1. Nucleotides in a nucleic acid polymer are attached to one another via phosphodiester bonds.  These bonds link:

a) 3’ carbon of the growing strand to 5’ carbon of the incoming NTP
a) 5’ carbon of the growing strand to 3’ carbon of the incoming NTP
a) 3’ carbon of the growing strand to 3’ carbon of the incoming NTP
a) 5’ carbon of the growing strand to 5’ carbon of the incoming NTP

Exact same question as question number 1 from the first quiz, except better written.

2. Rho independent transcription termination sequences

a) can form double-stranded structures
b) Often possess a string of A or T(U) bases
c) A&B
d) Contains stop codons.

Again, exact same question as on the first quiz.

3. Which of these features would the best candidates for a newly described gene or ORF include:

a) Start codon and stop codon
b) Ribosome binding site
c) Transcription terminator
d) Putative promoter and consensus sigma factor binding sequence
e) All of these

The ideal ORF would have all of these present.

4. Bacterial chromosomes are approximately:

a) Kilobases
b) Decabases
c) 100’s of bp
d) 1,000’s of bp
e) 1,000,000’s of bp

Chromosomes are millions of base-pairs in length.  Just one of those facts you need to memorize.

5. Which mutation results in auxotrophy

a) gyrA
b) rpoB
c) rpsL
d) proAB

Auxotrophy means that the media must be supplemented by some additional nutrient in order for the organism to grow.  gyrA, rpoB, and rpsL are all antibiotic resistance mutations; proAB is the only mutation that requires an additional nutrient.

6. What is the basis for mutagenesis by way of deamination or tautomerization?

a) A change in the chemical nature of the deoxyribose, making it less able to bind to the nitrogenous base.
b) A change in the chemical nature of the phosphodiester bonds, making them more susceptible to hydrolytic cleavage.
c) A change in the chemical structure of the nitrogenous bases, causing them to create random cross-links with adjacent bases.
d) A change in DNA polymerase, making it unable to properly read the template strand.
e) A change in the hydrogen bonding patterns of the nitrogenous bases, causing them to match with incorrect complementary bases during replication.

By changing the hydrogen bonding patterns of the base, mutagenesis by these pathways cause misreads when it is time to transcribe or replicate the DNA.  And no, they don’t create random crosslinks.

7. Which mutation results in a transversion?

a) A-T -> G-C
b) G-C -> A-T
c) A-T -> T-A
d) C-G -> T-A

Of these mutations, only choice C is one where the mutation changes the class of the nucleotide (purine to pyrimidine).

8. Which of the following could cause a frameshift mutation?

a) insertion
b) transition
c) transversion
d) deamination
e) none of the above

b, c, and d all are mutagenic events that preserve the reading frame.  a) is the only choice that alters the reading frame, causing the frameshift.

9. Consider a mutation that changes a codon from UAC to UAU.  Both of these triplets specify the amino acid tyrosine. Which term best describes this change?

a) frameshift mutation
b) missense mutation
c) silent mutation
d) nonsense mutation

Because the sense of the codon is preserved, this is a silent mutation, with no change in observed phenotype.

10.  Consider a mutation which changes a codon from UAC to UAG.  Which term best describes this change?

a) frame-shift mutation
b) missense mutation
c) silent mutation
d) nonsense mutation

UAG is a stop codon; therefore, this is a nonsense mutation.