BCHS 3201 FINAL EXAM UPDATED QUESTIONS AND
CORRECT ANSWERS
Question:
1. Making solutions from stock
Answer:
C1V1=C2V2
Question:
2. Molarity equation
Answer:
(formula weight)(volume desire)(molarity desired)= g needed
Question:
3. Why does plasmid DNA renature ful-ly, but chromosomal does not?
Answer:
Topologically intertwined, smaller RNA will also stay in solution
Question:
4. Why 90% Ethanol?
Answer:
Precipitates DNA: it's less polar than water and allows phosphate backbone to interact with sodium
ions.
Question:
5. Why 70% Ethanol?
Answer:
For washing: enough to prevent DNA from going back in solution, but allow washing off excess salt
Question:
6. Why TE/RNAse
Answer:
DNA more stable in TE buffer RNAse to remove soluable RNA and avoid smears in gel
Question:
7. Agarose Gel
Answer:
DNA is negatively charged (in pH=7), migrates towards positive pole, Separation by size, charge and
shape The higher the agarose %, the higher the separation power (resolution)
Question:
8. What is the purpose of EDTA?
Answer:
Chelate divalent metal cations so they are not available to DNAses as cofactors. Otherwise, they
would destroy the plasmid DNA
, Question:
9. Glucose
Answer:
Prevent premature cell lysis by osmotic shock
Question:
10. Alkaline pH (Tris pH=8)
Answer:
reduces electrostatic interactions between DNA and scaffolding proteins
Question:
11. SDS
Answer:
Disrupt cell membrane (amphipatic detergent, interacts with and disrupts amphiphatic phospholipid
bilayer of membrane
Question:
12. NaOH
Answer:
Denatures chromosomal & plasmid DNA
Question:
13. Sodium Acetate (pH=5.5)
Answer:
-Neutralize the lysis buffer -Basepairing of the plasmid DNA is restored -Precipitates the
proteins/lipids/chromosomal DNA out
Question:
14. Which DNA fragments run faster?
Answer:
Smaller
Question:
15. How does Ethidi-um Bromide/GelGreen work?
Answer:
Fluorescent dye, visible in UV, intercalates between base pairs
Question:
16. Why is GelGreen safer the EtBr?
Answer:
Cannot pass through cell membrane
Question:
17. Cleaves terminal residues from linear DNA
Answer:
-Exonuclease
CORRECT ANSWERS
Question:
1. Making solutions from stock
Answer:
C1V1=C2V2
Question:
2. Molarity equation
Answer:
(formula weight)(volume desire)(molarity desired)= g needed
Question:
3. Why does plasmid DNA renature ful-ly, but chromosomal does not?
Answer:
Topologically intertwined, smaller RNA will also stay in solution
Question:
4. Why 90% Ethanol?
Answer:
Precipitates DNA: it's less polar than water and allows phosphate backbone to interact with sodium
ions.
Question:
5. Why 70% Ethanol?
Answer:
For washing: enough to prevent DNA from going back in solution, but allow washing off excess salt
Question:
6. Why TE/RNAse
Answer:
DNA more stable in TE buffer RNAse to remove soluable RNA and avoid smears in gel
Question:
7. Agarose Gel
Answer:
DNA is negatively charged (in pH=7), migrates towards positive pole, Separation by size, charge and
shape The higher the agarose %, the higher the separation power (resolution)
Question:
8. What is the purpose of EDTA?
Answer:
Chelate divalent metal cations so they are not available to DNAses as cofactors. Otherwise, they
would destroy the plasmid DNA
, Question:
9. Glucose
Answer:
Prevent premature cell lysis by osmotic shock
Question:
10. Alkaline pH (Tris pH=8)
Answer:
reduces electrostatic interactions between DNA and scaffolding proteins
Question:
11. SDS
Answer:
Disrupt cell membrane (amphipatic detergent, interacts with and disrupts amphiphatic phospholipid
bilayer of membrane
Question:
12. NaOH
Answer:
Denatures chromosomal & plasmid DNA
Question:
13. Sodium Acetate (pH=5.5)
Answer:
-Neutralize the lysis buffer -Basepairing of the plasmid DNA is restored -Precipitates the
proteins/lipids/chromosomal DNA out
Question:
14. Which DNA fragments run faster?
Answer:
Smaller
Question:
15. How does Ethidi-um Bromide/GelGreen work?
Answer:
Fluorescent dye, visible in UV, intercalates between base pairs
Question:
16. Why is GelGreen safer the EtBr?
Answer:
Cannot pass through cell membrane
Question:
17. Cleaves terminal residues from linear DNA
Answer:
-Exonuclease
