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3.E: Biochemistry of the Genome (Exercises)

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    3.1: Structure and Function of DNA

    Nucleic acids are composed of nucleotides, each of which contains a pentose sugar, a phosphate group, and a nitrogenous base. Deoxyribonucleotides within DNA contain deoxyribose as the pentose sugar. DNA contains the pyrimidines cytosine and thymine, and the purines adenine and guanine. Nucleotides are linked together by phosphodiester bonds between the 5ʹ phosphate group of one nucleotide and the 3ʹ hydroxyl group of another.

    Multiple Choice

    Which of the following is not found within DNA?

    1. thymine
    2. phosphodiester bonds
    3. complementary base pairing
    4. amino acids
    Answer

    D

    If 30% of the bases within a DNA molecule are adenine, what is the percentage of thymine?

    1. 20%
    2. 25%
    3. 30%
    4. 35%
    Answer

    C

    Which of the following statements about base pairing in DNA is incorrect?

    1. Purines always base pairs with pyrimidines.
    2. Adenine binds to guanine.
    3. Base pairs are stabilized by hydrogen bonds.
    4. Base pairing occurs at the interior of the double helix.
    Answer

    B

    If a DNA strand contains the sequence 5ʹ-ATTCCGGATCGA-3ʹ, which of the following is the sequence of the complementary strand of DNA?

    1. 5ʹ-TAAGGCCTAGCT-3ʹ
    2. 5ʹ-ATTCCGGATCGA-3ʹ
    3. 3ʹ-TAACCGGTACGT-5ʹ
    4. 5ʹ-TCGATCCGGAAT-3ʹ
    Answer

    D

    During denaturation of DNA, which of the following happens?

    1. Hydrogen bonds between complementary bases break.
    2. Phosphodiester bonds break within the sugar-phosphate backbone.
    3. Hydrogen bonds within the sugar-phosphate backbone break.
    4. Phosphodiester bonds between complementary bases break.
    Answer

    A.

    Fill in the Blank

    The end of a nucleic acid strand with a free phosphate group is called the ________.

    Answer

    5ʹ end

    True/False

    The work of Rosalind Franklin and R.G. Gosling was important in demonstrating the helical nature of DNA.

    Answer

    True

    The A-T base pair has more hydrogen bonding than the C-G base pair.

    Answer

    False

    Short Answer

    What is the role of phosphodiester bonds within the sugar-phosphate backbone of DNA?

    What is meant by the term “antiparallel?”

    Why is DNA with a high GC content more difficult to denature than that with a low GC content?

    Critical Thinking

    A certain DNA sample is found to have a makeup consisting of 22% thymine. Use Chargaff’s rules to fill in the percentages for the other three nitrogenous bases.

    A DNA strand has 22% thymine. The percentages for adenine, guanine, and cytosine are blank.

    In considering the structure of the DNA double helix, how would you expect the structure to differ if there was base pairing between two purines? Between two pyrimidines?

    3.2: Structure and Function of RNA

    Ribonucleic acid (RNA) is typically single stranded and contains ribose as its pentose sugar and the pyrimidine uracil instead of thymine. An RNA strand can undergo significant intramolecular base pairing to take on a three-dimensional structure. There are three main types of RNA, all involved in protein synthesis. Messenger RNA (mRNA) serves as the intermediary between DNA and the synthesis of protein products during translation.

    Multiple Choice

    Which of the following types of RNA codes for a protein?

    1. dsRNA
    2. mRNA
    3. rRNA
    4. tRNA
    Answer

    B

    A nucleic acid is purified from a mixture. The molecules are relatively small, contain uracil, and most are covalently bound to an amino acid. Which of the following was purified?

    1. DNA
    2. mRNA
    3. rRNA
    4. tRNA
    Answer

    D

    Which of the following types of RNA is known for its catalytic abilities?

    1. dsRNA
    2. mRNA
    3. rRNA
    4. tRNA
    Answer

    C

    Ribosomes are composed of rRNA and what other component?

    1. protein
    2. polypeptides
    3. DNA
    4. mRNA
    Answer

    A

    Which of the following may use RNA as its genome?

    1. a bacterium
    2. an archaeon
    3. a virus
    4. a eukaryote
    Answer

    C

    Matching

    Match the correct molecule with its description:

    ___tRNA

    ___rRNA

    ___mRNA

    A. is a major component of ribosome

    B. is a copy of the information in a gene

    C. carries an amino acid to the ribosome
    Answer

    C, A, B

    True/False

    Ribosomes are composed mostly of RNA.

    Answer

    True

    Double-stranded RNA is commonly found inside cells.

    Answer

    False

    Short Answer

    What are the differences between DNA nucleotides and RNA nucleotides?

    How is the information stored within the base sequence of DNA used to determine a cell’s properties?

    How do complementary base pairs contribute to intramolecular base pairing within an RNA molecule?

    If an antisense RNA has the sequence 5ʹAUUCGAAUGC3ʹ, what is the sequence of the mRNA to which it will bind? Be sure to label the 5ʹ and 3ʹ ends of the molecule you draw.

    Why does double-stranded RNA (dsRNA) stimulate RNA interference?

    Critical Thinking

    Identify the location of mRNA, rRNA, and tRNA in the figure.

    A long strand is labeled ii. A small oval is attached to the bottom of this strand; and a large dome to the top. These two structures together are labeled iii. Smaller rectangles sit inside the large dome and are attached to small segments of the long strand. These rectangles are labeled i.

    Why does it make sense that tRNA and rRNA molecules are more stable than mRNA molecules?

    This page titled 3.E: Biochemistry of the Genome (Exercises) is shared under a CC BY license and was authored, remixed, and/or curated by OpenStax.

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