Adenyl cyclase -- A plasma membrane-bound enzyme catalyzing the formation of cAMP from ATP. It is an important component of some intracellular signaling pathways.

Adenosine monophosphate (AMP) -- One of the four nucleotides in an RNA molecule. Two phosphates are added to AMP to form ATP.

Adenosine triphosphate (ATP) -- Nucleoside triphosphate composed of adenine, ribose, and three phosphate groups. It is the primary carrier of chemical energy in cells. The terminal phosphate groups are highly reactive in the sense that their hydrolysis, or transfer to another molecule, takes place with the release of a large amount of free energy.

Adipose -- Fat.

Amplifier -- One of several small intracellular mediators or enzymatic cascades that amplify extracellular signals.

Cell Receptor, or discriminator point -- A chemical group or molecule, such as a protein, on a cell's surface or in the cell interior with an affinity for a specific chemical group, molecule, or virus.

Collagenase -- An enzyme that catalyzes the hydrolysis of the peptide bonds in triple helical regions of collagen molecules.

Cyclic adenosine monophosphate (cAMP) -- A nucleotide generated from ATP by adenylyl cyclase in response to the stimulation of many types of cell-surface receptors. cAMP acts as an intracellular signaling molecule by activating cyclic-AMP-dependent protein kinase.

Glucagon -- A hormone produced by the pancreas that stimulates an increase in blood sugar levels, and therefore counteracts the action of insulin.

G proteins -- A protein with GTPase activity that binds GTP, which activates the protein. The intrinsic GTPase activity eventually converts the GTP to GDP that activates the protein. These GTPases act as molecular switches in intracellular signaling pathways.

Guanosine triphosphate (GTP) -- A nucleoside triphosphate produced by phosphorylating, the metabolic process of introducing a phosphate group into an organic molecule, guanosine diphosphate (GDP). GTP has a special role in microtubule assembly, protein synthesis, and cell signaling. Like ATP, it releases a large amount of free energy on hydrolysis of its terminal phosphate group.

Heterotrimeric -- A macromolecule, a very large molecule built up from smaller chemical structure, composed of three subunits of which at least one differs from the other two.

Homogenate -- Any material consisting of similar elements or materials.

Insulin -- A polypeptide hormone secreted by beta cells in the pancreas. Insulin helps regulate glucose metabolism by promoting a decrease in the sugar content of the blood, functioning as a complement with glucagon.

Lipoprotein lipase -- An enzyme crucial to blood lipid metabolism. It hydrolyzes, or breaks down, lipoprotein triacylglycerols.

Nucleoside -- A molecule composed of a purine or pyrimidine base covalently linked to a ribose or deoxyribose sugar. When nucleosides add a phosphate molecule, they become nucleotides, the building blocks of DNA and RNA.

Nucleotide -- A unit that polymerizes into nucleic acids (DNA or RNA). Each nucleotide consists of a purine (adenine or guanine) or pyrimidine (cytosine, thymine, or uracil) base, a sugar (ribose in the case of RNA, deoxyribose in the case of DNA), and a phosphate molecule.

Signal transduction -- Mechanisms by which a biochemical signal generated by a hormone or neurotransmitter causes a biological effect inside a cell. This mechanism involves the relaying of a signal by conversion from one physical or chemical form to another.

Target cell -- Most hormones circulate in the blood and come into contact with essentially all cells. However, a given hormone usually affects only a limited number of cells, which are its target cells. A target cell responds to a hormone because it contains functional receptors for that hormone. Cells that do not have such a receptor cannot be influenced directly by that hormone.