Genetics Practice Problem Set I 1. A single stranded DNA molecule has the follow

Question

Genetics Practice Problem Set I 1. A single stranded DNA molecule has the following ratios Name What is its (A+GT + C) ratio? A complementary DNA strand is formed. Give the following ratios for this complementary strand: G/C (A+ G(T+ C- AC AG- 2. The base composition and base ratios of nucleic acids from eight different viruses are given below. fill in as much of the following as possible, indicate if the nucleic acid is DNA or RNA, or double stranded. Note again: It may not be possible to fill in all spaces. For each of the viruses andJor if these molecules are single Percentages AtTorU AG dsor DNA or Virus GCATU 1 19 19 31 3 19 19-31 31 31 31 19 19 5 25 18 25 32 you need for the above problems is Chargaffs Laws. Use these laws and your brain--synthesize information and think

Explanation / Answer

Chargaff draw a conclusion on the basis of his experiment that composition of base varied among species, however in every species the molar ratio of  [ A ] = [ T ] also [ C ] = [ G ], and the ratio [C+G] / [ A+T ] was usually less than unity, where [C+G] is less abundant. These ratios are explained as "Chargaff's Rules".

1) given that, A/T = 1/3, G/C = 4/3 and A+T/G+C = 8/7

according to chargaffs rule it should be A+G / T+C =7/8, because if it is given that A+T/G+C = 8/7, this means A & T should be present in equal ratio, hence A = 4 & T = 4. Similarly, for G and C, if we take G = 3 and C = 4, so that their sum should be 7. then we get A+C/T+G = 8/7. we can also get A/G = 1/4, A/C = 1/3.

2) for complementary strand, ratio will be reversed. thus, A/T = 3/1 because A always pair with T and G pairs with C. also G/C = 3/4. A+T/G+C = 7/8, A+G/T+C = 8/7, A+C/T+G = 7/8, A/G = 4/1 and A/C =3/1.

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