mRNA Synthesis (Transcription)

How does transcription differ from DNA synthesis? The primary difference between transcription and DNA replication is that only a single strand of mRNA is produced during transcription. During DNA replication both strands need to be copied and DNA polymerase needs to work on both strands at the same time. Because DNA polymerase can only add new bases onto the free 3’ end of a molecule the two strands cannot be synthesized in the same way. The leading strand is synthesized as a continuous chain. The lagging strand is synthesized in pieces. In contrast, the single mRNA molecule is synthesized as a continuous strand. The other difference between the two processes is that during DNA synthesis the entire chromosome is copied. During transcription specific genes are transcribed in response to signals such as transcription factors.

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


1	The segment of the DNA molecule where messenger RNA synthesis begins is called the...

		A)	promoter region.
		B)	sigma factor.
		C)	transcription terminator.
		D)	polymerase.
		E)	template.

2	The complimentary messenger RNA strand that would be synthesized from the DNA base sequence of CTGAC would be...

		A)	GACTG
		B)	UGACU
		C)	AGTUG
		D)	GACUG
		E)	GACGU

3	The name of the structure that causes the synthesis of RNA to cease is called the...

		A)	promoter region
		B)	sigma factor
		C)	transcription terminator
		D)	polymerase
		E)	template

4	The synthesis of messenger RNA is called translation.

		A)	True
		B)	False

5	Synthesis of a new strand of messenger RNA is in the 5' to 3' direction.

		A)	True
		B)	False

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