Biology 2.4

1. Biology 2.4 Energy and Chemical Reactions in Cells

2. Energy and Chemical Reactions Energy for Life Processes • Energy is the ability to move or change matter. • Energy exists in many forms; including light, heat, chemical energy, mechanical energy, and electrical energy.

3. Energy • Energy can be converted from one form to another. • In any transfer of energy or conversion of energy from one form to another, the total amount of energy does not change. • The total amount of usable energy however always decreases.

4. Energy • Heat causes a cooking egg to change color and solidify. • The energy transferred to the egg by heat rearranges the atoms and molecules in the egg.

5. Energy • Energy can be stored or released by chemical reactions. • A chemical reactionis a process during which chemical bonds between atoms are broken and new ones are formed, producing one or more different substances.

6. Energy • At any moment thousands of chemical reactions are occurring in every cell in your body. • The starting materials for chemical reactions are called reactants. • The newly formed materials are called products. Putting a Mentos mint into a Diet Coke will create a dramatic chemical reaction

7. Energy • Chemical reactions are summarized by chemical equations, which are written in the following format: Reactants  Products The arrow readsas “changes to” or “forms”. • For example, dissolving sodium chloride in water causes the following reaction: NaCl  Na+ +Cl-

8. Energy in Chemical Bonds • In chemical reactions, energy is absorbed or released when chemical bonds are broken and new ones formed. • Some chemical reactions release energy while other chemical reactions absorb energy.

9. Energy in Chemical Bonds • Freezing and melting of water are physical, not chemical, changes. • Freezing and melting are good examples of how energy is absorbed and released.

10. Energy in Chemical Bonds • When water freezes, the process that leads to the formation of ice crystals causes heat energy to be released. • When you place water in the freezer to make ice cubes, heat is released from the water as the water freezes.

11. Energy in Chemical Bonds • When you remove ice cubes from the freezer, the ice begins to melt. • As ice melts, it absorbs heat from the environment. • When you hold a piece of ice, your hand gets cold and heat is transferred from your hand to the ice as the ice begins to melt.

12. Energy in Chemical Bonds • Metabolism is the term used to describe all the chemical reactions that occur within an organism. A chemical reaction causes fireflies to give off bioluminescent light energy

13. Energy in Chemical Bonds • Your cells get most of the energy needed for metabolism from the food you eat. • As food is digested, chemical reactions convert the chemical energy in food molecules to forms of energy that can be used by the cells.

14. Activation Energy • The heat from a flame transfers enough energy to ignite the logs in a campfire. • The spark from a spark plug causes the gasoline in an automobile engine to ignite. • In both cases energy is needed to start a chemical reaction. • The energy needed to start a chemical reaction is called activation energy.

15. Activation Energy • Activation energy is a chemical push that gets a chemical reaction in motion. • Even in a chemical reaction that releases energy, activation energy must first be applied before the reaction can occur.

16. Enzymes • Like engines, cells consume fuel because they need energy to function. • Just like an engine requires a spark to begin burning gas, biochemical reactions that occur in cells need activation energy to occur.

17. Enzymes • The chemical reactions in cells occur quickly and at relatively low temperatures because of the actions of enzymes. • Enzymes are substances that increase the speed of chemical reactions. An enzyme speeds up a chemical reaction by lowering its energy of activation, the energy that must be supplied in order for molecules to react with one another.

18. Enzymes • Most enzymes are proteins. • Enzymes are catalysts, which are substances that reduce the activation energy of a chemical reaction.

19. Enzymes • Enzymes help organisms maintain homeostasis ( a constant body temperature) • Without enzymes, chemical reactions would not occur quickly enough to sustain life. • Enzymes speed up the chemical processes in the body. Enzymes are proteins, produced by different cells of humans, animals, plants and microorganisms, which accelerate the rate of chemical reactions in living organisms. Like all catalysts, enzymes work by lowering the amount of activation energy needed for a reaction to occur and thus dramatically accelerating the rate of the reaction.

20. Enzyme Specificity • A substance on which an enzyme acts during chemical reaction is called a substrate. • Enzymes act only on specific substrates. • For example, the enzyme amylase works only to breakdown starch to glucose. • In this reaction, starch is amylase’s substrate.

21. Enzymes • An enzyme’s shape determines it’s activity. • Typically, an enzyme is a large protein with one or more deep folds in it’s surface.

22. Enzymes • These folds form pockets called active sites. • An enzyme’s substrate fits into the active site. • An enzyme acts only on a specific substrate because only that substrate fits into it’s active site.

23. Enzymes • When an enzyme first attaches to a substrate during a chemical reaction, • the enzyme’s shape changes slightly so that the substrate fits more tightly in the enzyme’s active site.

24. Enzymes • At an active site, an enzyme and a substrate interact in a way that reduces the activation energy of the reaction, making the substrata more likely to react. • This makes it so far less activation energy is required for the reaction, therefore speeding up the reaction process.

25. Enzymes • The reaction is complete when products have formed. • The enzyme is now free to catalyze further reactions

26. Factors Enzyme Activity • Any factor that changes the shape of an enzyme can affect the enzyme’s activity. • For example, enzymes operate most efficiently within a certain range of temperatures. • Temperature’s outside an enzyme’s range can either break or strengthen some of the enzyme’s bonds, changing it’s shape.

27. Factors Enzyme Activity • Enzymes also operate best within a certain range of pH values. • A ph value outside of this normal range can cause enzymes to weaken and break, reducing or eliminating the enzyme’s effectiveness. • The enzymes that are present at any given time in a cell determine what happens in that cell.

28. Factors Enzyme Activity • Your body’s cells contain many kinds of enzymes and each enzyme sets off a particular type of special chemical reaction. • Different kinds of cells contain different kinds of enzymes that are specific to that cell’s function. • The enzymes present in nerve cells will be different combinations of enzymes than those found in blood cells in your body.