AP Biology : Understanding Nucleotides and Base Pairs

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #31 : Understanding Nucleotides And Base Pairs

What is one of the primary differences between the purines and pyrimidines of DNA?

Possible Answers:

Purines consist of a single ring, whereas pyrimidines consist of two rings

Purines consist of two rings, whereas pyrimidines consist of one ring

Purines have a lipid chain, whereas pyrimidines do not

The purines bond to the phosphates on the DNA backbone, whereas the pyrimidines bond to sugar

Correct answer:

Purines consist of two rings, whereas pyrimidines consist of one ring

Explanation:

One of the primary differences between purines and pyrimidines is that purines consist of two rings, whereas the pyrimidines consist of one ring. One way to help remember the differences between purines and pyrimidines is that pyrimidines are like pyramids: sharp. Sharp things CUT (Cytosine Uracil Thymine). Note that uracil is only present in RNA, while thymine is only present in DNA. All nitrogenous bases bond to the sugar in the DNA backbone. The sugar is also connected to a phosphate group via a phosphodiester bond.

Example Question #32 : Understanding Nucleotides And Base Pairs

Which of the following nitrogenous bases are purines?

Possible Answers:

Thymine and uracil

Thymine and guanine

Guanine and adenine

Adenine and thymine

Cytosine and adenine

Correct answer:

Guanine and adenine

Explanation:

Purines are adenine and guanine, while pyrimidines are cytosine, thymine, and uracil.

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