The Biochemical Basis of Heredity Practice Test (page 2)

By — McGraw-Hill Professional
Updated on Aug 21, 2011

DNA and Protein Synthesis Questions

  1. Given a single strand of DNA …3'-TACCGAGTACTGACT-5' … , construct
    1. the complementary DNA chain,
    2. them RNA chain that would be made from the given strand, and
    3. the polypeptide encoded (use Table 3-1).
    4. Which strand is the sense strand?
  2. In 1928, before DNA was recognized as the hereditary material, F. Griffith performed a series of experiments in which he infected mice with two different strains of pneumonia-causing bacteria (S. pneumonia). He had in his laboratory two strains of this bacterium; the S strain was virulent (disease-causing) and had a smooth colony appearance and the R strain was not virulent and had a rough colony appearance.
      Experiment 1: Mice infected with the S strain became sick and died.
      Experiment 2: Mice infected with the R strain did not become sick.
      Experiment 3: Mice infected with heat-killed S bacteria did not become sick.
      Experiment 4: Mice infected with a mixture of heat-killed S bacteria and live R bacteria became sick and died.
    1. How can the results of Experiment 4 be explained?
    2. Do these results provide evidence that DNA is the hereditary material?
  3. If the ratio (A+G)/( T + C) in one strand of DNA is 0.7, what is the same ratio in the complementary strand?
  4. The bacterial virus, phage T4, is a simple infectious agent that is composed of a DNA core and a protein coat. It infects a bacterial cell by attaching to its surface and then injecting material into the cell. This material then directs the synthesis of new viral particles. Using radioactive phosphorous (32P) and radioactive sulfur (35S), design an experiment using this virus to show that DNA is the hereditary material. (Hint: see Example 12.1.)
  5. How many different mRNAs could specify the amino acid sequence met-phe-ser-pro?
  6. If the coding region of a gene is estimated to consist of 450 nucleotide base pairs (bp), how many amino acids would the corresponding polypeptide chain contain?
  7. Given the hypothetical enzyme below with regions A, B, C, and D (* = disulfide bond; hatched area = active site), explain the effect of each of the following mutations in terms of the biological activity of the mutant enzyme:
    1. nonsense in DNA coding for region A,
    2. silent in region D,
    3. deletion of one complete codon in region C,
    4. missense in region B,
    5. nucleotide addition in region C.
  8. Infognana

  9. A large dose of ultraviolet irradiation can kill a wild-type cell even if the DNA repair system is unsaturated. How?
  10. A single base addition and a single base deletion approximately 15 bases apart in the mRNA specifying the protein lysozyme from the bacterial virus T4 caused a change in the protein from its wild-type composition … lys-ser-proser-leu-asn-ala-ala-lys… to the mutant form… lys-val-his-his-leu-met-ala-alalys…
    1. From the mRNA codons listed in Table 3.1, decipher the segment of mRNA for both the original protein and the double mutant.
    2. Which base was added? Which was deleted?
  11. If the DNA of an E. coli has 4:2 × 106 nucleotide pairs in its DNA, and if an average gene contains 1500 nucleotide pairs, how many genes does it potentially possess?
  12. The DNA of bacterial phage lambda has 1:2 × 105 nucleotides. How many proteins of molecular weight 40,000 could be coded by this DNA? Assume a molecular weight of 100 for the average amino acid.

Mutations Questions

  1. Acridine dyes can apparently cause a mutation in the bacteriophage T4 by the addition or deletion of a base in the DNA chain. A number of such mutants have been found in the rII region of T4 to be single base addition type (+) or deletion type (–) mutants. A normal or wild-type rII region produces a normal lytic period (small plaque size) in the host bacterium Escherichia coli strain B. Phage T4 mutants in the rII region rapidly lyse strain B, producing a larger plaque. Several multiple mutant strains of T4 have been developed. Determine the lytic phenotypes (large plaque or small plaque) produced by the following rII, single base mutations in E. coli B assuming a triplet codon (suppose the mutant sites are close together):
    1. ( + )
    2. ( + )( – )
    3. ( – )( – )
    4. ( + )( – )( + )
    5. ( + )( + )( + )
    6. ( – )( – )( + )
    7. ( – )( – )( – )
    8. ( + )( + )( + )( + )
    9. ( + )( – )( + )( + )( + )
  2. The "dotted" gene in maize (Dt) is a "mutator" gene influencing the rate at which the gene for colorless aleurone (a) mutates to its dominant allele (A) for colored aleurone. An average of 7.2 colored dots (mutations) per kernel was observed when the seed parent was dt/dt, a/a and the pollen parent was Dt/Dt, a/a. An average of 22.2 dots per kernel was observed in the reciprocal cross. How can these results be explained?
  3. Assuming no intensity effect is operative, which individual would carry fewer mutations: an individual who receives 25 roentgens in 5 h or an individual who receives only 0.5 roentgen per year for his or her normal lifetime (60 years)? In terms of percentage, how many more mutations would be expected in the individual with the higher total dosage?
  4. If the mutation rate of a certain gene is directly proportional to the radiation dosage, and the mutation rate of Drosophila is observed to increase from 3% at 1000 roentgens to 6% at 2000 roentgens, what percentage of mutations would be expected at 3500 roentgens?
  5. A number of nutritional mutant strains were isolated from wild-type Neurospora that responded to the addition of certain supplements in the culture medium by growth (+) or no growth (0).Given the following responses for single-gene mutants, diagram a metabolic pathway that could exist in the wild-type strain consistent with the data, indicating where the chain is blocked in each mutant strain.
    1. Infognana
    2. Infognana
    3. Infognana
  6. Point mutations correlated with amino acids in the active site in widely separated regions of a gene can render its enzymatic or antibody product inactive. What inference can be made concerning the three-dimensional structure of the active sites in such proteins?
  7. A nonsense point mutation in one gene can sometimes be at least partially suppressed in its phenotypic manifestation by a point mutation in a different gene. Offer an explanation for this phenomenon of second-site suppression.
  8. In addition to the kind of mechanism accounting for second-site suppression of nonsense mutations (see previous problem), give two other possible mechanisms for this type of suppression of missense mutations.
  9. Interallelic in vitro complementation has been observed in alkaline phosphatase enzymes and other proteins. How can a diploid heterozygote bearing two point mutations within homologous genes result in progeny with normal or nearly normal phenotypes (complementation)?
  10. Why are most mutations in protein-coding genes recessive to their wild-type alleles?
  11. Bacterial cells that are sensitive to the antibiotic streptomycin (strs) can mutate to a resistant state (strr). Such "gain of function" mutations, however, occur much less frequently than "loss of function" mutations such as mutation from the ability to make the amino acid histidine (his+) to the inability to do so (his), or mutation from the ability to metabolize the sugar lactose (lacþ) to the inability to do so (lac). Formulate a hypothesis that explains these observations.
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