Question

Table 2. Composition of biological media
Medium 1	Medium 2	Medium 3
Glucose 20 g	Sodium Citrate 50 g	Lactose 20 g
Peptone 5.0 g	Ammonium phosphate 1.0 g	Ammonium phosphate 1.0 g
Beef extract 3.0 g	Sodium chloride 5.0 g	Sodium chloride 5.0 g
Yeast extract 5.0 g	Magnesium sulfate 0.2 g	Magnesium sulfate 0.2 g
Sheep blood 10 g	Potassium phosphate 1.0g	Potassium phosphate 1.0 g
Sodium Chloride 8.0 g	All 20 amino acids (200 ?g each)	All 20 amino acids (200 ?g each)
Water 1 1iter	Guanine, adenine, thymine, cytosine, uracil (100 ?g each)	Guanine, adenine, thymine, cytosine, uracil (100 ?g each)
	Vitamin mixture* (100 mg)	Vitamin mixture* (100 mg)
	Water 1 1iter	Water 1 1iter
*Vitamin mixture = biotin, 0.15mg; nicotinic acid, 100mg; pyridoxal, 100 mg; calcium pantothenate, 500 mg; thiamine, 100mg; riboflavin, 100mg A mutation in what gene would prevent S. pneumoniae from growing in Medium 3 but not in Medium 1? Explain your answer. Why would this mutation only have an effect on growth in Medium 3?

Answer 1

ans- Due to the lacZ mutation orlac operon mutation would prevent S.pneumonia from growing on Medium 3.Lac z produced beta-galactosidase which catabolised the lactose and break down lactose into galactose and glucose. of lacZ gene mutated, B-galactosidase would not be expressed and lactose would not be metabolized for energy. Growth would still occur in medium 1or mutation would have no effect on S.pneumonia growth on medium 1 because it contain glucose and glucose metabolism won't be affected even if lac operon is not on and lac operon will be repressed.