adenosine triphosphate (ATP) - main energy currency used in cells 

• made of ribose, adenine (w/ 2 C-N rings), triphosphate group
• adenine forms the base, attracting hydrogen ions
• phosphates joined by unstable bonds, repelling each other
• energy of repulsion stored in bonds that hold phosphates together
• transferring a phosphate group transfers energy
• bonds easily broken, easily turned into adenosine diphosphate (ADP)
• nearly all endergonic reactions require less energy than provided by cleavage of ATP
• enzymes catalyzing endergonic reactions have 2 binding sites: 1 for reactant, other for ATP
• most cells only contain a few seconds' supply of ATP at a time

metabolism - all chemical reactions carried out by an organism  

• anabolism - reactions that use energy to make/change bonds
• catabolism - reactions that produce energy when breaking chemical bonds

biochemical pathways - sequence of reactions; organizational metabolic units  

• product of 1 reaction becomes substrate for next reaction
• evolved from a need of certain substances (new reactions would start when a certain substance was lacking)
• wasteful if more compounds than needed were produced
• feedback inhibition - where final product acts as an inhibitor on the chemical pathway, shutting it off when enough product has been created