hassafe.blogg.se - Difference between plasmid and cosmid

A multiple cloning site (MCS), containing sequences recognized by common restriction enzymes, and designed to allow simple insertion of a desired gene sequence.

Cloning vectors are used to replicate, modify, and temporarily store a specific desired gene sequence.Ī plasmid used as a cloning vector will typically contain:

One of the most frequent uses for a plasmid is as a “ cloning vector”. In molecular biology, plasmids are used as vectors, ferrying genetic material from one cell to another, for the purposes of replication or expression. to bring genetic material from one cell into another cell for the purposes of replication or expression). In molecular biology, a vector is a DNA molecule that is used for horizontal gene transfer (i.e. Plasmids occur naturally in many prokaryotes, and often contain critical genes necessary for antibiotic resistance, but they are also commonly adopted for co-opted for use in the life sciences as vectors. they containing their own origin of replication) Capable of autonomous replication (i.e.Circular (No distinct 5’ or 3’beginning or end).Extrachromsomal (not packaged inside a chromosome).Small (with respect to nearly any whole genome).Plasmids: A short definitionīy their simplest definition, plasmids are stretches of DNA that contain at least one gene and are: Like a hard disk drive, or a newspaper, a plasmid is little more than a vessel for a gene or set of genes. Genes are the smallest functional unit of inheritance, and are composed of linear double-stranded DNA sequences that carry the blueprint for every distinct heritable phenotypic trait. Like other forms of information, genetic information also must be expressed through a medium, and that medium is the gene. Written information is conveyed through language and syntax, the distinct arrangement of universal character set intended to convey a specific thought or concept. Digital information is carried electronically, a collection of billions or trillions of tiny, organized switches that can be in of two distinct positions (on or off / 1 or 0). What does that mean? All information must be carried or conveyed via some medium.

Stryer, Lubert (1995) Biochemistry 4th ed.Plasmids are fragments of double-stranded DNA that can replicate independently of chromosomal DNA, and usually carry genes.

Voyles (2002) The biology of viruses 2nd ed. To package even more DNA into a vector, bacterial artificial chromosomes or yeast artificial chromosomes can be used. Thus the practical upper limit of the insert size is around 40kb, since there will also need to be origins of replication, selection genes and multiple cloning sites. The cosQ site of next cosmid (as rolling circle replication often results in linear concatemers) is held by the terminase after the previous cosmid has been packaged, to prevent degradation by cellular DNases.Picture]īecause of the fixed size of the phage head, terminase can only package cosmids that are between 75% and 105% of the length of the normal phage. The cosB site holds the terminase while it is nicking and separating the strands. The DNA must be linear to fit into a phage head. This causes linearization of the circular cosmid with two "cohesive" or "sticky ends" of 12bp. They contain a cosN site where DNA is nicked at each strand, 12bp apart, by terminase. In this way, they are similar to using the lambda phage as a vector, but only that all the lambda genes have been deleted with the exception of the cos sequence.Ĭos sequences are ~200 base pairs long and essential for packaging. This is made possible by the cohesive ends, also known as cos sites.

To circumvent this, phage transduction is used instead. Plasmids become unstable after a certain amount of DNA has been inserted into them, because their increased size is more conducive to recombination. However, unlike plasmids, they can also be packaged in phage capsids, which allows the foreign genes to be transferred into or between cells by transduction. Those cells which did not take up the cosmid would be unable to grow. They frequently also contain a gene for selection such as antibiotic resistance, so that the transfected cells can be identified by plating on a medium containing the antibiotic. They can replicate as plasmids if they have a suitable origin of replication: for example SV40 ori in mammalian cells, ColE1 ori for double-stranded DNA replication or f1 ori for single-stranded DNA replication in prokaryotes. Guide to balance cleaning: 8 simple stepsĬosmids are able to contain 37 to 52 kbp of DNA, while normal plasmids are able to carry only 1-20 kbp.