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A

ABC model of the control of flowering
abl
[gene]
ABP1
Auxin-binding protein 1
Abscisic acid (ABA)
Plant hormone.
Abscission
Absorption spectrum
Electromagnetic spectrum whose intensity at each wavelength is a measure of the amount of energy at that wavelength that has passed through a selectively absorbing substance.
Acetylcholine
Substance secreted at the ends of many neurons. A neurotransmitter. [More] [At neuromuscular junction]
Acid
Molecule or ion that liberates protons, usually in water. [Discussion]
Acid rain
Rain more acid than normal (below pH 5.6). [More]
ACTH
adrenocorticotropic hormone
Actin filaments
[Discussion] [in cytokinesis] [in skeletal muscle]
Action potential
Action spectrum
Rate of physiological activity plotted against wavelength of light.
Active transport
Transfer of a molecule or ion across a cell membrane against its concentration gradient. Requires energy. [Discussion]
Activins
[in embryonic development] [sex hormones]
Acute lymphoblastic leukemia (ALL)
[More]
Acute myelogenous leukemia (AML)
Adaptation
Any characteristic of an organism that contributes to its survival in its environment.
Adaptive radiation
Evolution, from a single ancestral species, of a variety of descendant species adapted to different ways of life.
Adeno-associated virus (AAV).
As vector for somatic gene therapy.
Addison's disease
Adenine
[structure]
Adenosine deaminase (ADA)
and severe combined immunodeficiency (SCID)
Adenylyl cyclase
[and peptide hormones] [and odorant receptors]
ADH
antidiuretic hormone
Adherens junctions
Adhesion
Force of attraction between unlike molecules.
Adipose tissue
Fat. [More] [secretion of leptin by]
Adrenal glands
[Hormones of]
Adrenaline
Hormone produced by the adrenal glands that mobilizes the body to meet sudden stress. In the U.S., it is often called epinephrine. Adrenalin (without the e) is a trade name. [More]
Adrenocorticotropic hormone
ACTH
Adventitious root
Root that arises from a stem or leaf.
Aerobic
Requiring the presence of free oxygen.
AGAMOUS (AG)
Agent Orange
Mixture of herbicides sprayed by the U.S. military in VietNam. [More] [dioxin content]
Agonist
Drug that mimics the action of another.[Example]
AIDS
Acquired immunodeficiency syndrome. [and CD4 T cells] [HIV-1] [role of apoptosis]
Alanine
One of the 20 amino acids used in the synthesis of proteins. [Structure]
Aldosterone
Alga
A photosynthetic eukaryote generally found in damp or aquatic locations.
ALH84001
Martian meteorite. [More]
Alkylation
Addition of a carbon-containing group, such as a methyl or ethyl group, to another molecule.
Allantois
Allele
Alternative version of a gene.
Allergen
An antigen that provokes an allergic response.
Allergy
An exaggerated response to a normally harmless material; a hypersensitivity. [Discussion]
Allograft
Graft of tissue between genetically different members of the same species. [More]
Allopatric
Refers to populations living in separate, usually adjacent, geographic areas. If gene flow between adjacent populations is sufficiently low, they may evolve into separate races (= subspecies) and, ultimately, into separate species.
Allosteric
Refers to a change in the properties (usually including shape) of a protein following the binding of another molecule to the protein. [Example]
Allozyme
Allelic version of an enzyme. Heterozygotes synthesize both versions of the enzyme, which often can be distinguished by their different rates of migration during electrophoresis. If the enzyme is a homodimer, heterozygotes will synthesize three versions: AA, Aa, and aa.
Alpha helix
[in proteins]
Alternation of generations
[Discussion] [in ferns] [in mosses]
Alu sequence
One type of repetitive DNA consisting of a sequence of about 300 base pairs with some 300,000 copies in the human genome. The sequence is recognized by the restriction enzyme AluI.
Aluminum
Metallic element (Al). [More]
Ames Test
In vitro test for determining if a chemical is a mutagen. [More]
Amino acid
Monomer used in the assembly of proteins. [More]
Aminoglycosides
Aminopeptidase
Amino terminal
The end of a polypeptide with a free amino group. Synthesis of polypeptides proceeds from the amino terminal to the carboxyl terminal. [view]
AML
acute myelogenous leukemia
Ammonium ion
Amniocentesis
Removal of amniotic fluid from a pregnant woman in order to study its composition and/or culture the fetal cells contained in it.
Amnion
Amniota
All the vertebrates whose embryo is enveloped in an amnion: reptiles, birds, and mammals. [More]
AMPA receptors
Amphetamine
A drug that is similar in molecular structure to adrenaline and noradrenaline and shares their stimulatory properties. [Discussion]
Amphiphilic
Used to describe molecules containing both polar (hydrophilic) and apolar (hydrophobic) groups. Sodium stearate (a soap) is amphiphilic.
amygdala
Amylase
An enzyme that digests (hydrolyzes) starch. [pancreatic amylase]
Amylopectin
Amylose
Anabolic steroid
One of a number of synthetic steroids that, among other effects, seem to promote anabolism and hence an increase in body weight. They are all close relatives of the androgen, testosterone. [More]
Anabolism
Constructive metabolism in which complex substances are synthesized from simpler ones. [ More ]
Anaerobic
Not requiring the presence of free oxygen.
Analogous
Of structures (e.g., molecules, organs) in different species having similar function(s) but inherited from different precursors.
Anaphase
[mitosis][meiosis]
Anaphase Promoting Complex (APC)
in cell cycle
Anaphylaxis
[local] [systemic]
Androgen
One of a group of steroids in male vertebrates that promotes the development of their secondary sex characteristics. Testosterone is an example.
Anemia
Deficiency of red blood cells or hemoglobin in the blood. [More] [pernicious] [immune hemolytic]
Anesthetic
A substance that produces loss of sensation. [More]
Aneuploid
Having one or more extra (or fewer) chromosomes than the normal diploid (2n) set (e.g., 2n+1, 2n-1). [trisomy 21] [X chromosomes]
Angelman syndrome
An inherited disorder of genomic imprinting. [More]
Angiosperms
The flowering plants. [Discussion].
Angiostatin
Angiotensin
Angstrom (Å)
[defined]
Aniridia
[human gene]
Antenna pigments
[in photosynthesis]
Antennapedia (Antp)
Drosophila selector gene.[see encoded homeodomain]
Anther
Antheridia
[in ferns] [in mosses]
Antibiotics
[discussion]
Antibody
A protein that unites specifically with a particular antigen.
[Structures] [3D view]
Anticodon
The group of 3 adjacent nucleotides on a transfer RNA (tRNA) molecule that pairs with a complementary codon on a messenger RNA (mRNA) molecule. [More]
Antidepressant drugs
Antidiuretic hormone
ADH
Antigen
Macromolecule (usually a protein or polysaccharide) which, when introduced into the body of a vertebrate to which it is foreign, stimulates the formation of antibodies and/or of immune T cells. [Receptors on B and T cells][presentation to T lymphocytes]
Antigenic determinant
A part of an antigen to which the antibody binds. Also called an epitope.
Antigenic drift
of influenza viruses
Antiport pump.
Antisense strand
The strand of DNA used as the template for synthesizing RNA. [More] [Antisense oligodeoxynucleotides (ODNs)] [Antisense RNA]
Antiserum
Serum containing induced antibodies.
Antithymocyte globulin (ATG)
Antitoxin
Mixture of antibodies formed in response to injections of a toxin or toxoid.
APETALA
Apical dominance
Apomixis
Reproduction by seeds that have developed asexually rather than sexually.
Apoptosis
Programmed cell death. [Discussion]
Aquaporin
Aqueous humor
of human eye
Aquifer
A layer in the earth that is saturated with water.
Arabidopsis thaliana
[diploid number] [genome size]
Arachidonic acid
Archaea
Third kingdom of life. example: Methanococcus jannaschii
Archegonia
[in ferns] [in mosses]
Archenteron
Central cavity of the gastrula of an embryo which eventually becomes the alimentary canal. [view]
ARF1
Auxin response factor 1
Arginine
[structure]
Arteriosclerosis
Arthropod
A member of the phylum of invertebrate animals characterized by jointed legs and exoskeleton. Includes insects, arachnids, and crustaceans.
Ascorbic acid
vitamin C
Ascus
Tubular spore sac of ascomycetes in which eight (usually) ascospores are produced.
Asexual reproduction
Formation of a new individual from the cell(s) of a single parent.
Asparagine
[structure]
Aspartic acid
[structure]
Assortative mating
Mating between similar individuals; therefore a form of nonrandom mating.
Asthma
Discussion
Atherosclerosis
[More] [and cholesterol]
Atom
Smallest particle of an element that can combine with other elements. [More]
Atomic number
Atomic weight unit
One-twelfth the weight of an atom of carbon-12. Also called the dalton. [More]
Atopy
ATP (adenosine triphosphate)
[structure][yield in cellular respiration]
ATP synthase
[in photosynthesis][in mitochondria]
Atrial natriuretic peptide
ANP
Autocrine
Refers to the influence on a cell of molecules synthesized by the same cell. [More]
Autoimmune disease
Disease characterized by the mounting of an immune response against constituents of an individual's own tissues. Some examples: [Insulin dependent diabetes mellitus (IDDM)] [Immune hemolytic anemia] [Immune thrombocytopenic purpura] [Myasthenia gravis (MG)] [Multiple sclerosis (MS)] [Rheumatoid arthritis] [Systemic lupus erythematosus (SLE)] [Thyrotoxicosis (Graves' disease)]
Autonomic nervous system
in humans
Autosome
Any chromosome that is not a sex chromosome.
Autotrophic
Capable of synthesizing organic molecules from inorganic raw materials.[Photosynthesis]
Auxin
Plant hormone that, among other effects, promotes cell elongation. [Discussion]
[Auxin-binding protein 1 (ABP1)] [Auxin response factor 1 (ARF1)]
Several herbicides (2,4-D for example) have molecular structures similar to auxin.
Avogadro's number
Axon
Single extension of a neuron (usually long and often branched) which conducts nerve impulses (action potentials) away from the dendrites or cell body.
Azathioprine
Purine analog used as an immunosuppressant.
AZT
Azidodeoxythymidine. Drug used to treat HIV infection. Has no 3' OH, thus terminating DNA synthesis by reverse transcriptase. Also called zidovudine. [Structure]
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