Homework 6 - KEY
BIO 2
1.
ANSWER MUST BE HAND-DRAWN
Complete the drawing of the replication bubble below, indicating the location of the leading and
lagging strands, the location of RNA primers, and the direction of DNA synthesis by DNA polymerase.
2.
The restriction enzyme Not I has the following recognition site:
5’-GCGGCCGC-3’
3’-CGCCGGCG-3’
a.
How often (on average) would this enzyme cut a random sequence of DNA? Show your
calculation.
b.
About how many times would you expect this enzyme to cut the genome of E. coli,
which contains 4.6 million base-pairs? Show your calculation.
Bio 2
Page 1
Fall 2008
3.
MUST BE HAND-DRAWN
In the year 2033, NASA scientists isolate a single-celled microorganism from soil brought back
to Earth from the surface of Mars. Biochemical analysis of the microorganism reveals that it
has a double-helical information molecule very similar to DNA, including 4 nitrogen-rich bases
and a sugar-phosphate backbone, and that organism replicates its information molecule and
undergoes cell division about once every 75 minutes.
To study its replication mechanism, scientists grew the organism for several generations in
15N
and ran an experiment analogous to the famous one performed on bacteria in the 1950s by
Meselson and Stahl. To their surprise, the scientists found that the alien organism did not
replicate its DNA semi-conservatively but, rather, by a dispersive system.
Draw out the experiment the scientists performed and indicate what results they obtained.
Bio 2
Page 2
Fall 2008
4.
A culture of bacteria has 5.4 x 107 cells/ml. If you serially diluted this culture by a factor of
10,000 and grew up 38 colonies on a plate, how many ul of culture did you add to the plate
during the experiment? Show your entire calculation.
5.
A small part of the template strand of a gene has the following sequence:
5’-AAACACGGGCGCGGCTTTATTGCC-3’
a.
What is the sequence of the coding strand of the same region of DNA? Be sure to label
the 5’ and 3’ ends.
5’- GGCAATAAAGCCGCGCCCGTGTTT – 3’
b.
What is the sequence of the mRNA that would be made by transcription of this region
of the gene? Be sure to label the 5’ and 3’ ends.
5’- GGCAAUAAAGCCGCGCCCGUGUUU – 3’
c.
What is the sequence of the short polypeptide that would be produced via translation
of this region of the mRNA? Be sure to label the carboxyl and amino ends of the
polypeptide.
N – GLY-ASN-LYS-ALA-ALA-PRO-VAL-PHE - C
6-8. More practice with unit conversions and common lab calculations. Try to work these
problems without looking at your notes. Remember to show your entire calculation and to
strike through units to receive full credit!
6.
What is the melting temperature of a PCR primer with the following sequence?
5’-GGATGCGAAAGTAGGATGCTCCCT-3’
[(4 deg C)(13)] + [(2 deg C)(11)] = 74 deg C
Bio 2
Page 3
Fall 2008
7.
You have isolated DNA from the leaves of a tomato plant. You add 30 uL of the DNA to 600 uL
of sterile water, transfer the solution to a cuvette, and read the absorbance in a
spectrophotometer set for a wavelength of 260 nm.
If your undiluted DNA had a concentration of 450 ng/uL, what reading will you get on the
spectrophotometer?
8.
An undiluted DNA sample isolated from human cheek cells gives an A260 reading of 0.97 in a
spectrophotometer. You need to dilute the DNA to 25 ng/uL and you need at least 100 uL of
this dilution for a series of downstream PCR reactions. Indicate how you would perform
the dilution. Assume that the diluent is sterile water.
Bio 2
Page 4
Fall 2008