Question

QUESTION 8 The following situations (1-4) involve different types of gene regulation in prokaryotic cells as shown. OFF and ON reter to whether the gene is transcribed or not. Draw clearly-labelled regulatory proteins and effector molecules in each diagram to explain how the regulation works in each case. The first one has been done for you as an example a) (6 marks) Type of Regulation Regulatory protein effector molecule 1 DNA X negative inducible OFF ON 2 negative repressible DNA X OFF ON 3 positive inducible DNA X OFF ON 4 positive repressible DNA X OFF ON b) Four different E. coli strains (1-4) with mutations affecting lac gene expression were grown in medium without glucose but with or without lactose and had the phenotypes shown in the table below. Complete the table to indicate if genes in the lac operon would be transcribed (switched ON) or not transcribed (switched OFF) with or without lactose in mutants 1-4 (4 marks) Without lactose: With lactose lac genes ON or OFF Mutant Mutant phenotype lac genes ON or OFF OFF number wild type ON Repressor cannot bind to operator 2 Repressor cannot bind allolactose 3 lacl repressor gene is not transcribed 4 lacZ gene has a missense mutation

Answer 1

PEto ONA praten X ON sguatory pratin Eeckor Pasitive inducibla ONA CS Scannedwitff NO CamScanner

EHector guratory X cs Scanned with CamScanner Positve xuprussisla ON

Mutant number	Mutant phenotype	Without lactose: lac genes ON or OFF	With lactose: lac genes ON or OFF
	Wild type
1	Repressor cannot bind to operator	ON	ON
2	Repressor cannot bind allolactose	OFF	OFF
3	lacI repressor gene is not transcribed	ON	ON
4	lacZ gene has a missense mutation	OFF	ON