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P

P bodies
p16INK4a
[tumor suppressor gene] [and aging]
p53
[tumor suppressor gene] [detecting DNA damage]
Pachytene
Pacinian corpuscle
Packaging cell (for retroviral gene vectors)
Pain
Paleozoic era
Palindromes
Pancreas
[hormones of] [digestive enzymes]
Pandemic
Paneth cells
Pangaea
Para-aminobenzoic acid (PABA)
Paracrine
Refers to the influence on a cell of chemical signals released by neighboring cells. Compare autocrine and endocrine.
Parainfluenza virus (PIV)
Paralogous genes
Genes in one species that have arisen by duplication of an ancestral gene. Example: genes encoding olfactory receptors. Compare orthologous genes.
Paramecium caudatum
Paraphyletic
A term in taxonomy used to describe a group of organisms sharing a common ancestor (thus members of a clade) but that excludes one or more groups within that clade. Thus the class Reptilia is a paraphyletic group because reptiles share a common ancestor with the separately-classified birds (class Aves) and mammals (class Mammalia). An example. Another example.
Parasitism
[how parasites evade host defenses]
Parasympathetic nervous system
Parathion
Parathyroid hormone (PTH)
Parenchyma
p arm
Parthenogenesis
[ and imprinting ]
Passive immunity
Patch clamp technique
Patch test (for contact dermatitis)
Pathfinder mission to Mars
Pathogen
Disease-causing organism or virus.
Pathogen-Associated Molecular Patterns (PAMPs)
Pattern Recognition Receptors (PRRs)
Pax6
PCR (polymerase chain reaction)
Pdx-1 gene
P element
Pemphigoid and pemphigus
Penicillin
Pentose
Pepsin
Peptidase
Enzyme that hydrolyzes peptides into amino acids.
Peptide bond
Peptidoglycan
Perforin
Pericycle
Period (per) gene
Peripheral membrane protein
[Schematic (48K)]
Peripheral nervous system, human
Peroxisome-proliferator-activated receptors (PPARs)
Peroxisomes
[ peroxisomal targeting signal (PTS) ]
Peroxyacetyl nitrate (PAN)
Peroxyl (or peroxy) radical
PERV (porcine endogenous retrovirus)
Peyote
pH
[effect on enzyme action]
Phage display
Phagocytosis
Pharyngula
Phencyclidine (PCP)
Phenotype
Appearance of an organism, resulting from the interaction of its genotype and its environment.
Phenylalanine
Phenylketonuria (PKU)
Pheromones
[insect] [in mammals]
Philadelphia chromosome (Ph1)
PhiX174 (φX174)
Phloem
[function in translocation] [structure] [in roots]
Phosphatase
Enzyme that removes phosphate groups
Phosphate group
Phospholipids
Photoperiodism, in plants
Photophosphorylation
Photorespiration
Photosynthesis
[Calvin cycle] [light reactions] [energy relationships in] [history]
Photosystems I & II
Phototaxis
Phototropin
[ and phototropism ] [ and stomatal opening ]
Phototropism
Phylogenetic tree
[of hominoids]
Phylogeny
Evolutionary history of a species.
Phylum
Physiology
Study of the processes occurring in living organisms.
Phytochrome
[in etiolation] [in photoperiodism]
Pigment
Substance that absorbs light, often selectively. [antenna pigments] [absorption spectra]
Pilin
Pineal gland
Pinocytosis
PIN proteins
Pistil
PISTILLATA (PT)
Pituitary gland, hormones of
Pitx1
Placenta
[functions] [hormones] [as an allograft]
Plague
Planarian
Plankton
Plant
[cells] [growth] [kingdom] [succession] [tissues]
Plasma
Fluid matrix of the blood. [Discussion]
Plasma cell
Plasma membrane
Plasmid
Plasmin
Plasmodesmata
Plasmodium falciparum
[immune evasion]
Plasmolysis
Plastocyanin (PC)
Plastoquinone (PQ)
Platelets
[ and blood clotting ]
Platyhelminthes (the flatworms)
Pleiotropy
The production by a single gene of more than one effect on the phenotype.
Plesiomorphic
Plumule
Terminal bud of a plant embryo, usually consisting of embryonic leaves and the epicotyl. [Picture]
Pluripotent stem cells
Pneumococci (Streptococcus pneumoniae)
[rough and smooth] [types] [genome]
Poikilothermic
Having a body temperature that fluctuates with that of the surroundings. Commonly, "cold-blooded".
Polar body
[genetic screening of]
Poliovirus
Pollination
Polyadenylation
Polymer
Compound whose molecule consists of many repeated units linked together.
Polymerase chain reaction (PCR)
Polymorphism
Polyol
Polyp
Abnormal growth of tissue that is still benign and polyclonal. Some polyps tend in time to develop a malignant clone of cells. [in colon]
Polypeptide
[polypeptide antibiotics]
Polyploidy
Polysaccharide
Polysome
[in protein synthesis] [picture]
Polytene chromosomes
Pons
Populations
[ how regulated ] [ human ] [ cycles ]
Porifera (the sponges)
Porphyria, inheritance of
Positron-emission tomography (PET)
Post transcriptional gene silencing (PTGS)
Postzygotic isolating mechanisms
Potassium channels
involvement in hereditary deafness
Potential
[action potential] [excitatory postsynaptic potential (EPSP)]
[inhibitory postsynaptic potential (IPSP)] [resting potential]
PPM
Parts per million. [More]
Prader-Willi syndrome
Precocenes
Precursor
Substance from which another substance is formed.
Precursor activation
Predation
Living by devouring other organisms.
Pregnancy
[in humans] [hormones]
Premature termination codons (PTCs)
Pre-messenger RNA (pre-mRNA)
Prenatal Diagnosis
Pressure-Flow theory
Prezygotic isolating mechanisms
Primary host
Host normally used by a parasite during the adult stage of its life cycle.
Primary structure (Protein)
Primary transcript
Primates
Primitive
Similar to that occurring in the early evolutionary history of the structure or organism in question.
Primordial germ cells (PGCs)
Prion diseases
Producer
An organism that can synthesize organic molecules from inorganic ones (i.e., an autotroph). Producers start food chains.
Profundal zone
Progeria
Progesterone
Progestin
Any steroid that mimics the effects of progesterone.
Prokaryote
General term used for organisms that are not eukaryotes. Includes two evolutionarily-distinct groups: bacteria and archaea. Sometimes spelled procaryote.
Prolactin (PRL)
Proline
[structure] [in collagen]
Promoter
Region of DNA, usually on the 5' side of a gene, that is needed for the initiation of the transcription of that gene. RNA polymerase and other transcription factors bind to the promoter. [bacterial promoters] [eukaryotic promoters] [part of response element]
Pronucleus
The sperm nucleus and egg nucleus within the fertilized egg before their fusion to form the diploid zygote nucleus. [in humans] [making transgenic animals]
Proopiomelanocortin (POMC)
Prophage
Prophase
[in mitosis] [in meiosis I]
Proprioception
Prostaglandins
[role in birth] [role in allergies]
Prostate gland
Prosthetic group
The nonprotein part of a conjugated protein. Metal ions and a variety of organic molecules (e.g., vitamins, sugars, lipids) can serve as prosthetic groups. Prosthetic groups are usually bound covalently to their proteins. [More]
Protease
Enzyme that hydrolyzes peptide bonds whether in proteins or peptides. [serine proteases] [of HIV] [inhibitors]
Proteasomes
Proteinase
Enzyme that hydrolyzes the peptide bonds of proteins.
Protein C
Protein chips
Protein Kinases
[PKA (cAMP-dependent)] [and memory] [PKC (calcium-dependent)] [PKG (cGMP-dependent)]
Proteins
[general discussion] [protein synthesis] [protein kinesis] [protein domains]
Proteobacteria
Proteoglycans
Proteome
Prothallus
Prothoracicotropic hormone (PTTH)
Protists
Proton
Positively charged particle found in the nuclei of all atoms. The hydrogen ion (H+) is a proton. [More]
Protonema
Proto-oncogene
A normal cellular gene that, when mutated or inappropriately expressed, can cause a cell to become cancerous. Designated c-onc. They normally participate in the control of the cell cycle. [More]
Protoplast
A cell (plant or bacterial) from which the cell wall has been removed.
Protostomia
Protozoa
Proximal
Situated near the place of origin or attachment.
Prozac
Pseudoautosomal region
Pseudocyclic photophosphorylation
Pseudogene
Nonfunctional gene present in the genome of a population. Pseudogenes arise from two different mechanisms: Pseudogenes are designated with the Greek letter psi, e.g., ΨHBBP1 is a nonfunctional version of the gene encoding the beta chain of human hemoglobin. The human genome contains some 19,000 pseudogenes.
Psychedelic drugs
PTTH
Pulmonary system
[human lungs] [their blood supply] [lungs of other vertebrates]
Pupa
Pupil (of human eye)
Purines
[analogs used as immunosuppressants]
Pyramids of energy, biomass, and numbers
Pyrethroids
Pyrimidines
Pyrosequencing
PYY3-36
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