Chapter 4 : Nucleic Acids and RNA - Homework Questions

(Refer to table 2.2) Which chemical structure is represented by the yellow shape in the model?

A phosphate group

(Refer to table 2.3) In the accompanying image, a nucleotide is indicated by the letter _____. a.) E b.) B c.) C d.) D e.) A

B

Which of these is a difference between a DNA and an RNA molecule? a.) DNA contains five-carbon sugars, whereas RNA contains six-carbon sugars. b.) DNA is usually double-stranded, whereas RNA is usually single-stranded. c.) DNA contains uracil, whereas RNA contains thymine. d.) DNA is a polymer composed of nucleotides, whereas RNA is a polymer composed of nucleic acids. e.) DNA contains nitrogenous bases, whereas RNA contains phosphate groups.

B ; with some exceptions, DNA is a double-stranded molecule and RNA is a single-stranded molecule.

(table 2.4) A nitrogenous base is indicated by the letter _____.

C

In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand. a.) guanine ... adenine b.) cytosine ... thymine c.) thymine ... cytosine d.) uracil ... cytosine e.) cytosine ... uracil

C

Most biologists contend that the first life-form on Earth was a self-replicating RNA molecule, not DNA or protein. Which statement best explains why? a.) Structurally and chemically, RNA is more versatile than DNA or proteins. b.) Self-replicating RNA molecules have been discovered in living cells. c.) Only RNA can function as a catalyst and an information-containing entity. d.) Only RNA can furnish the information to make a copy of itself.

C

Which of the following describes the synthesis of nucleic acids? a.) Strands in a double helix are synthesized in a parallel direction such that one end of the molecule has two 3' ends and other has two 5' ends. b.) Nucleotides are added to the 5' end of a single nucleic acid strand. c.) Complementary pairing between bases is required for copying nucleic acids. d.) Nucleic acids are polymerized by the formation of peptide bonds between nucleotides.

C

(Table 2.4) You can tell that this is an image of a DNA nucleotide and not an RNA nucleotide because you see a _____. a.) thymine nitrogenous base, not a uracil nitrogenous base b.) double-stranded molecule, not a single-stranded molecule c.) sugar with two, and not three, oxygen atoms d.) phosphate group, not a uracil e.) uracil nitrogenous base, not a thymine nitrogenous base

C ; DNA nucleotides are composed of deoxyribose sugars, whereas RNA nucleotides are composed of ribose sugars.

Which statement best explains why G-T and A-C base pairs are not complementary? a.) G-T and A-C base pairs do not have the proper width to fit within the interior of the DNA Double double Helixhelix. b.) G-T and A-C pairs would violate Chargaff's rule of equal numbers of T's and A's, C's and G's. .c.) G-T and A-C base pairs cannot form as many hydrogen bonds as A-T and G-C base pairs. d.) G-T and A-C pairs would not contribute to the hydrophobic interactions that stabilize the DNA Double double helix.

C ; Given the bond angles and distances in a DNA double helix, a G-T pair can form only one hydrogen bond while an A-C pair can form none.

Chapter 4 : Nucleic Acids and RNA

Chapter 4 : Nucleic Acids and RNA

(Refer to table 2.4) This is an image of a(n) _____. a.) nucleic acid b.) thiol c.) amino acid d.) nucleotide e.) none of the above

D

An RNA molecule that can catalyze chemical reactions is called a_____. a.) stem-loop b.) protein c.) Tetrahymena d.) ribozyme

D

How are the structures of RNA and DNA similar? a.) Adenine pairs with thymine in both. b.) They both contain the sugar ribose. c.) They both have the same tertiary structure. d.) Their sugar-phosphate backbones are formed by phosphodiester linkages.

D

Nucleic acids are assembled in the _____ direction. a.) 4' to 5' b.) 5' to 1' c.) 2' to 3' d.) 5' to 3' e.) 1' to 5'

D

The chemical evolution theory states that the first living molecule needed these two attributes: a.) It could acquire energy and catalyze reactions. b.) It could acquire energy and serve as a replication template. c.) It could maintain homeostasis and acquire energy. d.) It could serve as a replication template and could catalyze reactions.

D

Which of these nitrogenous bases is found in DNA but not in RNA? a.) adenine b.) cytosine c.) uracil d.) thymine e.) guanine

D

If a DNA double helix contains 28% T nucleotides, then what is the percentage of A nucleotides? a.)56% b.) 44% c.) 22% d.) 28%

D ; A and T are complementary base pairs, so the amounts of A and T should be equal.

Several students have been practicing drawing their models of nucleotides. Whose model do you think is most consistent with the actual chemical structure of nucleotides?

...

(Refer to table 2.1) 1. This model shows six nucleotides bonded together. 2. This model shows that phosphate groups bond to nitrogenous bases. 3. This model shows that there is more than one kind of nitrogenous base. 4. The 3' and 5' carbon labels are in the correct locations in the model. 5. This model represents two nucleic acids bonded together. 6. This model shows that phosphate groups bond to sugars. 7. This model shows that there is more than one kind of sugar.

1. False 2. False 3. True 4. True 5. False 6. True 7. False

What is responsible for the decreased stability of RNA compared to DNA? (check all that apply) 1.) RNA's secondary structure is less stable because of hydrophobic interactions and hydrogen bonds that form between complementary bases of the two sugar-phosphate backbones. 2.) RNA is less resistant to cleavage because it lacks a hydroxyl group on the 2' carbon. 3.) RNA is less resistant to cleavage because it has a hydroxyl group on the 2' carbon. 4.) RNA's secondary structure is less stable because it includes short regions of double helices and looped structures.

3 and 4 only

In a nucleotide, the nitrogenous base is attached to the sugar's _____ carbon and the phosphate group is attached to the sugar's _____ carbon. a.) 1' ... 5' b.) 1' ... 3' c.) 2' ... 3' d.) 2' ... 1' e.) 1' ... 2'

A

According to the RNA world model, a ribozyme would replicate by creating a double-stranded RNA intermediate. Would you expect the intermediate to have the same catalytic activity as the original ribozyme? a.) yes b.) no

No. Catalytic activity in ribozymes depends on the tertiary structure generated from folding single-stranded molecules. Fully double-stranded forms of the RNA would not form the same tertiary structure.

Which symbol is generally used to represent a sugar in simple models of nucleotides?

Pentagon

(Table 2.4) The letter A indicates a _____.

Phosphate group