Problem Set 4
MBB 222 – Molecular Biology and Biochemistry
First Name: _____________________________________________________
Last Name: _____________________________________________________
Student Number: __________________________________
Tutorial Day and Time: ___________________________________________
Total marks for Problem Set = 33 marks
Your score = _______
Problem set is due on Wednesday, November 13 , 2013 in class.
Hand in your problem set to your Teaching Assistant for marking in class.
Write your answers in pen. Answers written in pencil will not be accepted.
Write CLEARLY! Zero marks will be given to questions with answers that are not legible!!
This problem set is worth 2% towards your final mark in the course.
1. Match the damage type or repair step on the left with a related enzyme/protein on the right. Only one
answer per blank and none of the answers are repeated(0.5 mark for each blank x 10 = 5 marks in total)
___ cytosine deamination (a) hypoxanthine-N-glycosylase
___ base loss (b) AP endonuclease
___ adenine deamination (c) mutH protein
___ binds to GATC sequences (d) DNA polymerase I
___ seals nicks (e) uracil N-glycosylase
___ binds to mismatch in DNA (f) mutS-mutL complex
___ direct chemical reversal of pyrimidine dimer formation (g) ABC excinuclease
___ O -methylguanine (h) DNA photolyase
___ double-strand break (i) O -methylguanine methyltransferase
___ excision of a lesion- containing oligonucleotide (j) DNA ligase
(l) RecA protein
ANSWER: e; b; a; c; j; f; h; i; m; g
2. In homologous genetic recombination, RecA protein is involved in: (2 marks)
A. introduction of negative supercoils into the recombination products.
B. nicking the two duplex DNA molecules to initiate the reaction.
C. formation of Holliday intermediates and branch migration. D. pairing a DNA strand from one duplex DNA molecule with sequences in another duplex, regardless of
E. resolution of the Holliday intermediate.
3. Rank the following organisms in order from smallest genome (number of base pairs of DNA) to largest
genome. (2 marks)
A. Human, fruit fly, E. coli bacterium
B. E. coli bacterium, human, fruit fly
C. E. coli bacterium, fruit fly, human
D. Fruit fly, E. coli bacterium, human
E. Fruit fly, human, E. coli bacterium
4. Which of the following statements is true? (2 marks)
A. Current estimates indicate that humans have about 300,000 genes. (FALSE: 30,000 genes)
B. Reverse transcriptase, mRNA, DNA polymerase and genomic DNA are needed to build a cDNA library
(FALSE: genomic DNA not needed…still need to have dNTPs)
C. Recombinant plasmids are commonly introduced into bacterial cells by transfection (FALSE:
D. Examples of viruses containing RNA are those that cause influenza, polio, and AIDS.(TRUE)
E. AZT (3'-azido-2',3'-dideoxythymidine), used to treat HIV infection, acts in HIV-infected cells by
inhibiting RNA polymerase II. (FALSE…inhibiting “reverse transcriptase”)
A is false since it is 30,000 genes. B is false since genomic DNA is not needed, instead you will need dNTPs.
C is false since recombinant plasmids are introduced into bacteria by transformation. E is false since AZT
inhibits reverse transcriptase.
5. A modified version of a restriction map is given below for the plasmid pBR322. Match each feature of the
plasmid (on the left) with one appropriate description presented (on the right). Only one answer per blank
and answers may be repeated. (0.5 mark for each blank x 6 = 3 marks in total) ____ amp sequence (a) Permits selection of bacteria containing the plasmid.
____ ori sequence (b) A sequence required for packaging recombinant plasmids
____ tet sequence into bacteriophage.
____ BamHI sequence (c) Origin of replication.
____ PstI sequence (d) Cleavage of the plasmid here does not affect antibiotic
____ PvuII sequence sequence resistance genes.
(e) Insertion of foreign DNA here permits identification of