1. the Degeneracy of the Genetic Code Refers to the Following Occurrence

Name______November 8, 2006 BIO 184 Genetics

Exam 2 This examination is worth 100 points. There are 33 questions on 7 pages. Read through the questions completely before answering. If you are unclear about a question, please ask me.

Part A: Multiple Choice: Answer with the best choice. Make sure that you clearly circle the correct answer and erase any erroneous marks. (2.5 pts each)

1. The degeneracy of the genetic code refers to the following occurrence: a. same number of codons as there are amino acids b. more amino acids than codons c. the code is used by nearly every living organism d. some amino acids have multiple codons e only one nucleotide triplet codes for an amino acid

2. The pattern or sequence in which a molecule of mRNA is deciphered by a ribosome is called the: a. code degeneration b. peptide transition c. reading frame d. P site e. A site

3. Which of the following is not true about the ribosome binding site (rbs): a. inhibitory proteins can bind to the rbs and prevent translation b. the rbs is a consensus sequence c. the rbs is found on the 5’ untranslated region (UTR) d. the rbs binds to a complementary region within the small ribosomal subunit e. none of the above

4. Which of the following is not a property of an anticodon? a. corresponds to the amino acid it carries b. complementary to the codon c. modified bases are often found within it d. the wobble position is at the 3’ end of the anticodon triplet e. none of the above

1 5. The enzyme that attaches free amino acids to the tRNA molecule is called: a. peptidyl transferase b. aminoacyl tRNA synthetase c. ligase d. polymerase e. amino acid attachase

6. Protein synthesis begins with the amino acid ______, as its codon is the one used as the “start codon” by nearly all organisms. a. methionine b. arginine c. cysteine d. leucine e. none of the above

7. Transcription occurs in the ______and translation occurs in the ______of EUKARYOTIC cells. a. nucleus; cytoplasm b. cytoplasm, nucleus c. nucleus; nucleus d. cytoplasm, cytoplasm

8. In prokaryotic systems, which of the following typically stops the process of translation? a. rho proteins b. aminoacyl tRNA synthetase c. rRNA d. stop codons e. introns

9. In the following sequence of DNA, the italicized, bold base has been mutated. What type of mutation is this? 5' - G A T C T C C G A A T T – 3' original strand 5' - G A T C T C C A A A T T – 3' mutated strand a. frameshift b. missense c. transition d. transversion e. neutral

2 10. Catabolic pathways (e.g. lac operon) that break down complex substances into more usable units are usually regulated by the: a. end products of the pathway b. substrate (or related compound) of an enzyme in the pathway c. other metabolites that are limiting d. attenuation e. none of the above

11. In the genotype presented (genomic plus plasmid genes), what will the expression phenotype for beta galactosidase be (I+ P+ Oc Z+ Y- // I- P+ O+ Z- Y+) a. constitutive b. inductive c. completey absent d. basal expression only e. lethal

12. How does Tryptophan function in attenuation of the trp operon? a. tryptophan binds to the repressor preventing it from binding to DNA thus allowing transcription of the operon b. tryptophan binds to the stem-loop structures and prevents transcription c. an abundance of tRNAs charged with tryptophan cause ribosome stalling d. the lack of tRNAs charged with tryptophan allows stem-loop structures to form that allows transcription e. RNA polymerase directly senses the amount of tRNAs charged with tryptophan

13. What site on the ribosome is primarily responsible for holding the growing polypeptide? a. A b. E c. P

14. Antisense RNA does which of the following? a. inhibits the formation of the open complex in transcription b. occupies the A and P sites of the ribosome c. binds to the mRNA and prevents translation d. prevents the correct folding of a newly formed peptide

3 15. Eukaryotic DNA methylation is involved in all the following except: a. regulating transcription by methylation at CpG islands b. enhancing heterochromatin formation c. protect “self” (meaning their genome) from restriction enzymes d. methylation-directed mismatch repair e. none of the above

16. Which one of the following is not a mechanism that regulates eukaryotic transcription factor activity? a. protein dimerization b. hormone binding c. phosphorylation d. attenuation e. none of the above

17. The regulation of protein function (e.g. feedback inhibition of enzymes), not gene expression, is called ______regulation. a. post-translational b. transcriptional c. translational d. post-transcriptional

18. An organism with four sets of chromosomes, two from one species genome and two from a different species genome is called: a. aneuploid b. autotetraploid c. allotetraploid d. autopolyploid e. tetrasomy

19. Which of the following types of plants would usually be a seedless variety? a. aneuploid b. diploid c. triploid d. tetraploid

4 20. When two sister chromatids end up in the same gamete, non-disjunction has occurred in: (hint: remember the colorblind example we covered in lecture) a. first division of meiosis b. second division of meiosis c. either division of meiosis is consistent d. both divisions of meiosis

21. Homologous chromosomes must separate from one another and move to opposite poles during: a. mitosis b. meiosis I c. meiosis II d. both a and b e. both a and c

Part B: Fill in the blank (2.5 pts each)

22. Thymine dimers are caused by ______.

23. DNA that contains instructions for including two or more structural genes on a single transcript is termed a ______mRNA.

24. A mutation in a gene that restores the wild type phenotype of a second gene is called a ______mutation.

Part C. Next to each of the following, determine whether they are cis-acting elements or trans-acting factors. Place the term cis or trans in the blank. (2 pts each)

25. Operator ______

26. TrpR ______

27. Enhancer ______

28. lacZ ______

5 Part D- Short answers (please write clearly and use the back of the page if needed):

29. Explain what a frameshift mutation is and what possible effects it has on a protein sequence. (4 pts)

30. A cross between a male donkey (62 chromosomes) and a female horse (64 chromosomes) produces a mule (63 chromosomes). Why are allodiploid species such as the mule usually infertile? (4 pts)

31. Why would a triploid individual be infertile? (4pts)

32. E. coli exhibit a diauxic growth shift caused by their regulation of sugar metabolism when glucose and lactose are in their medium. a. Explain what is meant by the term diauxic growth and illustrate the growth curve (4 pts).

6 b. Explain how the levels of glucose during this diauxic growth shift contribute to the regulatory mechanism. Be sure to include CAP in your explanation. (8 pts)

33. You have been given a purified chemical compound named “humic”, a derivative of lignin that is a byproduct from timber mills. You have been asked to test whether humic has mutagenic properties. How would you go about testing this compound? Be sure to use a negative control in your experimental design. (hints: Ames test, salmonella, his-) (8 pts)

7 ANSWERS: 1. d 2. c 3. e 4. d 5. b 6. a 7. a 8. d 9. c 10. b 11. a 12. d 13. e 14. c 15. c 16. d 17. a 18. c 19. c 20. b 21. b 22. uv light 23. polycistronic 24. intergenic suppressor 25. cis 26. trans 27. cis 28. trans