The following table shows several bacterial strain lac operon genotypes (some ar
ID: 7476 • Letter: T
Question
The following table shows several bacterial strain lac operon genotypes (some are partial diploids).a) Fill in the blanks in the “lactose absent” and “lactose present” columns in this table. (+) means significant levels of active ß-galactosidase enzyme can be detected. (–) means no significant levels of active ß-galactosidase enzyme. The first line is filled in for reference.
Strain genotype
Lactose absent
Lactose present
1. lacI+ lacP+ lacO+ lacZ+ lacY+
2. lacI+ lacP+ lacOc lacZ+ lacY+
3. lacI+ lacP+ lacOc lacZ– lacY+
4. lacIs lacP+ lacOc lacZ+ lacY+
5. lacI– lacP+ lacO+ lacZ+ lacY+ / lacI+
6. lacIs lacP+ lacO+ lacZ+ lacY+/ lac I+
b) If lactose is absent and glucose is present in the culture medium of strain 4, will significant levels of active ß-galactosidase enzyme be detected? Explain… in brief, just because there is lots of room left, you don’t need to fill it.
Explanation / Answer
(a) first strain - lactose present second strain - lactose present third strain - lactose present but lacZ gene is not expressed. lacY gene is expressed.So lactose is not broken down into glucose and galactose fourth strain - lactose present fifth strain - lactose present sixth strain - lactose present -------------------------------------------------------------------------------- (b) if glucose is present and lactose is absent in the culture medium of strain 4, there will be very low levels of ß-galactosidase in the cell. this is due to leaky transcription. There is always a low level of transcription of lac operon genes in the cell.
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