Gene library
Encyclopedia
A genomic library
is a population
of host bacteria, each of which carries a DNA
molecule that was inserted into a cloning vector
, such that the collection of cloned DNA
molecules represents the entire genome
of the source organism
. This term also represents the collection of all of the vector
molecules, each carrying a piece of the chromosomal DNA of the organism, prior to the insertion of these molecules into the host cells.
Creating a library
The DNA molecules of an organism of interest are isolated. The DNA molecules are then partially digested by an endonuclease
restriction enzyme
. Sometimes, the DNA molecules are digested for different lengths of time in order to ensure that all the DNA has been digested to manageable sizes. The digested DNA molecules are separated by size using agarose electrophoresis
, and a suitable range of lengths of DNA
pieces are isolated and ligated into vectors. The vectors can then be taken up by suitable hosts.The hosts are kept in liquid media
and can be frozen at -80°C for a long period of time. Usually the hosts are bacteria
that do not contain any plasmids, so as to be sensitive to antibiotics.
The process of subdividing genomic DNA
into clonable elements and inserting them into hosts is called creating a library, a clone bank or a gene bank. A complete library of host cell
s will contain all of the genomic DNA of the source organism
.
Library (biology)
In molecular biology, a library is a collection of DNA fragments that is stored and propagated in a population of micro-organisms through the process of molecular cloning...
is a population
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
of host bacteria, each of which carries a DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
molecule that was inserted into a cloning vector
Cloning vector
A cloning vector is a small piece of DNA into which a foreign DNA fragment can be inserted. The insertion of the fragment into the cloning vector is carried out by treating the vehicle and the foreign DNA with a restriction enzyme that creates the same overhang, then ligating the fragments...
, such that the collection of cloned DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
molecules represents the entire genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
of the source organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
. This term also represents the collection of all of the vector
Vector (molecular biology)
In molecular biology, a vector is a DNA molecule used as a vehicle to transfer foreign genetic material into another cell. The four major types of vectors are plasmids, viruses, cosmids, and artificial chromosomes...
molecules, each carrying a piece of the chromosomal DNA of the organism, prior to the insertion of these molecules into the host cells.
Types of vectors
- PlasmidPlasmidIn microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA. They are double-stranded and, in many cases, circular...
s: Have a capacity of 15 kb. - Phage (lambda)BacteriophageA bacteriophage is any one of a number of viruses that infect bacteria. They do this by injecting genetic material, which they carry enclosed in an outer protein capsid...
s: Have a capacity of 25 kb. - CosmidCosmidA cosmid, first described by Collins and Hohn in 1978, is a type of hybrid plasmid that contains cos sequences, DNA sequences originally from the Lambda phage. Cosmids can be used to build genomic libraries....
s or FosmidFosmidFosmids are similar to cosmids but are based on the bacterial F-plasmid. The cloning vector is limited, as a host can only contain one fosmid molecule. Fosmids are 40 kb of random genomic DNA...
s: Have a capacity of 35-45 kb. - Bacterial artificial chromosomeBacterial artificial chromosomeA bacterial artificial chromosome is a DNA construct, based on a functional fertility plasmid , used for transforming and cloning in bacteria, usually E. coli. F-plasmids play a crucial role because they contain partition genes that promote the even distribution of plasmids after bacterial cell...
s (BAC)(P-1 derived): Have a capacity of 50-300 kb. - Yeast artificial chromosomeYeast artificial chromosomeA yeast artificial chromosome is a vector used to clone DNA fragments larger than 100 kb and up to 3000 kb. YACs are useful for the physical mapping of complex genomes and for the cloning of large genes...
s (YAC): Have a capacity of 300- >1500 kb. - Human artificial chromosomeHuman artificial chromosomeA human artificial chromosome is a microchromosome that can act as a new chromosome in a population of human cells. That is, instead of 46 chromosomes, the cell could have 47 with the 47th being very small, roughly 6-10 megabases in size, and able to carry new genes introduced by human researchers...
s (HAC): Have a capacity of >2000 kb.
Creating a library
The DNA molecules of an organism of interest are isolated. The DNA molecules are then partially digested by an endonuclease
Endonuclease
Endonucleases are enzymes that cleave the phosphodiester bond within a polynucleotide chain, in contrast to exonucleases, which cleave phosphodiester bonds at the end of a polynucleotide chain. Typically, a restriction site will be a palindromic sequence four to six nucleotides long. Most...
restriction enzyme
Restriction enzyme
A Restriction Enzyme is an enzyme that cuts double-stranded DNA at specific recognition nucleotide sequences known as restriction sites. Such enzymes, found in bacteria and archaea, are thought to have evolved to provide a defense mechanism against invading viruses...
. Sometimes, the DNA molecules are digested for different lengths of time in order to ensure that all the DNA has been digested to manageable sizes. The digested DNA molecules are separated by size using agarose electrophoresis
Electrophoresis
Electrophoresis, also called cataphoresis, is the motion of dispersed particles relative to a fluid under the influence of a spatially uniform electric field. This electrokinetic phenomenon was observed for the first time in 1807 by Reuss , who noticed that the application of a constant electric...
, and a suitable range of lengths of DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
pieces are isolated and ligated into vectors. The vectors can then be taken up by suitable hosts.The hosts are kept in liquid media
Growth medium
A growth medium or culture medium is a liquid or gel designed to support the growth of microorganisms or cells, or small plants like the moss Physcomitrella patens.There are different types of media for growing different types of cells....
and can be frozen at -80°C for a long period of time. Usually the hosts are bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
that do not contain any plasmids, so as to be sensitive to antibiotics.
The process of subdividing genomic DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
into clonable elements and inserting them into hosts is called creating a library, a clone bank or a gene bank. A complete library of host cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
s will contain all of the genomic DNA of the source organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
.