Phonetic transcription is the visual representation of speech sounds. The most common type of phonetic transcription uses a phonetic alphabet, such as the International Phonetic Alphabet; the pronunciation of words in many languages, as distinct from their written form, has undergone significant change over time. Pronunciation can vary among dialects of a language. Standard orthography in some languages French and Irish, is irregular and makes it difficult to predict pronunciation from spelling. For example, the words bough and through do not rhyme in English though their spellings might suggest otherwise. In French, the sequence "-ent" is pronounced /ɑ̃/ in accent but is silent in "posent". Other languages, such as Spanish and Italian have a more consistent relationship between orthography and pronunciation. Therefore, phonetic transcription can provide a function, it displays a one-to-one relationship between symbols and sounds, unlike traditional writing systems. Phonetic transcription allows one to step outside orthography, examine differences in pronunciation between dialects within a given language and identify changes in pronunciation that may take place over time.
Phonetic transcription may aim to transcribe the phonology of a language, or it may be used to go further and specify the precise phonetic realisation. In all systems of transcription there is a distinction between broad transcription and narrow transcription. Broad transcription indicates only the most noticeable phonetic features of an utterance, whereas narrow transcription encodes more information about the phonetic variations of the specific allophones in the utterance; the difference between broad and narrow is a continuum. One particular form of a broad transcription is a phonemic transcription, which disregards all allophonic difference, and, as the name implies, is not a phonetic transcription at all, but a representation of phonemic structure. For example, one particular pronunciation of the English word little may be transcribed using the IPA as /ˈlɪtəl/ or. In North American English, there would be no difference at all between the pronunciation of little and the constructed word *liddle.
Indeed, middle. The advantage of the narrow transcription is that it can help learners to get the right sound, allows linguists to make detailed analyses of language variation; the disadvantage is that a narrow transcription is representative of all speakers of a language. Most Americans and Australians would pronounce the /t/ of little as a tap; some people in southern England would say /t/ as and/or the second /l/ as or something similar yielding. A further disadvantage in less technical contexts is that narrow transcription involves a larger number of symbols that may be unfamiliar to non-specialists. To most native English speakers those who don't merge /t/ and /d/ as in unstressed positions; the advantage of the broad transcription is that it allows statements to be made which apply across a more diverse language community. It is thus more appropriate for the pronunciation data in foreign language dictionaries, which may discuss phonetic details in the preface but give them for each entry.
A rule of thumb in many linguistics contexts is therefore to use a narrow transcription when it is necessary for the point being made, but a broad transcription whenever possible. Most phonetic transcription is based on the assumption that linguistic sounds are segmentable into discrete units that can be represented by symbols; the Avestan alphabet is an early phonetic alphabet developed in Sassanian Persia to write down the Avestan-language hymns of Zoroastrianism, or the Avesta, when Avestan was a dead language. The correct pronunciation of the prayers was considered to be important; the International Phonetic Alphabet is one of the most well-known phonetic alphabets. It was created by British language teachers, with efforts from European phoneticians and linguists, it has changed from its earlier intention as a tool of foreign language pedagogy to a practical alphabet of linguists. It is becoming the most seen alphabet in the field of phonetics. Most American dictionaries for native English-speakers—American Heritage Dictionary of the English Language, Random House Dictionary of the English Language, Webster's Third New International Dictionary—employ respelling systems based on the English alphabet, with diacritical marks over the vowels and stress marks.
Another encountered alphabetic tradition was created for the transcription of Native American and European languages, is still used by linguists of Slavic, Semitic and Caucasian languages. This is sometimes labeled the Americanist phonetic alphabet, but this is misleading because it has always been u
Bacterial transcription is the process in which messenger RNA transcripts of genetic material in bacteria are produced, to be translated for the production of proteins. Unlike in eukaryotes, bacterial transcription and translation can occur in the cytoplasm; this is impossible in eukaryotes, where transcription occurs in a membrane-bound nucleus while translation occurs outside the nucleus in the cytoplasm. In bacteria genetic material is not enclosed in a membrane-enclosed nucleus and has access to ribosomes in the cytoplasm. Transcription is carried out by RNA polymerase but its specificity is controlled by sequence-specific DNA binding proteins called transcription factors; the following steps occur, in order, for transcription initiation:. Promoter, |T| stands for the terminator; the DNA on the template strand between the +1 site and the terminator is transcribed into RNA, translated into protein. At this stage, the DNA is double-stranded; this holoenzyme/wound-DNA structure is referred to as the closed complex.
The DNA becomes single-stranded in the vicinity of the initiation site. This holoenzyme/unwound-DNA structure is called the open complex; the RNA polymerase transcribes the DNA, but produces about 10 abortive transcripts which are unable to leave the RNA polymerase because the exit channel is blocked by the σ-factor. The σ-factor dissociates from the core enzyme, elongation proceeds. Promoters can differ in "strength". Promoter strength is in many cases, a matter of how RNA polymerase and its associated accessory proteins bind to their respective DNA sequences; the more similar the sequences are to a consensus sequence, the stronger the binding is. Additional transcription regulation comes from transcription factors that can affect the stability of the holoenzyme structure at initiation. Most transcripts originate using adenosine-5'-triphosphate and, to a lesser extent, guanosine-5'-triphosphate at the +1 site. Uridine-5'-triphosphate and cytidine-5'-triphosphate are disfavoured at the initiation site.
Two termination mechanisms are well known: Intrinsic termination involves terminator sequences within the RNA that signal the RNA polymerase to stop. The terminator sequence is a palindromic sequence that forms a stem-loop hairpin structure that leads to the dissociation of the RNAP from the DNA template. Rho-dependent termination uses a termination factor called ρ factor, a protein to stop RNA synthesis at specific sites; this protein binds at a rho utilisation site on the nascent RNA strand and runs along the mRNA towards the RNAP. A stem loop structure upstream of the terminator region pauses the RNAP, when ρ-factor reaches the RNAP, it causes RNAP to dissociate from the DNA, terminating transcription; the termination of DNA transcription in bacteria may be stopped by certain mechanisms wherein the RNA polymerase will ignore the terminator sequence until the next one is reached. This phenomenon is utilised by certain bacteriophages. Bacterial Transcription – animation Video animation summarizing the process
In music, a reduction is an arrangement or transcription of an existing score or composition in which complexity is lessened to make analysis, performance, or practice easier or clearer. An orchestral reduction is a sheet music arrangement of a work for full symphony orchestra, rearranged for a single instrument, a smaller orchestra, or a chamber ensemble with or without a keyboard. A reduction for solo piano is sometimes called a piano piano score. During opera rehearsals, a répétiteur will read from a piano reduction of the opera; when a choir is learning a work scored for choir and full orchestra, the initial rehearsals will be done with a pianist playing a piano reduction of the orchestra part. Before the advent of the phonograph, arrangements of orchestral works for solo piano or piano four hands were in common use for enjoyment at home. A reduction for a smaller orchestra or chamber ensemble may be used when not enough players are available, when a venue is too small to accommodate the full orchestra, to accompany less powerful voices, or to save money by hiring fewer players.
A piano reduction or piano transcription is sheet music for the piano, compressed and/or simplified so as to fit on a two-line staff and be playable on the piano. It is considered a style of orchestration or music arrangement less well known as contraction scoring, a subset of elastic scoring; the most notable example is Franz Liszt's transcriptions for solo piano of Ludwig van Beethoven's symphonies, which are arguably the greatest work of transcription completed in the history of music. According to Arnold Schoenberg, a piano reduction should "only be like the view of a sculpture from one viewpoint", he advises that timbre and thickness should be ignored, since "the attempt to make a useful object usable for a variety of purposes is the way to spoil it completely". Piano-vocal score Social history of Jonathan. "Models and methods". Liszt as Transcriber. Pp. 9–40. ISBN 978-0-521-11777-7. Opus Transcribisticum Editions Poole
Transcription is the first step of gene expression, in which a particular segment of DNA is copied into RNA by the enzyme RNA polymerase. Both DNA and RNA are nucleic acids. During transcription, a DNA sequence is read by an RNA polymerase, which produces a complementary, antiparallel RNA strand called a primary transcript. Transcription proceeds in the following general steps: RNA polymerase, together with one or more general transcription factors, binds to promoter DNA. RNA polymerase creates a transcription bubble; this is done by breaking the hydrogen bonds between complementary DNA nucleotides. RNA polymerase adds RNA nucleotides. RNA sugar-phosphate backbone forms with assistance from RNA polymerase to form an RNA strand. Hydrogen bonds of the RNA–DNA helix break, freeing the newly synthesized RNA strand. If the cell has a nucleus, the RNA may be further processed; this may include polyadenylation and splicing. The RNA may exit to the cytoplasm through the nuclear pore complex; the stretch of DNA transcribed into an RNA molecule is called a transcription unit and encodes at least one gene.
If the gene encodes a protein, the transcription produces messenger RNA. Alternatively, the transcribed gene may encode for non-coding RNA such as microRNA, ribosomal RNA, transfer RNA, or enzymatic RNA molecules called ribozymes. Overall, RNA helps synthesize and process proteins. In virology, the term may be used when referring to mRNA synthesis from an RNA molecule. For instance, the genome of a negative-sense single-stranded RNA virus may be template for a positive-sense single-stranded RNA; this is because the positive-sense strand contains the information needed to translate the viral proteins for viral replication afterwards. This process is catalyzed by a viral RNA replicase. A DNA transcription unit encoding for a protein may contain both a coding sequence, which will be translated into the protein, regulatory sequences, which direct and regulate the synthesis of that protein; the regulatory sequence before the coding sequence is called the five prime untranslated region. As opposed to DNA replication, transcription results in an RNA complement that includes the nucleotide uracil in all instances where thymine would have occurred in a DNA complement.
Only one of the two DNA strands serve as a template for transcription. The antisense strand of DNA is read by RNA polymerase from the 3' end to the 5' end during transcription; the complementary RNA is created in the opposite direction, in the 5' → 3' direction, matching the sequence of the sense strand with the exception of switching uracil for thymine. This directionality is because RNA polymerase can only add nucleotides to the 3' end of the growing mRNA chain; this use of only the 3' → 5' DNA strand eliminates the need for the Okazaki fragments that are seen in DNA replication. This removes the need for an RNA primer to initiate RNA synthesis, as is the case in DNA replication; the non-template strand of DNA is called the coding strand, because its sequence is the same as the newly created RNA transcript. This is the strand, used by convention when presenting a DNA sequence. Transcription has some proofreading mechanisms, but they are fewer and less effective than the controls for copying DNA.
As a result, transcription has a lower copying fidelity than DNA replication. Transcription is divided into initiation, promoter escape and termination. Transcription begins with the binding of RNA polymerase, together with one or more general transcription factors, to a specific DNA sequence referred to as a "promoter" to form an RNA polymerase-promoter "closed complex". In the "closed complex" the promoter DNA is still double-stranded. RNA polymerase, assisted by one or more general transcription factors unwinds 14 base pairs of DNA to form an RNA polymerase-promoter "open complex". In the "open complex" the promoter DNA is unwound and single-stranded; the exposed, single-stranded DNA is referred to as the "transcription bubble."RNA polymerase, assisted by one or more general transcription factors selects a transcription start site in the transcription bubble, binds to an initiating NTP and an extending NTP complementary to the transcription start site sequence, catalyzes bond formation to yield an initial RNA product.
In bacteria, RNA polymerase holoenzyme consists of five subunits: 2 α subunits, 1 β subunit, 1 β' subunit, 1 ω subunit. In bacteria, there is one general RNA transcription factor: sigma. RNA polymerase core enzyme binds to the bacterial general transcription factor sigma to form RNA polymerase holoenzyme and binds to a promoter. In archaea and eukaryotes, RNA polymerase contains subunits homologous to each of the five RNA polymerase subunits in bacteria and contains additional subunits. In archaea and eukaryotes, the functions of the bacterial general transcription factor sigma are performed by multiple general transcription factors that work together. In archaea, there ar
Eukaryotic transcription is the elaborate process that eukaryotic cells use to copy genetic information stored in DNA into units of transportable complementary RNA replica. Gene transcription occurs in both prokaryotic cells. Unlike prokaryotic RNA polymerase that initiates the transcription of all different types of RNA, RNA polymerase in eukaryotes comes in three variations, each translating a different type of gene. A eukaryotic cell has a nucleus that separates the processes of translation. Eukaryotic transcription occurs within the nucleus where DNA is packaged into nucleosomes and higher order chromatin structures; the complexity of the eukaryotic genome necessitates a great variety and complexity of gene expression control. Eukaryotic transcription proceeds in three sequential stages: initiation and termination; the RNAs transcribed serve diverse functions. For example, structual components of the ribosome are transcribed by RNA polymerase I. Protein coding genes are transcribed by RNA polymerase II into messenger RNAs that carry the information from DNA to the site of protein synthesis.
More abundantly made are the so-called non-coding RNAs account for the large majority of the transcriptional output of a cell. These non-coding RNAs perform a variety of important cellular functions. Eukaryotes have each with distinct roles and properties. RNA polymerase I catalyses the transcription of all rRNA genes except 5S; these rRNA genes are organised into a single transcriptional unit and are transcribed into a continuous transcript. This precursor is processed into three rRNAs: 18S, 5.8S, 28S. The transcription of rRNA genes takes place in a specialised structure of the nucleus called the nucleolus, where the transcribed rRNAs are combined with proteins to form ribosomes. RNA polymerase II is responsible for the transcription of all mRNAs, some snRNAs, siRNAs, all miRNAs. Many Pol II transcripts exist transiently as single strand precursor RNAs that are further processed to generate mature RNAs. For example, precursor mRNAs are extensively processed before exiting into the cytoplasm through the nuclear pore for protein translation.
RNA polymerase III transcribes small non-coding RNAs, including tRNAs, 5S rRNA, U6 snRNA, SRP RNA, other stable short RNAs such as ribonuclease P RNA. RNA Polymerases I, II, III contain 14, 12, 17 subunits, respectively. All three eukaryotic polymerases have five core subunits that exhibit homology with the β, β’, αI, αII, ω subunits of E. coli RNA polymerase. An identical ω-like subunit is used by all three eukaryotic polymerases, while the same α-like subunits are used by Pol I and III; the three eukaryotic polymerases share four other common subunits among themselves. The remaining subunits are unique to each RNA polymerase; the additional subunits found in Pol I and Pol III relative to Pol II, are homologous to Pol II transcription factors. Crystal structures of RNA polymerases I and II provide an opportunity to understand the interactions among the subunits and the molecular mechanism of eukaryotic transcription in atomic detail; the carboxyl terminal domain of RPB1, the largest subunit of RNA polymerase II, plays an important role in bringing together the machinery necessary for the synthesis and processing of Pol II transcripts.
Long and structurally disordered, the CTD contains multiple repeats of heptapeptide sequence YSPTSPS that are subject to phosphorylation and other posttranslational modifications during the transcription cycle. These modifications and their regulation constitute the operational code for the CTD to control transcription initiation and termination and to couple transcription and RNA processing; the initiation of gene transcription in eukaryotes occurs in specific steps. First, an RNA polymerase along with general transcription factors binds to the promoter region of the gene to form a closed complex called the preinitiation complex; the subsequent transition of the complex from the closed state to the open state results in the melting or separation of the two DNA strands and the positioning of the template strand to the active site of the RNA polymerase. Without the need of a primer, RNA polymerase can initiate the synthesis of a new RNA chain using the template DNA strand to guide ribonucleotide selection and polymerization chemistry.
However, many of the initiated syntheses are aborted before the transcripts reach a significant length. During these abortive cycles, the polymerase keeps making and releasing short transcripts until it is able to produce a transcript that surpasses ten nucleotides in length. Once this threshold is attained, RNA polymerase passes the promoter and transcription proceeds to the elongation phase. Pol II-transcribed genes contain a region in the immediate vicinity of the transcription start site that binds and positions the preinitiation complex; this region is called the core promoter because of its essential role in transcription initiation. Different classes of sequence elements are found in the promoters. For example, the TATA box is the conserved DNA recognition sequence for the TATA box binding protein, TBP, whose binding initiates transcription complex assembly at many genes. Eukaryotic genes contain regulatory sequences beyond the core promoter; these cis-acting control elements bind transcriptional activators or repressors to increase or decrease transcription from the core promoter.
Well-characterized regulatory elements include enhancers and insulators. These regulatory sequences can be spread over a large genomic distance, sometimes located hundreds of kilobases from the core promoters. General transcription factors are a group of proteins in