MOLECULAR BIOLOGY - BIOC0005 EXAM QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED

MOLECULAR BIOLOGY - BIOC0005 EXAM QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED Describe the role of adenylyl cyclase in positive control of the lac operon Adenylyl cyclase catalyses the reaction of ATP to cAMP The IIA protein must be phosphorylated and bound to adenylyl cyclase for this to work The cAMP then goes on to bind with CAP to increase the transcription of lac operon Describe growth curve of E. coli grown with glucose AND lactose Diauxic growth so uses up glucose first Brief lag phase as glucose is used up then lactose is used Why is the CAP-cAMP complex essential for efficient transcription of the lac operon in the presence of lactose as a nutrient source? The 'weak' lac operon needs help to have RNA polymerase bind The CAP-cAMP complex binds DNA which bends it 90 degrees around centre of symmetry Increases the affinity of RNA polymerase so it can transcribe the lac operon Discuss why the presence of glucose inhibits lac operon transcription Glucose reduces the amount of cAMP This deprives the lac operon of its transcriptional activator Describe the features of an operon that encodes 3 genes for a metabolic pathway. Indicate how 3 proteins are synthesised from such an operon One promoter at the start of the strand of mRNA 3 genes following Each gene has a AUG at the start and UGA at the end (own start and end codons) Ribosomes join and translate the proteins in each of their sections simultaneously Which 2 reactions are catalysed by beta-galactosidase? Lactose → 2x glucose Lactose → allolactose Roles of subunits of RNA polymerase 2x Alpha = assembly of core enzyme and promoter recognition Beta = catalytic domain Beta prime = recognition of DNA template strand Sigma factor = promoter recognition Key phases of transcription Initiation