cells of living organisms are only able to perform the biochemical processes of life under the proper environmental conditions (such as temp & pH)
•All enzymes have specific environmental conditions under which they can function
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Optimum Temp & pH
The optimum temperature and pH is the temperature
and pH at which the reaction rate (of the
chemical reaction) / activity of the enzyme is HIGHEST
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Denatured Enzymes – enzymes whose shape has
been changed due to environmental conditions
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What might happen to the reaction rate in…
• Very low temperatures –
• Very high temperatures –
• Slight changes in pH –
• Major changes in pH -