Glossary of Terms used in Genetics and Molecular Biology

Active site: Part of a protein that carries out the typical function of the protein itself.

Adenine: One of the four bases found in DNA and RNA, that pairs with thymine (or uracil) by means of three hydrogen bonds.

Allele: An allele is half of a pair of genes coded for the same protein, present in two homologous chromosomes. (Example: the two X chromosomes carry a pair of alleles for FVIII, one in each chromosome).

Ampicillin: An antibiotic like penicillin, which kills growing bacteria.

Amplification: Production of many identical copies of DNA.

Anion: Substance with a negative electrical charge.

Antibiotic: A substance produced by fungi or bacteria which can inhibit the growth of other microorganisms; this ability makes them useful in the treatment of bacterial infections.

Antibody: A class of proteins produced by the immune system that recognizes and binds to foreign substances in the body.

Anticodon: A triplet of nucleotides complementary to the codon (or triplet) in mRNA, corresponding to an amino acid of a nascent protein.

Antigen: Foreign substance to the organism that induces the defensive production of specific antibodies.

Antihaemophilic globulin: An alternative name for factor VIII, indicating the rounded structure and the pro-coagulant function of the protein.

Asparagine: One of the 20 amino acids that occur in proteins; asparagine can be modified by attachment of sugar molecules.

B

Bacteria: Unicellular micro-organisms with a single chromosome, that normally replicate by binary division; they can cause infections in man (e.g. pulmonitis) and are combatted with antibiotics.

Base pair: see Pairing rule.

Biotechnology: Technology that exploits the biosynthetic capacities of microorganisms and other cells in manufacturing processes.

C

Carrier: Person whose genetic material contains a mutant gene that does not show in the phenotype, because it is masked by the healthy gene present in the homologous chromosome.

Cation: Substance with a positive electrical charge (e.g. Na+).

cDNA: Complementary synthesis DNA, transcribed by a mRNA by means of the enzyme reverse transcriptase with the sequence of nucleotides corresponding to the sequence of amino acids of a protein.

Cell: The basic unit of all living organisms. Cells contain cytoplasm bounded by a membrane and metabolically active organelles and genetic material, free in the cytoplasm of simple organisms (prokaryotes, such as bacteria) and enclosed in a nucleus in higher organisms (eukaryotes, such as animals and plants).

Cell division: Process of duplication of a cell; when a cell divides the DNA is duplicated and the two identical genomes are distributed to both daughter cells.

Cell membrane: The flexible boundary surface of a cell; membranes also surround organelles within the cell.

Cell wall: The rigid coat that surrounds bacterial (and plant) cells; the cell wall lies on the outer surface of the cell membrane.

"Central dogma": Not entirely serious term for the biological hypothesis that establishes the oneway flow of information (from the DNA to the RNA to the proteins), confirmed with the exception of some viruses and modern genetic procedures..

Chromatography: A method for the fractionation of mixtures; chromatography takes advantage of differences in size, electric charge and binding characteristics to separate proteins from contaminants and each other.

Chromosome: In eukaryotic cells, a single DNA molecule condensed into a complex with specific proteins.

Chromosome pair: Every cell in the body contains two sets of chromosomes, one inherited from the mother and one from the father. Human females have 23 chromosome pairs, including the sex-determining X chromosomes; males have one X and one Y chromosome, in addition to the 22 other pairs.

Clone: A group of cells that are genetically identical because they all descend from a single founder cell; hence "cloning" is the generation of identical cells by multiplication of a single founder cell.

Coagulation: Solidification of the blood leaving blood vessels, caused by the trapping of platelet aggregates in a fibrin mesh, the protein produced at the end of the coagulative cascade.

Codon (triplet): A sequence of three bases or nucleotides in DNA or RNA, which specifies an amino acid or a STOP signal (i.e., the end of a protein chain).

Collagen: Protein which constitutes a major part of bones, skin and connective tissue.

Complementarity: Close correspondence between the bases of a strand of DNA and the one opposite in the double helix: adenine with thymine and guanine with cytosine.

Colony: Visible collection of bacteria in culture on solid medium.

Crossed heredity: Transmission of a characteristic (and thus a gene) via the X chromosome and thus, from a male to the daughter and grandchild. Haemophilia A is an example.

Crossing over: The exchange of corresponding parts (and thus genes) between homologous chromosomes; this occurs during meiotic division and forms the basis of the difference between the child and its parent.

Culture: The growing of cells (bacteria or higher organisms) in glass containers (plate, flasks, etc).

Culture medium: Nutrient solution for the growth of microorganisms or cell lines.

Cysteine: One of the 20 amino acids that occur in proteins; crosslinks can be formed between cysteines in a protein.

Cytoplasm: The fluid or jelly-like substance within the cell membrane, in which most metabolic reactions take place.

Cytosine: One of the four bases that are found in DNA and RNA.

D

Denaturation: Separation by physical or chemical means of two DNA strands. Alternatively, disruption of the natural structure of a protein by heating or chemicals.

Deoxyribonucleic acid: see DNA.

Deoxyribose: The sugar component in DNA.

Differentiation: The process by which cells in organisms become specialized for particular functions during development.

Diploid: A set of chromosome pairs e.g. the set of 46 chromosomes in a human cell (excluding germ cells).

Discontinuous gene: Gene formed from segments translated into a protein (exons) alternated with segments not translated into a protein (introns).

DNA: Deoxyribonucleic acid, the genetic material.

Double helix: The three-dimensional structure of the giant DNA molecule, with two strands wound around each other and held together by hydrogen bonds between the bases.

E

Endonuclease: Enzyme able to cut the phosphodiesterase bonds between the nucleotides of a DNA strand; the restriction enzymes are endonucleases.

E. coli (Escherichia coli): A bacterium that inhabits the human gut; the E. coli strain K- 12, which can only survive and grow under laboratory conditions, is the microorganism most widely used in gene technology.

Embryo: Immature stage in the development of a higher organism.

Endoplasmic reticulum (ER): A system of channels enclosed by membranes in the interior of a eukaryotic cell; proteins that are destined for export (secretion) from the cell are first directed into the ER

Enzyme: A protein that serves to catalyze (accelerate) a biochemical reaction.

Eukaryote: An organism whose cells contain a nucleus; prokaryotes have cells without a nucleus.

Evolution: The process of diversification of living organisms from primordial forms.

Exon: Protein-coding segment in a eukaryotic gene, specifying part of the amino acid sequence of a protein. Introns, in contrast, contain no protein-coding information.

Expression: Production of RNA and protein encoded by a gene. Not all genes are expressed at all times, the expression of genes can be caused by hormones and other signals within the body.

Expression cassette: A block of DNA sequence that contains all the information required for synthesis of a protein, comprising promoter, coding sequence and terminator.

F

Factor VIII: A protein factor required for blood clotting; inability to produce functional Factor VIII causes the disorder Haemophilia A.

Fermenter: A vessel in which microorganisms and cell lines can be grown.

G

Gamete: A haploid gene cell (containing half the normal number of chromosomes) designed to fuse with another gamete to create the first cell (diploid) of a new organism; in mammals, the egg cell and spermatozoon (germ cells) are haploids.

GAO: Genetically altered organism.

Gene: The basic unit of heredity; a defined stretch of DNA containing the information for synthesis of RNA or protein.

Gene library: All the fragments of cDNA transcribed by the mRNA of a cell and amplified using molecular cloning techniques.

Gene technology (Genetic engineering): The set of methods that enable identification and isolation of genes, their artificial recombination and transfer from one organism to another.

Genetic code: The "language" of the genetic material; a sequence of three elements (nucleotides) determines the incorporation of one specific amino acid into a protein. Alterations of nucleotides (mutations) can lead to genetic diseases.

Genetics: The branch of biology concerned with the study of heredity.

Genome: The sum total of the genetic information of an organism.

Genotype: The genetic information of an individual.

Glycoprotein (glycosylated protein): A protein that has been modified by the attachment of sugar molecules to certain amino acids; many secreted proteins, including Factor VIII (exported into the bloodstream by liver cells) are glycosylated.

Golgi apparatus: A stack of membrane-bounded compartments in the interior of higher (eukaryotic) cells within which proteins undergo various modifications, such as glycosylation. All secreted proteins must pass through the Golgi apparatus.

Guanine: One of the four bases in DNA.

H

Haemophilia A: Hereditary disorder characterized by disruption of blood clotting; caused by lack of functional Factor VIII.

Haemoglobin: Protein present in red blood cells that binds oxygen for transport to distant tissues.

Haploid: Unpaired set of chromosomes, e.g. the set of 23 chromosomes of a germ cell (spermatozoon and egg-cell).

Hepatitis B: A serious liver disease, caused by the hepatitis B virus (HBV).

Heterologous chromosomes: Chromosomes that are different in shape, size and gene contents (e.g. The X and Y chromosomes in man).

Homologous chromosomes: Chromosomes that are similar in shape, size and gene contents.

Hormone: Messenger substance, often synthesized in specialized glands, that is secreted into the bloodstream and specifically taken up by other cell types, where it alters their activity; many hormones, such as insulin, are proteins.

Host cell: A cell that contains a foreign structure, such as an introduced plasmid or an invasive virus.

Hybrid: The result of the combination of two strands of nucleic acid of different origin, or, the result of the crossing of two different species (as in plant breeding).

Hydrogen bond: Weak bond between the bases of two opposite DNA strands, important in regulating complementarity.

I

Immune system: A system of cells (lymphocytes) and molecules responsible for recognising and eliminating foreign substances that have penetrated an organism. Major components are antibodies and "killer cells" that eat bacteria.

Immunoglobulin: Protein with an antibody function.

Inhibitory antibody: with regard to haemophilia, an antibody that binds and deactivates therapeutically given Factor VIII. Results from the recognition of Factor VIII as a "foreign" protein in a body that lacks it.

Intron: A segment of a eukaryotic gene that is transcribed into RNA but not translated into protein (see Exon).

In vitro: Experiment conducted outside an organism, "in a test tube".

In vivo: Experiment conducted on an organism, "in the living (animal)".

L

Ligase: An enzyme that joins DNA molecules.

Lymphocytes: Cells of the immune system that protect the organism from infectious agents, recognising the foreign proteins (antigens) and forming specific antibodies against them or destroying them directly.

M

Macromolecule: A series of molecules of a similar nature that are bound together: DNA is a macromolecule comprising several nucleotides; proteins are macromolecules comprising several amino acids.

Marker gene: A gene, such as an antibiotic resistance gene, that can be used to identify recombinant cells.

Medium: Material of controlled composition, used as a cell culture nutrient.

Meiosis: The division of a diploid cell into haploid daughter cells; this occurs during maturation of the germ cells (ovules and spermatozoa).

Metabolism: A series of chemical reactions in a living being, usually accelerated by enzymes. It enables the organism to gain energy from food, and make new cells and building blocks for the body.

Methionine: One of the 20 amino acids that occur in proteins; the first methionine codon following the promoter signals the start of translation.

Microbiology: The branch of biology concerned with the study of microorganisms.

Microorganisms: Single-celled organisms that can only be seen under a microscope.

Mitochondrion: Organelle in eukaryotic cells which generates the energy necessary for cellular processes. Cells usually contain many mitochondria.

Mitosis: The division of a diploid cell into two daughter cells that are also diploid; this occurs during the growth and renewal of body tissue.

Molecule: Any chemical compound consisting of linked atoms. The smallest quantity of a substance existing in a free state.

Molecular biology: The branch of biology concerned with the study of molecules involved in cellular processes.

mRNA: see RNA.

Mutation: Any change in the base sequence of the genetic material DNA.

N

Nonsense codon: The three triplets of the genetic code (UAA, UAG, UGA) which, since they do not correspond to any amino acid, terminate the synthesis of a nascent protein.

Nucleotide: Structural building block of nucleic acids, comprising phosphoric acid, sugar, and one of four bases.

Nucleus: Membrane-bound structure in cells of higher (eukaryotic) organisms which contains the DNA (chromosomes).

O

Organ: Group of tissues with specialised functions.

Organelle: Membrane-bound compartment with a specialized function in a cell, for example a mitochondrion.

Ovalbumin: Protein found in eggwhite.

P

Pairing rule: The fact that only the bases A and T (or A and U), and G and C can form structurally compatible base pairs in nucleic acids.

Palindrome: Symmetrically arranged sequence of DNA; many restriction enzymes recognise palindromic sequences.

PCR (Polymerase Chain reaction): Test tube technique of amplifying a DNA fragment (by means of the DNA-polymerase enzyme) without the use of cell "multipliers" (such as bacteria).

Peptide: Group of compounds comprising amino acids; part of a protein.

Peptide bond: Strong bond between the adjacent amino acids in a protein.

Phage (or Bacteriophage): Virus that infects a bacterium, but not higher organisms.

Phenotype: The observable characteristics of the genotype. Due to the existence of dominant and recessive genes, a certain property can be present in the genotype without eliciting a phenotype.

Phosphodiesterase bond: Strong bond between the two sugars of adjacent nucleotides via a phosphate group.

Plasmids: Small circular DNA molecules, found mainly in microorganisms; plasmids can carry genes that render their host cells resistant to antibiotics.

Plaque: A clear area in a bacterial culture, caused by the death of bacteria infected by a phage.

Point mutation: Alteration of a single nucleotide in a gene.

Polysome: Ribosomes, engaged in synthesis of a protein, arrayed along the length of an mRNA.

Probe: Artificial sequence of nucleotides that recognises the segments of a nucleic acid characterised by a complementary sequence. It is labelled with a special marker to make it visible in experiments (e.g. fluorescence, radioactivity).

Producer cell: Cell selected for the large-scale production of proteins.

Promoter: Regulatory sequence that controls transcription.

Prokaryote: Organism made up of a cell that lacks a nucleus.

Protein: Chain of amino acids linked in a defined sequence, which determines its shape and function. Examples include insulin, coagulation Factor VIII, collagen, and enzymes.

Protein biosynthesis: Translation of the base sequence of an mRNA into the amino acid sequence of a protein by ribosomes.

Purine: Type of nucleic acid base, comprising adenine and guanine.

Pyrimidine: Type of nucleic acid base, comprising cytosine and thymine.

R

Recombinant: Generated by linkage of DNA from different sources; for example recombinant organism, recombinant DNA, recombinant protein.

Recombination: Production of new DNA by joining segments or genes previously separated; the crossing-over between chromosomes is a natural form of recombination.

Regulator gene: Gene that allows or inhibits the expression of a structural gene.

Replication: Duplication of a DNA strand in the double helix.

Resistance gene: A gene that confers on a microorganism the ability to grow in the presence of an antibiotic.

Restriction enzyme: Enzyme that binds to a specific DNA sequence and cleaves the molecule at that sequence.

Retrovirus: Virus with an RNA genome. In order to multiply within an infected cell, the retroviral RNA is first copied into DNA. HIV-1, the human immunodeficiency virus that causes AIDS, is a retrovirus.

Reverse transcriptase: A viral enzyme that copies a molecule of RNA to a complementary strand of DNA (cDNA); the spontaneous passage of RNA to DNA is normally impossible in cells. Retroviruses use this enzyme.

Ribose: The sugar component of RNA.

Ribosomes: Structures in the cell cytoplasm consisting of proteins and RNA, sites of mRNA-directed protein synthesis (translation).

RNA: Ribonucleic acid; single-stranded nucleic acid, found in the nucleus and the cytoplasm; messenger RNA (mRNA) molecules are copies (transcripts) of individual gene sequences and serve to carry this information to the ribosomes where it is translated into amino acid sequences. In this process, small transfer RNA (tRNA) molecules act as adaptor molecules, which match codons in the mRNA with the corresponding amino acids.

S

Sequence: Series of bases on nucleic acids or of amino acids on proteins.

Splicing: The maturing of mRNA with the excision of sequences of introns and the linking up of sequences of exons.

Secretion
Export of substances, particularly proteins, from the cell in which they were synthesized.

Sex chromosomes: Chromosomes that determine the sex of an individual organism; in humans females have a pair of X chromosomes, males a single X inherited form the mother and the male-determining Y inherited from the father.

Sickle cell anaemia: A genetic disease of red blood cells, caused by a single mutation in the beta chain of the haemoglobin molecule.

Single helix: see RNA.

Splicing: Formation of an mRNA from a primary RNA transcript by removal of the introns and assembly of the exons in the correct order.

Structure: Complex of characteristics relating to the composition (primary structure) and spatial arrangement (secondary and tertiary structure) of a nucleic acid or a protein (e.g. the structure of factor VIII folded back on itself).

T

Template: Sequence of DNA nucleotides which, according to the complementarity rules, determines the type and order of the bases on a nucleic acid transcribed by it.

Terminator: Regulatory sequence that signals the point at the end of a gene, at which transcription ceases.

Thymine: One of the four bases in DNA; in RNA molecules thymine is replaced by uracil.

Toxin alpha: A poisonous protein in snake venom.

Transcription: The process of copying the DNA sequence of a gene into RNA.

Transformation: Alteration of the characteristics of a cell by introduction of foreign DNA.

Translation: Conversion of an mRNA sequence into the amino acid sequence of a protein.

Triplet: See Codon.

U

Uracil: One of the four bases in RNA; in DNA, thymine replaces uracil.

V

Vector: A carrier, usually a plasmid, used to transfer a DNA sequence of interest into a cell.

Virus: A nucleic acid, which can be DNA or RNA, packed in a particle made of protein; viruses can only reproduce inside cells because they have few genes and no independent metabolism; they replicate their nucleic acid by exploiting the structures and enzymes of their host cell. Viruses are not considered as living organisms on their own.

Z

Zygote: The diploid cell resulting from the fusion of two haploid cells (cell-egg and spermatozoon) and capable of dividing a large number of times to form a new organism.