Proteins: Enzymes

• What is a chemical reaction?• Do they happen on their own?– If we stare at the piece of paper, are we going to

be able to make the oxygen molecules in the air collide with the cellulose in the paper?

– What do we need to do?• What are reactants?• What are products?

Examples of endothermic reactions:Melting of ice absorbs energy Dissolving ammonium nitrate in water( the essence of commercial cold packs)

Examples of exothermic reactions:Digestion of food releases energy All combustion reactions (fires) C + O2 CO2 + EAdding an alkali metal to water 2 Na + 2 H2O 2 NaOH + H2 + E

Condensation of water Explosion of bombs

Endothermic Reactionsthe reactants have less potential energy than do the products. Energy must be input in order to raise the particles up to the higher energy level.Energy + A + B --> AB

Exothermic Reactionsthe reactants have more potential energy than the products have. The extra energy is released to the surroundings. A + B --> AB + Energy

Enzymes• Enzyme– Catalyst

• Anything that speeds up the rate of a reaction by lowering the ACTIVATION ENERGY– Activ. E: energy required for a chem.

Rxn to start making products– used to regulate the rate (speed) of chemical

reactions– Protein that helps speed up a reaction that occurs

in a biological system– Name of enzymes end in –ASE

• all enzymes are proteins, but not all proteins are enzymes

• each chemical reaction in an organism requires its own specific enzyme

• enzymes are never changed by their reactions!

SubstrateMolecule/compound that attaches to enzyme

Active SiteSpecific location on enzyme for substrate to attachWhere the enzymatic reaction occurs

Enzyme-substrate complexWhen substrate binds to active site of enzyme

Productsmolecules produced at the end of an

enzymatic reaction

Factors that Effect the Rate of Reactions• Temperature

– Hot• Breaks bonds that give proteins its tertiary structure

DENATURES

– Cold• Slow down chemical reaction (formation of enzyme

substrate complex)

• pH– Acids and bases produce OH- and H+ ions

• too many ions are present, the enzyme may be denatured (twisted and pulled so out of shape that it can no longer function)

• Inhibitors– Non-competitive

• react with portions of the active site, changing of its shape

• Allosteric Inhibitors– Change shape of the enzyme– Attach to regulatory site (not active site) and change the

shape of the entire enzyme (specifically the active site)

– Competitive• look like substrate, bind to active site, but do not make

the intended product

• Acetylcholinesterase– catalyzes the breakdown of the neurotransmitter

acetylcholine at several types of synapses as well as at the neuromuscular junction — the specialized synapse that triggers the contraction of skeletal muscle.

– One molecule of acetylcholinesterase breaks down 25,000 molecules of acetylcholine each second

– makes possible the rapid "resetting" of the synapse for transmission of another nerve impulse.

Lock and Key Model

Class work! Label Each box!

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