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10.E: Biochemistry of the Genome (Exercises)

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    10.1: Using Microbiology to Discover the Secrets of Life

    DNA was discovered and characterized long before its role in heredity was understood. Microbiologists played significant roles in demonstrating that DNA is the hereditary information found within cells. In the 1850s and 1860s, Gregor Mendel experimented with true-breeding garden peas to demonstrate the heritability of specific observable traits. In 1869, Friedrich Miescher isolated and purified a compound rich in phosphorus from the nuclei of white blood cells; he named the compound nuclein.

    Multiple Choice

    Frederick Griffith infected mice with a combination of dead R and live S bacterial strains. What was the outcome, and why did it occur?

    1. The mice will live. Transformation was not required.
    2. The mice will die. Transformation of genetic material from R to S was required.
    3. The mice will live. Transformation of genetic material from S to R was required.
    4. The mice will die. Transformation was not required.
    Answer

    D

    Why was the alga Acetabularia a good model organism for Joachim Hämmerling to use to identify the location of genetic material?

    1. It lacks a nuclear membrane.
    2. It self-fertilizes.
    3. It is a large, asymmetrical, single cell easy to see with the naked eye.
    4. It makes a protein capsid.
    Answer

    C

    Which of the following best describes the results from Hershey and Chase’s experiment using bacterial viruses with 35S-labeled proteins or 32P-labeled DNA that are consistent with protein being the molecule responsible for hereditary?

    1. After infection with the 35S-labeled viruses and centrifugation, only the pellet would be radioactive.
    2. After infection with the 35S-labeled viruses and centrifugation, both the pellet and the supernatant would be radioactive.
    3. After infection with the 32P-labeled viruses and centrifugation, only the pellet would be radioactive.
    4. After infection with the 32P-labeled viruses and centrifugation, both the pellet and the supernatant would be radioactive.
    Answer

    A

    Which method did Morgan and colleagues use to show that hereditary information was carried on chromosomes?

    1. statistical predictions of the outcomes of crosses using true-breeding parents
    2. correlations between microscopic observations of chromosomal movement and the characteristics of offspring
    3. transformation of nonpathogenic bacteria to pathogenic bacteria
    4. mutations resulting in distinct defects in metabolic enzymatic pathways
    Answer

    B

    According to Beadle and Tatum’s “one gene–one enzyme” hypothesis, which of the following enzymes will eliminate the transformation of hereditary material from pathogenic bacteria to nonpathogenic bacteria?

    1. carbohydrate-degrading enzymes
    2. proteinases
    3. ribonucleases
    4. deoxyribonucleases
    Answer

    D

    Fill in the Blank

    The element ____________ is unique to nucleic acids compared with other macromolecules.

    Answer

    phosphorus

    In the late 1800s and early 1900s, the macromolecule thought to be responsible for heredity was ______________.

    Answer

    protein

    Short Answer

    Why do bacteria and viruses make good model systems for various genetic studies?

    Why was nucleic acid disregarded for so long as the molecule responsible for the transmission of hereditary information?

    Bacteriophages inject their genetic material into host cells, whereas animal viruses enter host cells completely. Why was it important to use a bacteriophage in the Hershey–Chase experiment rather than an animal virus?

    Critical Thinking

    In the figure shown, if the nuclei were contained within the stalks of Acetabularia, what types of caps would you expect from the pictured grafts?

    A diagram showing a. mediterranea and A. crenulata. Graft A is of the foot of A. mediterranea and the upper stalk of A. crenulata. Graft B is of the foot of A. crenulata and the upper stalk of A. mediterranea.

    Why are Hershey and Chase credited with identifying DNA as the carrier of heredity even though DNA had been discovered many years before?

    10.2: 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?

    10.3: 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?

    10.4: The Structure and Function of Cellular Genomes

    The entire genetic content of a cell is its genome. Genes code for proteins, or stable RNA molecules, each of which carries out a specific function in the cell. Although the genotype that a cell possesses remains constant, expression of genes is dependent on environmental conditions. A phenotype is the observable characteristics of a cell (or organism) at a given point in time and results from the complement of genes currently being used.

    Multiple Choice

    Which of the following correctly describes the structure of the typical eukaryotic genome?

    1. diploid
    2. linear
    3. singular
    4. double stranded
    Answer

    A

    Which of the following is typically found as part of the prokaryotic genome?

    1. chloroplast DNA
    2. linear chromosomes
    3. plasmids
    4. mitochondrial DNA
    Answer

    C

    Serratia marcescens cells produce a red pigment at room temperature. The red color of the colonies is an example of which of the following?

    1. genotype
    2. phenotype
    3. change in DNA base composition
    4. adaptation to the environment
    Answer

    B

    Which of the following genes would not likely be encoded on a plasmid?

    1. genes encoding toxins that damage host tissue
    2. genes encoding antibacterial resistance
    3. gene encoding enzymes for glycolysis
    4. genes encoding enzymes for the degradation of an unusual substrate
    Answer

    C

    Histones are DNA binding proteins that are important for DNA packaging in which of the following?

    1. double-stranded and single-stranded DNA viruses
    2. archaea and bacteria
    3. bacteria and eukaryotes
    4. eukaryotes and archaea
    Answer

    D

    True/False

    Within an organism, phenotypes may change while genotypes remain constant.

    Answer

    True

    Noncoding DNA has no biological purpose.

    Answer

    False

    Fill in the Blank

    Plasmids are typically transferred among members of a bacterial community by ________ gene transfer.

    Answer

    horizontal

    Short Answer

    What are some differences in chromosomal structures between prokaryotes and eukaryotes?

    How do prokaryotes and eukaryotes manage to fit their lengthy DNA inside of cells? Why is this necessary?

    What are some functions of noncoding DNA?

    In the chromatin of eukaryotic cells, which regions of the chromosome would you expect to be more compact: the regions that contain genes being actively copied into RNA or those that contain inactive genes?

    Critical Thinking

    A new type of bacteriophage has been isolated and you are in charge of characterizing its genome. The base composition of the bacteriophage is A (15%), C (20%), T (35%), and G (30%). What can you conclude about the genome of the virus?

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