BCHS 3201 FINAL EXAM | 2025/2026 UPDATE |
QUESTIONS AND ANSWERS | WITH COMPLETE
SOLUTION!!
Making solutions from stock Answer - C1V1=C2V2
Molarity equation Answer - (formula weight)(volume desire)(molarity
desired)= g needed
Why does plasmid DNA renature fully, but chromosomal does not? Answer -
Topologically intertwined, smaller RNA will also stay in solution
Why 90% Ethanol? Answer - Precipitates DNA: it's less polar than water and
allows phosphate backbone to interact with sodium ions.
Why 70% Ethanol? Answer - For washing: enough to prevent DNA from going
back in solution, but allow washing off excess salt
Why TE/RNAse Answer - DNA more stable in TE buffer RNAse to remove
soluable RNA and avoid smears in gel
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)
, 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
Glucose Answer - Prevent premature cell lysis by osmotic shock
Alkaline pH (Tris pH=8) Answer - reduces electrostatic interactions between
DNA and scaffolding proteins
SDS Answer - Disrupt cell membrane (amphipatic detergent, interacts with and
disrupts amphiphatic phospholipid bilayer of membrane
NaOH Answer - Denatures chromosomal & plasmid DNA
Sodium Acetate (pH=5.5) Answer - -Neutralize the lysis buffer
-Basepairing of the plasmid DNA is restored
-Precipitates the proteins/lipids/chromosomal DNA out
Which DNA fragments run faster? Answer - Smaller
How does Ethidium Bromide/GelGreen work? Answer - Fluorescent dye,
visible in UV, intercalates between base pairs
Why is GelGreen safer the EtBr? Answer - Cannot pass through cell membrane
Cleaves terminal residues from linear DNA Answer - -Exonuclease
QUESTIONS AND ANSWERS | WITH COMPLETE
SOLUTION!!
Making solutions from stock Answer - C1V1=C2V2
Molarity equation Answer - (formula weight)(volume desire)(molarity
desired)= g needed
Why does plasmid DNA renature fully, but chromosomal does not? Answer -
Topologically intertwined, smaller RNA will also stay in solution
Why 90% Ethanol? Answer - Precipitates DNA: it's less polar than water and
allows phosphate backbone to interact with sodium ions.
Why 70% Ethanol? Answer - For washing: enough to prevent DNA from going
back in solution, but allow washing off excess salt
Why TE/RNAse Answer - DNA more stable in TE buffer RNAse to remove
soluable RNA and avoid smears in gel
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)
, 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
Glucose Answer - Prevent premature cell lysis by osmotic shock
Alkaline pH (Tris pH=8) Answer - reduces electrostatic interactions between
DNA and scaffolding proteins
SDS Answer - Disrupt cell membrane (amphipatic detergent, interacts with and
disrupts amphiphatic phospholipid bilayer of membrane
NaOH Answer - Denatures chromosomal & plasmid DNA
Sodium Acetate (pH=5.5) Answer - -Neutralize the lysis buffer
-Basepairing of the plasmid DNA is restored
-Precipitates the proteins/lipids/chromosomal DNA out
Which DNA fragments run faster? Answer - Smaller
How does Ethidium Bromide/GelGreen work? Answer - Fluorescent dye,
visible in UV, intercalates between base pairs
Why is GelGreen safer the EtBr? Answer - Cannot pass through cell membrane
Cleaves terminal residues from linear DNA Answer - -Exonuclease
