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Working on the Amazon River, a biologist isolated DNA from two unknown organisms, P and Q. He discovered that the adenine content of P was 15% and the cytosine content of Q was 42%. This means that:
a. the amount of guanine in P is 15%.
b. the amount of guanine and cytosine combined in P is 70%.
c. the amount of adenine in Q is 42%.
d. the amount of thymine in Q is 21%.
e. it takes more energy to unwind the DNA of P than theDNA of Q.
Introduction:
The genetic material in DNA (deoxyribonucleic acid) contains four types of nucleotides. These nucleotides consist of sugar, deoxyribose, a phosphate group, and a nitrogen base. There are four types of nitrogenous bases that are present in DNA. These are guanine, adenine, cytosine, and thymine. The guanine and adenine are purines and cytosine and thymine are pyrimidines.
Answer to Problem 1TYK
Correct answer:
The content of guanine and cytosine combined in P is 70%.
Explanation of Solution
Justification for the correct answer:
Option (b) states that the amount of guanine and cytosine combined in P is 70%. The amount of adenine content of P was 15%, which means that the amount of thymine must also be 15%. This makes up 30%, which means that the other two bases guanine and cytosine constitute 70% of the content. Hence, option (b) is correct.
Justification for the incorrect answers:
Option (a) states that the amount of guanine in P is 15%. The amount of adenine and thymine is 15% and the sum of the other two bases guanine and cytosine is 70%. The amount of guanine is equal to that of cytosine, so each base must be 35% and not 15%. So, it is an incorrect option.
Option (c) states that the amount of adenine in Q is 42%. The amount of cytosine in Q is 42% and because the amount of guanine is equal to that of cytosine, the sum of cytosine and guanine in Q must be 84%. The other two bases adenine and thymine, thus constitute 16% of the content, which means that adenine must be 8% and not 42%. So, it is an incorrect option.
Option (d) states that the amount of thymine in Q is 21%. The amount of cytosine in Q is 42% and because the amount of guanine is equal to that of cytosine, the sum of cytosine and guanine in Q must be 84%. The other two bases adenine and thymine constitute 16% of the content, which means that thymine must be 8% and not 21%. So, it is an incorrect option.
Option (e) states that it takes more energy to unwind the DNA of P than to unwind the DNA of Q. There are three hydrogen bonds between guanine and cytosine and two between adenine and thymine. It will take more energy to break three hydrogen bonds than to break two hydrogen bonds. The sum of guanine and cytosine content in P is 70% of the content and in Q is 84% of the content. Thus, it takes more energy to unwind the DNA of Q than to unwind the DNA of P. So, it is an incorrect option.
Hence, options, (a), (c), (d), and (e) are incorrect.
Thus, it can be concluded that the total content of guanine and cytosine in the organism P is 70%. This is because the amount of adenine is equal to that of thymine and the amount of adenine is equal to that of thymine in DNA. The total amount of adenine and thymine in the organism P is 30%.
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Chapter 14 Solutions
Biology: The Dynamic Science (MindTap Course List)
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