Ch. 4 Study Questions

Question 1

After gel electrophoresis, a 0.5 microgram aliquot of DNA isolated from a bacterial culture produce only a faint smear at the bottom of the gel lane. Is this an acceptable DNA sample?

Answer 1

No. This amount of bacterial DNA should produce a bright smear near the top of the gel lane. The DNA is probably degraded.

Question 2

Contrast the measurement of DNA concentration by spectrophotometry with analysis by fluorometry with regard to staining requirements and accuracy.

Answer 2

Spectrophotometry requires no staining; fluorometry does.

Fluorometry may be more accurate since dsDNA must be intact to stain and generate a signal, whereas single nucleotides will absorb light in spectrophotometry.

Question 3

A blood sample was held at RT for 5 days before being processed for RNA isolation. Will this sample likely yield RNA?

Answer 3

No, due to degradation of the RNA and changes in gene expression.

Question 4

Name three factors that will affect yield of RNA from a paraffin-embedded tissue sample.

Answer 4

1. Type of fixative used
2. Age/length of storage of the tissue
3. Preliminary handling of the original specimen

Question 5

How do you calculate the concentration of DNA from the absorbance?

Answer 5

Concentration = (A260)(Dilution)(50 micrograms/mL)

Question 6

How do you calculate the yield of DNA from the concentration?

Answer 6

(Concentration)(Volume)

Question 7

What is an acceptable A260/A320 ratio?

Answer 7

1.7-2.0

Question 8

The _______ the A260/A320 ratio, the _______ contaminated the sample is.

Answer 8

lower; more