NOTES: 2.4 – Chemical Reactions and Enzymes. CHEMICAL REACTIONS ● Living things are made up of chemical compounds – some simple, some complex ● plus…EVERYTHING.

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 CHEMICAL REACTIONS!

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

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?...

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

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!

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!)

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

PROTEINS WORKING AS ENZYMESPROTEINS WORKING AS ENZYMES

ENZYMES:

● are proteins

● control / regulate the speed of reactions (often they increase the speed of reactions)

ENZYMES:

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

● each enzyme is specific to a SUBSTRATE

● SUBSTRATE = the substance the enzyme acts on

Substrate ==> enzyme-sub.==> product

+ complex +

enzyme enzyme

● 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

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)

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)

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