Nucleic Acids Questions & Answers PDF

**What are nucleic acids?** Nucleic acids are formed by sequences of nucleotides. 11. **How can A distinguish T from C?** On the basis of the number and direction of hydrogen bonds T or C can form with A. Each base can form either two or three hydrogen bonds in a matched pair. The AT...

**What are nucleic acids?** Nucleic acids are formed by sequences of nucleotides. 11. **How can A distinguish T from C?** On the basis of the number and direction of hydrogen bonds T or C can form with A. Each base can form either two or three hydrogen bonds in a matched pair. The AT pair forms two, and the GC pair, three. However, when C is lined up against A, no hydrogen bonds can be formed (because donors do not line up with acceptors). **Answer:** Hydrogen bonding, which holds the two DNA strands together, determines which nucleotides will form complementary base-pairs. Adenine is able to form two hydrogen bonds and so it lines up with thymine, which is also able to form two hydrogen bonds. Cytosine, which is a smaller nucleotide like thymine, does not base-pair with adenine because their hydrogen-bonding atoms would not line up correctly. Likewise, guanine is able to form three hydrogen bonds and so it lines up with cytosine. which is also able to form three hydrogen bonds. Guanine, which is larger like adenine, does not-base pair with thymine because their hydrogen-bonding atoms would not line up correctly. 12. **From an extract of human cells growing in tissue culture, you obtain a white, fibrous substance. How would you distinguish whether it was DNA, RNA, or protein?** **Answer:** First you could test the substance for the presence of amino acids; if present, the substance is a protein. If the substance does not contain amino acids, it is one of the two nucleic acids. To determine which nucleic acid, you can either test the substance for the presence of ribose or deoxyribose or you can test the substance for the presence of thymine or uracil. The presence of thymine or deoxyribose indicates the substance is DNA. The presence of uracil or ribose indicates the substance is RNA. **13. Which of these statements about eukaryotic DNA is true?** **A** It contains the complementary base pair A--U. **B** The majority of the molecule comprises repetitive sequences. **C** It does not contain histone proteins. **14. The enzyme responsible for separating the DNA double helix during replication is:** **A** DNA polymerase I. **B** DNA polymerase III. **C** helicase. **3\' --C--C--G--A--A--T--G--T--C-- 5\'** **A** 3\' --G--G--C--U--U--A--C--A--G-- 5\' **B** 3\' --G--G--C--T--T--A--C--A--G-- 5\' **C** 5\' --G--G--C--U--U--A--C--A--G-- 3\' ----------------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------------------------------------- http://www.biology.arizona.edu/molecular\_bio/problem\_sets/nucleic\_acids/graphics/trnag.gif **With what mRNA codon would the tRNA in the diagram be able to form a codon-anticodon base pairing interaction?** ----------------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------------------------------------- **A.** [[3\'-AUG-5\']](http://www.biology.arizona.edu/molecular_bio/problem_sets/nucleic_acids/14c.html) -------- --------------------------------------------------------------------------------------------------------------- **B.** [[3\'-GUA-5\']](http://www.biology.arizona.edu/molecular_bio/problem_sets/nucleic_acids/14t.html) **C.** [[3\'-CAU-5\']](http://www.biology.arizona.edu/molecular_bio/problem_sets/nucleic_acids/14t.html) **D.** [[3\'-UAC-5\']](http://www.biology.arizona.edu/molecular_bio/problem_sets/nucleic_acids/14t.html) **E.** [[3\'-UAG-5\']](http://www.biology.arizona.edu/molecular_bio/problem_sets/nucleic_acids/14t.html)