Select all of the following E. coli genotypes that will degrade lactose if lacto
ID: 67536 • Letter: S
Question
Select all of the following E. coli genotypes that will degrade lactose if lactose is present in the culture media. 5 marks total
a) I^+ P^ – O ^+ Z^ + Y^+ A^+
b) I^s P^+ O^+ Z^+ Y^+ A^+
c) I^– P^+ O^+ Z^+ Y^+ A^+
d) I^s P^+ O^c Z^+ Y^– A^+
e) I^+ P^+O^c Z^– Y^+ A^+
2. For the following E. coli merodiploids lactose is present in the culture media. Use “YES” to indicate if lactose is utilized and “NO” if it is not. Explain why or why not for each.
Chromosome/Plasmid Lactose Utilization Explanation
a.I^s P^+ O^c Z^+ Y^+ A^+ / I^+ P^– O^c Z^+ Y^– A^+
b.I^s P^+ O^c Z^+ Y^– A^+ / I^s+ P^– O^c Z^– Y+ A^+
Explanation / Answer
1. Lactose degradation needs the presence of the enzyme - galactosidase, which can hydrolyse - galactoside bond and hydrolyse lactos to glucose and galactose.
a) I^+ P^ – O ^+ Z^ + Y^+ A^+ ------------> No (operon is not expressed because RNA polymerase cannot bind)
b) I^s P^+ O^+ Z^+ Y^+ A^+ ------------------> Yes
c) I^– P^+ O^+ Z^+ Y^+ A^+ -----------------> Yes (Operon is constitutively expressed)
d) I^s P^+ O^c Z^+ Y^– A^+ -------------> No (Because lactose cannot enter the cell)
e) I^+ P^+O^c Z^– Y^+ A^+ ---------------> NO (beta galactosidose cannot be produced)
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