Here is the answer to Where would RNA polymerase attach?
Where would RNA polymerase attach?
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RNA polymerase is an enzyme that synthesizes RNA using a DNA strand or RNA as a template and ribonucleoside triphosphate as a substrate and polymerizes it through phosphodiester bonds.
This enzyme requires four ribonucleotide triphosphates (NTP: ATP, GTP, CTP, and UTP) as substrates for RNA polymerase, DNA as a template, and divalent metal ions Mg2+ and Mn2+ as essential cofactors for the enzyme. The reaction catalyzed by it is expressed as (NMP)n+NTP→(NMP)n+1+PPi.
The synthesis direction of the RNA chain is also 5’→3′, and the first nucleotide carries 3 phosphate groups. Each subsequent addition of a nucleotide deletes a pyrophosphate to form a phosphodiester bond, and the energy of rapid pyrophosphate hydrolysis drives the polymerization reaction. Unlike DNA polymerase, RNA polymerase does not require primers, it can synthesize RNA strands directly on the template; RNA polymerase can partially unwind both strands of DNA, so it is not necessary to completely unwind the DNA double-strand when transcribing, RNA polymerase has no proofreading function.
RNA polymerase catalyzes the synthesis of RNA, which has many of the same catalytic features as DNA polymerase.
1) Using DNA as a template.
2) catalyzing the synthesis of nucleotides by polymerization reactions.
3) the polymerization reaction is a reaction in which nucleotides form 3′, 5′ a phosphodiester bond
4) reading the template in the 3’→5′ direction and synthesizing the nucleic acid in the 5’→3′ direction.
5) Faithful transcription of the template sequence according to the base-pairing principle.
RNA polymerases can usually be classified into prokaryotic RNA polymerases and eukaryotic RNA polymerases according to the class of organisms.
Prokaryotic and eukaryotic RNA polymerases share common features but differ in structure, composition, and properties.
1) Prokaryotic RNA polymerase is the most well-studied RNA polymerase of E. coli. The enzyme is a hexamer composed of five subunits (α2ββ’ωσ) with a molecular weight of about 500,000. α2ββ’ω is called the core enzyme, and the σ factor is called the full enzyme after binding to the core enzyme.
The main role of the σ factor is to recognize the promoter on the DNA template. It cannot bind to the DNA template when it is present alone, and it is only after binding to the core enzyme to form the holoenzyme that the holoenzyme can bind to the promoter on the template DNA. When it binds to a specific base sequence of the promoter gene, the DNA double-strand unravels partially, allowing transcription to begin, so the σ factor is also known as the initiation factor.
Seven σ-factors have been identified in E. coli, and different σ-factors can compete to bind the core enzyme to determine which gene is transcribed. One of them, σ70 (the number indicates its molecular weight size), assists in identifying the promoters of housekeeping genes. Environmental changes can induce the production of specific σ-factors that initiate the transcription of specific genes.
There is only one core enzyme, which is involved in the entire transcription process and catalyzes the transcriptional synthesis of all RNAs. The RNA polymerases of other prokaryotes are structurally and functionally similar to E. coli. The antibiotic rifampicin or rifamycin specifically inhibits the RNA polymerase of prokaryotes and becomes an anti-tuberculosis drug for mycobacterial therapy.
It binds specifically to the beta subunit of RNA polymerase. If rifampicin is added after the start of transcription, it can still play its role in inhibiting transcription, which indicates that the β-subunit foot plays a role in the whole process of transcription.
2) Eukaryotic RNA polymerases Eukaryotes have three different cytosolic RNA polymerases, namely RNA polymerase I, RNA polymerase II and RNA polymerase III.
These three RNA polymerases differ not only in their functional and physicochemical properties but also in their sensitivity to α a gooseberry mushroom (a cyclic octapeptide toxin contained in a poisonous mushroom).
The structures of the three cytosolic RNA polymerases of eukaryotes are more complex than those of prokaryotes, and all three RNA polymerases have two different large subunits, two α-like subunits, and one ω-like subunit, which are homologous to the β and β’, two α and ω subunits of the core enzyme of E. coli, respectively. In addition to the above five subunits, the three RNA polymerases contain 7 to 11 small subunits each.
When synthesizing RNA, prokaryotic cells rely on each subunit of RNA polymerase to complete the transcription process, while eukaryotic cells also need some protein factors to participate and to process and modify the transcription products.
Eukaryotic mitochondria have their own RNA polymerase that catalyzes the synthesis of mitochondrial mRNA, tRNA, and rRNA. mitochondrial RNA polymerase is similar in function and properties to prokaryotic RNA polymerase, and its activity can also be inhibited by rifampin or rifamycin.
Here is the correct answer to Where would RNA polymerase attach?
RNA polymerase should attach A.
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