Parasympathetic Division: One of two divisions of the autonomic nervous system; generally enhances body activities that gain and conserve energy, such as digestion and reduce heart rate.
Phosphate group: A functional group important in energy transfer.
Phosphorylation: The process of adding phosphate groups to a compound, particularly important in the transduction processes of G-protein receptors.
Plasma membrane: The membrane at the boundary of every cell that acts as a selective barrier, thereby regulating the cells chemical composition.
Plasmid: A small ring of DNA that carries accessory genes separate from those of a bacterial chromosome.
Point mutation: A change in the chromosome at a single nucleotide within a gene.
Polymerase chain reaction (PCR): A technique for amplifying DNA in vitro by incubating with special primers, DNA polymerase molecules and nucleotides.
Polypeptide: A polymer (chain) of many amino acids linked together by peptide bonds.
Postsynaptic Membrane: The surface of the cell on the opposite side of the synapse from the synaptic terminal of the stimulating neuron that contains receptor proteins and degradative enzymes for the neurotransmitter.
Protein: A three dimensional biological polymer constructed from a set of 20 different monomers called amino acids.
Protein Kinase: An enzyme that regulates the activity of another protein by adding a phosphate group (phosphorylation).
Receptor Potential: (often referred to as the end plate potential or epp) An initial response of a receptor cell to a stimulus, consisting of a change in voltage across the receptor membrane proportional to the stimulus strength. The intensity of the receptor potential determines the frequency of action potentials traveling to the nervous system.
Recombinant DNA: DNA formed by joining pieces of DNA from two or more organisms.
Refractory Period: The short time immediately after an action potential in which the neuron cannot respond to another stimulus, owing to an increase in potassium permeability.
Resting Potential: The membrane potential characteristic of a non-conducting, excitable cell, with the inside of the cell more negative than the outside.
Reverse Transcriptase: An enzyme encoded by some RNA viruses that use RNA as a template for DNA synthesis.
Ribonucleic Acid (RNA): A single stranded nucleic acid molecule involved in protein synthesis, the structure of which is specified by DNA.
Ribose: The sugar component of RNA.
Ribosome: A cell organelle constructed in the nucleolus, consisting of two subunits and functioning as the site of protein synthesis in the cytoplasm.
RNA polymerase: An enzyme that links together the growing chain of ribonucleotides during transcription.
Rough ER: That portion of the endoplasmic reticulum studded with ribosomes.