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A-B-C-D-E-F-G-H-I-J-K-L-M-N-O-P-Q-R-S-T-U-V-W-X-Y-Z
- p53
- Tumor suppressor gene
- p arm
- [of chromosome]
- Packaging cell
- for retroviral gene vectors
- Paleozoic era
- Pancreas
- [hormones of] [digestive enzymes]
- Pandemic
- caused by antigenic shift of the influenza virus
- Para-aminobenzoic acid (PABA)
- Paracrine
- Refers to the influence on a cell of chemical signals released by neighboring cells. Compare autocrine and
endocrine.
- Parasite
- Organism living on or in another organism from which it derives its food and which it harms to some extent.
- Parasympathetic nervous system
- in humans
- Parathyroid hormone (PTH)
- [and calcium]
- Parenchyma
- Plant tissue consisting of thin-walled cells, often loosely-packed, that function in photosynthesis and/or food storage. [View]
- Parthenogenesis
- Development of an unfertilized egg into a new individual. Often occurs naturally in certain plants and animals (e.g., aphids).
- Patch test
- [for contact dermatitis]
- Pathfinder
- [Mission to Mars]
- Pathogen
- Disease-causing organism or virus.
- PCR
- polymerase chain reaction
- Penicillin
- Pentose
- A sugar containing 5 carbon atoms. Deoxyribose and ribose are pentoses.
- [structure]
- Pepsin
- Peptide bond
- Covalent bond that links amino acids in a polypeptide. [More]
- Peptidoglycan
- Peripheral membrane protein
- [More] [Schematic (48K)]
- Peroxisomes
- PERV
- porcine endogenous retrovirus
- Peyote
- pH
- Negative logarithm of the hydrogen ion concentration (in moles per liter) of a solution, which thus provides a measure of acidity and alkalinity. [More] [Effect on enzyme action]
- Phagocytosis
- Engulfing of solid particles by a cell.[More]
- Phencyclidine (PCP)
- Phenotype
- Appearance of an organism, resulting from the interaction of its genotype and its environment.
- Phenylalanine
- [structure]
- Phenylketonuria (PKU)
- Pheromone
- Substance secreted externally by an animal which influences the behavior of other members of the same species.
- Phloem
- Complex vascular tissue of plants that translocates food throughout the plant. [More]
- Phosphate group
- [Structure]
- Phospholipid
- [Discussion]
- Photoperiodism
- Developmental or behavioral response of an organism to the duration of daylight or darkness.
- Photophosphorylation
- [More]
- Photosynthesis
- [Calvin cycle][light reactions]
- Photosystems I & II
- [Discussion]
- Phototropism
- Phylogenetic tree
- Diagram of the deduced evolutionary (genealogical) relationships (history) of a group of organisms. A dendrogram.
- Phylogeny
- Evolutionary history of a species.
- Phylum
- Major taxonomic category comprising one or more classes. In plant classification the term division is often used instead.
- Physiology
- Study of the processes occurring in living organisms.
- Pigment
- Substance that absorbs light, often selectively.[antenna]
- Pineal gland
- and melatonin
- Pinocytosis
- Pistil
- PISTILLATA (PT)
- Pituitary gland
- hormones of
- Placenta
- [functions] [hormones] [as an allograft]
- Plankton
- Floating, generally microscopic, protistan and animal life in a body of water.
- Plasma
- Fluid matrix of the blood. [Discussion]
- Plasma cell
- Antibody-secreting cell. [More]
- Plasma membrane
- Plasmid
- Small molecule of DNA that is replicated within the cell (usually of a bacterium) independent of the chromosome(s) of its host cell.[More]
- Plasmodesmata
- Plasmolysis
- Shrinkage of the cytoplasm away from the wall of a plant cell, placed in a hypertonic medium, because of the loss of water by osmosis.
- Platelets
- Pleiotropy
- The production by a single gene of more than one effect on the phenotype.
- Plumule
- Terminal bud of a plant embryo, usually consisting of embryonic leaves and the epicotyl. [Picture]
- Poikilothermic
- Having a body temperature that fluctuates with that of the surroundings. Commonly, "cold-blooded".
- Polar body
- The smaller of the cells produced by meiosis I and meiosis II during oogenesis.
- Pollination
- Polyadenylation
- [in pre-mRNA processing]
- Polymer
- Compound whose molecule consists of many repeated units linked together.
- Polymerase chain reaction (PCR)
- Polymorphism
- Occurrence of several distinct phenotypes in a population (e.g., queen, drone, and worker bees). Also, occurrence of allelic versions of a gene in at least 1% of a population.
- Polyp
- Abnormal growth of tissue that is still benign and polyclonal. Some polyps tend in time to develop a malignant clone of cells.
- Polypeptide
- Molecule consisting of amino acids linked together in a single chain. Proteins are made of one or more polypeptides. [
More] [polypeptide antibiotics]
- Polyploidy
- Having 3 or more complete (=haploid) sets of chromosomes.
- Polysaccharide
- Carbohydrate (e.g., starch, cellulose) that is made up of 3 or more monosaccharides linked together. [More]
- Polysome
- [in protein synthesis] [Picture]
- Polytene
- Used to describe the multistranded ("giant") interphase chromosomes found in certain metabolically active cells of insects.
- Pongid
- Group of primates to which the great apes (e.g., chimpanzee, gorilla, orangutan) belong.
- Pons
- Population
- All the members of a single species present in a defined area.
- Porphyria
- Inheritance
- Positron-emission tomography (PET)
- Potential
- [action potential] [resting potential]
- PPB
- Parts per billion.
[More]
- PPM
- Parts per million.[More]
- PPT
- Parts per trillion.
[More]
- Prader-Willi syndrome
- An inherited disorder of genomic imprinting. [More]
- Precursor
- Substance from which another substance is formed.
- Precursor activation
- The activation of the last enzyme in a metabolic pathway by the substrate of the first enzyme in that pathway. [Discussion]
- Predation
- Living by devouring other organisms.
- Pregnancy
- [in humans] [hormones]
- Pre-messenger RNA (pre-mRNA)
- [Discussion]
- Primary host
- Host normally used by a parasite during the adult stage of its life cycle.
- Primary structure
- [Protein]
- Primary transcript
- The original RNA molecule synthesized by transcription of a eukaryotic gene. Further processing of the primary transcript produces the final mRNA or tRNA or rRNA molecule.The primary transcript of mRNA molecules is also called a pre-mRNA molecule.[More]
- Primitive
- Similar to that occurring in the early evolutionary history of the structure or organism in question.
- Producer
- An organism that can synthesize organic molecules from inorganic ones (i.e., an autotroph). Producers start food chains.
- Progesterone
- A steroid hormone vital for the establishment and maintenance of pregnancy. [More]
- Progestin
- Any steroid that mimics the effects of progesterone.
- Prokaryote
- An organism, one of the bacteria, whose cell contains neither a membrane-bound nucleus nor other membrane-bound organelles such as mitochondria and plastids. 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.[part of response element] [bacterial promoters]
- Pronucleus
- The sperm nucleus and egg nucleus within the fertilized egg before their fusion to form the diploid zygote nucleus.[More]
- Prophase
- [mitosis][meiosis I]
- Prostaglandin
- Any of a number of 20-carbon organic acids that are synthesized in the body from unsaturated fatty acids and are responsible for a variety of metabolic activities. [role in birth] [role in allergies plus graphic]
- 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.
- Protein
- Macromolecule composed of one or more polypeptides. Often associated with other molecules (e.g., carbohydrates and lipids) and ions.
[More] [Synthesis] [kinesis]
- Proteinase
- Enzyme that hydrolyzes the peptide bonds of proteins.
- Prothallus
- Protist
- Eukaryotes that are either unicellular or, if multicellular, lack the variety of specialized cells and tissues characteristic of plants and animals.
- 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.
- Protozoan
- A unicellular, heterotrophic, often motile, eukaryote. The amoeba is a familiar example.
- Proximal
- Situated near the place of origin or attachment.
- Prozac
- PSA
- Prostate specific antigen
- Pseudoautosomal region
- A region on the X and Y chromosomes where pairing (synapsis) occurs and carrying homologous genes so that two copies of the gene are present in males as well as females. There are at least two pseudoautosomal regions in humans. Genes in them are inherited like any other autosome (accounting for the name); that is, males can inherit an allele originally present on the X chromosome of their father and females can inherit an allele originally present on the Y chromosome of their father. [More]
- Psychedelic drugs
- Pulmonary system, human
- Pupa
- Stage, usually dormant, between the larva and the adult of insets having complete metamorphosis.
- Pupil
- of human eye
- Purine
- Double-ring, nitrogen-containing base that is a component of nucleic acids and several other biologically active substances. Adenine (A) and guanine (G) are purines. [Structures] [analogs used as immunosuppressants]
- Pyrimidine
- Single-ring, nitrogen-containing base that is a component of nucleic acids. Thymine (T), cytosine (C), and uracil (U) are pyrimidines.
[Structures]