Glossary

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Jacqui
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305079
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Glossary
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2015-07-11 23:43:48
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Glossary for Biology
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  1. A (amino acid) site
    One of three binding sites for tRNA during translation, it holds the tRNA carrying the next amino acid to be added to the polypeptide chain; A stands for aminoacyl-tRNA site.
  2. Activated precursor
    Energised forms of monomers (or building blocks) used to make a polymer. For example ATP is an activated precursor used in RNA synthesis.
  3. Activator
    A transcription factor that binds to an enhancer and stimulates transcription of a gene.
  4. Active site
    The specific portion of an enzyme that attaches to the substrate by means of weak chemical bonds.
  5. Adenine
    (A) a nitrogenous base of the purine family, found in nucleotides.
  6. Allele
    An alternative form of a gene.
  7. Allosteric Site
    A specific receptor site on some part of an enzyme molecule remote from the active site.
  8. Alternative RNA splicing
    A type of regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript depending on which RNA segments are treated as exons and which as introns.
  9. Amino acid
    An organic molecule possessing both carboxyl and amino groups. Amino acids serve as the monomers of proteins.
  10. Amino acid activation
    The attachment of an amino acid to its tRNA that involves an input of energy from ATP. This occurs prior to polypeptide synthesis.
  11. Amino group
    A functional group that consists of a nitrogen atom bonded to two hydrogen atoms; can act as a base in solution, accepting a hydrogen ion and acquiring a charge of +1.
  12. Aminoacyl-tRNA synthetase
    An enzyme that joins each amino acid to the correct tRNA.
  13. Amphipathic molecule
    A molecule that has both a hydrophilic region and a hydrophobic region.
  14. Anaphase
    The fourth subphase of mitosis, in which the chromatids of each chromosome have separated and the daughter chromosomes are moving to the poles of the cell.
  15. Animal cloning
    Production of an animal that is genetically identical to its parent without the involvement of meiosis or sex.
  16. Anti-parallel
    Term used to describe how the two strands of DNA in a double helix run in opposite directions (whilst one is 5’ to 3’, the other is 3’ to 5’).
  17. Anticodon
    A specialized base triplet at one end of a tRNA molecule that recognizes a particular complementary codon on an mRNA molecule.
  18. Antisense
    The name given to a nucleic acid strand that is complementary to mRNA or the DNA coding strand.
  19. Aqueous solution
    A solution in which water is the solvent.
  20. Asexual reproduction
    Reproduction involving only one parent which results in genetically identical offspring by mitotic cell division.
  21. Atom
    The smallest unit of matter that retains the properties of an element.
  22. Autosome
    A chromosome that is not directly involved in sex determination.
  23. Bacteriophage
    A virus that infects bacteria. Also called phage.
  24. Base pairing
    Term used to describe the association, by hydrogen bonding, between nitrogenous bases (A with G and C with T or U) in a DNA or RNA molecule.
  25. Binary fission
    The type of cell division by which prokaryotes reproduce. Each dividing daughter cell receives a copy of the single parental chromosome.
  26. Building block principle
    Describes how the large complex molecules found in living systems are quite simple in their basic construction, being polymers made of a chain of monomeric ‘building blocks’.
  27. Capsid
    The protein coat of a virus that encloses the nucleic acid.
  28. Carbohydrate
    A sugar (monosaccharide) or one of its dimers (disaccharides) or polymers (polysaccharides).
  29. Carboxyl group
    A functional group present in organic acids and consisting of a single carbon atom double-bonded to an oxygen atom and also bonded to a hydroxyl group.
  30. Carrier
    An individual who is heterozygous with one potentially harmful recessive allele
  31. Cell fractionation
    The disruption of a cell and separation of its organelles by centrifugation.
  32. Cell membrane
    A lipid bilayer, containing proteins, that surrounds cells and keeps the cellular contents together. May have additional roles in regulating the flow of materials in and out of the cell, communicating information and carrying out specific biochemical functions.
  33. Cell theory
    All living organisms are composed of cells. The cell is the basic unit of life. Cells arise by division of pre-existing cells.
  34. Cell wall
    A protective layer external to the plasma membrane in plant cells, bacteria, fungi, and some protists. In plant cells, the wall is formed of cellulose fibers embedded in a polysaccharide-protein matrix. The primary cell wall is thin and flexible, whereas the secondary cell wall is stronger and more rigid and is the primary constituent of wood.
  35. Central vacuole
    A membranous sac in a mature plant cell with diverse roles in reproduction, growth, and development.
  36. Centriole
    A structure in an animal cell composed of cylinders of microtubule triplets arranged in a 9 + 0 pattern. An animal cell usually has a pair of centrioles involved in cell division.
  37. Centromere
    The centralized region joining two sister chromatids.
  38. Character
    A heritable feature (e.g. flower colour) that differs between individuals.
  39. Chloroplast
    An organelle found only in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water.
  40. Chromatin
    The complex of DNA and proteins that makes up a eukaryotic chromosome. When the cell is not dividing, chromatin exists as a mass of very long, thin fibers that are not visible with a light microscope.
  41. Chromosome
    A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins. See chromatin.
  42. Cis/trans face
    Alternative (official) names for the receiving (cis) and shipping (trans) faces of the Golgi apparatus.
  43. Clone
    A population of genetically identical cells. For example those containing identical recombinant DNA molecules.
  44. Co-dominance
    Where both alleles are equally evident in the phenotype
  45. Codon
    A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code.
  46. Confocal microscope
    A special type of fluorescence microscope that allows you to see objects in 3 dimensions.
  47. Conformation
    Term used to describe the 3-dimensional shape of a protein.
  48. Conjugation
    The direct transfer of genes between two cells that are temporarily joined
  49. Constitutive
    Term used to describe the expression of a gene that is expressed all the time.
  50. Control elements
    Segments of noncoding DNA that help regulate transcription of a gene by binding proteins called transcription factors.
  51. Control experiment
    Experiment set up to ensure that only one variable is tested when performing an experiment to test a hypothesis.
  52. Corepressor
    A molecule (e.g. tryptophan) that binds to an allosteric repressor protein and enables it to prevent transcription.
  53. Covalent bond
    A type of strong chemical bond in which two atoms share one pair of valence electrons.
  54. Cyanobacteria
    Photosynthetic oxygen-producing bacteria.
  55. Cytokinesis
    The division of the cytoplasm to form two separate daughter cells immediately after mitosis.
  56. Cytoplasm
    The entire contents of the cell, exclusive of the nucleus, and bounded by the plasma membrane.
  57. Cytosine
    (C), a nitrogenous base of the pyrimidine family, found in nucleotides.
  58. Cytoskeleton
    A network of microtubules, microfilaments, and intermediate filaments that branch throughout the cytoplasm and serve a variety of mechanical and transport functions.
  59. Cytosol
    The semifluid portion of the cytoplasm.
  60. DNA Fingerprint/profile
    A pattern of fragments that differs between genomes due to differences in the DNA sequence.
  61. DNA hybridisation
    The pairing of two DNA molecules with complementary base sequences by hydrogen bonding.
  62. DNA ligase
    A linking enzyme essential for DNA replication; catalyses the covalent bonding of the 3' end of a new DNA fragment to the 5' end of a growing chain.
  63. DNA methylation
    The addition of methyl groups (-CH3) to bases of DNA after DNA synthesis; may serve as a long-term control of gene expression.
  64. DNA polymerase
    An enzyme that catalyses the elongation of new DNA at a replication fork by the addition of nucleotides to the existing chain.
  65. Denaturation
    For proteins, a process in which a protein unravels and loses its native conformation, thereby becoming biologically inactive. For DNA, the separation of the two strands of the double helix. Denaturation occurs under extreme conditions of pH, salt concentration, and temperature.
  66. Deoxyribonucleic acid (DNA)
    A double-stranded, helical nucleic acid molecule capable of replicating and determining the inherited structure of a cell's proteins.
  67. Dihybrid cross
    A breeding experiment in which parental varieties differing in two characters are mated (e.g. seed colour and seed shape).
  68. Diploid
    A cell containing two sets of chromosomes one inherited from each parent.
  69. Disaccharide
    A double sugar, consisting of two monosaccharides joined by dehydration synthesis.
  70. Discontinuous synthesis
    Synthesis of DNA that occurs in short fragments on the lagging strand. The fragments are joined together by DNA ligase.
  71. Discovery science
    Descriptive science that involves making careful and repeatable measurements or observations.
  72. Dominant allele
    The allele that is fully expressed in the phenotype of a heterozygote.
  73. Double helix
    The form of native DNA, referring to its two adjacent polynucleotide strands wound into a spiral shape.
  74. Duplication
    A piece of a chromosome is repeated.
  75. Electron
    A subatomic particle with a single negative charge; one or more electrons move around the nucleus of an atom.
  76. Electron configuration
    The distribution of electrons in an atom's electron shells.
  77. Electron microscopy
    A microscope that focuses an electron beam through a specimen, resulting in resolving power a thousandfold greater than that of a light microscope. A transmission electron microscope (TEM) is used to study the internal structure of thin sections of cells. A scanning electron microscope (SEM) is used to study the fine details of cell surfaces.
  78. Element
    Any substance that cannot be broken down to any other substance.
  79. Elongation
    The stage of translation in which the main part of protein synthesis occurs (the polpeptide is elongated as more amino acids are added).
  80. Endocytosis
    The cellular uptake of macromolecules and particulate substances by localized regions of the plasma membrane that surround the substance and pinch off to form an intracellular vesicle.
  81. Endomembrane system
    The collection of membranes inside and around a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles.
  82. Endoplasmic reticulum
    An extensive membranous network in eukaryotic cells, continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-free (smooth) regions.
  83. Endosomes
    Intracellular organelles originating from endocytosis.
  84. Endosymbiotic theory
    A theory about the origin of the eukaryotic cell maintaining that the forerunners of eukaryotic cells were symbiotic associations of prokaryotic cells living inside larger prokaryotes.
  85. Enhancer
    A DNA sequence that recognizes certain transcription factors that can stimulate transcription of nearby genes.
  86. Enzyme
    A protein serving as a catalyst, a chemical agent that changes the rate of a reaction without being consumed by the reaction.
  87. Epistasis
    When one gene alters the expression of another gene.
  88. Euchromatin
    The more open, unraveled form of eukaryotic chromatin that is available for transcription.
  89. Eukaryotic cell
    A type of cell with a membrane-enclosed nucleus and membrane-enclosed organelles, present in protists, plants, fungi, and animals; also called eukaryote.
  90. Exocytosis
    The cellular secretion of macromolecules by the fusion of vesicles with the plasma membrane.
  91. Exon
    A coding region of a eukaryotic gene. Exons, which are expressed, are separated from each other by introns.
  92. Fat (triacylglycerol)
    A biological compound consisting of three fatty acids linked to one glycerol molecule.
  93. Fatty acid
    A long carbon chain carboxylic acid. Fatty acids vary in length and in the number and location of double bonds; three fatty acids linked to a glycerol molecule form fat.
  94. Fluid mosaic model
    The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of individually inserted protein molecules drifting laterally in a fluid bilayer of phospholipids.
  95. Fluorescence microscope
    A light microscope that uses light with a shorter wavelength than visible light (UV) to excite dyes that then emit light (fluorescence) at a longer wavelength.
  96. Frameshift mutation
    An insertion or deletion mutation which disrupts the grouping of nucleotides into the correct codons.
  97. Functional group
    A specific configuration of atoms commonly attached to the carbon skeletons of organic molecules and usually involved in chemical reactions.
  98. G1 phase
    The first growth phase of the cell cycle, consisting of the portion of interphase before DNA synthesis begins.
  99. G2 phase
    The second growth phase of the cell cycle, consisting of the portion of interphase after DNA synthesis occurs.
  100. Gene
    A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses).
  101. Gene cloning
    Producing many identical copies of a gene.
  102. Genetic code
    The dictionary that translates between the language of nucleotide sequence and the language of amino acid sequence.
  103. Genetic drift
    Changes in the gene pool of a small population due to chance.
  104. Genetic engineering
    Manipulation of genetic information for some purpose. Also known as Recombinant DNA Technology.
  105. Genetic map
    An ordered list of genetic loci along a chromosome.
  106. Genetic recombination
    General term for the production of offspring that combine traits of the two parents.
  107. Genome
    An organism's genetic material.
  108. Genomic library
    A collection of vector-based clones containing DNA representative of a organism?s genome.
  109. Genomics
    The study of genomes and genes based on DNA sequencing.
  110. Genotype
    The genetic components of an organism.
  111. Glycosylation
    The covalent addition of carbohydrates (usually oligosaccharides) to proteins in the ER and Golgi apparatus.
  112. Golgi apparatus
    An organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and route products of the endoplasmic reticulum.
  113. Guanine
    (G), a nitrogenous base of the purine family, found in nucleotides.
  114. Haploid
    A cell containing only one set of chromosomes.
  115. Helicase
    An enzyme that untwists the double helix of DNA at the replication forks.
  116. Hemizygous
    Genotype description for X-linked genes in males who only have one allele.
  117. Heterochromatin
    Nontranscribed eukaryotic chromatin that is so highly compacted that it is visible with a light microscope during interphase.
  118. Heterozygous
    Having two different alleles for a given trait.
  119. Histone
    A small protein with a high proportion of positively charged amino acids that binds to the negatively charged DNA and plays a key role in its chromatin structure.
  120. Histone acetylation
    The attachment of acetyl groups to certain amino acids of histone proteins.
  121. Homologous chromosomes
    A pair of chromosomes having the same genes in the same positions. One inherited from the mother one from the father.
  122. Homozygous
    Having two identical alleles for a given trait.
  123. Human genome project
    An international project to map and sequence the entire DNA of the human genome.
  124. Hydrogen bond
    A type of weak chemical bond formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule.
  125. Hydrophilic
    Having an affinity for water.
  126. Hydrophobic
    Having an aversion to water; tending to coalesce and form droplets in water.
  127. Hydrophobic interaction
    A type of weak chemical bond formed when molecules that do not mix with water coalesce to exclude the water.
  128. Hypothesis
    A possible explanation for an observation that is testable by experiment.
  129. Hypothetico-deductive science
    Involves making a hypothesis to explain observations and testing the hypothesis by experiment
  130. Incomplete dominance
    Where heterozygotes have a phenotype intermediate between those of individuals homozygous for the two alleles.
  131. Inducer
    A specific small molecule that inactivates the repressor in an operon.
  132. Inducible operon
    An operon whose default state is OFF, e.g. the lac operon. Transcription is stimulated when a small molecule (inducer) interacts with a regulatory molecule.
  133. Initiation
    Term used to describe the beginning of protein synthesis in translation, and of RNA synthesis in transcription.
  134. Initiator codon
    The first codon (usually AUG) used in translation that is recognised by a special initiator tRNA.
  135. Integral protein
    Typically transmembrane proteins with hydrophobic regions that completely span the hydrophobic interior of the membrane.
  136. Interphase
    The period in the cell cycle when the cell is not dividing. During interphase, cellular metabolic activity is high, chromosomes and organelles are duplicated, and cell size may increase. Interphase accounts for 90% of the cell cycle.
  137. Intron
    A noncoding, intervening sequence within a eukaryotic gene.
  138. Ionic bond
    A chemical bond resulting from the attraction between oppositely charged ions.
  139. Kinetochore
    A specialized region on the centromere that links each sister chromatid to the mitotic spindle.
  140. Lagging strand
    A discontinuously synthesized DNA strand that elongates in a direction away from the replication fork.
  141. Leading strand
    The new continuous complementary DNA strand synthesized along the template strand in the mandatory 5' 3' direction.
  142. Ligation
    Joining of two DNA molecules by forming covalent bonds between the free end of their sugar-phosphate backbones.
  143. Light microscope
    An optical instrument with lenses that refract (bend) visible light to magnify images of specimens.
  144. Limit of resolution
    The minimum distance between which two objects can be discriminated.
  145. Linked genes
    Genes that are located on the same chromosome
  146. Lipid
    One of a family of compounds, including fats, phospholipids, and steroids, that are insoluble in water.
  147. Lipid bilayer
    An assembly of two layers of amphipathic phopholipids found in membranes, in which the polar head groups are oriented outwards and the non-polar fatty acid tails are buried in the interior.
  148. Locus
    The particular position in a chromosome where a gene is placed.
  149. Lysogenic cycle
    A type of phage reproduction in which the viral genome becomes incorporated into the host bacterial chromosome.
  150. Lysosome
    A membrane-enclosed bag of hydrolytic enzymes found in the cytoplasm of eukaryotic cells.
  151. Lytic cycle
    A type of phage reproduction in which many new phage particles are released by bursting of the host cell.
  152. Macromolecule
    A giant molecule formed by the joining of smaller molecules, usually by a condensation reaction. Polysaccharides, proteins, and nucleic acids are macromolecules.
  153. Magnification
    Appearing to make objects look larger such that very small objects such as cells can be seen by the human eye.
  154. Meiosis
    A two-stage cell division that results in cells with half the number of chromosomes than the original cell.
  155. Messenger RNA (mRNA)
    A type of RNA, synthesized from DNA, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein.
  156. Metaphase
    The third subphase of mitosis, in which the spindle is complete and the chromosomes, attached to microtubules at their kinetochores, are all aligned at the metaphase plate.
  157. Microarray
    A miniature glass or silicon device for testing the hybridisation of thousands of nucleic acid molecules simultaneously. Also known as a DNA chip.
  158. Microsatellite
    Repeated sequences (of 1-6 bp) that occur in the eukaryotic genome. Also known as Short Tandem Repeats (STRs).
  159. Missense mutation
    A base-pair substitution that alters an amino acid codon so that it codes for a different amino acid.
  160. Mitochondrion
    (plural, mitochondria) An organelle in eukaryotic cells that serves as the site of cellular respiration.
  161. Mitosis
    A process of nuclear division in eukaryotic cells conventionally divided into five stages: prophase, prometaphase, metaphase, anaphase, and telophase. Mitosis conserves chromosome number by equally allocating replicated chromosomes to each of the daughter nuclei.
  162. Mitotic spindle
    An assemblage of microtubules and associated proteins that is involved in the movements of chromosomes during mitosis.
  163. Molecular breeding
    The use of DNA markers in conventional breeding.
  164. Molecule
    Two or more atoms held together by covalent bonds.
  165. Monohybrid cross
    A breeding experiment that uses parental types which differ only in a single character.
  166. Monomer
    The subunit that serves as the building block of a polymer.
  167. Monosaccharide
    The simplest carbohydrate, active alone or serving as a monomer for disaccharides and polysaccharides. Also known as simple sugars, the molecular formulas of monosaccharides are generally some multiple of CH2O.
  168. Multiple alleles
    More than two alleles at one gene locus.
  169. Mutation
    A change in the nucleotide sequence in a cell (or virus).
  170. Nascent protein
    A partly synthesised protein (in the process of being made by translation).
  171. Negative control
    A type of control used in some experiments to check for background effects or contamination. For example in PCR a negative control containing no template DNA should not give any amplified product.
  172. Nitrogenous base
    Includes purines and pyrimidines such as adenine, cytosone, guanine, thymine and uracil that are components of nucleotides.
  173. Nonpolar covalent bond
    A type of covalent bond in which electrons are shared equally between two atoms of similar electronegativity.
  174. Nonsense mutation
    A base-pair substitution that changes an amino acid codon to a stop codon.
  175. Nuclear envelope
    The membrane in eukaryotes that encloses the nucleus, separating it from the cytoplasm.
  176. Nuclear lamina
    A netlike array of protein filaments that maintains the shape of the nucleus.
  177. Nucleic acid
    A polymer (polynucleotide) consisting of many nucleotide monomers; serves as a blueprint for proteins and, through the actions of proteins, for all cellular activities. The two types are DNA and RNA.
  178. Nucleoid
    A dense region of DNA in a prokaryotic cell.
  179. Nucleolus
    (plural, nucleoli) A specialized structure in the nucleus, formed from various chromosomes and active in the synthesis of ribosomes.
  180. Nucleoside
    An organic molecule consisting of a nitrogenous base joined to a five-carbon sugar.
  181. Nucleosome
    The basic, beadlike unit of DNA packaging in eukaryotes, consisting of a segment of DNA wound around a protein core composed of two copies of each of four types of histone.
  182. Nucleotide
    The building block of a nucleic acid, consisting of a five-carbon sugar covalently bonded to a nitrogenous base and a phosphate group.
  183. Nucleus
    • (1) An atom's central core, containing protons and neutrons.
    • (2) The chromosome-containing organelle of a eukaryotic cell.
  184. Null hypothesis
    A hypothesis expressed in the negative to avoid accusation of bias.
  185. Numerical aperture
    An expression of the resolving power of a lens that is calculated from the refractive index of the medium and the angular aperture (half the angle of light entering the lens).
  186. Oncogene
    A cancer-causing gene.
  187. Operator
    In prokaryotic DNA, a sequence of nucleotides near the start of an operon to which an active repressor can attach. The binding of the repressor prevents RNA polymerase from attaching to the promoter and transcribing the genes of the operon.
  188. Operon
    A unit of genetic function common in bacteria and phages, consisting of coordinately regulated clusters of genes with related functions.
  189. Organelle
    One of several formed bodies with specialized functions, suspended in the cytoplasm of eukaryotic cells.
  190. Origins of replication (ori)
    Sites where the replication of a DNA molecule begins.
  191. P (peptidyl) site
    One of three binding sites for tRNA during translation, it holds the tRNA carrying the growing polypeptide chain; P stands for peptidyl-tRNA site).
  192. Pedigree
    A family tree describing the inheritance of a particular character.
  193. Pentose
    A five-carbon sugar such as is found in nucleotides.
  194. Peripheral protein
    Protein appendages loosely bound to the surface of the membrane and not embedded in the lipid bilayer.
  195. Peroxisome
    A microbody containing enzymes that transfer hydrogen from various substrates to oxygen, producing and then degrading hydrogen peroxide.
  196. Pharming
    Term coined to describe the production of pharmaceutical proteins in transgenic animals.
  197. Phenotype
    The physical (observed or measured) traits of an organism.
  198. Phosphate group
    A functional group important in energy transfer.
  199. Phospholipid
    A molecule that is a constituent of the inner bilayer of biological membranes, having a polar, hydrophilic head and a nonpolar, hydrophobic tail.
  200. Plastid
    The general name for the class of plant organelles that includes the chloroplasts.
  201. Point mutation
    A mutation limited to one or a few base-pairs.
  202. Polar covalent bond
    A type of covalent bond between atoms that differ in electronegativity. The shared electrons are pulled closer to the more electronegative atom, making it slightly negative and the other atom slightly positive.
  203. Polycistronic
    "Many genes" - term used to describe a mRNA transcribed from an operon that encodes several independent polypeptides.
  204. Polygenic inheritance
    When two or more genes have an additive effect on a single phenotypic character.
  205. Polyhedral
    Having many sides.
  206. Polymer
    A long molecule consisting of many similar or identical monomers linked together.
  207. Polynucleotide
    A polymer consisting of many nucleotide monomers; serves as a blueprint for proteins and, through the actions of proteins, for all cellular activities. The two types are DNA and RNA.
  208. Polypeptide
    A polymer (chain) of many amino acids linked together by peptide bonds.
  209. Polysaccharide
    A polymer of up to over a thousand monosaccharides, formed by dehydration reactions.
  210. Pore complex
    Elaborate protein structures forming holes (pores) in the nuclear envelope.
  211. Positive control
    A control experiment that should give an expected result - designed to test that the experimental system is working correctly.
  212. Primary structure
    The level of protein structure referring to the specific sequence of amino acids.
  213. Primase
    An enzyme that joins RNA nucleotides to make the primer.
  214. Primer
    Short single-stranded DNA which when annealed to complementary DNA is a start point for synthesis.
  215. Prokaryotic cell
    A type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles; found only in the domains Bacteria and Archaea.
  216. Prometaphase
    The second subphase of mitosis, in which discrete chromosomes consisting of identical sister chromatids appear, the nuclear envelope fragments, and the spindle microtubules attach to the kinetochores of the chromosomes.
  217. Promoter
    A specific nucleotide sequence in DNA that binds RNA polymerase and indicates where to start transcribing RNA.
  218. Prophase
    The first subphase of mitosis, in which the chromatin is condensing and the mitotic spindle begins to form, but the nucleolus and nucleus are still intact.
  219. Protein
    A three-dimensional biological polymer constructed from a set of 20 different monomers called amino acids.
  220. Protist
    A diverse kingdom of unicellular eukaryotes and their relatively simple multicellular eukaryotes.
  221. Protobionts
    Aggregates of abiotically produced molecules.
  222. Purine
    One of two families of nitrogenous bases found in nucleotides. Adenine (A) and guanine (G) are purines.
  223. Pyrimidine
    One of two families of nitrogenous bases found in nucleotides. Cytosine (C), thymine (T), and uracil (U) are pyrimidines.
  224. Quaternary structure
    The particular shape of a complex, aggregate protein, defined by the characteristic three-dimensional arrangement of its constituent subunits, each a polypeptide.
  225. RNA polymerase
    An enzyme that links together the growing chain of ribonucleotides during transcription.
  226. RNA splicing
    The removal of noncoding portions (introns) of the RNA molecule after initial synthesis.
  227. Recessive allele
    The allele that is completely masked in the phenotype of a heterozygote.
  228. Recombinant DNA
    A DNA molecule made with segments from different sources.
  229. Refractive index
    A measure of the ability of a lens to deflect light into a concentrated point.
  230. Replication fork
    A Y-shaped region on a replicating DNA molecule where new strands are growing.
  231. Repressible operon
    An operon whose default state is ON, e.g. the trp operon. Transcription is inhibited when a small molecule (co-repressor) interacts with a regulatory molecule.
  232. Repressor
    A protein that suppresses the transcription of a gene.
  233. Resolving power
    A measure of the ability of a lens to discriminate between two objects.
  234. Restriction endonuclease
    An enzyme that cleaves the sugar-phosphate backbone of a DNA molecule.
  235. Retrovirus
    An RNA virus that reproduces by reverse-transcribing its RNA into DNA then inserting the DNA into the host chromosome.
  236. Reverse Transcriptase
    A retroviral enzyme that can make a DNA copy of RNA.
  237. Ribonucleic acid (RNA)
    A type of nucleic acid consisting of nucleotide monomers with a ribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and uracil (U); usually single-stranded; functions in protein synthesis and as the genome of some viruses.
  238. Ribosomal RNA (rRNA)
    The most abundant type of RNA, which together with proteins, forms the structure of ribosomes. Ribosomes coordinate the sequential coupling of tRNA molecules to mRNA codons.
  239. Ribosome
    A cell organelle constructed in the nucleolus and functioning as the site of protein synthesis in the cytoplasm; consists of rRNA and protein molecules, which make up two subunits.
  240. Ribozyme
    An RNA molecule with catalytic/enzymatic activity.
  241. Rough ER
    That portion of the endoplasmic reticulum studded with ribosomes.
  242. S phase
    The synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated.
  243. SNP
    Single nucleotide polymorphism - a single nucleotide substitution in DNA snRNP (small nuclear ribonucleoproteins) One of a variety of small particles in the cell nucleus, composed of RNA and protein molecules; functions are not fully understood, but some form parts of spliceosomes, active in RNA splicing.
  244. Scanning electron microscope (SEM)
    A microscope that uses an electron beam to scan the surface of a sample to study details of its topography.
  245. Secondary structure
    The localized, repetitive coiling or folding of the polypeptide backbone of a protein due to hydrogen bond formation between peptide linkages.
  246. Selectable marker
    A gene carried by a vector which confers a detectable phenotype eg. ampicillin resistance on a transformed cell.
  247. Semi-conservative replication
    Type of DNA replication in which the replicated double helix consists of one old strand, derived from the old molecule, and one newly made strand.
  248. Sex Chromosome
    One of the pair of chromosomes responsible for determining the sex of an individual.
  249. Sex-linked genes
    Genes which are located on the sex chromosomes (usually X in mammals).
  250. Sexual reproduction
    A type of reproduction in which the offspring have unique combinations of genes inherited from the gametes of the two parents.
  251. Signal sequence (peptide)
    A stretch of amino acids on a polypeptide that targets the protein to a specific destination in a eukaryotic cell.
  252. Silent mutation
    A base-pair substitution that alters an amino acid codon but still codes for the same amino acid due to degeneracy of the code.
  253. Single-strand binding protein
    During DNA replication, molecules that line up along the unpaired DNA strands, holding them apart while the DNA strands serve as templates for the synthesis of complimentary strands of DNA.
  254. Sister chromatids
    Replicated forms of a chromosome joined together by the centromere and eventually separated during mitosis or meiosis II.
  255. Smooth ER
    That portion of the endoplasmic reticulum that is free of ribosomes.
  256. Solute
    A substance that is dissolved in a solution.
  257. Solvent
    The dissolving agent of a solution. Water is the most versatile solvent known.
  258. Spindle microtubules
    Protein cables used to achieve chromosome separation and cell elongation during cell division.
  259. Stem cells
    Cells that have the ability to continuously divide in culture and develop into various kinds of tissue.
  260. Stromatolites
    Fossilised mats of ancient prokaryotes found in banded domes of sedimentary rock.
  261. Substrate
    The reactant on which an enzyme works.
  262. T-DNA
    • A specific portion of the tumour-inducing (Ti) plasmid from Agrobacterium that is transferred and integrated into the plant genome.
    • Telomerase
    • An enzyme that catalyzes the lengthening of telomeres. The enzyme includes a molecule of RNA that serves as a template for new telomere segments.
  263. Telomere
    The protective structure at each end of a eukaryotic chromosome. Specifically, the tandemly repetitive DNA at the end of the chromosome's DNA molecule. See also repetitive DNA.
  264. Telophase
    The fifth and final subphase of mitosis, in which daughter nuclei are forming and cytokinesis has typically begun.
  265. Template strand
    The DNA strand that provides the template for ordering the sequence of nucleotides in an RNA transcript.
  266. Termination
    The final phase of translation in which a stop codon is recognised by protein release factors. Also used in the context of transcription.
  267. Terminator
    A special sequence of nucleotides in DNA that marks the end of a gene. It signals RNA polymerase to release the newly made RNA molecule, which then departs from the gene.
  268. Tertiary structure
    Irregular contortions of a protein molecule due to interactions of side chains involved in hydrophobic interactions, ionic bonds, hydrogen bonds, and disulfide bridges.
  269. Testcross
    Breeding of an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype.
  270. Thymine
    (T), a nitrogenous base of the pyrimidine family, found in nucleotides.
  271. Topoisomerase
    An enzyme that alters the degree of twisting or supercoiling of a DNA double helix.
  272. Trait
    Each variant of a character (e.g. pink or white flowers).
  273. Transcription
    The synthesis of RNA on a DNA template.
  274. Transcription factor
    A regulatory protein that binds to DNA and stimulates transcription of specific genes.
  275. Transduction
    The transfer of genes from a donor cell to a recipient cell by a virus.
  276. Transfer RNA (tRNA)
    An RNA molecule that functions as an interpreter between nucleic acid and protein language by picking up specific amino acids and recognizing the appropriate codons in the mRNA.
  277. Transformation
    The process of gene transfer in which a bacterial cell takes up DNA from the surroundings
  278. Transgene
    A foreign gene that has been moved from one organism to another using gene manipulation (recombinant DNA) techniques.
  279. Transgenic organism
    An organism into which a gene(s) from another species has been incorporated.
  280. Translation
    The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule. There is a change of "language" from nucleotides to amino acids.
  281. Transmission electron microscope (TEM)
    A microscope that passes an electron beam through very thin sections, primarily used to study the internal ultrastructure of cells.
  282. True breeding
    When all offspring are of the same variety.
  283. Uracil (U)
    a nitrogenous base of the pyrimidine family, found in nucleotides.
  284. Van der Waals interactions
    Weak attractive forces between molecules or atoms that are close together, caused by temporary fluctuations of the positions of electrons.
  285. Vector
    A DNA molecule capable of replicating in a host cell into which foreign DNA is inserted.
  286. Watson-Crick model
    A model of the structure of double-stranded DNA in which purines (A or G) are based-paired with pyrimidines (T or C).
  287. Weak interactions
    Non-covalent bonds or other interactions that result in weak attraction between molecules. Includes ionic interactions, Van der Waals interactions, hydrogen bonds and hydrophobic interactions.
  288. Wobble
    A violation of the base-pairing rules in that the third nucleotide (5' end) of a tRNA anticodon can form hydrogen bonds with more than one kind of base in the third position (3' end) of a codon.
  289. microevolution
    A change in the gene pool of a population from generation to generation.

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