Figure 1015

During transcription, the enzyme RNA polymerase "reads" one of the chains, the template strand. RNA polymerase adds and then joins complementary RNA nucleotides, resulting in an rNa

RNA polymerase binds to the gene's promoter. The two DNA strands unwind and separate.

Transcription is the process by which the genetic instructions in a specific gene are transcribed or "rewritten" into an RNA molecule. Transcription takes place in the nucleus of eukaryotic cells and in the DNA-containing region in the cytoplasm of prokaryotic cells.

Steps of Transcription

Transcription occurs in three steps, as shown in Figure 10-15. In step O, RNA polymerase, an enzyme that catalyzes the formation of RNA on a DNA template, binds to a promoter. A promoter is a specific nucleotide sequence of DNA where RNA polymerase binds and initiates transcription. After RNA polymerase binds to the promoter, the DNA strands unwind and separate.

In step 6, RNA polymerase adds free RNA nucleotides that are complementary to the nucleotides on one of the DNA strands. The resulting chain is an RNA molecule. As in DNA replication, complementary base pairing determines the nucleotide sequence in the newly made RNA. For example, if the bases on the DNA strand was ATCGAC, the bases on the RNAstrand would be UAGCUG. Unlik DNA replication, transcription uses only a specific region (a ge> on one of the two DNA strands to serve as the template. As ' A polymerase moves past, the separated DNA strands rewind.

During step Q, RNA polymerase reaches a termination ,nal, a specific sequence of nucleotides that marks the end of gene. Upon reaching this "stop" signal, RNA polymerase relea s both the DNA and the newly formed RNA. The RNA made d' ng transcription can be one of many types including mRN tRNA, or rRNA. Thenewly made RNAcan nowperform itsjobir ie cell, and the RNA polymerase can transcribe another gene.

^^ Complementary RN

>NA and new RNA id by the polymerase.

RNA polymerase binds to the gene's promoter. The two DNA strands unwind and separate.

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