Genetics: Analysis and Principles 5th Edition by Robert Brooker

Exercise 53

On further analysis of the DNA described in conceptual question C21, you discover that the triplex DNA in this alien organism is composed of a double helix, with the third helix wound within the major groove (just like the DNA in Figure 9.18). How would you propose that this DNA is able to replicate itself In your answer, be specific about the base pairing rules within the double helix and which part of the triplex DNA would be replicated first.FIGURE 9.18 The structure of triplex DNA. (a) As seen in the ribbon model, the third, synthetic strand binds within the major groove of the double-stranded structure. (b) Within triplex DNA, the third strand hydrogen bonds according to the rule T to AT, and C to GC. The cytosine bases in the third strand are protonated (i.e., positively charged).
a.
Question C21
Let's suppose you have recently identified an organism that was scraped from an asteroid that hit the earth. (Fortunately, no one was injured.) When you analyze this organism, you discover that its DNA is a triple helix, composed of six different nucleotides: A, T, G, C, X, and Y. You measure the chemical composition of the bases and find the following amounts of these six bases: A = 24%, T = 23%, G = 11%, C = 12%, X = 21%, Y = 9%. What rules would you propose that govern triplex-DNA formation in this organism Note: There is more than one possibility.