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2.4 Notes

Published on Nov 19, 2015

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PRESENTATION OUTLINE

2.4 Notes

Chemical reactions and Enzymes 
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Living things are made up of chemical compounds but chemistry isn't just what life is made of - chemistry is also what life DOES.

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Chemical Reactions

 
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Chemical reactions involve changes in the chemical bonds that join atoms in compounds

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A chemical reaction is a process that changes, or transforms, one set of chemical into another by changing the chemical bonds that join atoms in compounds.

Mass and energy are conserved during transformations, including chemical reactions that occur in living organisms.

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EACH REACTION HAS

  • Reactants: the elements or compounds that ENTER into a chemical reaction.
  • Products: the elements or compounds PRODUCED by a chemical reaction.
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ENERGY IN REACTIONS

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How do energy changes affect whether a chemical reaction will occur?

Chemical reactions that release energy often occur on their own, or spontaneously.

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Chemical reactions that absorb energy will NOT occur without a source of energy

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ENERGY CHANGES

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Energy is released or absorbed whenever chemical bonds are formed or broken during chemical reactions.

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Energy is released in the form of heat, and sometimes when hydrogen gas explodes - light and sound.

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ENERGY SOURCE

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Every organism must have a source of energy to carry out the chemical reactions it needs to stay alive.

Plants: trap and store energy from sunlight into energy-rich compounds.

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Animals: consume plants or other animals.

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Humans: release the energy needed to grow, breathe, think, and even dream through chemical reactions that occur when we metabolize, or break down, digested food.

The energy that is needed to get a reaction started is called its activation energy.

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Enzymes speed up chemical reactions that take place in cells.

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Temperature, pH, and regulatory molecules affect the activity of enzymes.

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A catalyst is a substance that speeds up the rate of a chemical reaction by lowering the reaction's activation energy

Enzymes are proteins that act as biological catalysts.

Enzymes act by lowering the activation energies, which has a dramatic effect on how quickly the reactions are completed.

Enzymes are very specific, generally catalyzing only one chemical reaction.

ENZYME-SUBSTRATE COMPLEX

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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.

Enzymes provide a site where reactants can be brought together to react. Such a site reduces the energy needed for a reaction.

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The reactants of enzyme-catalyzed reactions are known as substrates.

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The substrates bind to a site on the enzyme called the active site.

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The active site and the substrates have complementary shapes.

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The fit is so precise that the active site and substrates are often compared to a lock and key.

Temperature, pH, and regulatory molecules can affect the activity of enzymes.

Enzymes produced by human cells generally work best at temperatures close to 37*C, the normal temperature of the human body.

Photo by Takeshi Kawai

Enzymes work best at certain pH values, for example, the stomach enzyme pepsin, which begins protein digestion, works best under acidic condions.

The activities of most enzymes are regulated by molecules that carry chemical signals within cells, switching enzymes "on" or "off" as needed.

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