Download Exam 4 Key Fa08

Biol 211, Fall 2008
Exam #4
Name ____________________
Section 1. Questions in this section can be answered with one or a few words.
For the following definitions, provide the correct term.
1. Small proteins that are involved in chromatin packing. (1 pt)
[histones]
2. Enzyme that transcribes RNA template into DNA in retroviruses. (1 pt)
[reverse transcriptase]
3. A sequence of 3 nitrogenous bases in mRNA that code for a specific amino acid. (1 pt)
[codon]
4. Mis-folded protein that causes degenerative brain diseases. (1 pt)
[prion]
5. The progressive restriction of the developmental potential of a cell to only one specific fate. (1 pt)
[determination]
6. Sequence of nucleotides in a bacteria’s DNA to which an active repressor can attach that prevents
transcription of a cluster of genes. (1 pt)
[operator]
7. Any observable trait in an individual. (1 pt)
[phenotype]
Answer the following questions.
8. What do homeotic genes control? (1 pt)
[pattern formation]
9. What effect does microRNAs (miRNAs) have on messenger RNA (mRNA)? (1 pt)
[Degrades it or stops it from being translated]
10. Transcribe the following single strand of DNA into a strand of RNA: ATCCGCTAAGTCAG (1 pt)
[UAGGCGAUUCAGUC]
11. What is the function of a splicesome? (1 pt)
[to process primary RNA into mRNA – cut out introns and join exons]
12. Briefly describe one way that expression of a gene can be regulated after the pre-mRNA (primary
transcript) has been made? (1 pt)
[Many possible answers – at initiation of translation, alternative RNA splicing, mRNA
degradation, protein processing, etc.]
13. Can genes located within heterochromatin regions be transcribed (Y/N)?(1 pt)
[No]
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Biol 211, Fall 2008
Exam #4
Name ____________________
14. What is one way we get emerging viruses (appearance of new viruses)? (1 pt)
[virus mutates, disseminates from isolated population, jumps from other animal to human]
15. What are the components of an operon? (1 pt)
[operator, promoter and cluster of genes]
Section 2. Short Answer.
16. Provide a concise definition for each that will clearly distinguish between the following pairs of
terms. Be sure to include how the two terms are related to one another. (2 pts each):
a) lytic cycle / lysogenic cycle
b) repressible operon / inducible operon
c) transcription / translation
Answer the following questions.
17. How do cyctoplasmic determinants influence cell differentiation? (3 pts)
[Cytoplasmic determinants act as activators or repressors on enhancers. They will stimulate or repress
the expression of specific genes, whose products (proteins) will then determine what type of cell it is to
become. Cytoplasmic determinants are not found equally in all cell types]
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Biol 211, Fall 2008
Exam #4
Name ____________________
18. Describe how the structure of tRNA allows it to change the nucleic acid “language” of mRNA into
amino acid “language”. (3 pts)
[tRNA has an anticodon at one end which is complementary to the bases on the mRNA strand. The
other end attaches to only one specific amino acid, which allows it to match (or translate) the mRNA
codon to a specific amino acid]
19. Why is the phrase “one gene, one polypeptide” inaccurate? (2 pts)
[Genes code for RNA as well as for polypeptides. ]
20. What would happen in the lactose metabolic pathway of a bacteria grown in a petri dish where
glucose concentrations are low and there is no allolactose present? Explain why. (3 pts)
[Nothing. If there is no allolactose, then the repressor protein will remain bound to the operator
and no transcription will occur, regardless of whether there is activated CAP bound to the promoter]
21. Describe the early experiment that determined that bacteria was not the cause of tobacco mosaic
disease. (2 pts)
[Extract from plant with disease put on new plant. Extract taken from new plant and passed through
bacteria filter and put on another plant. Both plants develop the disease, so must be something other than
bacteria, and something that is able to reproduce in host]
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Biol 211, Fall 2008
Exam #4
Name ____________________
22. Why do we have to get new flu vaccine shots every year? ( 2 pts)
[viruses mutate – especially RNA viruses that do not get proofread]
23. Describe two ways that adding chemical groups to chromatin affects whether or not a gene gets
expressed. (3 pts)
[histone acetylation, phosphorylation – un-condenses, deacetylation, histone methylation and DNA
methylation condenses]
24. What is one possible effect on a cell if a mutation occurred in the p53 gene? Be specific. (3 pts)
[No transcription of cell cycle inhibitors, so cell cycle can continue leading to cancer. No production
of p21 gene, so no way of halting cell cycle if DNA damaged. No production of series of “suicide”
genes to destroy damaged cells]
25. How is it possible that a mutation causing a base-pair substitution can cause no change in the
expression of the gene? ( 3pts)
[If the base switch is the third codon, may not effect amino acid because it may code for the same
amino acid due to the “wobble” – overlap in the dictionary of the genetic code – several codons code for
the same amino acid, and the only difference is in the 3 base]
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Biol 211, Fall 2008
Exam #4
Name ____________________
Bonus Question (2pts)
Answer only one of the question below.
1. Linked genes violate Mendel’s Law of Independent Assortment (LIA). Under what circumstances
might it appear that Mendel’s LIA holds true for linked genes?
[traits found on the same chromosome travel together - do not assort independently. genes
located further apart are subject to crossing over, which make the traits travel independently]
2 What is the role of PEP Carboxylase in photosynthesis and why is it important?
[Attaches CO2 to PEP in C4 cycle (used by both C4 and CAM plants). Rubisco binds O2 when CO2
levels low. Provides way to increase amount of CO2 and decrease chance of photorespiration.]
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