A. Enzymes are catalysts produced and used by organisms

B. Catalysts are substances that speed up chemical reactions without being used up in the reaction

C. Enzymes are protein molecules, but some RNA molecules also act as catalysts and are called ribosomes

D. Activation energy - the energy required to initiate a chemical reaction

1. enzymes do not provide activation energy
2. enzymes lower the amount of activation energy required to start a reaction

E. Substrate - the substance that an enzyme works on

F. Active site - the region of an enzyme to which the substrate attaches

1. lock and key model
2. induced fit model

G. Cofactors are required for some enzymes to work properly. Organic cofactors are called coenzymes

H. Rate of reaction is affected by

1. substrate concentration
2. enzyme concentration
3. environmental conditions
a. temperature
b. pH
c. salt concentration
4. inhibitors (substances that bind to enzymes and "deactivate" them)
a. competitive inhibitors
b. noncompetitive inhibitors

I. Allosteric enzymes

1. consist of two or more subunits
2. have one or more active sites and one or more allosteric sites
3. active sites are on catalytic subunits; allosteric sites are on regulatory subunits
4. changes in shape of one subunit can affect shape of other subunits

J. There can be cooperativity between catalytic subunits.

K. Effectors are either activators or noncompetitive inhibitors. Effectors bind to the allosteric site
L. Allosteric enzymes are critical to the regulation of metabolic pathways.

1. Feedback inhibition

M. The initial production of enzymes by the cell are another way that metabolic pathways are controlled.