UNIVERSITY OF THE FREE STATE MAIN CAMPUS GENE2626 DEPARTMENT: GENETICS Semester test 1 ASSESSOR(S): 1. Dr M Gryzenhout MODERATOR(S): 1. Mrs L Wessels TIME: 60 min MARKS: 50 Instructions Read questions carefully. All answers must be written in pen except for marking on the optical sheet. Number all your answers correctly. Question 1 [14] 1. Which of the following enzyme/proteins have this function during replication: Binds to the Ori. *a. Initiator protein b. Helicase c. Single-strand binding proteins (SSBPs) d. Primase e. DNA polymerase III 2. Which of the following enzyme/proteins have this function during replication: Replaces the RNA primer with DNA. a. Initiator protein b. Helicase c. Single-strand binding proteins (SSBPs) d. Primase e. DNA polymerase III *f. DNA polymerase I 3. Which of the following enzymes/proteins have this function during error repair of DNA: Cuts DNA backbone at an apurinic site. a. DNA glycosylase *b. AP endonuclease c. DNA exonuclease d. DNA endonuclease 1 e. Topoisomerase 4. Match the critical enzyme to the process: Methyl directed mismatch repair. a. Sloppy DNA polymerase b. UvrA-UvrB complex c. PKcs *d. Adenine methylase e. RNA polymerase f. DNA glycosylase 5. Which of the following sequence motifs have this function during transcription: Signal for ribonuclease. a. Promoter b. Terminator c. Enhancer *d. AAUAA on mRNA transcript e. Splice donors and acceptors 6. Which of the following is typical to prokaryotes: a. Promoter b. Enhancer *c. fMet d. UTR’s e. Start codon f. Stop codon 7. Why were only male flies exposed to X-rays in the X-ray mutagen experiment? a. Male flies have a Y chromosome that is unique b. Females were difficult to work with *c. Male flies have only 1 X chromosome that can be tracked by mating with females d. Only exposed males will immediately show effects to the X rays. e. Male flies have only 1 Y chromosome that can be tracked by mating with females 8. Match the following mutation to a definition: Antimorphic allele. *a. Prevents normal protein function b. Gene product has weak, but detectable, activity c. Phenotype varies continuously with the amount of functional gene product d. Phenotype is sensitive to gene dosage (i.e. 50% of gene product) e. Generate more gene product or the same amount of a more efficient gene product f. Generate gene product with new function or that is expressed at inappropriate time or place 9. Which of the following is an example of posttranslational processing using enzymes? *a. Zymogen b. Glycosylation c. Lipidation d. Ubiquitination e. Phosphorylation 2 10. Which do not form part of a prokaryotic ribosome? *a. 5S rRNA b. 23S rRNA c. 5.8S rRNA d. 16S rRNA 11. Which of the following sequences of DNA dictates where translation will start? a. Activator b. DNMT c. Poly-A signal d. Stop codon *e. Start codon 12. Which of the following proteins also contain RNA? *a. Spliceosome b. DNA ligase c. RNA polymerase d. Nucleosome e. β chain of hemoglobin 13. Choose the best answer: Which of the following components of the Ames test is used to ensure that a modified version of the tested compound could be carcinogenic? a. Plates with histidine b. Plates without histidine c. Test compound *d. Rat liver enzymes e. Bacteria 14. Which structure fits best with the following enzyme: RPA proteins. *a. Displacement loop b. 3’ single stranded tails c. Holliday junction d. Invaded strand e. Heteroduplex Question 2 [10] Indicate if the following statements are true or false and MOTIVATE your answer 2.1 The 3’ end of mRNA corresponds with the N terminus of the resulting polypeptide chain. (2) False, 5’ of mRNA or C of polypeptide 2.2 In the experiments of Avery to determine which compound is the transforming principle, cells were not transformed when the RNA was degraded. (2) False, only when DNA was degraded 2.3 A nucleoside consist of phosphor, a ribose sugar and nitrogenous base. (2) False, that is a nucleotide/only consist of ribose and N base 3 2.4 The protein dosage of a heterozygote (A+/a1) will be enough to produce wild type eye color if A+ is the wild type allele, and a1 is a null allele. (2) True, dosage by the one wild type allele is enough even though the null allele gives nothing 2.5 Eukaryotes have multiple ribosome binding sites (RBSs). (2) False, only a single binding site Question 3 [10] Give one outcome of the following experiments or events. Read the questions carefully 3.1 The branch migration step of the cross-over pathway during molecular DNA recombination. (1) Heteroduplex enlarges 3.2 Band position in the Meselson-Stahl experiment (bottom and/or middle and/or top) after the second replication event, that tested which DNA replication model was the correct one, if the dispersive model turned out to be correct. (1) Middle only 3.3 Viability of second generation Drosophila male flies in the control experiment testing whether X-rays can be a mutagen. (1) All would still live 3.4 Viability of second generation Drosophila male flies in the X-ray experiment testing whether X-rays can be a mutagen. (1) Some will die 3.5 If Leu and its correct corresponding mini-mRNA is added during the mini-mRNA experiment. (1) Radioactivity would be in ribosomes on filter 3.6 Addition of proflavin to bacteriophages. (1) Deletions of insertions 3.7 Base excision repair in a DNA string. (1) Cuts out an uracil base and replace with correct DNA 3.8 When the tRNA charged with methionine is docked in the P site of the ribosome (1). The next charged tRNA moves into the A site based on the codon position. 3.9 When the sigma (σ) factor is released from the RNA polymerase during transcription (1). RNA polymerase can move along mRNA 3.10 The length of the DNA strand during trinucleotide repeat contraction of triplet repeats in the DNA strand during replication. Shorter/fewer repeats Question 4 [16] Answer the following short questions. 4.1 Give two differences (4x0.5=2) and one similarity (1) between DNA replication and RNA transcription. (Total=3) 4 Any two differences: DNA polymerase (0.5) vs RNA polymerase(0.5); makes 2 new DNA strands (0.5) vs makes 1 RNA strand(0.5); DNA has T (0.5) RNA had U(0.5)... Any two similarities: Both makes new nucleic acid strands(1); both have 5’-3’ direction(1); DNA double helix has to unwind in both cases (1); both have initiation and elongation stages (1).... 4.2.1 Give any two regions in DNA that are not in exons where mutations can still disrupt gene expression. (2) 4.2.2 Why will mutations in these regions disrupt gene expression? (1) Interferes with binding of enzymes or ribosomes/interferes processes of transcription or translation 4.3.1 Illustrate by using DNA strands that are going for two rounds of replication, how oxidative damage of a guanine in a DNA strand can cause a T-A substitution. (6x0.5=3) each DNA double strand is 0.5 4.3.2 Is this an example of a natural mutation or is it caused by a mutagen? (1) Natural 4.4 Why is the one gene-one enzyme hypothesis technically not correct? (1) A multimeric enzyme with different subunits requires more than one gene 4.5 Name any two events or processes that made it possible to do the mini-mRNA experiment to determine the codon sequences for amino acids. (2) Discovery of mRNA Synthetic mRNA 5 Cellular extracts in test tubes 4.6.1 Pose the two hypotheses for the Hershey-Chase Waring blender experiment that used radioactivity and bacteriophages. (2x0.5=1) DNA is the transforming principle/makes up genes (0.5) Protein is the transforming principle/makes up genes (0.5) 4.6.2 What were the results and which hypothesis was proven? (2x0.5=1) DNA-inked radioactivity was in the bacteria (0.5), therefore DNA is principle (0.5) 4.6.3 What would the control experiments of these be? (1) No radioactivity 6