Biology, Eighth Edition (Raven)

Chapter 15: Genes and How They Work

Stages of Transcription

Are both strands of DNA used in making RNA? DNA is a two stranded molecule. Only one strand is used to transcribe mRNA. During transcription the two strands separate and RNA polymerase synthesizes mRNA based on the sequence of one the two strands. Then the two DNA strands join together again. Either strand may be used to produce mRNA. One strand does not exclusively code for mRNA while the other does not. But for any given mRNA strand only one of the DNA strands is used.

The complementary nature of DNA would make it very unlikely that both strands could code simultaneously for functional proteins. Here is an analogy with language. Imagine that each letter in the alphabet had a complementary letter. For example A might match with Q, B with X, and so on. If we were to write a normal English word the complementary sequence would be determined by the letters in that word and could not be changed. It is very unlikely that the complementary sequence would be a recognizable word.

View the animation below, then complete the quiz to test your knowledge of the concept.



1.

Which of the following best describes transcription?
A)DNA -> DNA
B)DNA -> RNA
C)DNA -> Protein
D)RNA -> DNA
E)RNA -> Protein
2.

The enzyme that accomplishes transcription is termed
A)DNA polymerase.
B)RNA polymerase.
C)DNA ligase.
D)RNA ligase.
E)RNA replicase.
3.

The transcription enzyme first attaches to the ________ of the gene.
A)coding region
B)promoter
C)operator
D)regulator
E)initiator
4.

The terminator of a gene is located upstream of the coding region.
A)True
B)False
5.

Initial attachment of the transcription enzyme to the gene, results in a structure termed the closed complex.
A)True
B)False
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