George is studying a computer model of a DNA molecule, in which the letters A, C, G, and T are listed in a very long sequence. T
he model includes a total of 2000 genes that are scattered along the full length of the molecule. The genes make up only a small fraction of the molecule. George wants to identify the locations of the genes. Which would be the MOST USEFUL first step to follow?
A. Divide the model molecule into 2000 segments of equal size.
B. Identify all of the start codons in the model molecule.
C. Identify the promoter regions in the model molecule.
D. Divide the model molecule into three-letter pieces.
The correct answer is: B. Identify all of the start codons in the model molecule.
One of two ways of finding gene locations is mapping the molecular locations (other is cytogenetic location, using chromosomes).
Finding the molecular location of the gene refers to finding the location of that gene in terms of base pairs. It means scan the DNA for start and stop codons. This can be complicated by the fact that there is some variation in start codons.
Finding the molecular location of one gene allows determination of exactly how far that gene is from other genes on the same chromosome.
C. Identify the promoter regions in the model molecule.
Explanation:
Promoters are the sequences present close to the upstream of start site. Promoter is the sequence that serves as binding site for RNA polymerase to start the process of transcription. Since promoter sequences are consensus sequences and all genes have promoters associated with them; identification of promoter sequences can give location of the gene on the otherwise large DNA molecule.
