1. NOTES: 2.4 – Chemical Reactions and Enzymes

2. CHEMICAL REACTIONS
● Living things are made up of chemical compounds – some simple, some complex ● plus…EVERYTHING that happens in a living organism (growth, reproduction, movement, response to stimulus, etc.) is based on CHEMICAL REACTIONS!

3. CHEMICAL REACTIONS
● a chemical reaction is a process that changes one set of chemicals into another ● REACTANTS: the substances that enter into a chemical reaction ● PRODUCTS: the substances produced by a chemical reaction ● EX: CO2 + H2O  H2CO3

5. Energy in Reactions:
● some chemical reactions release energy, and other reactions absorb it ● living organisms carry out many reactions that require, or absorb, energy ● this means every organism must have a source of energy ● HOW do living things obtain energy?...

6. Energy in Reactions:
● PLANTS can trap energy from sunlight & store it in energy-rich organic compounds ● ANIMALS get their energy when they consume plants or other animals ● humans (& other animals) release the energy needed to grow, think, dream…through the chemical reactions that occur when we metabolize digested food

8. Activation Energy:
● most reactions require an initial burst of energy to get them going… ● ACTIVATION ENERGY: the energy that is needed to get a reaction started ● example: paper will burn vigorously, but only after it is lit with a match or spark first..the lit match provides the activation energy!

10. Enzymes as Biological Catalysts
● What is a catalyst? ● a CATALYST is a substance that speeds up the rate of a chemical reaction ● catalysts work by lowering a reaction’s activation energy ● many reactions critical to life are too slow to make them practical for living cells…unless we speed them up with CATLYSTS…(ENZYMES!)

12. ENZYMES!
● ENZYMES speed up chemical reactions that take place in cells… ● they work by lowering the activation energy of a reaction ● EX: CO2 + H2O  H2CO3 ● the reaction above removes CO2 from our blood…without the enzyme that speeds it up, CO2 would build up in the body & cause damage

15. PROTEINS WORKING AS ENZYMES
● are proteins
● control / regulate the speed of reactions (often they increase the speed of reactions)

16. ENZYMES:
● are not changed or “used up” by a reaction; can be used over and over

17. ● each enzyme is specific to a SUBSTRATE
● SUBSTRATE = the substance the enzyme acts on
Substrate ==> enzyme-sub.==> product
complex
enzyme enzyme

19. ● ACTIVE SITE = region of an enzyme which binds to the substrate
is usually a pocket or groove on surface
compatible “fit” between shape of enzyme’s active site and shape of substrate
“Lock and Key” analogy

23. Factors Affecting Enzyme Activity
1) Temperature:
-as temp increases, reaction rate increases
-BUT, if temp gets too high, enzyme denatures
and loses its shape and function
-optimal range for human enzymes: 35-40°C (human body temp is 37°C)

25. 2) pH:
-optimal range for most human enzymes: pH 6-8
*some enzymes operate best at extremes of pH (e.g. the digestive enzyme PEPSIN, found in the acidic environment of the stomach, works best at pH 2)

26. 3) Regulatory molecules: -most enzymes are regulated by the presence of other molecules in the cell -these “regulatory” molecules act as chemical signals that can switch an enzyme “on” or “off” as needed