BACE - Biotechnician Assistant Credentialing DNA Extraction and Analysis Questions and Answers

Question 1

During agarose gel electrophoresis, what is the primary reason that DNA fragments migrate towards the positive electrode?

Accepted Answer

The phosphate backbone of DNA carries a strong negative charge.

Answer

The agarose gel matrix is positively charged.

Answer

The buffer system creates a pH gradient that attracts the DNA.

Answer

Smaller DNA fragments are naturally drawn to a positive pole.

Question 2

A biotechnician is performing a plasmid DNA extraction from E. coli using a spin-column based kit. The final step involves adding an elution buffer to the silica membrane. What is the primary purpose of this step?

Accepted Answer

To release the bound plasmid DNA from the silica membrane.

Answer

To precipitate the plasmid DNA out of the solution.

Answer

To wash away any remaining proteins and salts.

Answer

To digest any remaining RNA in the sample.

Question 3

Which of the following is a critical step for precipitating DNA from an aqueous solution after cell lysis and removal of cellular debris?

Accepted Answer

Adding ice-cold ethanol or isopropanol.

Answer

Adding a detergent to the solution.

Answer

Heating the solution to 95°C.

Answer

Vortexing the sample vigorously for 5 minutes.

Question 4

After running a DNA sample on a 1% agarose gel, a technician observes a single, very bright band located very close to the loading well. What is the most likely interpretation of this result?

Accepted Answer

The sample contains high molecular weight, undigested genomic DNA.

Answer

The sample contains very small DNA fragments.

Answer

The electrophoresis was run for too long.

Answer

The incorrect buffer was used to make the gel.

Question 5

A technician needs to isolate DNA from a tough plant tissue sample for PCR analysis. Which of the following steps is most likely required at the beginning of the extraction protocol for this sample type, but not for a bacterial cell culture?

Accepted Answer

Mechanical disruption, such as grinding in liquid nitrogen.

Answer

Addition of a lysis buffer containing detergents.

Answer

Centrifugation to pellet the cellular material.

Answer

Precipitation of DNA using isopropanol.

Question 6

To assess the purity of a DNA sample extracted from mammalian cells, a spectrophotometer is used to measure the absorbance at 260 nm and 280 nm. A ratio of A260/A280 of approximately 1.8 is generally considered to indicate a pure DNA sample. What does a significantly lower ratio (e.g., 1.5) suggest?

Accepted Answer

The sample is contaminated with protein.

Answer

The sample is contaminated with RNA.

Answer

The DNA concentration is very high.

Answer

The sample is contaminated with salts from the buffer.