BACTERIAL IDENTIFICATION VIRTUAL LAB
PRACTICE TEST SOLUTIONS 2026 FULL
ANSWERS
⩥ Describe the process of extracting bacterial DNA (sample
preparation) Answer: 1. dissolve the cell wall with digestive buffer
2. heat sample in a water bath 100°C to denature proteolytic enzymes
from digestive buffer
3. spin sample in centrifuge
4. transfer supernatant (the liquid) to PCR tube
⩥ Why do you heat the sample after adding the digestive buffer?
Answer: The buffer contains proteolytic enzymes that dissolve the cell
wall so DNA can be extracted. Once it does this, we must denature the
buffer to prevent the proteolytic enzymes from interfering with the
other enzymes used during PCR
⩥ Where is the extracted bacterial DNA in the centrifuge tube?
Answer: The cellular debris is spun down in the centrifuge and
appears as a solid deposit (pellet). The DNA is contained in the
supernatant (the liquid) that is transferred to the PCR tube
⩥ how do you dissolve the cell wall to extract the bacterial DNA?
Answer: proteolytic enzymes in digestive buffer dissolve the cell wall
, ⩥ what is PCR Answer: polymerase chain reaction is a technique that
allows many copies of DNA to be made from a small original sample
⩥ describe what happens in PCR Answer: In normal cells, the dsDNA
is unzipped with an enzyme to start the replication process. In PCR,
ssDNA is made by heating a chromosome fragment to 95°C. It is then
cooled.
⩥ Why is the sample cooled after the 95°C water bath? Answer: so
that the primers anneal to the og DNA strands and DNA polymerase
can bind and copy each strand
⩥ what is used to obtain the desired portion of the DNA in this lab??
Answer: oligonucleotide primers that specifically bind to regions
flanking the 16s rRNA gene. This binding initiates the replication
process
⩥ describe the steps of PCR Answer: 1. add PCR Master Mix solution
to sample DNA, positive control, and negative control
2. add positive and negative controls to their tubes
3.load tubes into thermocycler (PCR machine), run and then remove
4. insert microconcentrator column of appropriate size into collection
tubes
5. add 400µL of buffer to columns
6. add entire PCR content (~100µL) to column
7. put positive and negative control tubes on ice
8. Spin column at 3,000 rpm in a fixed-angle centrifuge for 15min
PRACTICE TEST SOLUTIONS 2026 FULL
ANSWERS
⩥ Describe the process of extracting bacterial DNA (sample
preparation) Answer: 1. dissolve the cell wall with digestive buffer
2. heat sample in a water bath 100°C to denature proteolytic enzymes
from digestive buffer
3. spin sample in centrifuge
4. transfer supernatant (the liquid) to PCR tube
⩥ Why do you heat the sample after adding the digestive buffer?
Answer: The buffer contains proteolytic enzymes that dissolve the cell
wall so DNA can be extracted. Once it does this, we must denature the
buffer to prevent the proteolytic enzymes from interfering with the
other enzymes used during PCR
⩥ Where is the extracted bacterial DNA in the centrifuge tube?
Answer: The cellular debris is spun down in the centrifuge and
appears as a solid deposit (pellet). The DNA is contained in the
supernatant (the liquid) that is transferred to the PCR tube
⩥ how do you dissolve the cell wall to extract the bacterial DNA?
Answer: proteolytic enzymes in digestive buffer dissolve the cell wall
, ⩥ what is PCR Answer: polymerase chain reaction is a technique that
allows many copies of DNA to be made from a small original sample
⩥ describe what happens in PCR Answer: In normal cells, the dsDNA
is unzipped with an enzyme to start the replication process. In PCR,
ssDNA is made by heating a chromosome fragment to 95°C. It is then
cooled.
⩥ Why is the sample cooled after the 95°C water bath? Answer: so
that the primers anneal to the og DNA strands and DNA polymerase
can bind and copy each strand
⩥ what is used to obtain the desired portion of the DNA in this lab??
Answer: oligonucleotide primers that specifically bind to regions
flanking the 16s rRNA gene. This binding initiates the replication
process
⩥ describe the steps of PCR Answer: 1. add PCR Master Mix solution
to sample DNA, positive control, and negative control
2. add positive and negative controls to their tubes
3.load tubes into thermocycler (PCR machine), run and then remove
4. insert microconcentrator column of appropriate size into collection
tubes
5. add 400µL of buffer to columns
6. add entire PCR content (~100µL) to column
7. put positive and negative control tubes on ice
8. Spin column at 3,000 rpm in a fixed-angle centrifuge for 15min
