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Bio272W Spring 2016
Extra credits for Exam 3
Due Tuesday April 12th by 4:30pm (email, mail box, my office)
Please give a FULL explanation, not just the answer.
For question 1-4, please pick the correct answer, explain why it is correct and then explain why
every other answer is incorrect:
1. In Meselson and Stahl's experiment, what kind of DNA molecules would be found after four
A) Only intermediate DNA (15N-14N)
B) Only light DNA (14N-14N)
C) Both heavy (15N-15N) and light DNA (14N-14N)
D) Both heavy (15N-15N) and intermediate DNA (15N-14N)
E) none of the above
2. Posttranscriptional deletion of nucleotides that do not contain instructions for protein
synthesis is called
A) RNA capping.
B) RNA editing.
C) RNA processing.
D) RNA splicing.
E) RNA modification.
3. In a gene sequence, the DNA codon for tryptophan experiences a mutation at the first base
position, changing it to T. What will the resulting amino acid be?
A) Tryptophan (no change)
E) None (a stop codon will halt translation)
The function of tRNA is to
Provide a site for polypeptide synthesis
Transport amino acid to the ribosome
Travel to the ribosome to direct the assembly of polypeptides
5. List the different chromosome mutations and define each one
6. What is the difference between primary Down syndrome and Familiar Down syndrome?
How does each form arise?
7. How will DNA replication be affected if DNA polymerase I has a mutation that inactivates
its 5'-to-3' exonuclease activity, in bacteria and in eukaryotic cells?
8. The diploid set of chromosomes in Drosophila embryos replicates six times faster than the
single E. coli chromosome, even though there is about 100 times more DNA in Drosophila
than in E. coli and the rate of movement of the replication fork in Drosophila is much slower.
How is this so?
10. The sequence of a template strand of DNA is 3'-CATTACGCTT-5'. What is the sequence of
the corresponding mRNA?
11. How did von Ehrenstein et al. demonstrate that the specificity of codon recognition lies in the
tRNA molecule and not in the amino acid it carries?
12. The human B-globin (HBB) gene provides instructions for making a protein called betaglobin. Beta-globin is a component (subunit) of a larger protein called hemoglobin, which is
located inside red blood cells. In adults, hemoglobin normally consists of four protein
subunits. Each of these protein subunits is attached (bound) to an iron-containing molecule
called heme; each heme contains an iron molecule in its center that can bind to one oxygen
molecule. Hemoglobin within red blood cells binds to oxygen molecules in the lungs. These
cells then travel through the bloodstream and deliver oxygen to tissues throughout the body.
Several mutations in the B-globin gene have been identified that can cause an altered
phenotype. For example, some mutations can cause thalassemia, or the reduced or null
production of beta-globin. Others can produce sickle cell anemia, where a modified globin is
made that actually sticks together forming long rigid molecules. What modifications could be
occurring in the HBB gene that can cause those malfunctional globin proteins? How can two
different mutations in the same gene cause very different disease phenotypes?
13. Draw a "generic" amino acid as it exists under physiological conditions (in water at neutral
pH). Define the main components of the molecule and label the acidic part and the basic
part of the molecule. Which functional group would be involved in a peptide bond
formation? Which group would involved in weak interactions, essential for the formation of
the 3D structure of a functional protein?
14. Briefly describe the process of translation using the following terms not more than once:
nucleus, cytoplasm, small subunit of the ribosome, large subunit of the ribosome, mRNA,
codon on the mRNA, activated tRNA adaptor molecule, appropriate amino acid,
complementary anticodon, aminoacyl-tRNA synthetase, amino acid activation, anticodon on
tRNA, A-site, P-site, E-site, growing peptide chain, free tRNA, peptide bond forms