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Lytic Cycle
The LYTIC CYCLE (/ˈlɪtɪk/ LIT-ək ), is one of the two cycles of viral reproduction , the other being the lysogenic cycle . The lytic cycle results in the destruction of the infected cell and its membrane. A key difference between the lytic and lysogenic phage cycles is that in the lytic phage, the viral DNA
DNA
exists as a separate molecule within the bacterial cell, and replicates separately from the host bacterial DNA. The location of viral DNA
DNA
in the lysogenic phage cycle is within the host DNA, therefore in both cases the virus/phage replicates using the host DNA
DNA
machinery, but in the lytic phage cycle, the phage is a free floating separate molecule to the host DNA. CONTENTS* 1 Description * 1.1 Penetrating * 1.2 Gene regulation biochemistry * 1.3 Maturation and lysis * 1.3.1 Lytic cycle
Lytic cycle
without lysis * 2 References DESCRIPTIONViruses that only use lvytic cycle are called virulent viruses (in contrast to temperate viruses). The lytic cycle is a six-stage cycle. In the first stage, called "penetration", the virus injects its own nucleic acid into a host cell. In some viruses this genetic material is circular and mimics a bacterial plasmid . The virus hijacks the cell's replication and translation mechanisms, using them to make more viruses
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Lysis
LYSIS (/ˈlaɪsɪs/ LY-sis ; Greek λύσις lýsis, "a loosing" from λύειν lýein, "to unbind") refers to the breaking down of the membrane of a cell , often by viral , enzymic , or osmotic (that is, "lytic" /ˈlɪtɪk/ LIT-ək ) mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a lysate. In molecular biology , biochemistry , and cell biology laboratories, cell cultures may be subjected to lysis in the process of purifying their components, as in protein purification , DNA extraction , RNA extraction , or in purifying organelles . Many species of bacteria are subject to lysis by the enzyme lysozyme , found in animal saliva , egg white , and other secretions . Phage lytic enzymes (lysins) produced during bacteriophage infection are responsible for the ability of these viruses to lyse bacterial cells. Penicillin
Penicillin
and related β-lactam antibiotics cause the death of bacteria through enzyme-mediated lysis that occurs after the drug causes the bacterium to form a defective cell wall . If cell wall is completely lost, the bacterium is referred as a protoplast if penicillin was used on gram-positive bacteria , and spheroplast when used on gram-negative bacteria
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Virus
I: ds DNA viruses II: ss DNA viruses III: ds RNA viruses IV: (+)ss RNA viruses V: (−)ss RNA viruses VI: ssRNA-RT viruses VII: dsDNA-RT viruses A VIRUS is a small infectious agent that replicates only inside the living cells of other organisms . Viruses can infect all types of life forms , from animals and plants to microorganisms , including bacteria and archaea . Since Dmitri Ivanovsky 's 1892 article describing a non-bacterial pathogen infecting tobacco plants, and the discovery of the tobacco mosaic virus by Martinus Beijerinck in 1898, about 5,000 virus species have been described in detail, although there are millions of types. Viruses are found in almost every ecosystem on Earth and are the most abundant type of biological entity. The study of viruses is known as virology , a sub-speciality of microbiology . While not inside an infected cell or in the process of infecting a cell, viruses exist in the form of independent particles. These VIRAL PARTICLES, also known as VIRIONS, consist of two or three parts: (i) the genetic material made from either DNA or RNA , long molecules that carry genetic information; (ii) a protein coat, called the capsid , which surrounds and protects the genetic material; and in some cases (iii) an envelope of lipids that surrounds the protein coat when they are outside a cell
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Reproduction
REPRODUCTION (or PROCREATION or BREEDING) is the biological process by which new individual organisms – "offspring" – are produced from their "parents". Reproduction is a fundamental feature of all known life ; each individual organism exists as the result of reproduction. There are two forms of reproduction: asexual and sexual . In asexual reproduction, an organism can reproduce without the involvement of another organism. Asexual reproduction is not limited to single-celled organisms . The cloning of an organism is a form of asexual reproduction. By asexual reproduction, an organism creates a genetically similar or identical copy of itself. The evolution of sexual reproduction is a major puzzle for biologists. The two-fold cost of sexual reproduction is that only 50% of organisms reproduce and organisms only pass on 50% of their genes . Sexual reproduction typically requires the sexual interaction of two specialized organisms, called gametes , which contain half the number of chromosomes of normal cells and are created by meiosis , with typically a male fertilizing a female of the same species to create a fertilized zygote . This produces offspring organisms whose genetic characteristics are derived from those of the two parental organisms
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Lysogenic Cycle
LYSOGENY, or the LYSOGENIC CYCLE, is one of two cycles of viral reproduction (the lytic cycle being the other). Lysogeny is characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome or formations of a circular replicon in the bacterial cytoplasm. In this condition the bacterium continues to live and reproduce normally. The genetic material of the bacteriophage, called a prophage , can be transmitted to daughter cells at each subsequent cell division, and at later events (such as UV radiation or the presence of certain chemicals) can release it, causing proliferation of new phages via the lytic cycle. Lysogenic cycles can also occur in eukaryotes , although the method of DNA incorporation is not fully understood. The distinction between lysogenic and lytic cycles is that the spread of the viral DNA occurs through the usual prokaryotic reproduction, while the lytic phage is spread through the production of thousands of individual phages capable of surviving and infecting other cells. The key difference between the lytic cycle and the lysogenic cycle is that the lysogenic cycle does not lyse the host cell. Phages that replicate only via the lytic cycle are known as virulent phages while phages that replicate using both lytic and lysogenic cycles are known as temperate phages. In the lysogenic cycle, the phage DNA first integrates into the bacterial chromosome to produce the prophage
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Cell (biology)
The CELL (from Latin
Latin
cella, meaning "small room" ) is the basic structural, functional, and biological unit of all known living organisms . A cell is the smallest unit of life that can replicate independently, and cells are often called the "building blocks of life". The study of cells is called cell biology . Cells consist of cytoplasm enclosed within a membrane , which contains many biomolecules such as proteins and nucleic acids . Organisms can be classified as unicellular (consisting of a single cell; including bacteria ) or multicellular (including plants and animals ). While the number of cells in plants and animals varies from species to species, humans contain more than 10 trillion (1012) cells. Most plant and animal cells are visible only under a microscope , with dimensions between 1 and 100 micrometres . The cell was discovered by Robert Hooke in 1665, who named the biological units for their resemblance to cells inhabited by Christian monks in a monastery
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Virulent
VIRULENCE is a pathogen or microbe's ability to infect or damage a host. In the context of gene for gene systems, often in plants, virulence refers to a pathogen's ability to infect a resistant host. In most other contexts, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host . The pathogenicity of an organism - its ability to cause disease - is determined by its virulence factors . The noun virulence derives from the adjective virulent. Virulent can describe either disease severity or a pathogen's infectivity. The word virulent derives from the Latin word virulentus, meaning "a poisoned wound" or "full of poison." In an ecological context, virulence can be defined as the host's parasite-induced loss of fitness . Virulence can be understood in terms of proximate causes —those specific traits of the pathogen that help make the host ill—and ultimate causes —the evolutionary pressures that lead to virulent traits occurring in a pathogen strain. CONTENTS* 1 Virulent bacteria * 1.1 Methods by which bacteria cause disease * 2 Virulent viruses * 3 Evolution
Evolution
* 4 See also * 5 References VIRULENT BACTERIAThe ability of bacteria to cause disease is described in terms of the number of infecting bacteria, the route of entry into the body, the effects of host defense mechanisms, and intrinsic characteristics of the bacteria called virulence factors
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Temperateness (virology)
In VIROLOGY , TEMPERATE refers to the ability of some bacteriophages (notably coliphage λ ) to display a lysogenic life cycle . Many (but not all) temperate phages can integrate their genomes into their host bacterium\'s chromosome, together becoming a lysogen as the phage genome becomes a prophage . A temperate phage is also able to undergo a productive, typically lytic life cycle, where the prophage is expressed, replicates the phage genome, and produces phage progeny, which then leave the bacterium . With phage the term virulent is often used as an antonym to temperate, but more strictly a virulent phage is one that has lost its ability to display lysogeny through mutation rather than a phage lineage with no genetic potential to ever display lysogeny (which more properly would be described as an obligately lytic phage). NOTES * ^ Barksdale, L., and S. B. Ardon. 1974. Persisting bacteriophage infections, lysogeny, and phage conversions. Annu. Rev. Microbiol. 28:265-299. This virus -related article is a stub . You can help by expanding it . * v * t * e Retrieved from "https://en.wikipedia.org/w/index.php?title=Temperateness_(virology) additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy .® is a registered trademark of the Wikimedia Foundation, Inc
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Plasmid
A PLASMID is a small DNA molecule within a cell that is physically separated from a chromosomal DNA and can replicate independently. They are most commonly found in bacteria as small circular, double-stranded DNA molecules; however, plasmids are sometimes present in archaea and eukaryotic organisms . In nature, plasmids often carry genes that may benefit the survival of the organism, for example antibiotic resistance . While the chromosomes are big and contain all the essential genetic information for living under normal conditions, plasmids usually are very small and contain only additional genes that may be useful to the organism under certain situations or particular conditions. Artificial plasmids are widely used as vectors in molecular cloning , serving to drive the replication of recombinant DNA sequences within host organisms. Plasmids are considered _replicons _, a unit of DNA capable of replicating autonomously within a suitable host. However, plasmids, like viruses , are not generally classified as life . Plasmids can be transmitted from one bacterium to another (even of another species) via three main mechanisms: transformation , transduction , and conjugation . This host-to-host transfer of genetic material is called horizontal gene transfer , and plasmids can be considered part of the mobilome
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Virions
I: ds DNA
DNA
viruses II: ss DNA
DNA
viruses III: ds RNA
RNA
viruses IV: (+)ss RNA
RNA
viruses V: (−)ss RNA
RNA
viruses VI: ssRNA-RT viruses VII: dsDNA-RT viruses A VIRUS is a small infectious agent that replicates only inside the living cells of other organisms . Viruses can infect all types of life forms , from animals and plants to microorganisms , including bacteria and archaea . Since Dmitri Ivanovsky 's 1892 article describing a non-bacterial pathogen infecting tobacco plants, and the discovery of the tobacco mosaic virus by Martinus Beijerinck in 1898, about 5,000 virus species have been described in detail, although there are millions of types. Viruses are found in almost every ecosystem on Earth and are the most abundant type of biological entity. The study of viruses is known as virology , a sub-speciality of microbiology . While not inside an infected cell or in the process of infecting a cell, viruses exist in the form of independent particles
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Cell Wall
A CELL WALL is a structural layer surrounding some types of cells , situated outside the cell membrane . It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mechanism. Cell walls
Cell walls
are present in most prokaryotes (except mycoplasma bacteria), in algae , plants and fungi but rarely in other eukaryotes including animals. A major function is to act as pressure vessels, preventing over-expansion of the cell when water enters. The composition of cell walls varies between species and may depend on cell type and developmental stage. The primary cell wall of land plants is composed of the polysaccharides cellulose , hemicellulose and pectin . Often, other polymers such as lignin , suberin or cutin are anchored to or embedded in plant cell walls. Algae
Algae
possess cell walls made of glycoproteins and polysaccharides such as carrageenan and agar that are absent from land plants. In bacteria, the cell wall is composed of peptidoglycan . The cell walls of archaea have various compositions, and may be formed of glycoprotein S-layers , pseudopeptidoglycan , or polysaccharides . Fungi
Fungi
possess cell walls made of the glucosamine polymer chitin . Unusually, diatoms have a cell wall composed of biogenic silica
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Osmotic Pressure
OSMOTIC PRESSURE is the minimum pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane . It is also defined as the measure of the tendency of a solution to take in water by osmosis . POTENTIAL OSMOTIC PRESSURE is the maximum osmotic pressure that could develop in a solution if it were separated from distilled water by a selectively permeable membrane. The phenomenon of osmosis arises from the propensity of a pure solvent to move through a semi-permeable membrane and into a solution containing a solute to which the membrane is impermeable . This process is of vital importance in biology as the cell's membrane is semipermeable. CONTENTS * 1 Background * 2 Applications * 3 Derivation of the van \'t Hoff formula * 4 Non-ideal solutions * 5 See also * 6 References * 7 External links BACKGROUND Osmosis
Osmosis
in a U-shaped tube. A Pfeffer cell used for early measurements of osmotic pressure In order to visualize this effect, imagine a U-shaped tube with equal amounts of water on each side, separated by a water-permeable membrane made from dialysis tubing at its base that is impermeable to sugar molecules. Sugar has been added to the water on one side
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Plasma Membrane
The CELL MEMBRANE (also known as the PLASMA MEMBRANE or CYTOPLASMIC MEMBRANE) is a biological membrane that separates the interior of all cells from the outside environment . The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. The basic function of the cell membrane is to protect the cell from its surroundings. It consists of the lipid bilayer with embedded proteins . Cell membranes are involved in a variety of cellular processes such as cell adhesion , ion conductivity and cell signalling and serve as the attachment surface for several extracellular structures, including the cell wall , glycocalyx , and intracellular cytoskeleton . Cell membranes can be artificially reassembled
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RNA
RIBONUCLEIC ACID (RNA) is a polymeric molecule essential in various biological roles in coding , decoding , regulation , and expression of genes . RNA
RNA
and DNA
DNA
are nucleic acids , and, along with lipids , proteins and carbohydrates , constitute the four major macromolecules essential for all known forms of life . Like DNA, RNA
RNA
is assembled as a chain of nucleotides , but unlike DNA
DNA
it is more often found in nature as a single-strand folded onto itself, rather than a paired double-strand. Cellular organisms use messenger RNA
RNA
(_MRNA_) to convey genetic information (using the letters G, U, A, and C to denote the nitrogenous bases guanine , uracil , adenine , and cytosine ) that directs synthesis of specific proteins. Many viruses encode their genetic information using an RNA
RNA
genome . Some RNA
RNA
molecules play an active role within cells by catalyzing biological reactions, controlling gene expression , or sensing and communicating responses to cellular signals. One of these active processes is protein synthesis , a universal function where RNA molecules direct the assembly of proteins on ribosomes . This process uses transfer RNA
RNA
(_TRNA_) molecules to deliver amino acids to the ribosome, where ribosomal RNA
RNA
(_RRNA_) then links amino acids together to form proteins
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DNA
DEOXYRIBONUCLEIC ACID (/diˈɒksiˌraɪboʊnjʊˌkliːɪk, -ˌkleɪɪk/ ( listen ); DNA) is a molecule that carries the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms and many viruses . DNA and ribonucleic acid (RNA) are nucleic acids ; alongside proteins , lipids and complex carbohydrates (polysaccharides ), they are one of the four major types of macromolecules that are essential for all known forms of life . Most DNA molecules consist of two biopolymer strands coiled around each other to form a double helix . The two DNA strands are called polynucleotides since they are composed of simpler monomer units called nucleotides . Each nucleotide is composed of one of four nitrogen-containing nucleobases — cytosine (C), guanine (G), adenine (A), or thymine (T) — a sugar called deoxyribose , and a phosphate group . The nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone . The nitrogenous bases of the two separate polynucleotide strands are bound together, according to base pairing rules (A with T, and C with G), with hydrogen bonds to make double-stranded DNA. The total amount of related DNA base pairs on Earth is estimated at 5.0 x 1037 and weighs 50 billion tonnes
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Transcription (genetics)
TRANSCRIPTION is the first step of gene expression , in which a particular segment of DNA
DNA
is copied into RNA
RNA
(especially m RNA
RNA
) by the enzyme RNA
RNA
polymerase . Both DNA
DNA
and RNA
RNA
are nucleic acids , which use base pairs of nucleotides as a complementary language. During transcription, a DNA
DNA
sequence is read by an RNA
RNA
polymerase, which produces a complementary, antiparallel RNA
RNA
strand called a primary transcript . Transcription proceeds in the following general steps: * RNA
RNA
polymerase, together with one or more general transcription factors , binds to promoter DNA
DNA
. * RNA