MCDB 101A – Midterm exam

MCDB 101A – Midterm exam

Subject: Chemistry    / General Chemistry
Question

Circle the best answer for each of the multiple choice questions (3 points each)
1.    A temperature sensitive (ts) mutation in 50 S ribosomal subunit protein prevents the binding of tRNAs to the ribosome “E” at the non-permissive temperature. How many amino acids would be found in the longest polypeptide chain that could be synthesized in this strain at the non-permissive temperature?
a.    0b.    1
c.    2d.    3e.    4
2.    In the presence of lactose, a merodiploid of genotype I-DP+O+ Z-Y+/I+ P-OCZ+Y- will producea.    Both ? galactosidase and permeaseb.    ? galactosidase but no permeasec.    Permease but no ? galactosidased.    Neither ? galactosidase nor permeasee.    Blue colonies on X-gal media
3.    The presence of short nucleotide repeats or exposure of DNA to intercalating agents can producea.    nonsense mutationsb.    nucleotide insertionsc.    nucleotide deletionsd.    frameshift mutations
e.    all of the above
4.    When running a northern blot you must denature the RNA prior to its transfer to the blotting membrane. What is the purpose of denaturing the RNA?a.    To prevent the RNA from forming double-stranded molecules
b.    To prevent the RNA from forming intramolecular base pairsc.    To provide RNA with a negative charged.    To fragment the RNA prior to gel electrophoresise.    To release the RNA from the polyacrylamide gel matrix used in the electrophoresis
5.    Polarity may increase the survival of bacteria in their natural environment by reducinga.    unnecessary transcription of monocistronic genesb.    unnecessary transcription of polycistronic genes
c.    unnecessary translation of polycistronic genesd.    the mutation frequency of monocystronic genese.    the mutation frequency of polycystronic genes
6.    A mutation that changes one amino acid to another without altering protein function is known as aa.    silent mutation
b.    neutral mutationc.    missense mutationd.    nonsense mutatione.    reversion mutation
17.    Which of the following is true of the blue-white cloning assay?a.    It is based on ? complementationb.    Insertion of a gene into a blue-white cloning vector is detected by the appearance of blue coloniesc.    It requires recombination between the plasmid and the host genomed.    The genome copy of the ?-galactosidase gene must contain a mutation in its C-terminal domaine.    Both a and d are correct
8.    Which of the following is a potentially mutagenic effect of ionizing radiation?
a.    Formation of oxygen radicalsb.    single base pair insertions or deletionsc.    Deaminationd.    Formation of intrastrand covalent linkagese.    all of the above
9.    (4 points; insert correct numbers in blanks) Wobble base pairing deceases the number of different tRNA genes required to pair with all of the isoleucine (Ile) codons from ___________ to _____________.
10.    (6 points) Can deaminination of cytosine lead to the reversion of a nonsense mutation, resulting in the restoration of a sense codon at that location in the DNA molecule? Explain.
11. (5 points) Explain why a small amount of histidine is added to growth media used in the Ames test.
12. (5 points) Following electrophoresis, a gel used in the Southern blotting procedure is soaked in a sodium hydroxide (NaOH) solution. What effect does NaOH have on DNA and why is this step necessary?
13. You have isolated a mutant protein that is only half the size of its wild type counterpart. The gene that codes for the mutant protein is the same length as the wild type gene and contains a single base change. The mutation is located within a glycine (gly) codon.
a.    (3 points) Give the mRNA sequence of the glycine codon before the mutation occurred.
b.    (3 points) Give the RNA sequence of the mutant codon (mark the 5’ and 3’ ends of each sequence).

14.    (4 points) For the genotype given below, is ?-galactosidase production absent, inducible or constitutive?I+P+OCZ+Y+/ ISP+O+Z+Y-
15.    Shown to the right is the imino form of the base __ _____________.
This tautomer pairs with the ____ _______________ tautomer of the base
_________ _______________ (2 points for each correctly filled in blank)
16. (3 points) An E. COLI cell with a nonsense suppressor tRNA could theoretically produce a fusion protein consisting of the combined amino acid sequences encoded LACZ, LACY, AND LACA. Give one reason why this event would be unlikely to occur.
17. Regulation of the E. COLI arabinose operon involves the binding of C protein to the ARA I DNA sequence, located just upstream of the transcription initiation site for the B, A, and D genes. The C protein binds to ARAI only when arabinose is present in the media, and the binding of C to ARAI stimulates the transcription of the polycistronic RNA that encodes the BAD proteins.
a.    (3 points) Is this an example of positive or negative transcriptional regulation?
b.    (4 points) Give the name of an assay that could be used to demonstrate that C protein binds to ARAI.

18. Ten individual tubes of media were inoculated with T1 sensitive E. COLI. These were allowed to grow until each reached a concentration of 1 X 107 cells/ml. One ml of a solution containing 1 X 106 T1 phage/ml was combined with 0.1 ml of each bacterial culture and added to plates of solid media. The # of bacterial colonies/plate is shown below. Show your work in the space provided.

PLATE # 1 2 3 4 5 6 7 8 9 10 #COLONIES 22 23 20 25 21 20 26 22 24 21
a. (5 points) Use the information above (not the Poisson formula) to directly calculate the MOI.b. (5 points) Use the Poisson formula and the MOI you calculated above to determine the probability of finding two colonies on any given plate.c. (6 points) Are the findings of this study consistent with the hypothesis that the T1 resistant colonies were a consequence of random mutations? Why or why not?
19. You have used molecular biology techniques to create a phage lambda construct that is identical to a wild type ? phage except that the PR promoter has been replaced with the lac operon promoter-operator DNA sequence. You infect an E. COLI LEU- auxotroph that is growing in rich lactose media with this phage.
a.    (3 points) Which of the following types of media would be most favorable for lysogeny? 1. rich lactose media
2. minimal lactose media3. rich glucose media4. miminal glucose media
b.    (6 points) Give a detailed explanation for your answer to part a. Briefly describe the basic function(s) of any proteins you mention in your explanation.
c. (5 points) Would lysogeny occur in the media you chose for part a in an E. COLI strain with the genotype I+P+O+ Z-Y+? Why or why not?