DNA Transcription

http://biology.about.com/od/cellularprocesses/ss/Dna-Transcription.htm


DNA Transcription


By Regina Bailey, About.com Guide


DNA Transcription



National Human Genome Research Institute

.DNA transcription is a process that involves the transcribing of genetic information from DNA to RNA. The transcribed DNA message is used to produce proteins. DNA is housed within the nucleus of our cells. It controls cellular activity by coding for the production of enzymes and proteins. The information in DNA is not directly converted into proteins, but must first be copied into RNA. This ensures that the information contained within the DNA does not become tainted.

DNA Transcription

DNA consists of four nucleotide bases [adenine (A), guanine (G), cytosine (C) and thymine (T)] that are paired together (A-T and C-G) to give DNA its double helical shape.



There are three main steps to the process of DNA transcription.

•RNA Polymerase Binds to DNA



DNA is transcribed by an enzyme called RNA polymerase. Specific nucleotide sequences tell RNA polymerase where to begin and where to end. RNA polymerase attaches to the DNA at a specific area called the promoter region.





•Elongation



Certain proteins called transcription factors unwind the DNA strand and allow RNA polymerase to transcribe only a single strand of DNA into a single stranded RNA polymer called messenger RNA (mRNA). The strand that serves as the template is called the antisense strand. The strand that is not transcribed is called the sense strand.



Like DNA, RNA is composed of nucleotide bases. RNA however, contains the nucleotides adenine, guanine, cytosine and uricil (U). When RNA polymerase transcribes the DNA, guanine pairs with cytosine and adenine pairs with uricil.





•Termination



RNA polymerase moves along the DNA until it reaches a terminator sequence. At that point, RNA polymerase releases the mRNA polymer and detaches from the DNA.

Since proteins are constructed in the cytoplasm of the cell by a process called translation, mRNA must cross the nuclear membrane to reach the cytoplasm. Once in the cytoplasm, mRNA along with ribosomes and another RNA molecule called transfer RNA, work together to produce proteins. Proteins can be manufactured in large quantities because a single DNA sequence can be transcribed by many RNA polymerase molecules at once.



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