Biol 253 Study Guide Questions And Correct Answers

Protein degradation in regulating cell cycle {Ans: - cell cycle propelled forward by protein degradation that complements periodic activation of cyclin-CDK complexes - early stages of cell cycle progression required sequential activation of cyclin-CDKs - entry into each new phase also requries0 destruction of cyclins used in previous phase - later stages of cell cycle - progression controlled by proteolysis alone - key role - anaphase promoting complex (APC/C)}Provide examples of chemical mutagens and describe how they cause mutations {Ans: 1. base analogs: mutagenic effects of 5-bromouracil (5BU) behaves like thymine in normal state, in rare state behaves like cytosine and pairs with guanine . mutagenic action of 5BU for AT-GC transition: 5BU incorporated in normal state as T, 5BU shifts to rare state in DNA replication, 5BU shifts to normal state leading to a transition mutation (instead of AT it is CG) 2. base modifying agents: nitrous acid deaminates - cytosine+ nitrous acid = modified base (uracil) which pairs with adenine leading to CG->TA adenine + nitrous acid -> hyoxanthine which pairs with cytosine leading to AT-GC - hydroxylamine - hydroxylates base leading to CG -> TA - MMS methylates (guanine) leading to O^6-methylguanine pairing with thymine,