Biology, Eighth Edition (Raven)

Chapter 16: Control of Gene Expression

Transcription Complex and Enhancers

Why are molecules other than RNA polymerase needed for transcription? RNA polymerase is the molecule that makes mRNA. However it is not the only molecule needed for transcription. Other molecules recognize the site where transcription should start and create a complex that allows RNA polymerase to bind to the DNA and begin RNA synthesis. RNA polymerase does not have the ability to detect where it should start making mRNA . Without an initiation complex mRNA synthesis might start at random locations. Other molecules control the rate of mRNA synthesis. Not all gene products are required in equal amounts so other molecules are used to increase or decrease the rate of synthesis.

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


Assembly of basal transcription factors begins at the ________ sequence in the promoter.

Which of the following statements about basal transcription factors is TRUE?
A)they are essential for transcription
B)they cannot increase the rate of transcription by themselves
C)they can decrease the rate of transcription by themselves
D)A and B
E)A, B and C

Which of the following statements about enhancers is TRUE?
A)they are sequences to which activators bind
B)they are found in the promoter of a gene
C)they are only found in certain chromosomal locations
D)A and B
E)A, B and C

The interaction of activators, coactivators and basal transcription factors involves the formation of a loop in the DNA.

Regulatory proteins called repressors can decrease the rate of transcription by binding to the promoter.
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