Which enzyme transcribes dna

Following transcription, 30S and 50S ribosomal subunits attach to the mRNA and tRNA inserts the correct amino acids which are subsequently joined to form a polypeptide or a protein through a process called translation. This enzyme initiates transcription, joins the RNA nucleotides together, and terminates transcription. To initiate transcription in bacteria, a variety of proteins called sigma factors bind to RNA polymerases.

This complex can then bind to a specific sequence of usually about 40 deoxyribonucleotide bases called the promoter located along the DNA prior to the coding region of the gene. As mentioned earlier in this unit, the 3' end of a strand of nucleic acid has a hydroxyl OH group on the 3' carbon of the deoxyribose or ribose and is not linked to another nucleotide. RNA is synthesized by complementary base pairing of free ribonucleotides with the deoxyribonucleotides of a gene.

The enzyme responsible for transcription is RNA polymerase. Xs represent the ribonucleotides for the ribosome binding site prior to the Start codon AUG. The phosphodiester bond refers to the phosphate on the 5'C of the newly inserted nucleotide covalently bonding to the 3'C of the last ribonucleotide in the mRNA chain.

The mRNA polymerizes at a rate of about 30 nucleotides per second. This process continues until the RNA polymerase encounters a "stop" signal or transcription terminator at the end of the gene.

This causes the completed mRNA to drop off the gene. Transcription is under control of the enzyme RNA polymerase which is not shown here. Once the RNA polymerase moves beyond the promotor region, a new molecule of RNA polymerase can bind to the promotor and start a new round of transcription. In this way, a single gene can be transcribed multiple times. Transcription is summarized in Figs. There are 22 amino acids that can be encoded by the genetic information carried on mRNA.

The mRNA molecule is divided up into codons. A codon is a series of three consecutive mRNA bases coding for one specific amino acid. There are 64 codons. Alternative start codons are different from the standard AUG codon and are found occasionally in both prokaryotes and eukaryotes. In bacteria, a mRNA can be monocistronic or polycistronic.

A monocistronic mRNA is a transcript of a single gene. A polycistronic mRNA carries a transcript of multiple genes, often involved in a single biochemical pathway. All rights reserved. Strand Elongation. Transcription Termination. Figure 5: Rho-independent termination in bacteria. Inverted repeat sequences at the end of a gene allow folding of the newly transcribed RNA sequence into a hairpin loop.

This terminates transcription and stimulates release of the mRNA strand from the transcription machinery. References and Recommended Reading Connelly, S. Genes and Development 4 , — Dennis, P. Journal of Molecular Biology 84 , — Dragon.

Journal of Biological Chemistry , — Kritikou, E. Methods in Molecular Biology , 23—37 Logan, J. Article History Close. Share Cancel. Revoke Cancel. Keywords Keywords for this Article. Save Cancel. Flag Inappropriate The Content is: Objectionable.

Flag Content Cancel. Email your Friend. Submit Cancel. This content is currently under construction. Explore This Subject. Applications in Biotechnology. DNA Replication. Jumping Genes. Discovery of Genetic Material. Gene Copies. No topic rooms are there. Or Browse Visually. Other Topic Rooms Genetics.

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Codons are complementary groups of bases in mRNA. Transcription takes place in three steps: initiation, elongation, and termination. The steps are illustrated in Figure 2. Figure 2. Transcription occurs in the three steps—initiation, elongation, and termination—all shown here. Initiation is the beginning of transcription. It occurs when the enzyme RNA polymerase binds to a region of a gene called the promoter.