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Homework7Solution - as G and C but since G must equal C we...

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Biol 214/414 Homework #7 Due 10-9-09 The chromosome of a certain bacterium is a circle of double stranded DNA that is 4.2 million base pairs long. If the DNA is 20 % A (considering the composition of both strands together), how many G deoxynucleotides are there in one copy of this chromosome? How many deoxyriboses are there in one copy of the chromosome? If the chromosome is cleaved in both strands at the same location to convert it to a linear molecule and this linear molecule is laid out straight, how long will it be? 1. If the DNA molecule has 4.2 million base pairs , it has 8.4 million nucleotides (and also 8.4 million bases, as there is one base for every nucleotide). If 20 % of these are A’s, then 20 % must be T’s (because the A composition always equals the T composition due to the base pairing rules). So A and T together comprise 40 % of the bases, leaving 60 %
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Unformatted text preview: as G and C, but since G must equal C, we know that G = C = 30 %. 30 % of 8.4 million is 2.52 million G’s in one copy of the chromosome. 2. If there are 8.4 million deoxynucleotides in one copy of the chromosome (see part 1 above), there must also be 8.4 million deoxyriboses, as there is one deoxyribose in each deoxynucleotide. 3. There is, on average, a distance of 3.4 Å (= 0.34 nm = 3.4 E-10 meters) between adjacent base pairs. So the total length of one chromosome will be (3.4 E-10 meters/bp) (4.2 E6 bp) = 1.428 E-3 meters =1.428 mm. If you wanted to be more precise you could say that for 4.2 million bp there are really only 4,199, 999 3.4 Å spaces between bp and so the actual distance is 3.4 Å less than 1.428 mm, but 1.428 mm is plenty good enough for these purposes!...
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