The initiation of transcription requires melting of the DNA double helix, i.e. separating hydrogen-bonded base pairs, immediatel
y upstream of the +1 site. How is this melting accomplished in E. coli? a. Bases at the promoter region flip outward from the double helix into pockets on the polymerase.
b. DNA helicase first unwinds the double helix around the +1 site.
c. RNA polymerase gets the energy to cause separation of strands from ATP hydrolysis.
d. Topoisomerase first returns the linking number to Lk0. DnaA:ATP complexes bind to and twist the double helix at the +1 site.
The correct answer is B. DNA helicase first unwinds the double helix around the +1 site.
Explanation:
The helicase is an enzyme that specifically breaks the hydrogen bonds of the bases in the transcription process. As E. Coli is a prokaryote, then, the transcription only occurs in one point of the circular DNA. The promoter region indicates where the DNA polymerase has to start replicating and the Topoisomerase unwinds the parts of the DNA that are being excessively twisted because of the separation of the two strands.
When a person starts exercising (running) the increase in energy expenditure causes an elevation of oxygen consumption and carbon dioxide production. To compensate for this the respiratory control center senses the LOW oxygen level in blood and the HIGH carbon dioxide level and signals the diaphragm to contract and relax more often (INCREASE THE RATE).
