Winter Quarter Midterm Exam

Transcription

1 1. For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogens. Thus, labeling the nitrogens would provide a stronger signal than labeling the phosphates. Why won't this experiment work? a. There is no radioactive isotope of nitrogen. b. Radioactive nitrogen has a half-life of 100,000 years, and the material would be too dangerous for too long. c. Meselson and Stahl already did this experiment. d. Although there are more nitrogens in a nucleotide, labeled phosphates actually have 16 extra neutrons; therefore, they are more radioactive. e. Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins. 2. Which of the following is true for both prokaryotic and eukaryotic gene expression? a. After transcription, a 3' poly-a tail and a 5' cap are added to mrna. b. Translation of mrna can begin before transcription is complete. c. RNA polymerase binds to the promoter region to begin transcription. d. mrna is synthesized in the 3' 5' direction. e. Introns are spliced out of the pre-mrna before export from the nucleus. 3. Cytosine makes up 38% of the nucleotides in a sample of DNA from an organism. Approximately, what percentage of the nucleotides in this sample will be thymine? a. 12 b. 24 c. 31 d. 38 e. It cannot be determined from the information provided. 4. Which of the following statements is false when comparing prokaryotes with eukaryotes? a. The prokaryotic chromosome is circular, whereas eukaryotic chromosomes are linear. b. Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many. c. The rate of elongation during DNA replication is higher in prokaryotes than in eukaryotes. d. Prokaryotes produce Okazaki fragments during DNA replication, but eukaryotes do not. e. Eukaryotes have telomeres, and prokaryotes do not. 5. Ribosomes are made of. a. DNA and RNA b. Lipids and Proteins c. DNA and Protein d. Carbohydrates and RNA e. None of these are correct 6. What determines the nucleotide sequence of the newly synthesized strand during DNA replication? a. the particular DNA polymerase catalyzing the reaction b. the relative amounts of the four nucleoside triphosphates in the cell c. the nucleotide sequence of the template strand d. the primase used in the reaction e. both A and D 1

2 7. Using RNA as a template for protein synthesis instead of translating proteins directly from the DNA is advantageous for the cell because a. RNA is much more stable than DNA. b. RNA acts as an expendable copy of the genetic material, allowing the DNA to serve as a permanent, pristine repository of the genetic material. c. many mrna molecules can be transcribed from a single gene, increasing the potential rate of gene expression. d. B and C only e. A, B, and C 8. The genetic code is essentially the same for all organisms. From this, one can logically assume all of the following except a. a gene from an organism could theoretically be expressed by any other organism. b. all organisms have a common ancestor. c. DNA was the first genetic material. d. the same codons in different organisms usually translate into the same amino acids. e. different organisms have the same number of different types of amino acids. 9. All of the following are directly involved in translation except a. mrna. b. trna. c. ribosomes. d. DNA. e. aminoacyl-trna synthetase enzymes. 10. There are 61 mrna codons that specify an amino acid, but only 45 trnas. This is best explained by the fact that a. some trnas have anticodons that recognize two or more different codons. b. the rules for base pairing between the third base of a codon and trna are flexible. c. many codons are never used, so the trnas that recognize them are dispensable. d. A and B only e. A, B, and C 11. Which point mutation would be most likely to have a catastrophic effect on the functioning of a protein? a. a base substitution b. a base deletion near the start of a gene c. a base deletion near the end of the coding sequence, but not in the terminator codon d. deletion of three bases near the start of the coding sequence, but not in the initiator codon e. a base insertion near the end of the coding sequence, but not in the terminator codon 12. How does active CAP induce expression of the genes of the lactose operon? a. It terminates production of repressor molecules. b. It degrades the substrate allolactose. c. It stimulates splicing of the encoded genes. d. It stimulates the binding of RNA polymerase to the promoter. e. It binds steroid hormones and controls translation. 2

3 13. Within the same individual organism, muscle cells and nerve cells owe their differences in structure to a. having different genes. b. having different chromosomes. c. using different genetic codes. d. differential gene expression. e. having unique ribosomes. 14. In both eukaryotes and prokaryotes, gene expression is primarily regulated at the level of a. transcription. b. translation. c. mrna stability. d. mrna splicing. e. protein stability. 15. Given the following primary transcript: which of the following is not a possible result of RNA splicing? a. b. c. d For a hypothetical 1000 base-pair gene: a. Which individual process will use more energy: replication, transcription, or translation of a single copy? Explain your answer. b. On a whole cell basis, which process uses more total energy in the cell? Explain your answer. 3

4 17. Select and answer ONE of the following: a. Make a rough labeled diagram of DNA replication including the following: DNA double helix, DNA polymerase, leading strand, lagging strand, single deoxyribonucleotides, triplets, Okazaki fragments, DNA ligase, helicase enzyme. Indicate the sequence of the steps. b. Make a rough labeled diagram of RNA transcription, including the following: DNA template, single ribonucleotides, RNA polymerase, promoters, initial RNA transcript, RNA splicing, mrna, rrna, trna, and codons. Indicate the sequence of the steps. c. Make a rough labeled diagram of translation including the following: mrna, ribosomes, amino acids, trna, anticodons, codons, aminoacyl-trna synthetase, peptide bond, and protein, P site and A site. Indicate the sequence of the steps. 4

5 18. Based on the hypothetical DNA sequence below, write out the sequence of primers that you could use to amplify the target sequence by PCR with Taq DNA polymerase (indicate the strand orientation). 5 ATGCATGCAGT...NNN..TARGET SEQUENCE..NNN...GGGAAACCCTTT 3 3 CCCTTTGGGAAA5 <- Primer 2 Primer 1 -> 5 ATGCATGCAGT3 3 TACGTACGTCA...NNN..TARGET SEQUENCE..NNN...CCCTTTGGGAAA How did researchers detect the production of the period protein in different tissues, as described in the fly lab? 20. Where in the human body does meiosis take place? 21. Approximately how many base pairs and how many protein encoding genes does the human genome contain? In general, how do these numbers compare to the mustard weed and the mouse? 22. Approximately, how similar is your DNA from other students in your class? 5

6 23. Name three factors that contribute to the fact that individual humans have an approximate uniqueness of one in seventy trillion. (In other words, how is this number derived). 24. Draw a picture (showing all of the steps) on how a rare recombinant event (not androgen insensitivity etc.) can result in a phenotypic male having an XX karyotype and a phenotypic female having an XY karyotype. What gene is involved in this? 6

7 25. How does recombination unlink genes on the same chromosome, generating recombinant types? (you can use diagrams to explain) 7