P-type pumps   A class of ATP-driven pumps comprising structurally and functionally related multipass transmembrane proteins that phosphorylate themselves during the pumping cycle. The class includes many of the ion pumps responsible for setting up and maintaining gradients of Na+, K+, H+, and Ca2+ across cell membranes. (Figure 11–12) p53   A transcription regulatory protein that is activated by damage to DNA and is involved in blocking further progression through the cell cycle. (Figures 20–37 and 20–40) p53   Tumor suppressor gene that is mutated in about half of human cancers. Encodes a transcription regulator that is activated by damage to DNA and is involved in blocking further progression through the cell cycle. (Figure 20–27) pair-rule gene In Drosophila development, a gene expressed in a series of regular transverse stripes along the body of the embryo and which helps to determine its segments. (Figure 21–19) pairing In meiosis, the lining up of the two homologous chromosomes along their length. (Figure 17–54) papillomaviruses   Class of viruses responsible for human warts and a prime example of DNA tumor viruses, being a cause of cancer of the uterine cervix.
paracrine signaling Short-range cell–cell communication via secreted signal molecules that act on neighboring cells.  (Figure 15–2) paralogs   Genes or proteins that are similar in sequence because they are the result of a gene duplication event occurring in an ancestral organism. Those in two different organisms are less likely to have the same function than are orthologs. Compare orthologs. (Figure 1–21) parasitism   Ecological relationship between microbes and their host in which the microbe benefits to the detriment of the host, as is often the case for pathogens.
passengers   Mutations that have occurred in the same cell as driver mutations, but which are irrelevant to the development of the cancer.
passive transport (facilitated diffusion) Transport of a solute across a membrane down its concentration gradient or its electrochemical gradient, using only the energy stored in the gradient. (Figure 11–4) patch-clamp recording   Electrophysiological technique in which a tiny electrode tip is sealed onto a patch of cell membrane, thereby making it possible to record the flow of current through individual ion channels in the patch.  (Figure 11–34)
Patched   Transmembrane protein predicted to cross the plasma membrane 12 times; much is in intracellular vesicles and some is on the cell surface where it binds the Hedgehog protein.
pathogen (adjective pathogenic) An organism, cell, virus, or prion that causes disease.
pathogen-associated molecular patterns (PAMPs) Microbe-associated molecules, either not present or sequestered in the host organism, that often occur in repeating patterns that are recognized by pattern recognition receptors (PRRs) in or on cells of the innate immune system. PAMPs are present in various microbial molecules, including nucleic acids, lipids, polysaccharides, and proteins.
pattern recognition receptor (PRR) Receptor present on or in cells of the innate immune system that recognizes and is activated by microbial pathogen-associated molecular patterns (PAMPs).