Question

1. How does transcription differ from replication in terms of where the process starts?

2. How does transcription differ from replication in terms of which strand(s) is/are used as the template? Is transcription a continuous or discontinuous process or both?

3. In general, what would happen to the position of the transcription start site on the DNA strand if the promoter sequence were moved toward the 3' end of the strand?

Answer 1

Q.1. Answer-

Replication initiates at a particular sequence in the chromosome is known as origin of replication and transcription starts at a particular sequence at the upstream of gene is known as transcription start site.

Q 2. Answer-

1. In replication both strands of DNA acts as template as DNA synthesis is semiconservative process and in daughter DNA one strand comes from parent DNA and another strand is newly synthesized. During DNA synthesis 5' to 3' strand of DNA is continuously synthesized and it is leading strand and another strand 3' to 5' is synthesized discontinuously so that it is known as lagging strand.

2. In transcription 3' to 5' strand of DNA acts as template strand onto which mRNA is synthesized in 5' to 3' direction. This mRNA is continuously synthesized as direction of RNA polymerase is 5' to 3'.

Q.3. In all genes promoter is located upstream (5' end) of the gene and gene is transcribed in downstream (3' gene) direction. So that if promoter is moved towards 3' end gene then that particular gene cannot be transcribed as promoter is regulatory sequence of gene at which RNA polymerase binds and starts transcription.