Does plasmid RNA exist Are plasmids typically double or sing

Does plasmid RNA exist? Are plasmids typically double- or single-stranded polynucleotides? What is the purpose of SDS in the cell lysis solution? What is the function of the alcohol solution? Why can chromosomal DNA be separated from plasmid DNA during cell lysis with buffers > pH 7?

Solution

# Does plasmid RNA exist?

Plasmids are defined as extra-chromosomal genetic elements, occurring chiefly in bacteria and rarely in eukaryotic organisms. In bacteria, plasmids are circular double-stranded DNA molecules which contain genes controlling a wide variety of functions. In yeast (Saccharomyces cerevisiae) an RNA plasmid has been found.

# What is the purpose of SDS in the cell lysis solution?

The lysis buffer solution contains sodium hydroxide (NaOH) and the detergent Sodium Dodecyl (lauryl) Sulfate (SDS). SDS is there to solubilize the cell membrane. NaOH helps to break down the cell wall, but more importantly it disrupts the hydrogen bonding between the DNA bases, converting the double-stranded DNA (dsDNA) in the cell, including the genomic DNA (gDNA) and your plasmid, to single stranded DNA (ssDNA). This process is called denaturation and is central part of the procedure, which is why it’s called alkaline lysis. SDS also denatures most of the proteins in the cells, which helps with the separation of the proteins from the plasmid later in the process.

# What is the function of the alcohol solution?

Alcohol is used in DNA extraction to force the DNA to precipitate in a solution. In order to collect a DNA sample, cells are broken down through agitation, then mixed with water, salt and ethanol to create an aqueous solution. Alcohol and salt work to prevent the DNA from dissolving into the water, instead causing it to precipitate out so it can be separated and extracted using a centrifuge.

# Why can chromosomal DNA be separated from plasmid DNA during cell lysis with buffers > pH 7?

Genomic DNA extraction is the simpler of the two procedures because all that is needed is a good strong lysis to release the genomic DNA into solution. A more universal method of lysis for genomic DNA extraction involves mechanically breaking the cell wall. The chromosome is going to break during purification because it is much too big to stay in one piece. But for most applications this is not a problem and for PCR or qPCR, the breakage will be an advantage because it allows better melting the DNA and result in a more efficient reaction.

# Are plasmids typically double- or single-stranded polynucleotides?

Pasmid DNA is double - stranded supercoiled DNA molecule. Plasmid used in mammalian cell transfection.AS-Ons are single stranded polynucleotides that are typical 10-15 nucleotides long and thus have molecular weights.