Plasmid Extraction Buffers

Buffer P1 (Resuspension Buffer)

suspend bacterial cells, maintain pH 8, inactivate DNases, and remove RNA.

Tris-HCl in Buffer P1 do

Acts as a buffer to maintain a constant pH of 8.0.

What is the role of EDTA in Buffer P1?

Binds divalent cations (Mg²⁺, Ca²⁺) to inactivate DNases and weaken the cell membrane for easier lysis.

Why is RNase A added in Buffer P1?

degrade RNA so it does not contaminate the plasmid DNA.

LyseBlue and its purpose

pH indicator that turns blue at alkaline pH to visually confirm proper buffer mixing; optional but prevents handling errors.

appearance does the solution have after Buffer P1

Cloudy, showing suspended bacterial cells.

What is the purpose of Buffer P2 (Alkaline Lysis Buffer)?

To lyse cells, denature DNA, and solubilize cellular proteins.

What do NaOH and SDS do in Buffer P2?

NaOH denatures DNA into single strands

SDS breaks membranes and solubilizes proteins.

appearance does the solution have after Buffer P2

Clear, indicating lysis and solubilization of cellular components; turns blue if LyseBlue was added.

Buffer N3 (Neutralization Buffer)

neutralize the alkaline solution, allow plasmid DNA to renature, and precipitate proteins, chromosomal DNA, and debris.

guanidine hydrochloride play in Buffer N3

a chaotropic salt that precipitates denatured proteins, chromosomal DNA, and SDS, while plasmid DNA stays in solution.

potassium acetate do in Buffer N3

Helps precipitate SDS, proteins, and cellular debris.

What is the appearance of the solution after Buffer N3?

Milky, with insoluble debris settled; plasmid DNA remains in the supernatant.

• Color changes from blue to colorless if LyseBlue was used.

How does plasmid DNA bind to a spin column?

presence of guanidine hydrochloride, plasmid DNA binds to the silica membrane due to dehydration by chaotropic salts.

purpose of Buffer PE (Wash Buffer)

wash away salts and contaminants while keeping plasmid DNA bound to the column.

ethanol in Buffer PE important?

Dehydrates DNA to improve silica binding and removes contaminants

Why is an extra centrifugation step needed after Buffer PE?

remove residual ethanol that could inhibit downstream enzymatic reactions.

purpose of eluting plasmid DNA with distilled water

dissolve and recover purified plasmid DNA by restoring hydration shells around DNA molecules.

pGLO plasmid was transformed into

E. coli bacterial cells

How is the +pGLO Amp culture prepared?

transferring a single transformed E. coli colony from an LB/Amp agar plate into LB broth with ampicillin and incubating overnight at 37°C with shaking.

How is the +pGLO Amp/Ara culture prepared?

transferring a single transformed E. coli colony from an LB/Amp agar plate into LB broth with ampicillin and L(+) arabinose and incubating overnight at 37°C with shaking

vigorous shaking important during incubation

provides continuous oxygen for fast bacterial growth

How are cells collected for plasmid extraction?

Cells are pelleted by centrifugation from the overnight cultures.

What is the basis of the QIAprep Spin Miniprep Kit?

Alkaline lysis of bacterial cells followed by DNA adsorption onto silica in the presence of high salt.

alkaline lysis

Cell membranes break, releasing cellular contents including plasmid and chromosomal DNA.

Why is the lysate neutralized and adjusted to high-salt conditions?

allow plasmid DNA to remain soluble while chromosomal DNA and proteins precipitate.

Why does chromosomal DNA precipitate while plasmid DNA stays in solution?

Chromosomal DNA is much larger, takes longer to renature, and is less soluble under acidic/high-salt conditions.

plasmid DNA separated from chromosomal DNA?

centrifugation: chromosomal DNA forms a pellet, plasmid DNA stays in the supernatant.

How does the QIAprep 2.0 column work?

Plasmid DNA binds selectively to a silica membrane in high-salt buffer and is later eluted in low-salt buffer.

What is the purpose of Buffer PE wash?

remove salts and contaminants from the column while keeping plasmid DNA bound.

How is plasmid DNA eluted?

50–100 μl of Buffer EB or water.

Why is RNase added to Buffer P1?

degrade RNA, ensuring the plasmid DNA extract is free of RNA contamination.