DNA Transcription

While the process of DNA replication copies entire DNA helices, the process of DNA transcription only copies short stretches of DNA from just one strand. During DNA replication, once a helix is unwound, the two strands remain separated permanently whereas in DNA transcription, only small regions of the helix are opened up at a time. Substrates for DNA transcription are ribonucleoside triphosphates, not deoxyribonucleside triphosphates. Additionally, transcriptional substrates contain uracils instead of thymines as base groups. DNA replication is a highly regulated process within a cell. DNA transcription is turned on and off by specific signals. RNA polymerase, unlike DNA polymerase is able to initiate synthesis on its own.

The start site and the promoter region.

The sigma subunit.

Conformity to the consensus sequence determines promoter strength. By adjusting the 17 base pair spacing, you not only bring the two regions either closer together or farther apart, but also adjust their rotational orientation. This is a result of the helical nature of DNA. A movement from one base to the next moves you not only up or down the helix, but also around the helix. This change in orientation can make it difficult for RNA polymerase to bind to both the –10 and –35 regions at the same time, significantly decreasing promoter strength.

UP element.