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Learning objectives

  • Describe the lytic and lysogenic life cycles
  • Describe the replication process of animal viruses
  • Describe unique characteristics of retroviruses and latent viruses
  • Discuss human viruses and their virus-host cell interactions
  • Explain the process of transduction
  • Describe the replication process of plant viruses

All viruses depend on cells for reproduction and metabolic processes. By themselves, viruses do not encode for all of the enzymes necessary for viral replication. But within a host cell, a virus can commandeer cellular machinery to produce more viral particles. Bacteriophages replicate only in the cytoplasm, since prokaryotic cells do not have a nucleus or organelles. In eukaryotic cells, most DNA viruses can replicate inside the nucleus, with an exception observed in the large DNA viruses, such as the poxviruses, that can replicate in the cytoplasm. RNA viruses that infect animal cells often replicate in the cytoplasm.

The life cycle of viruses with prokaryote hosts

The life cycle of bacteriophages has been a good model for understanding how viruses affect the cells they infect, since similar processes have been observed for eukaryotic viruses, which can cause immediate death of the cell or establish a latent or chronic infection. Virulent phages typically lead to the death of the cell through cell lysis. Temperate phages , on the other hand, can become part of a host chromosome and are replicated with the cell genome until such time as they are induced to make newly assembled viruses, or progeny virus es .

The lytic cycle

During the lytic cycle of virulent phage, the bacteriophage takes over the cell, reproduces new phages, and destroys the cell. T-even phage is a good example of a well-characterized class of virulent phages. There are five stages in the bacteriophage lytic cycle (see [link] ). Attachment is the first stage in the infection process in which the phage interacts with specific bacterial surface receptors (e.g., lipopolysaccharides and OmpC protein on host surfaces). Most phages have a narrow host range and may infect one species of bacteria or one strain within a species. This unique recognition can be exploited for targeted treatment of bacterial infection by phage therapy or for phage typing to identify unique bacterial subspecies or strains. The second stage of infection is entry or penetration . This occurs through contraction of the tail sheath, which acts like a hypodermic needle to inject the viral genome through the cell wall and membrane. The phage head and remaining components remain outside the bacteria.

This figure outlines the stages of the lytic cycle. Step 1 is attachment when the phage attaches to the surface of the host. The bacteriophage is shown sitting on the surface of the bacterial host cell. Step 2 is penetration when the viral DNA enters the host cell. The image shows DNA from within the virus being injected into the host DNA. Step 3 is biosynthesis when the phage DNA replicates and the phage proteins are made. The image shows various pieces of virus being built within the cell. Step 4 is maturation when the new phage particles are assembled. This shows the viral components being put together in the cell. The fifth step is lysis when the cell lyses and the newly made phages are released. This shows the cell bursting and built viruses being released.
A virulent phage shows only the lytic cycle pictured here. In the lytic cycle, the phage replicates and lyses the host cell.

The third stage of infection is biosynthesis of new viral components. After entering the host cell, the virus synthesizes virus-encoded endonucleases to degrade the bacterial chromosome. It then hijacks the host cell to replicate, transcribe, and translate the necessary viral components (capsomeres, sheath, base plates, tail fibers, and viral enzymes) for the assembly of new viruses. Polymerase genes are usually expressed early in the cycle, while capsid and tail proteins are expressed later. During the maturation phase, new virions are created. To liberate free phages, the bacterial cell wall is disrupted by phage proteins such as holin or lysozyme. The final stage is release. Mature viruses burst out of the host cell in a process called lysis and the progeny viruses are liberated into the environment to infect new cells.

Questions & Answers

how psychrophiles live at such a low temperature that their proteins dont get denatured
Harsh Reply
anti freeze proteins are synthesized to prevent such denaturations..
okay thank u
can you suggest me a book for food microbiology
and for industrial microbiology
food microbiology by M.R Adam and M.O.Moss
Industrial microbiology by L.E.casida.
maam can you suggest a best book that have applied microbiology concepts
mem can you suggest a best book of microscopy
for applied microbiology K.R.Aneja and other book by Allen Laskin
for microscopy Kirsteen Roger.
Define sterilization
Pramod Reply
Sterilization refers to any process that removes, kills, or deactivates all forms of life and other biological agents like prions present in a specific surface, object or fluid, for example food or biological culture media.
sterilization is the process of making an aseptic condition or microbe free environment to keep the objects from any kind of contamination.
Cool. I work for a Sterilisation company in India. We do Gamma Radiation, Steam Sterilisation and Ethylene Oxide Sterilisation
Explain the polymerization reaction of DNA polymerase enzyme?
Swetha Reply
I think in my opinion polymerization means monomers connects and produce large molecular chain
DNA polymerase I catalyzes the polymerization of dNTPs into DNA. This occurs by the addition of a dNTP (as dNMP) to the 3' end of a DNA chain, hence chain growth occurs in a 5' to 3' direction.Thus in this reaction, a phosphoanhydride bond in the dNTP is broken, and a phosphodiester is formed.
Thank you
ok..Thank you
Nicely explained
Welcome 🙏
write a note of microbiology with definition
Lucky Reply
Microbiology is the study of all living organisms that are too small to be visible with the naked eye. This includes bacteria, archaea, viruses, fungi, prions, protozoa and algae, collectively known as 'microbes'.
write down the difference branches of microbiology
Baccteriolog: the study of bactera. Immunology: the study of the immune system. It looks at the relationships between pathogens such as bacteria and viruses and their hosts. Mycology: the study of fungi, such as yeasts and molds. Nematology:the study of nematodes (roundworms).
Bacteriology: the study of bacteria. Immunology: the study of the immune system. It looks at the relationships between pathogens such as bacteria and viruses and their hosts. Mycology: the study of fungi, such as yeasts and molds. Nematology: the study of nematodes (roundworms).
Parasitology :the study of parasites. Phycology: the study of algae. Protozoology : the study of protozoa, single-celled organisms like amoebae. Virology:the study of viruses.
Parasitology: the study of parasites. Not all parasites are microorganisms, but many are. Protozoa and bacteria can be parasitic; the study of bacterial parasites is usually categorized as part of bacteriology. Phycology: the study of algae. Protozoology: the study of protozoa, single-celled organis
Virology: the study of viruses.
difference between gram negative and gram positive bacteria.
the difference between gram negative and gram positive bacteria is the colour which is obtained after staining techniques.. Gram positive bacteria stain violet due to the presence of a thick layer of peptidoglycan in their cell walls, which retains the crystal violet these cells are stained with.
Father of paleobotany?
The father of paleobotany is Birbal Sahni...
It is the study and recovery of ancient plants and geological contents
Father of immunology
Louis pasture was really father of immunology,despite Edward jenner poineering by introducing the vaccine against smallpox.
thank you anna
define a cell?
thank you Kaviya
Cells have many parts, each with a different function. Some of these parts, called organelles, are specialized structures that perform certain tasks within the cell.
cell is the basic structural and functional unit of life.
In biology, a cell ([sɛl], ”plural: cells”) is defined as the structural, functional, and biological unit of all organisms. It is an autonomous self-replicating unit that may exist as a functional independent unit of life (as in the case of a unicellular organism), or as a sub-unit in a multicellula
thank you
all bacterial cells have
Millie Reply
refamycin kills bacterial cell by acting on ...?
Yogesh Reply
monensin kills bacterial cell by acting on
genetic linkage cross over ratio ?
what is microbiology?
onuoha Reply
Hi!!! wants to know the meaning of microbiology
Christian Reply
Microbiology, study of microorganisms, or microbes, a diverse group of generally minute, simple life-forms that include bacteria, archaea, algae, fungi, protozoa, and viruses. The field is concerned with the structure, function, and classification of such organisms .
to study the life of microorganisms or microbes by knowing their characteristics types and relative species in lab
Microbiology is simply the study of microbial world.
Microbiology is the branch of biology in which we study microorganisms those which cannot be seen with naked eye these are bacteria,fungi,viruses Protozoa etc.
thanks for that information
microbiology, is a study of microorganisms adiversegroup of generally, simple life,
Thanks ever so much for the discussion.
Can anyone help with Organic Chemistry, and types?
which topic in organic chemistry
Introduction to organic chemistry.
Organic chemistry is the chemistry of carbon, an element that forms strong chemical bonds to other carbon atoms as well as to many other elements like hydrogen, oxygen, nitrogen, and the halogens. ... Many are composed of only carbon and hydrogen, collectively called hydrocarbons.
microbiology is the study of microorganisms like (bacteria ,viruses,fungi,protozoa and algae) their relationship to environment and their impact on environment .
can one tell me what are reservoirs and their types with explanation.
structure of protists
Rayyanu Reply
what is enzyme engineering
swati Reply
what is the difference between prokaryotes and eukaryotes?
Guirlaine Reply
Prokaryotes lack nucleus in their cells while eukaryotes have well defined nucleus in their cells
Prokaryotes are organisms that consist of a single prokaryotic cell. Eukaryotic cells are found in plants, animals, fungi, and protists. They range from 10–100 μm in diameter, and their DNA is contained within a membrane-bound nucleus. Eukaryotes are organisms containing eukaryotic cells.
The Day Jimmy"s Boa Ate the Wash by TRINKA HAKES NOBLE pictures by STEVEN KELLOGG
Alexia Reply
cytoplasmic membrane system in eukaryotes is called
Myerlyn Reply
I study in French,but I guess it's the same: we call it as the procaryotes "cytoplasme" but it's structure "cytosquelette" hope I helped.
hi bennini , I studied in English but I want to pursue in French .could u plz help me with French .thanks in advance
hi Si Yo, yes,of course how can I help you?
here can I download it where I could study it with relax dear
meaning of contagium vivum?
Royce Reply
explain transglutaminase cycle ?
Dilsath Reply

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