BIOL 214 Final Exam 2020/2021 Questions and Answers

BIOL 214 Final Exam 2020/2021 Questions and Answers 1. Figure 1 is a two base pair of DNA a. Identify W – Guanine (purine acceptable) b. Identify Y – deoxyribose sugar c. Identify Z - phosphate d. Which direction is the left hand strand orientated, top to bottom? 5’ to 3’ e. Identify one mistake evident in this drawing. No -OH groups on 3’ ends; N bases are not attached to 1’ carbon on sugar 2. Strains of E. coli have been isolated that contain temperature-sensitive mutations in the genes encoding different proteins involved in replication. These strains produce non-functional mutated proteins when cultured at temperatures above 44°C and functional normal proteins when cultured at temperatures below 44°C. In an experiment, individual strains are grown at 37°C for many generations and then abruptly switched to 47°C. After one round of DNA replication at 47°C, the DNA from each strain is isolated and analyzed. What characteristics would you expect to see in the DNA isolated from each strain with a temperature-sensitive mutation in its gene that codes for the following proteins? a. DNA ligase DNA ligase is required to seal the nicks left after DNA polymerase I removes the RNA primers used to begin DNA synthesis. If DNA ligase is not functioning, multiple nicks in the lagging strand would be expected and the Okazaki fragments would not be joined. However, DNA replication will take place. b. DNA polymerase I RNA primers are removed by DNA polymerase I. After one round of replication, the DNA molecule would still contain RNA primers since DNA polymerase is not functioning. However, replication of the DNA will take place. c. DNA polymerase III No replication would be expected. DNA polymerase is the primary replication enzyme. If it is not functioning, then neither the lagging nor the leading strand DNA synthesis will take place. However, replication bubbles would still form because the helicase is still active and functioning. d. Primase No replication would be expected. Primase synthesizes the short RNA molecules that act as primers for DNA synthesis. If the RNA primers are not synthesized, then no free 3-OH will be available for DNA polymerase to attach nucleotides. Thus DNA synthesis will not take place. e. Helicase No replication would be expected. Helicase is required to unwind the DNA helix at the origin of replication at the start of replication. If helicase is not functioning, the double stranded molecule would not be separated into single stranded regions and the primase has nowhere to place primers.