AP Bio- Unit 3

Cellular Energetics

Enzymes

Proteins that act as catalysts; they speed up chemical reactions by lowering activation energy.

Substrate

reactant in enzyme catalyzed reaction

Enzyme-Substrate Complex

When an enzyme binds to its substrates

Active Site

binding site, a pocket on the enzyme surface where catalysis occurs; enzymes are specific to the reaction they catalyze

Induced Fit

Interactions between the substrate and active site slightly change the shape of the enzyme to hold the substrate better

Activation energy

energy required to contort reactant molecules so the bonds can break

How Enzymes Lower Activation Energy

• Provide a template for reactants to come together

• stretch substrate towards transitional state

• Provide correct microenvironment (lower pH)

• Amino acids in the active site can participate in the reaction

Optimal Temperature

High temps increase a reaction to a point, enzymes denature when they get too warm

Optimal pH

6-8(neutral)

renature

enzymes that were denatured become active again

Relative concentration of substrates/products

determine efficiency of enzymatic reaction

cofactors

non-protein helpers

coenzymes

organic molecules, mostly vitamins

competitive Inhibitors

A molecule with a similar shape to a substrate that blocks the substrate from the binding site

Noncompetitive Inhibitors

Interacts with a different part of the enzyme (allosteric site)

Allosteric Regulation

can lead to inhibition/stimulation of an enzyme reaction

Evolution of enzymes

Mutations can lead to changes in one or more amino acids, which can alter the binding site’s shape and function

What requires input of energy?

All living things

1st law of thermodynamics

Energy can’t be created or destroyed

2nd Law of thermodynamics

Every energy transfer increases entropy

Entropy

chaos

maintaining order/powering cell processes

Energy input must exceed energy loss

Significant loss of order/energy flow

results in cell death

Metabolism

All chemical reactions in an organism

Metabolic Pathways

start with one reactant and move through a series of steps to make a new product

catabolic pathways

breakdown; release energy

anabolic pathways

building; require energy input