For vocabulary, see Glossary of gene expression terms

Genes are expressed by being transcribed into RNA, and this transcript may then be translated into protein.

Gene expression is the process by which inheritable information from a gene, such as the DNA sequence, is made into a functional gene product, such as protein or RNA. History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance A DNA sequence or genetic sequence is a succession of letters representing the Primary structure of a real or hypothetical DNA Molecule A gene product is the biochemical material either RNA or Protein, resulting from expression of a Gene. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Ribonucleic acid ( RNA) is a Nucleic acid that consists of a long chain of Nucleotide units

Several steps in the gene expression process may be modulated, including the transcription step and the post-translational modification of a protein. Transcription is the synthesis of RNA under the direction of DNA Posttranslational modification (PTM is the chemical modification of a Protein after its translation. Gene regulation gives the cell control over structure and function, and is the basis for cellular differentiation, morphogenesis and the versatility and adaptability of any organism. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called In Developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized Cell type. MOrphogenesis is an EP by Industrial Black metal band.And Oceans. Gene regulation may also serve as a substrate for evolutionary change, since control of the timing, location, and amount of gene expression can have a profound effect on the functions (actions) of the gene in the organism.

Non-protein coding genes (e. g. rRNA genes, tRNA genes) are not translated into protein. Ribosomal RNA ( rRNA) is the central component of the Ribosome, the protein manufacturing machinery of all living cells. Transfer RNA (abbreviated tRNA) is a small RNA (usually about 74-95 nucleotides that transfers a specific Amino acid to a growing polypeptide chain at Translation is the first stage of Protein biosynthesis (part of the overall process of Gene expression)

Measurement

The expression of many genes is regulated after transcription (i. e. , by microRNAs or ubiquitin ligases), so an increase in mRNA concentration need not always increase expression. In Genetics, microRNAs ( miRNA) are single-stranded RNA molecules of about 21–23 Nucleotides in length which regulate Gene expression A ubiquitin ligase (also called an E3 ubiquitin ligase is a Protein that covalently attaches Ubiquitin to a Lysine on a target protein via an Isopeptide Nevertheless, mRNA levels can be quantitatively measured by Northern blotting, a process in which a sample of RNA is separated on an agarose gel and hybridized to a radio-labeled RNA probe that is complementary to the target sequence. The northern blot is a technique used in Molecular biology research to study Gene expression. Agarose Gel electrophoresis is a method used in Biochemistry and Molecular biology to separate DNA, or RNA molecules by size Northern blotting requires the use of radioactive reagents and can have lower data quality than more modern methods (due to the fact that quantification is done by measuring band strength in an image of a gel), but it is still often used. It does, for example, offer the benefit of allowing the discrimination of alternately spliced transcripts.

A more modern low-throughput approach for measuring mRNA abundance is real-time polymerase chain reaction (The term RT-PCR is used to refer to both reverse transcription PCR as well as real-time PCR, which is also known as quantitative RT-PCR or quantitative PCR (qPCR). In Molecular biology, real-time polymerase chain reaction, also called quantitative real time polymerase chain reaction (qPCR or kinetic polymerase chain reaction In Molecular biology, real-time polymerase chain reaction, also called quantitative real time polymerase chain reaction (qPCR or kinetic polymerase chain reaction With a carefully constructed standard curve qPCR can produce an absolute measurement such as number of copies of mRNA per nanolitre of homogenized tissue. The lower level of noise in data obtained via qPCR often makes this the method of choice, but the price of the required equipment and reagents can be prohibitive.

In addition to low-throughput methods, transcript levels for many genes at once (expression profiling) can be measured with DNA microarray technology or "tag based" technologies like Serial analysis of gene expression (SAGE) or the more advanced version SuperSAGE, which can provide a relative measure of the cellular concentration of different messenger RNAs. For terminology see glossary below A DNA microarray is a High-throughput technology used in Molecular biology and in Serial analysis of gene expression (SAGE is a technique used by molecular biologists to produce a snapshot of the Messenger RNA population in a sample of interest SuperSAGE is the most advanced derivate of the Serial analysis of gene expression technology (SAGE for the analysis of expressed genes in eukaryotic organisms ( gene expression In Chemistry, concentration is the measure of how much of a given substance there is mixed with another substance Messenger ribonucleic acid ( mRNA) is a molecule of RNA encoding a chemical "blueprint" for a Protein product Recent advances in microarray technology allow for the quantification, on a single array, of transcript levels for every known gene in the human genome. The great advantage of tag-based methods is the "open architecture", allowing for the exact measurement of any transcript, known or unknown. Especially SuperSAGE recommends itself therefore also for studying organisms with unknown genomes.

Protein levels themselves can be estimated by a number of means. The most commonly used method is to perform a Western blot against the protein of interest, whereby cellular lysate is separated on a polyacrylamide gel and then probed with an antibody to the protein of interest. The western blot (alternatively immunoblot) is an Analytical technique used to detect specific Proteins in a given sample of tissue homogenate or Lysis ( Greek, lysis from lyein = to separate refers to the death of a cell by breaking of the cellular membrane often by viral or osmotic A Polyacrylamide Gel is a separation matrix used in electrophoresis of Biomolecules, such as Proteins or DNA fragments The antibody can either be conjugated to a fluorophore or to horseradish peroxidase for imaging or quantification. A fluorophore, in analogy to a Chromophore, is a component of a molecule which causes a molecule to be Fluorescent. The Enzyme horseradish peroxidase (HRP found in Horseradish, is used extensively in Molecular biology applications primarily for its ability to amplify Another commonly used method for assaying the amount of a particular protein in a cell is to fuse a copy of the protein to a reporter gene such as Green fluorescent protein, which can be directly imaged using a fluorescent microscope. The green fluorescent protein ( GFP) is composed of 238 Amino acids (26 Because it is very difficult to clone a GFP-fused protein into its native location in the genome, however, this method often cannot be used to measure endogenous regulatory mechanisms (GFP-fusions are therefore most often expressed on extra-genomic DNA such as an expression vector). An expression vector, otherwise known as an expression construct, is generally a Plasmid that is used to introduce and express a specific Gene into a target Fusing a target protein to a reporter can also change the protein's behavior, including its cellular localization and expression level.

The pattern of detection of a gene or gene product may be described using terms such as facultative, constitutive, circadian, cyclic, housekeeping, or inducible. ^[1]

Regulation of gene expression

Main article: Regulation of gene expression

Regulation of gene expression is the cellular control of the amount and timing of appearance of the functional product of a gene. Gene modulation redirects here For information on therapeutic regulation of gene expression see Therapeutic gene modulation. Any step of gene expression may be modulated, from the DNA-RNA transcription step to post-translational modification of a protein. Transcription is the synthesis of RNA under the direction of DNA Posttranslational modification (PTM is the chemical modification of a Protein after its translation. Gene regulation gives the cell control over structure and function, and is the basis for cellular differentiation, morphogenesis and the versatility and adaptability of any organism. In Developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized Cell type. MOrphogenesis is an EP by Industrial Black metal band.And Oceans.

Expression system

An expression system consists, minimally, of a source of DNA and the molecular machinery required to transcribe the DNA into mRNA and translate the mRNA into protein using the nutrients and fuel provided. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known A molecular machine has been defined as a discrete number of molecular components that have been designed to perform mechanical-like movements (output in response to specific stimuli Transcription is the synthesis of RNA under the direction of DNA Messenger ribonucleic acid ( mRNA) is a molecule of RNA encoding a chemical "blueprint" for a Protein product Translation is the interpreting of the meaning of a text and the subsequent production of an equivalent text likewise called a " translation Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl In the broadest sense, this includes every living cell capable of producing protein from DNA. However, an expression system more specifically refers to a laboratory tool, often artificial in some manner, used for assembling the product of a specific gene or genes. It is defined as the "combination of an expression vector, its cloned DNA, and the host for the vector that provide a context to allow foreign gene function in a host cell, that is, produce proteins at a high level". An expression vector, otherwise known as an expression construct, is generally a Plasmid that is used to introduce and express a specific Gene into a target ^[2][3]

In addition to these biological tools, certain naturally observed configurations of DNA (genes, promoters, enhancers, repressors) and the associated machinery itself are referred to as an expression system, as in the simple repressor 'switch' expression system in Lambda phage. Enterobacteria phage λ ( Lambda phage) is a temperate bacteriophage that infects Escherichia coli It is these natural expression systems that inspire artificial expression systems, (such as the Tet-on and Tet-off expression systems). Tetracycline Controlled Transcriptional Activation is a method of inducible expression where transcription is reversibly turned on or off in the presence of the

Each expression system has distinct advantages and liabilities, and may be named after the host, the DNA source or the delivery mechanism for the genetic material. In Biology, a host is an organism that harbors a Virus or Parasite, or a mutual or Commensal Symbiont, typically providing nourishment For example, common expression systems include bacteria (such as E.coli), yeast (such as S.cerevisiae), plasmid, artificial chromosomes, phage (such as lambda), cell lines, or virus (such as baculovirus, retrovirus, adenovirus). The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Yeasts are a growth form of eukaryotic Microorganisms classified in the kingdom Fungi, with about 1500 Species currently described Saccharomyces cerevisiae is a Species of Budding Yeast. It is perhaps the most useful Yeast owing to its use since ancient times A plasmid is an extra-chromosomal DNA molecule separate from the chromosomal DNA which is capable of replicating independently of the chromosomal DNA This article is about a biological infectious particle for other uses see Phage (disambiguation. Enterobacteria phage λ ( Lambda phage) is a temperate bacteriophage that infects Escherichia coli Cell culture is the process by which prokaryotic, or eukaryotic cells are grown under controlled conditions A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable The baculoviruses are a family of large rod-shaped Viruses that can be divided to two genera Nucleopolyhedroviruses (NPV and Granuloviruses (GV A retrovirus is any Virus belonging to the viral family Retroviridae. Adenoviruses are medium-sized (90–100 nm) Nonenveloped (naked Icosahedral viruses composed of a nucleocapsid and a double-stranded linear DNA

Overexpression

In the laboratory, the protein encoded by a gene is sometimes expressed in increased quantity. This can come about by increasing the number of copies of the gene or increasing the binding strength of the promoter region.

Often, the DNA sequence for a protein of interest will be cloned or subcloned into a plasmid containing the lac promoter, which is then transformed into the bacterium Escherichia coli. Cloning in Biology is the process of producing populations of genetically-identical individuals that occurs in nature when organisms such as Bacteria, Insects In Molecular biology, subcloning is a technique used to move a particular Gene of interest from a parent vector to a destination vector A plasmid is an extra-chromosomal DNA molecule separate from the chromosomal DNA which is capable of replicating independently of the chromosomal DNA The lac operon is an Operon required for the transport and Metabolism of Lactose in Escherichia coli and some other In Molecular biology, transformation is the genetic alteration of a cell resulting from the uptake genomic incorporation and expression of foreign Addition of IPTG (a lactose analog) causes the bacteria to express the protein of interest. Isopropyl β-D-1-thiogalactopyranoside, abbreviated IPTG, is a Molecular biology reagent Lactose (also referred to as milk sugar) is a Sugar which is found most notably in Milk. However, this strategy does not always yield functional protein, in which case, other organisms or tissue cultures may be more effective. Tissue culture is the growth of tissues and/or cells separate from the organism For example, the yeast Saccharomyces cerevisiae is often preferred to bacteria for proteins that undergo extensive posttranslational modification. Yeasts are a growth form of eukaryotic Microorganisms classified in the kingdom Fungi, with about 1500 Species currently described Saccharomyces cerevisiae is a Species of Budding Yeast. It is perhaps the most useful Yeast owing to its use since ancient times Posttranslational modification (PTM is the chemical modification of a Protein after its translation. Nonetheless, bacterial expression has the advantage of easily producing large amounts of protein, which is required for X-ray crystallography or nuclear magnetic resonance experiments for structure determination. X-ray crystallography is a method of determining the arrangement of Atoms within a Crystal, in which a beam of X-rays strikes a crystal and scatters

Gene networks and expression

Main article: Gene regulatory network

Genes have sometimes been regarded as nodes in a network, with inputs being proteins such as transcription factors, and outputs being the level of gene expression. A Gene regulatory network (also called a GRN or genetic regulatory network) is a collection of DNA segments in a cell which interact with each In the field of Molecular biology, a transcription factor (sometimes called a sequence-specific DNA binding factor is a Protein that binds to specific sequences The node itself performs a function, and the operation of these functions have been interpreted as performing a kind of information processing within cell and determine cellular behaviour. Information processing is the change (processing of Information in any manner detectable by an observer.

Techniques and tools

• Primer Used to facilitate expression
• Shuttle Vector

See also

• Bookmarking
• Expression profiling
• Expressed sequence tag
• Paramutation
• Sequence profiling tool
• Genetically modified organism
• Genetic engineering
• SuperSAGE
• Epigenetics

References

External links

• Genes & Gene Expression. The Virtual Library of Biochemistry and Cell Biology. BioChemWeb. org (2005-12-04). Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. "December 4th" redirects here For the song by Jay-Z, see December 4th (song. Retrieved on 2008-06-10. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1190 - Third Crusade: Frederick I Barbarossa drowns in the Sally River while leading an army to Jerusalem
• John Kryk (2008-05-28). 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 585 BC - A Solar eclipse occurs as predicted by Greek philosopher and scientist Thales, while Alyattes is battling DNA makes RNA. Retrieved on 2008-06-10. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1190 - Third Crusade: Frederick I Barbarossa drowns in the Sally River while leading an army to Jerusalem