Biology, Eighth Edition (Raven)

Chapter 25: Evolution of Development

Transcription Factors

What is meant by gene activation? In a multicellular organism every cell contains every gene found in the organism. Not all genes are actually used in every cell. The specialization of cell into different types means that some genes are used in some cells and not in others. Also many genes are only used at certain times. How are genes turned on and off? There are many different mechanisms for controlling transcription of mRNA. If a gene is ‘turned on’ then transcription proceeds followed by translation and production of a protein. If a gene is ‘turned off’ then transcription is halted. Different kinds of cells have different patterns of transcription (known as gene expression). Gene expression also varies within a cell depending on the influence of external factors.

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


1.	Transcription is carried out by the enzyme

		A)	DNA polymerase.
		B)	RNA polymerase.
		C)	RNAse.
		D)	topoisomerase.
		E)	reverse transcriptase.

2.	Which of the following statement(s) about basal transcription factors is(are) 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

3.	The assembly of transcription factors begins

		A)	upstream from the transcription start site.
		B)	downstream from the transcription start site.
		C)	upstream from the translation start site.
		D)	downstream from the translation start site.
		E)	downstream from the translation stop site.

4.	Eukaryotic transcription factors include activators and coactivators.

		A)	True
		B)	False

5.	The various transcription factors bind to the promoter.

		A)	True
		B)	False