CHAPTER 6

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LIFE IS FULL OF CHEMICAL REACTIONS

Chemical reactions

Reactants – what you start with

Products – what you end with!

Reactants that are acted upon

by an enzyme are called substrates

WHAT IS AN ENZYME?

Enzyme = molecules that make chemical reactions faster than they would be on their own (organic catalyst)

- most are proteins, some are RNA

- most are not used up in a reaction – they can be used again and again

-common ending = -ase

HOW DO ENZYMES WORK

Proteins (polypeptide chains) are folded into a 3D shape and have one or more active site

Active sites = pockets where substrates bind to a protein and the reaction occurs

WHAT FACTORS INFLUENCE THE RATE ENZYMES WORK?

Toothpickase Lab

-Do all trials without the person looking.

-All members must have their own graphs.

-You may choose to complete your questions (complete sentences) as a group or as individuals (turn in 3 graph papers and 1 or 3 question sheets)

ENZYME FUNCTION

In the liver, alcohol dehydrogenase helps break down toxic alcohols, but at the expense of liver function and energy metabolism

REACTIONS REQUIRE OR RELEASE ENERGY

-We can predict whether a reaction requires or releases energy by comparing the bond energies of reactants with those of products

- Endergonic (“energy in”)Reactions that require a net input of energy

- Exergonic (“energy out”)Reactions that end with a net release of energy

WHY THE WORLD DOESN’T GO UP IN FLAMESActivation energyThe minimum amount of energy needed to get a reaction started

Some reactions require a lot of activation energy, others do not

ACTIVATION ENERGY

MECHANISMS OF ENZYME-MEDIATED REACTIONS

Binding at enzyme active sites may bring on the transition state by 4 mechanisms

Helping substrates get togetherOrienting substrates in positions that favor reaction

Inducing a fit between enzyme and substrate (induced-fit model)

Shutting out water molecules

EFFECTS OF TEMPERATURE, PH, AND SALINITY

Raising the temperature boosts reaction rates by increasing a substrate’s energy

High temperatures denature enzymes

Each enzyme has an optimum pH range In humans, most enzymes work at ph 6 to 8

Salt levels affect the hydrogen bonds that hold enzymes in their three-dimensional shape

ENZYMES AND TEMPERATURE

Warm = dark fur

HELP FROM COFACTORS

CofactorsAtoms or molecules (other than proteins) that are necessary for enzyme function

Example: Iron atoms in catalase

CoenzymesOrganic cofactors such as vitaminsMay become modified during a reactionWhite board Cofactor and Coenzyme

CATALASE AND COFACTORS

Catalase is an antioxidant that neutralizes free radicals (atoms or molecules with unpaired electrons that attack biological molecules)

Catalase works by holding a substrate molecule close to one of its iron atoms (cofactors)

Iron pulls on the substrate’s electrons, bringing on the transition state

The enzyme song

ALLOSTERIC SITES

Allosteric sites – a region away from an active site that can bind regulatory molecules

Kahn Allosteric Competition Short Allosteric Regulation

FEEDBACK INHIBITION

Feedback Inhibition = the end product inhibits the first enzyme in a series

BIOLUMINESCENCEBioluminescenceLight emitted from metabolic reactions in living organisms

-Bioluminescent organisms emit light when enzymes (generic = luciferases) convert chemical bond energy in luciferins to light energy

luciferin + ATP → luciferin-ADP + Pi

luciferin-ADP + O2 → oxyluciferin + AMP + CO2 + light

BIOLUMINESCENCE VIDEOS

National Geographic

Waves Explained

BBC - deep sea