Chemical Reactions and Enzymes Specialized Proteins 10/5/2011

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

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.

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

Activation Energy The energy needed to get a reaction started is called the activation energy

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

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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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

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

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

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

Denatured Enzymes – enzymes whose shape has been changed due to environmental conditions

What might happen to the reaction rate in… Very low temperatures – Very high temperatures – Slight changes in pH – Major changes in pH -