1. This presentation includes the following:
Chemical Reactions
Energy in Reactions
Enzymes
Enzyme Action

2. Chemical Reactions Chemical Reaction: Reactants: Products:
A process that changes one set of chemicals into another set of chemicals
Reactants:
Elements entered into the reaction
Products:
Elements or Compounds produced by the reaction
Always involves the breaking of bonds in reactants and forming of new bonds in products.
REACTANTS PRODUCTS

3. Chemical reactions Existing bonds are broken and new bonds are formed
Requires exchange of energy between molecules and environment
Reactant molecules absorb energy for their bonds to break
Energy is released when bonds of product are formed

4. Example of a chemical reaction: Carbon Dioxide in your Blood
Your cells produce carbon dioxide as waste
Carried to your lungs via the bloodstream
Carbon dioxide isn’t very soluble in water
As it enters the blood, it reacts with water
Carbon dioxide plus water produces a soluble compound called carbonic acid and is carried through the blood
CO2 + H2O H2CO3
In the lungs the reaction is reversed
H2CO CO2 + H2O
You exhale and get rid of the carbon dioxide gas!

5. Energy in Reactions:
Energy is either released or absorbed in chemical reactions…Why?
Because bonds are formed or broken!
Exothermic reactions
Reactions that release energy
Often occur spontaneously
EX: Hydrogen gas burning + oxygen water vapor
Endothermic reactions
Absorb energy
Will not occur without a source of energy
EX: Water hydrogen + oxygen gas

6. What does energy have to do with anything?
Organisms have to carry out reactions that require energy in order to stay alive
THUS: every organism needs a source of energy to carry out chemical reactions
Even exothermic reactions (releasing energy) do not always occur spontaneously
This is a good thing 
They need energy to get started

7. Activation energy
The energy needed to get a reaction started is called…Activation Energy
 The energy required to break bond in the reactants

8. Some chemical reactions are too slow
Some have an activation energy that is too high
BUT…your body has solved these dilemmas by using catalysts

9. Enzymes Proteins that act as biological catalysts. Catalyst: Enzymes:
A substance that speeds up the rate of chemical reactions.
It lowers the activation energy required for the reaction to occur.
Enzymes:
Proteins that act as biological catalysts.
Cells use enzymes to speed up chemical reactions that take place in the cell.

10. Please open your books to page 51 Figure 2-20
With the person sitting next to you…
Describe the reaction if enzymes were NOT present.
Would a reaction take a longer time or a shorter time with an enzyme?

11. Answers
Without an enzyme, the reaction would need more activation energy
With an enzyme, the reaction would take a shorter amount of time

12. Enzymes
Basically:
Enzymes make reactions that would occur eventually in the cell anyway happen faster
This lets the cell have a dynamic metabolism

13. Enzyme Action:
For a chemical reaction to take place, the reactants must collide with enough energy so that the existing bonds will be broken and new bonds will be formed in the product.

14. Enzyme-Substrate Complex:
Enzymes provide a site where reactants can be brought together to react.
The reactants are known as substrates.

15. Enzymes-Substrate Complex
The enzyme binds to its substrate
The catalytic action of the enzyme converts the substrate to the product
Enzymes usually end in “-ase”
enzyme
SUBSTRATE(S) PRODUCT(S)

16. Please turn to page 52 With the person sitting next to you…
Define “active site”
Describe the relationship between a substrate and the active site
What holds the enzyme and the substrate together?

19. Remember…
Enzymes provide a site where substrates can be brought together to react.
Such a site reduces the energy needed for a reaction
The active site is where the substrate binds to the enzyme
Each enzyme (protein) has a specific shape
Each substrate has a complementary shape
The fit is like a lock and key
The enzyme remains unchanged!

20. Regulation of Enzyme Activity
Enzymes can be affected by: pH
Temperature
Enzymes can be either “on” or “off” pH

21. Regulation of Enzyme Activity: Temperature
What group of organic compounds do enzymes belong to?
Proteins!
Proteins (thus enzymes) are temperature sensitive

22. Regulation of Enzyme Activity: Temperature
Up to a point, an increase in temperature is beneficial for the enzyme
Remember—temperature increase causes molecules to move faster
Thus more substrates are being brought to the active site of the enzyme
Each enzyme has conditions that it likes to function in
What do you think is the optimal temperature for enzymes in your body?

23. Regulation of Enzyme Activity: Temperature
A change in the optimal temperature can cause a protein to lose its shape
This is called “denaturing”
When an enzymes denatures, it loses its shape and cannot function properly anymore

24. Regulation of Enzyme Activity: pH
Just as each enzyme has an optimal temperature, an optimal pH exists as well
Usually pH of 6-8
Exceptions
Pepsin (digestive enzyme in your stomach) functions best at pH 2
It is adapted to the conditions of your stomach!