Gene expression

Solutions to Practice Problems for Molecular Biology, Session 3: Transcription, Translation ? ? Question 1 ? ? Fill in the table: ? Transcription Translation Where does this process occur in a nucleus cytoplasm eukaryotic cell? What is the enzyme that carries out RNA polymerase Ribosome this process? What is the template that is read DNA RNA during this process? In what direction is the template 3? ? 5? 5? ? 3? read? What is the start signal/sequence for promoter Start codon this process? What is the polymer that is formed? RNA polypeptide What monomer is used to form this ribonucleotides Amino acids polymer? What type of bond is formed phosphodiester peptide between monomers? In what direction is the new polymer 5? ? 3? N ? C

Solutions to Practice Problems for Molecular Biology, Session 5: Gene Regulation and the Lac Operon ? ? Question 1 ? ? ? a) How does lactose (allolactose) promote transcription of LacZ? 1) Lactose binds to the polymerase and increases efficiency. 2) Lactose binds to a repressor protein, and alters its conformation to prevent it from binding to the DNA and interfering with the binding of RNA polymerase. 3) Lactose binds to an activator protein, which can then help the RNA polymerase bind to the promoter and begin transcription. 4) Lactose prevents premature termination of transcription by directly binding to and bending the DNA. Solution: 2) Lactose binds to a repressor protein, and alters its conformation to prevent it from binding to the DNA

glucose lactose operator (repressor binding site) PromoterZYA lacZ lacY lacAcrp lacI repressor active activator inactive PromoterIPromotercrp + - mRNA mRNA activator binding site polymerase RNA polymerase RNA operator (repressor binding site) PromoterZYA lacZ lacY lacAcrp lacI repressor active repressor lactose inactive activator inactive cAMP activator active PromoterIPromotercrp mRNA mRNA mRNA LacZ (?gal) LacY LacA activator binding site polymerase RNA polymerase RNA repressor active can metabolize lactose!cAMP + - + lactose + cAMP activator active polymerase RNA DNA DNA The lac operon: a model of gene regulation in E. coli MIT OpenCourseWare http://ocw.mit.edu 7.01SC Fundamentals of Biology Fall 2011

Solutions to Molecular Biology Unit Exam Question 1 Consider the following origin of replication that is found on a chromosome. The sequence of region 1 is shown below. Region 1: 5??CTGACTGACA?3? 3??GACTGACTGT?5? 5? 3? 5? 3? Region 1 ori top ? bottom ? a) Within Region 1, which strand will be the template for leading strand synthesis, the top or the bottom? The bottom strand will be the template for leading strand synthesis. b) If we assume that a lagging strand fragment is made from region 1, what will be its sequence? 5? T G T C A G T C A G 3? c) You examine DNA replication in an E. coli mutant, which has a partially defective DNA polymerase. In vitro