Molecular Biology BIMM100 Fall 2009 midterm

Molecular Biology BIMM100 Fall 2009 midterm - 1...

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1 Name:______ANSWERS____________ October 29, 2009 BIMM 100 MOLECULAR BIOLOGY MIDTERM EXAM WAIVER: (please sign): By signing this waiver I give permission for this exam to be left in 2150 Bonner Hall for me to pick up. I realize this procedure may expose my grade to public scrutiny. Signature________________________________ QUESTION POINTS QUESTION POINTS 1 (5 points) Tyler Sloan 8 (5 points)_____Shubhanga Mani 2 (10 points) Tyler Sloan 9 (5 points)_____Bin Wang 3 (5 points) ___ Tri Le___ 10 (10 points) ___Bin Wang 4 (5 points) ___ Tri Le___ 11(5 points)___Jake Alexander 5 (10 points) __Tam Tran 12 (10 points)__Jake Alexander 6 (10 points)___Tam Tran 13 (5 points)___Katie Greenham 7 (5 points___Shubhanga Mani 14 (10 points)___Katie Greenham TOTAL / (100)
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2 Name:______ANSWERS____________ 1) a) Why is the ratio of adenine to thymine always the same while the ratio of adenine to guanine varies in the DNA of different organisms? Adenine in one strand is always hydrogen bonded to thymine in the other strand. In double stranded DNA the percentage of adenine will always be the same as the percentage of thymine. However, the ratio of adenine to guanine will only depend on the total percentage A+T in the genome which has been seen to vary from 20% to 85%. G+C makes up the remainder. b) What aspects of the structure of DNA are essential for its consistant width? The purines ( adenine and guanine) are the same size and hydrogen bond between the two strands with the smaller pyrimidines (thymine and cytosine) that are the same size as each other. So the total distance across the two strands is constant. The deoxyribose phosphate backbone connects each of the nucleic acid bases at regular intervals along the DNA strands. 2) What was the experimental evidence showing that DNA replicates semiconservatively? E. coli bacteria were grown in medium that contain 15 N (heavy) and then shifted to medium with 14 N (light). DNA was prepared at various times and its density was determined by high speed ultracentrifugation in gradients of CsCl. Initially the DNA banded at a lower position in the gradient than when collected after the number of bacteria had doubled (one generation). After 2 generations the DNA was even lighter (ie. banded at a higher position). The results showed that initially both strands of DNA were heavy (HH); after one generation the DNA was intermediate (HL); and after another generation both strands were light (LL). This proves that DNA replication is semi-conservative such that newly replicated double helix contains one old and one new strand.
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3 Name:______ANSWERS____________ 3) What is the likely reason that the basic mechanisms of DNA replication, RNA transcription and protein synthesis are all the same in bacteria, plants and animals? Bacteria that used DNA, transcribed it into RNA and then translated into proteins were far more successful and adaptable than any other form of life early in the history of this planet. They took over the world but were still able to exchange genes among themselves ie. they were all essentially the same species. The optimal procsses and their components were fixed in the population before
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