Microbiology Chapter 8: Gene Transfer and Genetic Engineering

transposition

The ability of a genetic sequence to move from one location to another.

specialized transduction

Only specific genes are transferred, phages usually insert at a specific location when they integrate with a chromosome. Is the process by which a restricted set of bacterial genes is transferred to another bacterium. The genes that get transferred (donor genes) depend on where the phage genome is located on the chromosome.

prophage

Phage DNA that is incorporated into the host bacterium's DNA.

temperate phage

Does not cause a disruptive infection. Instead the phage DNA is incorporated into a bacterium's DNA and is replicated with it. Can carry out both generalized and specialized transduction.

conjugation

Genetic information is transferred fro one bacterial cell to another through contact between recipient and donor cells. it also transfers much larger quantities of DNA.

recombination

The combining of genes (DNA) from two different cells. The rearrangement of genetic material, especially by crossing over in chromosomes or by the artificial joining of segments of DNA from different organisms.

protoplast

Is an organism with its cell wall removed.

F- cells

Lack F plasmids.

plasmid

Extrachromosomal DNA molecules.

F plasmid

Fertility factors that direct the synthesis of proteins that self assemble into conjugation pili.

transfer of F' plasmid

When the F plasmid in an Hfr cell separates from the bacterial chromosome, it may carry some chromosomal DNA with it. Such an F' plasmid may then be transferred by conjugation to an F- cell. The recipient cell will then have two copies of some genes- one on its chromosome and one on the plasmid.

gene transfer mechanisms compared

1. In transformation, less than 1 percent of the DNA in one bacterial cell is transferred to another, and the transfer involves only chromosomal DNA. 2. In transduction, the quantity of DNA transferred varies from a few genes to large fragments of the chromosome, bacteriophage is always involved in the transfer. 3. In conjugation, the quantity of DNA transferred is highly variable, depending on the mechanism. A plasmid is always involved in the transfer, a F plasmid itself can be transferred.

significance of transduction

1. It transfers genetic material from one bacterial cell to another and alters the genetic characteristics of the recipient cell. 2. The incorporation of phage DNA into a bacterial chromosome demonstrates a close evolutionary relationship between the prophage and host bacterial cell. 3. The discovery that a prophage can exist in a cell for a long period of time suggests a similar possible mechanism for the viral origin of cancer. If a prophage can exist in a bacterial cell and at some point alter the expression of a cell's DNA. 4. Provides a way to study gene linkage.

transformation

A change in an organism's characteristics because of the transfer of genetic information. Is the genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous genetic material from its surroundings through the cell membrane(s). Uptake of DNA occurs only at a certain stage in a cell's growth cycle, in response to high cell density and depletion of nutrients. DNA entry depends on such factors as modifications of the cell wall and the formation of specific receptor sites on the plasma membrane that can bind DNA. Once DNA reaches entry sited, endonuclease cut double stranded DNA into units of 7000 and 10000 nucleotides. only one strand enters and must combine by base pairing with a portion of recipient chromosome.

competence factor

A surface protein that binds extracellular DNA and enables the cell to be transformed. Is the ability of a cell to take up extracellular ("naked") DNA from its environment in the process called transformation.

transposon

A transposable element that contains the genes for transposition and one or more other genes. A chromosomal segment that can undergo transposition, especially a segment of bacterial DNA that can be translocated as a whole between chromosomal, phage, and plasmid DNA in the absence of a complementary sequence in the host DNA.

restriction fragment length polymorphism

A variation in the length of restriction fragments produced by a given restriction enzyme in a sample of DNA. Such variation is used in forensic investigations and to map hereditary disease.

bacteriophage

A virus that can infect a bacteria. They are composed of a core of nucleic acids covered by a protein coat. Infect their host and reproduce within them.

protoplast fusion

Accomplished by enzymatically removing the cell walls of organisms of two strains and mixing the resulting protoplasts. This allows fusion of the cells and their genetic material; that is material from one strain recombines with that from the other strains before new cell walls are produced.

genetic fusion

Allows transposition of genes from one location on a location on a chromosome. It can also involve deletion of a DNA segment, resulting in the coupling of portions of two operons.

generalized transduction

Any bacterial gene can be transferred by the phage. Once a phage particle with its newly acquired bacterial DNA leaves the infected host, it may infect another susceptible bacterium thereby transferring the bacterial genes. Each bacterial fragment from the host cell chromosome has an equal chance of accidentally becoming a part of phage particles during the phage's replication cycle.

virulent phage

Capable of causing infection and eventually the destruction and death of a bacterial cell.

resistance plasmid

Carry genes that provide resistance to various antibiotics such as chloramphenicol and tetracycline and to heavy metals such as arsenic and mercury. Generally contain two components: resistance transfer factor and resistance genes. The RTF implements transfer by conjugation of the whole resistance plasmid and is essential for the transfer of resistance from one organism to another. Each R gene carries information that confers resistance to a specific antibiotic or to a toxic metal

F+ cells

Contain extrachromosomal DNA called fertility plasmids.

recombinant DNA

DNA that contains information from two different two different species of organisms. Involves three processes: 1. The manipulation of DNA in vitro- that is outside cells. 2. The recombination of another organism's DNA with bacterial DNA in a phage or a plasmid. 3. The cloning, or production of many genetically identical progeny, of phages or plasmids that carry foreign DNA. DNA from cells is removed from cells and cut into small segments. The donor DNA segments are then incorporated into a vector or self replicating carrier such as a phage or a plasmid.

transfer of F plasmids

F plasmids carry information for the synthesis of proteins that for F pili, a bridge by which it attaches to F- cells when F+ and F- cells conjugate. A copy of plasmid DNA is then transferred as a single strand via a conjugation bridge or mating channel.

high frequency recombination

Hfr strains arise from F+ strains when the F plasmid is incorporated into the bacterial chromosome at one of several possible sites. When an Hfr cell serves as a donor in conjugation, the F plasmid initiates transfer of chromosomal DNA. Usually, only part of the F plasmid called the initiating segment is transferred along with some chromosomal genes. Genes are transferred in linear sequence, and the number of genes transferred depends on the duration of conjugation and whether the DNA strand breaks or remain intact.

gene amplification

Is a process by which plasmids or in some cases bacteriophages are induced to reproduce within cells at rapid rate. Increasing the number of plasmids will increase production of the substance by the host cells. Increased reproduction of plasmids would then greatly increase the number of copies of genes that act in antibiotic synthesis.

colicin

Is a type of bacteriocin produced by and toxic to some strains of Escherichia coli. They are released into the environment to reduce competition from other bacterial strains.

transduction

Method of transferring genetic material from one bacterium to another. DNA is carried by a bacteriophage. Happens when instead of only phage DNA being packed into newly forming phage heads some bacterial DNA is also packed into the heads.

genetic engineering

Refers to the purposeful manipulation of genetic material to alter the characteristics of an organism in a desired way.

vertical gene transfer

Sexual reproduction of plants and animals when genes pass from parents to offsprings. Bacteria do this when the reproduce asexually through binary fission. The transfer of genetic material is from parents to offspring. It may be through sexual or asexual reproduction.

frederick griffith

Studied pneumococcal infections in mice. These bacteria infect mice. He used a type III-S (smooth), which were pathogenic, and type II-R (rough) strain. He injected one group of mice with heat killed smooth pneumococci, a second group with live smooth pneumococci, a third group with live rough pneumococci, and a fourth group with a mixture of live rough and heat killed smooth pneumococci. What he observed : *He injected mice with the Type II-R strain and the mice survived. *He injected mice with the Type III-S strain and the mice died. *He heat killed the Type III-S strain and then injected the mice with the dead bacteria and the mice lived. *He injected dead Type III-S strain and live Type II-R strain into the mice and the mice died. He then detected the presence of live Type III-S strain bacteria with live Type II-R strain bacteria in the blood of the dead mice. This experiment led him to conclude that the dead the Type II-R bacteria had been transformed by the Type III-S bacteria enabling it to develop a polysaccharide cover and take on its virulent properties.

lysogenic cycle

The DNA of a temperate phage enters the host cell, becomes incorporated into the bacterial chromosome as a prophage, and replicates along with the chromosome through many cell divisions.

gene transfer

The movement of genetic information between organisms. In most eukaryotes, it is an essential part of the organism's life cycle and usually occurs by sexual reproduction. In prokaryotes (bacteria), it is not an essential part of the life cycle.

horizontal gene transfer

The movement of genetic material from a donor organism to a recipient organism that is not its offspring. There are three known mechanisms: 1. Transformation 2.Transduction 3.Conjugation

lytic cycle

The phage DNA directs the cell's metabolism to produce viral components- proteins and copies of phage DNA. When the cell becomes filled with a hundred or more phages, phage enzymes rupture the cell releasing newly formed phages which can infect other cells. phage attaches to receptor site on another bacterial cell wall, penetrates it, and inserts its DNA.