1. Chemical Reactions and Enzymes
The Chemistry of Life
Chemical Reactions and Enzymes

2. Chemical Reactions
Everything that happens in an organism – it’s reproduction, its interactions with the environment, and even its movement – is based on chemical reactions.

3. Chemical Reactions
A chemical reaction is a process that changes, or transforms, one set of chemicals into another.
An important scientific principle is that mass and energy are conserved during chemical transformations.

4. The parts of a chemical reaction
Reactants: the elements or compounds that enter into a chemical reaction
Products: the elements or compounds produced by a chemical reaction
For example: carbon dioxide and water reaction in the blood stream to produce carbonic acid, which enables it to be carried to the lungs
CO2 + H2O
H2CO3

5. Energy in Reactions
Energy is released or absorbed whenever chemical bonds form or are broken.
Because chemical reactions involve breaking and forming bonds, they involve changes in energy.
Chemical reactions that release energy often occur spontaneously, but not always. Chemical reactions that absorb energy will not occur without a source of energy.

6. Energy in Reactions
Activation Energy: the energy that is needed to get a reaction started
Products
Products
Reactants
Activation Energy
Reactants
Activation Energy

7. Energy in Reactions
Activation energy is a factor in whether the overall chemical reaction releases energy or absorbs it.

9. 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 tissues.
These reactions are made possible by catalysts.

10. Enzymes
A catalyst is a substance that speeds up the rate of a chemical reaction by lowering a reaction’s activation energy.
Enzymes are proteins that act as biological catalysts. They speed up chemical reactions that take place in cells.
Lowering the activation energy has a dramatic effect on how quickly the reaction is completed.

11. Enzymes
Activation energy without enzyme
Activation energy with enzyme

12. 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.
Enzymes end in –ase.

13. Enzymes
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 the reactants do not have enough energy, they will be unchanged after the collision.

14. Enzymes
Enzymes provide a site where reactants can be brought together to react.
Such a site reduces the energy needed for reaction.
The reactants of enzyme-catalyzed reactions are known as substrates.

16. Enzymes

17. Enzymes
The enzyme and substrate are bound together by intermolcular forces and form an enzyme-substrate complex.

18. Enzymes
The enzyme-substrate complex remain bound together until the reaction is done.
Then the products are released and the enzyme is free to start the process again.
Therefore the amount of enzymes does not have to equal the amount of substrates it is acting upon.

19. Enzymes
Because they are catalysts for reactions, enzymes can be affected by any variable that influences a chemical reaction.
Some of those variable are: pH
Temperature

20. Enzymes
Cells can regulate the activation of enzymes in a variety of ways.
Most cells contain proteins that help to turn key enzymes “on” or “off” at critical stages in the life of the cell.

21. Enzymes Enzymes play essential roles in: Regulating chemical pathways
Making materials that cells need
Releasing energy
Transferring information

22. 2. Substrates bind to the enzyme at the active site
Products
Substrate
1. Enzyme Active Site
Substrate
4. Products are released
2. Substrates bind to the enzyme
at the active site
3. Substrates are converted into products