Answers for Chapter-1
1. In considering Figure 1-2 if you were to extend the diagram, what would be the next two stages of
“magnification” beyond DNA be?
Answer1)
The next two stages of magnification would be-nucleotides and their organic molecular parts: a) nucleotides, which includes-deoxyribose sugar, a phosphate group and nitrogenous bases (adenine, thymine, guanine and cytosine) and b) atomic composition of these organic molecules (C, H, O, P and N).
2. In considering Figure 1-3, a. what do the small spheres represent? b. what do the brown slabs represent? c. do you agree with the analogy that DNA is structures like a ladder?
Answer 2) a) Blue ribbon represents sugar phosphate backbone while the blue spheres represent atoms. b) Brown slabs show complementary bases (A, T, G and C) c) Yes , it is a helical structure.
3. In Figure1-4 can you tell if the number of hydrogen bonds between adenine and thymine is the same as that between the cytosine and guanine? Do you think a DNA molecule of high A+T content will be more stable than one with high G+C content.
Answer 3)
There are two hydrogen bonds between adenine and thymine (A=T) and three hydrogen bonds between cytosine and guanine (G=C). Thus the bond between cytosine and guanine (G=C) is more stable.
6. In Figure 1-8, Is it true that the direction of transcription is from right to left as written for all the genes shown in these chromosomal segments?
Answer 6) No, There is one gene that will be read from left to right as RNA polymerase can only assemble nucleotides in 5’-3’ direction.
8. From Figure 1-12, what is the main difference in the locales of transcription and translation?
Answer 8) Transcription occurs in nucleus whereas translation occurs in the cytoplasm
11. In the Figure 1-18 calculate the number of nucleotide differences between humans and dogs in the cytochrome c gene. Repeat for humans and moths. Considering that the gene is several hundred nucleotides long, do these numbers seem large or small to you? Explain.
Answer 11) Cytochrome c gene from humans appears somewhat different when compared with that of dog with 14 nucleotide substitutions and even more from that of moths with 32 nucleotide substitutions.

Yet these differences do not affect the function of the gene. Thus is can be inferred that cytochrome c is highly conserved due to its significance in metabolism of aerobic organisms.
12. In Figure 1-21 why are colored ladders of bands shown in all electrophoretic gels? If the molecular labels used in all cases were radioactive , do you think the black bands in the bottom part of the figure would all be radioactive?
Answer 12) Three different types of electrophoresis is shown in this figure- DNA (Southern blot), RNA
Northern blot and protein Western blot. Yes they can hybridize with a radioactive probe based on the sequence complementarity of the probe and the macromolecular fragments (DNA, RNA or protein) and corresponding bands will incorporate radioactivity.
14. It has been said that DNA RNA protein discovery was the “Rosetta stone” of biology. Do you agree?
Answer 14) DNA RNA protein also known as central dogma of molecular biology is indeed comparable to the Rosetta stone as understanding of this essential concept of life gives us an insight into another, such as evolution, nature of mutations as a basic source of variability upon which evolutionary process might act.
15 Who do you think has the greatest impact on biology, Charles Darwin or Watson and Crick?
Answer 15) It is hard to say whose contribution is greater, both of the findings have an enormous impact on biological sciences.
17. Assume human body contains a trillion cells. We know that human genome contains 1 meter of DNA.
If all the DNA of your body were laid end-to-end, do you think it could stretch to the Moon and back.
Justify your answer. (the average distance to Moon is 385,000 km)
Answer 17) Yes, number of cells in human body (1,000,000,000,000)* length of each cell’s DNA (1 m or
0.001 km)=1,000,000,000 km enough to reach the Moon and return.