Biol 239 Genetics Exam Review Questions PartB answers
(Part A is under Quizzes and consists of some sample multiple choice questions)
Note: this is NOT representative of the final exam its just some practice questions!
The final exam consists of approximately 105 multiple choice questions covering
approximately 20% pre-midterm material and 80% post-midterm. There are no
tutorial-specific questions. The final exam format is entirely Multiple Choice.
These questions are to assist you with studying only.
1. Describe the experiment that provided proof for semiconservative DNA replication. Who
were the researches who did it?
This one is straight out of the textbook and notes. Meselson and Stahl.
2. Draw a DNA replication fork. On your drawing, identify (1) origin of replication, (2) polarity
(5' and 3' ends) of all template strands and newly synthesized strands, (3) leading and lagging
strands, (4) Okazaki fragments, and (5) location of primers (6) regions of continuous and
discontinuous DNA synthesis.
discontinuous Lagging Strand Leading Strand
3' 5' 3' 5 '
3' 3' 5 '
5' Unwinding 3 ' Unwinding 3 '
5' 3' 5'
continuous Leading Strand Lagging Strand
RNA Primers synthesis
1 3. a) Draw all the elements you would expect to see in an operon encoding 2 genes.
SD-like sequence for
ORF 1 ORF 2
RBS ATG.. Stop RBS Stop
O P consensus codon consensus ATG. codon TT
-35, -10 ribosome TAG or
(TATA binding TGA or
box) site TAA
The operon is defined at the level of DNA. Remember it is only found in prokaryotes.
Note* the operator (O) can be on either side of the promoter (P)
b) Draw the resulting mRNA with all the needed elements. Assume this is in E. coli.
SD AUG SD AUG UAG
UAG or UGA 3
5 or UGA
NOTE: always label 5 and 3 ends
c) If a frameshift mutation occurs near the 5 end of the coding region (ORF) of gene 1, will it
affect gene 2/ORF 2? Explain why/why not?
No it will not affect gene 2 because both genes are independently translated from the
mRNA. They are not translated as a single combined protein.
d) Why dont eukaryotes make polycistronic mRNA? Explain in molecular terms.
Eukaryotes cannot read more than one ORF from a single mRNA because of the
dependence for ribosome binding at the 5 cap. The small subunit binds at the cap and
then scans the mRNA until it finds the first AUG codon and translation begins and ends
at the first in-frame stop codon. Then the ribosome falls off. If there is a second ORF, the
ribosome will never get to it.
4. List the possible genotypes of single-mutant E. coli cells demonstrating the following
phenotypes for b-galactosidase production:
- + + + + + + + c + + + + + - + + +
a) constitutive IP O Z Y A or+I - + Z+Y+A +or I+P +Z + - )+ + + + + + - +
b) repressive (non-inducible) I PO Z Y A or I P O ZY A or I P O Z YA (or
I P O Z Y A , although we did not cover IS in lecture, only tutorial so it wont be
asked for on the exam)
c) inducible must be wildtype for all genes/elements
25. What is the sequence transcribed from the DNA coding strand information shown below?
5' C T G G C G T T A A T T A A G C T A A G T C T G C T A A C G C T A.. 3'
H The question identifies the sequence as the coding strand. What does that mean?
F This question is testing to see if you know what the term coding strand means. The
sequence of the coding strand (shown above) looks just like the sequence on the mRNA,
except T is U. The mRNA sequence begins at the +1 of transcription, identified in the
6. The sequence shown is part of an open reading frame (coding sequence).