NOTES: 2.4 – Chemical Reactions and Enzymes
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 !
● a chemical reaction is a process that changes one set of chemicals into another
● REACTANTS: the substances that
● PRODUCTS: the substances
● EX:CO2 + H2O H2CO3
Energy in Reactions:
● some chemical reactions , and other reactions absorb it
● living organisms carry out many reactions that require, or absorb, energy
● this means every organism
● HOW do living things obtain energy?...
● PLANTS can & store it in energy-rich organic compounds
● ANIMALS get their energy when they
● humans (& other animals) release the energy needed to grow, think, dream…through the chemical reactions that occur when we
Activation Energy:
● most reactions require an initial burst of energy to get them going…
● ACTIVATION ENERGY:
● example: paper will burn vigorously, but only after it is lit with a match or spark first..the lit
match provides the activation energy!
Enzymes as Biological Catalysts
● What is a catalyst?
● a CATALYST is a substance that 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!)
● ENZYMES
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
PROTEINS WORKING AS ENZYMES
ENZYMES:
●
●control / regulate the speed of reactions (often they )
● are not changed or “used up” by a reaction;
● each enzyme is specific to a SUBSTRATE
*SUBSTRATE =
Substrate==> enzyme-sub.==> product
+complex +
enzyme enzyme
●ACTIVE SITE =
-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
Factors Affecting Enzyme Activity
1) Temperature:
-as temp increases, reaction rate increases
-BUT, if temp gets too high, enzyme denatures and
-optimal range for human enzymes:(human body temp is 37°C)
2) pH:
-optimal range for most enzymes:
*some enzymes operate best at extremes of pH
(e.g. digestive enzyme PEPSIN, found in the acidic environment of the stomach, works best at pH 2)
3) Regulatory molecules:
-most enzymes are regulated by the presence of other molecules in the cell
-these “regulatory” molecules act as as needed