A scientist is using an ampicillin-sensitive strain of bacteria that cannot use lactose because it has a nonfunctional gene in the lac operon. She has two plasmids. One contains a functional copy of the affected gene of the lac operon, and the other contains the gene for ampicillin resistance. Using restrictions enzymes and DNA ligase, she forms a recombinant plasmid containing both genes. She then adds a high concentration of the plasmid to a tube of the bacteria in a medium for bacterial growth that contains glucose as the only energy source. This tube ( ) and a control tube (-) with similar bacteria but no plasmid are both incubated under the appropriate conditions for growth and plasmid uptake. The scientist then spreads a sample of each bacterial culture ( and -) on each of the three types of plates indicated below

Explanation:

"A scientist is using an ampicillin-sensitive strain of bacteria that cannot use lactose because it  has a nonfunctional gene in the lac operon. She has two plasmids. One contains a functional copy of the affected  gene of the lac operon, and the other contains the gene for ampicillin resistance. Using restriction enzymes and  DNA ligase, she forms a recombinant plasmid containing both genes. She then adds a high concentration of the  plasmid to a tube of the bacteria in a medium for bacterial growth that contains glucose as the only energy source.  This tube (+) and a control tube (-) with similar bacteria but no plasmid are both incubated under the appropriate  conditions for growth and plasmid uptake. The scientist then spreads a sample of each bacterial culture (+ and -) on  each of the three types of plates indicated below.

1. If no new mutations occur, it would be most reasonable to expect bacterial growth on which of the following  plates?

2. The scientist used restriction enzymes for what purpose in the experiment?

3. If the scientist had forgotten to use DNA ligase during the preparation of the recombinant plasmid, bacterial  growth would most likely have occurred on which of the following?"

ANSWER

1. If no new mutations occur, it would be most reasonable to expect bacterial growth on which of the following  plates? 1, 2, 3, 4

If the + bacteria takes up the recombinant plasmid, then it is now ampicillin resistant and able to use lactose, thus it can grow in the glucose medium, and the medium containing ampicillin and lactose, 1,2,3.

Meanwhile the - bacteria is ampicillin sensitive and so cannot grow in medium 5 and 6 which contain ampicillin. It can only grow on 4.

2. The scientist used restriction enzymes for what purpose in the experiment? To make cuts in the plasmid DNA

DNA restriction enzymes cleave (cut) DNA at specific sites. In this experiment, the scientist used it to cleave the specific genes she wanted.

3. If the scientist had forgotten to use DNA ligase during the preparation of the recombinant plasmid, bacterial  growth would most likely have occurred on which of the following? 1 and 4 only

DNA ligase joins DNA strands together. It catalysis the formation of a phosphodiester bond between DNA strands. If DNA ligase were absent their would be no recombinant DNA as DNA would not be able to join. Hence there would be no plasmid to confer the ability to grow in the presence of ampicillin of use lactose.