How does mRNA replicate the nucleotide sequence of DNA

Molecular Biology Glossary

With the establishment of molecular biology in research, development and diagnostics, numerous new terms have found their way. With this glossary we would like to give you brief explanations of some basic and frequently occurring terms.

3 'end The end of a strand of DNA with a hydroxyl group on the 3'-carbon atom of the sugar.

5 'end The end of a DNA strand with a mono-, di-, or triphosphate on the 5'-carbon atom of the sugar.

-ase Appendages for enzymes (proteins with catalytic properties).

Adenine a nitrogenous base with a purine ring system (abbr .: A), part of DNA and RNA.

Allele One of two or more different expressions at a gene location (gene locus). An individual inherits i. d. Usually one allele of a gene from the mother and one from the father. If these alleles are identical, they are called homozygous for this gene, if they are different, they are called heterozygous.

Allosomes Sex chromosomes. With woman XX, with man XY.

amino acid Carboxylic acid with an amino group ("aminocarboxylic acid") and an aliphatic or aromatic side chain. Polymerized A. form peptides or proteins whose sequence of genes is determined by the genetic code.

Annealing specific attachment (hybridization) of two complementary nucleic acid strands under specific (stringent) reaction conditions. A. is usually used as a designation in PCR.

Amplification (Duplication). Production of many copies of DNA from a DNA or RNA target sequence. A. is most frequently associated with PCR.

Amplicon, specific DNA fragment, which was synthesized with the help of the PCR (syn. amplificate or PCR product).

antigen Molecule or target area within a molecule that can be recognized by antibodies.

antibody Molecule (glycoprotein) that can specifically bind to an antigen.

Autosomes Chromosomes that are not involved in sex determination. In the diploid human genome there are usually 22 homologous pairs and 1 pair of sex chromosomes (allosomes.

bacterium unicellular microorganism without a real nucleus (prokaryote).

(nitrogenous) base In molecular biology, the basic molecular component with a purine or pyrimidine ring system within the nucleotide structure.

Base pair Structure linked by hydrogen bonds that forms between two complementary nucleotides.

Base pairing Within a DNA double strand, specific interactions between the bases A and T or G and C are formed by 2 or 3 hydrogen bonds. Correct B. always takes place between a purine and a pyrimidine base. This fact is exploited in the hybridization of single-stranded nucleic acid molecules.

biotechnology A wide range of molecular biology techniques that were developed through basic research and can now be applied in research and product development. In particular, techniques for the production and expression of recombinant DNA and for cell fusion are used in industry.

cDNA complementary or copy DNA synthesized on an RNA template by the enzyme reverse transcriptase.

Centromere Chromosomal region to which the fibers of the spindle apparatus attach during meiosis.

Chromosomes Self-replicating cell structures in which most of the genetic information is stored in the form of linearly arranged genes. The rest of the genetic information is located in the mitochondria and, in plants, also in the plastids. In prokaryotes, the chromosomal DNA is circular and the entire information is stored on a Ch. ("Bacterial chromosome"). Eukaryotic genomes consist of several Ch., Which are associated with various proteins. A normal human cell contains 23 pairs of chromosomes (male 22XY, female 22XX).

Compound heterozygosity: In people with a recessive heritable disease, both chromosomes have different mutations (e.g. heterozygous presence of the mutations H63D and C282Y in hemochromatosis).

Crossing over The exchange of homologous DNA segments between (paternal and maternal) chromosomes during meiosis. C. can e.g. B. lead to allele exchange.

Cytosine a nitrogenous base with a pyrimidine ring system (abbr .: C), part of DNA and RNA.

Deletion: Lack of a chromosome or DNA segment.

Denaturation Breaking of non-covalent bonds of proteins or nucleic acids by heating to temperatures above 90 ° C or by adding a strongly alkaline solution (e.g. NaOH).

Diploidy the presence of two complete double sets of chromosomes in the nucleus of organisms with sexual reproduction.

DNA Deoxyribonucleic Acid (Deoxyribonucleic Acid). Carrier of the primary genetic information. It is created by polymerizing the four nucleotides dATP, dCTP, dGTP and dTTP.

DNA cloning Incorporation of a DNA fragment into a vector (e.g. plasmid). This recombinant DNA molecule is then propagated in a host organism (e.g. bacterium).

DNA ligase Enzyme that repairs single-strand breaks in double-stranded DNA molecules by restoring the covalent bond.

DNA polymerase Enzyme that synthesizes new complementary strands of DNA using a primer as a starting point and a DNA template.

dNTPs Deoxyribonucleotide triphosphates; monomeric building blocks for nucleic acids z. B. dATP, dCTP, dGTP, dTTP.

domain A specific area in a protein with its own function. The combination of several D. determines its overall function.

Dominance In heterozygosity, the predominance of one allele over the other. The expression of the "weak" allele is suppressed or switched off and referred to as recessive. If both alleles occur independently of one another, we speak of codomination (e.g. blood group genes A and B).

Double helix Natural structure of DNA from two antiparallel, complementary polynucleotide chains, which are held together by hydrogen bonds and are twisted around each other in a helical manner (right-hand a-double helix).

Escherichia (E.) coli Due to its small genome, its normally non-pathogenic properties, rapid growth and simple culture conditions, the E. coli bacterium is THE workhorse in molecular biology laboratories.

Electrophoresis Separation of molecules in a direct current field due to their electrical charge.

Enzymes A protein with catalytic properties. E. So increase the reaction rate by lowering the activation energy, but have no influence on the equilibrium of the reaction they catalyze.

Eukaryo (n) t Organism with organelles, compartmentalization and real cell nucleus (all organisms except bacteria, viruses and blue-green algae).

Exon Gene segment with a protein-coding function.

Extension Extension of the DNA chain by incorporation of dNTPs using a template during replication. In the PCR, the E. is carried out by thermostable DNA polymerase (e.g. Taq polymerase).

extraction Isolation of the nucleic acids to be examined from the sample material using different chemical or physical aids. There are commercially available reprocessing kits for a wide variety of native material.

FISH Fluorescence in-situ hybridization. Molecular cytogenetic method for the colored representation of selected chromosomes or chromosome segments by fluorescence microscopy. The hybridization of the DNA probes takes place in situ on the chromosome or cell preparations.

Gametes mature female or male reproductive cells (sperm or egg cells) with a haploid set of chromosomes.

Gel electrophoresis Molecules with comparable electrical charges (e.g. DNA) separate according to their size. In molecular biology, nucleic acids are separated by gel electrophoresis in a gel matrix (polyacrylamide or agarose). Due to their negative charge, they migrate to the positive pole (anode) at different speeds depending on their size.

gene DNA segment in the genome that codes for an RNA and / or polypeptide molecule and contains the regulatory units required for this.

Gene library A collection of clones that contain overlapping fragments of the entire genome of a particular organism (genomic library). Alternatively, the (m) RNA can also be isolated from cells of organisms or organs, reverse transcribed into cDNA and cloned [(m) RNA library. The clones of a G. are produced with the help of vectors.

Gene dose: All autosomal genes are present in duplicate in the genome and many genes must also be expressed by both alleles to ensure normal cell function. If one allele of a gene is defective, half the gene dose may no longer be sufficient for normal cell function. In the case of predisposition alleles for certain diseases, the severity of the disease can also depend on whether this allele is heterozygous or homozygous (e.g. shared epitopes in rheumatoid arthritis).

genetics The science of studying genes.

genetic code The rules that determine the assignment of a nucleotide triplet to a defined amino acid during translation (e.g. ATG to the amino acid methionine). With the g. C. the protein sequence can therefore be predicted from the mRNA.

Gene expression: All processes in which the gene product (RNA and / or protein) is produced on the basis of the nucleotide sequence of a gene. An RNA copy (mRNA) is produced by transcription, by means of which the corresponding protein is then synthesized on the ribosomes by translation. For certain genes (e.g. rRNA and tRNA genes), the RNA is already the gene product.

Genome The entire set of genes in a cell or an organism that contains the instructions for the formation of an organism and for its vital functions.

genotype Description of the genetic makeup of an organism.

Gene product: The biochemical material (RNA or protein) that results from gene expression. The amount of G. produced provides information about the gene activity; abnormal amounts can be an indication of disease-causing alleles.

Gene probes Process in which, with the aid of a labeled nucleic acid molecule (the probe), complementary nucleic acid molecules can be identified on the basis of the formation of specific hybrids. Gene probe analysis is often used in diagnostics to detect pathogens.

Genetic engineering Any method used to create, study, and use recombinant DNA molecules.

Guanine A nitrogenous base with a purine ring system (abbr .: G), part of DNA and RNA.

Haploidy The presence of a complete simple set of chromosomes, mostly in sex cells of diploid organisms.

Hemizygosity The situation when a gene is only present once in the genotype. In humans, these are usually the genes of the man on the X chromosome, which is normally only present once. A normally recessive allele that is on a man's X chromosome manifests itself accordingly in the man's phenotype.

Heterozygosity The hereditary property of a diploid cell to contain two different alleles of a particular gene in both homologous chromosomes.

(Sequence) homology Degree of relationship between nucleic acid or protein sequences, often given in percent of identical nucleotides or amino acids.

Homozygosity The hereditary trait of a diploid cell to contain two identical alleles of a particular gene in both homologous chromosomes.

Hybridization Process in which two nucleic acid single strands connect with each other through complementary base pairings. The greater the homology of both strands, the more stable the resulting double strand.

Inhibitor Substance that interferes with the amplification ability of the DNA polymerase and thus z. B. the PCR amplification reduced or stopped entirely. Examples of PCR inhibitors are heparin or hemoglobin.

Intron Non-coding gene segment between two exons of a gene that is cut out when the mRNA matures.

Karyogram: Pairs of homologous metaphase chromosomes according to their size and the position of the centromeres for systematic analysis.

Karyotype: Chromosome set of an individual, defined by the number and morphology of the chromosomes in the metaphase of mitosis. The normal, diploid K. has 46 chromosomes in humans (man: 44XY, woman: 44XX).

Kit Ready-made and packaged reagent assortments for carrying out a wide variety of purifications and reactions.

clone Population of genetically identical cells or organisms. Often used in molecular biology for cells that contain the same recombinant DNA molecules.

Cloning The production of multiple, exact copies of a gene or other DNA segment using special technologies and vectors. Another type of C. uses natural cell division in order to be able to produce many genetically identical cells (cell lines). Tumor cells are also often of clonal origin. In addition, complete, genetically identical organisms can be produced, e.g. B. the clone sheep "Dolly".

Complementarity Property of nucleotides or nucleic acid sequences that can specifically form base pairings with one another. Adenine and thymine (or uracil), cytosine and guanine are complementary to each other. 5´-ATCGTC-3´ is complementary to 5´-GACGAT-3´.

contamination Due to the exponential amplification, the PCR is also susceptible to contamination. Therefore, when using PCR diagnostically, special measures to exclude contamination are essential.

Number of copies The number of copies of a gene, transposon or repetitive elements within a genome.

Pathogens infectious agent (bacteria, viruses, fungi, protozoa, arthropods, helminths, prions) that causes disease.

Culture Widely used method for the detection of vital pathogens, which is often the diagnostic method of choice. With the direct detection of nucleic acids by the PCR, no statement can be made about the vitality of the pathogen.


LCR, Ligase chain reaction Process comparable to PCR, which uses a heat-stable ligase to connect oligonucleotides that are complementary to the template sequence.

Reading frame One of the three overlapping sequences of triplet codons contained in every DNA sequence.

Locus Position of a gene or other genetic marker on the chromosomes.

Marker molecules Synthetically produced nucleic acids can be covalently provided with M. at their ends, which serve as an aid for the subsequent detection of the specific nucleic acids (e.g. digoxigenin, biotin or fluorescent dyes).

die Template; In molecular biology, single-stranded DNA to which a complementary new strand is synthesized.

meiosis Process that comprises two successive cell divisions and results in haploid sex cells from diploid cells [4 sperm or 1 egg cell (with 3 polar bodies) per precursor cell in humans].

Methylation Enzymatic modification of a DNA or RNA base by incorporating a methyl group, often used in nature for the (reversible) inactivation of genes. In humans, almost exclusively C is methylated.

Mismatch Unusual base pairing (not C with G or A with T / U). A mismatch base pairing forms fewer hydrogen bonds and thus has less binding energy and thus reduces the stability of a double-stranded DNA molecule.

Mitosis The process of cell nucleus division that ultimately results in two genetically identical daughter cells whose genome is also identical to that of the parent cell.

Molecular biology Department of biology, which deals with the study of the molecular properties of nucleic acids, proteins and their biochemical reactions in organisms. It also deals with the structure and reproduction of viruses separately.

Molecular Diagnostics Different analysis methods of nucleic acids and proteins for the detection of diseases.

Monogenic diseases They are caused by mutations in a specific gene.

Monomer single molecules, from which polymers can be built up through various chemical reactions.

mRNA (messenger = messenger RNA) Processed template (transcript) of a protein-coding gene.

Multiplex PCR A special version of PCR in which several target sequences can be amplified simultaneously using several primer pairs in one PCR approach.

Mutagen Chemical or physical agent that can cause a mutation in a nucleic acid molecule.

Mutant Cell or organism with abnormal genetic makeup.

mutation Change in the nucleotide sequence of a nucleic acid.

NTP Ribonucleotide triphosphates; monomeric building blocks for ribonucleic acids (RNA), e.g. B. ATP, CTP, GTP, UTP.

Nuclease Enzyme that catalyzes the breakdown of nucleic acid molecules.

nucleic acid Original name of the acidic substance isolated from the nucleus of eukaryotic cells. Currently, N. denotes the polymeric molecules DNA and RNA, which contain nucleotide monomers. They consist of sugar molecules, organic bases and phosphate groups. If the sugar molecule consists of ribose, the nucleic acid is called RNA, if the sugar molecule is deoxyribose (one hydroxyl group is missing), DNA.

Nucleoside Connection of a purine or pyrimidine base with a sugar, e.g. B. Adenosine (A), guanosine (G), cytidine (C), thymidine (T), uridine (U).

Nucleotide A compound of a purine or pyrimidine base, a sugar (deoxyribose or ribose) and phosphate. As monophosphate nucleotides, they form the monomeric units of DNA and RNA, which are synthesized by polymerizing triphosphate nucleotides with elimination of pyrophosphate.

Oligonucleotides Natural or synthetically produced nucleotide sequences (approx. 20 to 40-mer) that are used as probes or primers.

palindrome Word (or sentence) that reads itself the same forwards and backwards (e.g. "Anna" or "Otto"). In molecular biology, a nucleotide sequence that is a mirror image on the complementary strand (e.g. 5'-GAATTC-3 '). P. often serve as recognition sequences for restriction enzymes.

PCR (polymerase chain reaction). Enzymatic DNA amplification of a target sequence in which primers are extended along a template DNA in several rounds of amplification (= cycles). The temperature changes periodically so that the DNA is repeatedly denatured and the primers attach and can be extended. The DNA sequence enclosed by the primer molecules is increased exponentially. The PCR is carried out in a so-called thermal cycler.

Phenotype The appearance of a cell or an organism, which is caused by the genotype and environmental factors.

Phosphodiester bond The chemical (covalent) bond that connects neighboring nucleotides in nucleic acids.

Plasmid Circular DNA molecule found in bacteria, independent of the host genome. P. are smaller than the bacterial chromosome and mostly replicate autonomously, i. H. independent of the rest of the DNA in the bacterial cell. They are transmitted between bacteria and often mediate antibiotic resistance. With the help of molecular biological methods, a piece of foreign DNA can be inserted into a plasmid and multiplied.

polymer Chemical substance whose molecules are long chains of identical or similar subunits.

(DNA) polymerase Enzyme that can synthesize new strands of DNA in the 3 '? 5' direction using a single-stranded DNA template. The strand extension initializes on starter molecules (primers) with free nucleotides (dNTP) as substrate. For the PCR, v. a. uses the thermostable Taq DNA polymerase. There are also RNA polymerases analogously.

Polymorphism: In genetics, the occurrence of two or more different genotypes in a population. The different genotypes can be traced back to DNA sequence variations, which are found in a certain percentage (> 1%) in the population.

Primer Short oligonucleotide that hybridizes to a single-stranded DNA molecule and thus forms a starting point for DNA synthesis. In the PCR, primers of a defined length and sequence are used to replicate the DNA template. The primer has a free 3´-OH group to which the (thermostable) polymerase attaches nucleotides.

Prokaryo (n) t Living things without a real nucleus and some cell organelles typical of eukaryotes. The bacteria and blue-green algae belong to the P. Viruses, on the other hand, are not living beings; they need hosts for replication and are known as infectious units.

Proof reading. Some polymerases are able to remove incorrectly incorporated nucleotides during the synthesis of a new DNA strand (3´®5´ exonuclease activity).

Protease Protein degrading enzyme.

Proteins Amino Acid Subunit Polymers

Processivity average number of nucleotides per unit of time that are incorporated by a polymerase before it leaves the template.

buffer Name for a solution or a reagent that keeps the pH value stable even by adding acids or bases.

Point mutation Mutation, which is usually based on the exchange of a single nucleotide in a DNA molecule.

Purine aromatic ring structure of one of the two types of nitrogen bases that are components of nucleotides (e.g. adenine, guanine).

Pyrimidine aromatic ring structure of one of the two types of nitrogen bases that are components of nucleotides (e.g. cytosine, thymine, uracil).

Purification of nucleic acids Removal of cell components and possible inhibitors from the sample extract, with the aim of a nucleic acid solution that is as pure as possible.

recombinant DNA molecule DNA molecule that was created in vitro by combining DNA fragments of different origins that do not naturally belong together (e.g. plasmid with an artificially integrated DNA sequence that codes for an insulin subunit).

Renaturation The return of a denatured molecule to its natural state.

Replication The process of DNA doubling during cell division in order to ensure that all genetic material is passed on to the daughter cells.

Restriction endonuclease Enzyme that cuts double-stranded DNA molecules only at a defined number of specific (often palindromic) base sequences (interface).

Reverse transcriptase Enzyme of viral origin, which catalyzes the synthesis of complementary DNA (cDNA) from an RNA template, i.e. reverses the transcription.

Reverse transcription Formation of a complementary DNA (cDNA) based on an RNA template with the aid of a primer and reverse transcriptase.

Recessivity see dominance

Ribonuclease RNA degrading enzyme.

RNA (Ribonucleic Acid) Ribonucleic acid. One of the two types of nucleic acids in living cells.

rRNA (ribosomal RNA) RNA molecules that serve as structural elements in ribosomes. Certain rRNA genes are used to classify the organisms in terms of their phylogenetic history.

(DNA) sequencing, Sequence analysis (automated) analysis of the nucleotide sequence in a DNA molecule.

Stringency Reaction conditions that affect the assembly of two single-stranded nucleic acid molecules. The more stringent the conditions, the more perfectly the DNA molecules have to match each other so that they can assemble (complementarity).

Taq DNA polymerase Heat-stable DNA polymerase derived from the Thermus aquaticus bacterium. The optimum activity of T. is 70-80 ° C and it is not destroyed by the high denaturation temperatures (approx. 93 ° C - 96 ° C) during the PCR.

Target sequence see target sequence.

Template Template, template for replication. (PCR: e.g. specific DNA section of a pathogen).

Thermal cycler Programmable and automated heating block that can switch very quickly between the temperatures required for a PCR (example for a PCR program: 94 ° C, 30 s; 55 ° C, 30 s; 72 ° C, 30 s / 30 x repetitions).

Thermus aquaticus Bacterium that lives in hot water springs above 75 ° C. Its DNA polymerase can withstand temperatures of over 90 ° C for a long time without any loss of function.

Thymine A nitrogenous base with a pyrimidine ring system (abbr .: T), part of DNA.

Transcript RNA copy of a gene.

transcription The synthesis of an mRNA copy from a gene. From the coding strand of the genomic DNA a precursor RNA is produced in the cell nucleus, which still contains the intron sequences. After transport into the cytoplasm, the intronic areas are cut out (splicing) and the molecule ends are modified in a maturation process. The mature mRNA is created.

Translation The synthesis of a polypeptide on ribosomes with an mRNA as a template. The protein sequence is determined by the nucleotide sequence of the mRNA according to the rules of the genetic code (triplet code).

Transposition The movement of a genetic element on DNA from one place to another.

tRNAs (transfer RNAs) Class of small RNA molecules with a characteristic secondary structure ("clover leaf shape"). They contain a triplet nucleotide sequence that is complementary to the triplet nucleotide sequence of the mRNA. Exactly one amino acid fits every tRNA. The task of tRNAs in protein biosynthesis is to couple the amino acids and transfer them to the ribosomes. So they provide the substrate for the translational apparatus.

UNG Uracil-N-glycosylase. Enzyme that catalyzes the breakdown of synthetic DNA fragments synthesized with dUTP instead of dTTP. The use of UNG and dUTP in the diagnostic use of PCR is a standard method for avoiding contamination that is based on the carry-over of PCR products.

Uracil A nitrogenous base with a pyrimidine ring system (abbr .: U), part of RNA.

vector DNA molecule that is capable of independent replication and is suitable for the incorporation of foreign DNA fragments (e.g. plasmids, phages, cosmids and so-called artificial chromosomes such as BAC, PAC, YAC). V. can be transferred into host cells in which they themselves and / or their (recombinant) gene products can be reproduced in large quantities.

Inheritance The transmission of traits from parents to offspring.

Viruses (Virus lat. Mucus, poison) Group of infectious units that contain either only DNA or only RNA and have no metabolism of their own. For their reproduction they are therefore necessarily dependent on a host organism whose biosynthetic apparatus they use for their reproduction. There are single-stranded RNA viruses such as HIV or HCV, and double-stranded RNA viruses such as parvovirus; and double stranded DNA viruses such as B. Herpes simplex 1 and 2. The viral genome is surrounded by a protein shell - the capsid. Genome and capsid are called nucleocapsid. Some viruses have naked nucleocapsids and others have envelopes made of lipids and glycoproteins. Viruses that infect bacteria are called phages.

Virion Protein envelope of a virus.

Hydrogen bonds Weak intra- or intermolecular polar (i.e. non-covalent) bond between a hydrogen atom or proton donor and a proton acceptor. W. determine inter alia. essentially the spatial structure of proteins and the spatial structure of DNA.

Wild type A gene, cell or organism with the typical phenotype and / or genotype of the species in question is considered to be the "normal form".

Cell nucleus Complex of DNA and basic proteins, which is enclosed by a double membrane.

Target sequence Defined known nucleotide sequence of the DNA or RNA of an organism. It is preserved and therefore suitable for specific detection in diagnostics.