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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

what are the prokaryotic
Lungu Reply
prokaraytotic is a unicellular organizm that lacks membrane bound nucleus
and whats eukaryotic
eukaryotic cell are cell which contain anuclues and organells
Explain on the Francisco reddi did to prove the theory of spontaneous generation
Diana Reply
what is parasite
Abdirizack Reply
designing of aseptic area
Aashish Reply
I don't know
what is rickettsia
what is microbiology
Is the science that works with microorganisms.
richettsa is small microorganisms that cause disease in human like typhus; they are like viruses that can grow only inside living cells, they're transmitted by mites, ticks or lices.
what is plasmid?
plasmid is extra chromosomal body present in bacteria...which have additional genetic functions example... antibiotic resistance genes....etc etc
state the theory of spontaneous generation of micro oranisms and germ theory of disease
what are the advantages of high note numerical aperture
Genius Reply
list if non flagellated pritozoa
Mepung Reply
Can someone that's understanding of the Kreb Cycle please explain & breakdown it down to me in the simplest way without giving me the dictionary version or Google version. Basically in there own words of knowledge....!
please can someone help explain positive and negative feedback in simple term
negative feedback is the arresting of reaction or reverse of the reaction according to the response and postive feed back is the direct response without reversing or arresting a reaction.
pls can someone explained Kinney stone in memorising in shot time
what tyoebif microorganism will be killed by antibiotic trwatmeant
Mary Reply
I don't really don't understand aerobic respiration anaerobic respiration and fermentation. Can someone explain & breakdown this in the simplest way please.
Anaerobic Respiration in which foodstuffs are partially oxidized, with the release of chemical energy, in a process not involving atmospheric oxygen, such as alcoholic fermentation, in which one of the end products is ethanol.
aerobic respiration A type of respiration in which foodstuffs are completely oxidized to carbon dioxide and water, with the release of chemical energy, in a process requiring atmospheric oxygen.
please can someone explain what pseudomonas species and biofilm is?
Fermentation is the growth of cells or microorganisms in bioreactors (fermenters) to synthesize special products. Fermentation in biochemistry refers to the biodegradation of carbon compounds by cells or organisms under anaerobic (lack of oxygen) conditions.
Please under which conditions does pathogens become established in the human tissues and can cause diseases
please the life cycle of plasmodium parasite
who is John Needham
Mary Reply
John Needham is one of the researcher in microbiology. He also experimented when scientists did not believe animals could arise spontaneously ,but did believe microbes could.
okay is he late
by the way what are the list of courses offered by a newly admitted student for microbiology
Needham's experiments with beef gravy and infusions of plants material reinforced this idea.
what drugs are given to a person with Otis nerve problem(ear problem)
Gum Reply
good morning to you all.
Muhammad Reply
Dr.A.K.S.P.G. college Akbarpur Ambedkar Nagar
Shailesh Vishwakarma BSc 1st year
differentiate between eukaryotes en prikaryotes
eukaryotes are organisms with complex cellular structure(presence of nucleus and mitochondrial) like plants and animals whilst prokaryotes are organisms with simple cellular structure (absence of nucleus, mitochondrial) like arthropods.
hello sir
I am Pankaj from bihar
I am study in NDRI karnal in btech in dairy
I am Pankaj from bihar
thanks am studying biomedical sciences in zambia.chikankata
Am a studying Disease Control in Ghana(kintampo)
I'm studying Environmental health in Zimbabwe 🇿🇼
am Joyce mwale studying nursing in Lusaka Zambia
hi pankaj
hi frds iam from India
IAM studying degree (micro biology)
Hi I am microbiologist
Hi friends I'm from Nigeria studying Microbiology
i am biotechnologist from pakistan
hi feds iam from india
hy frnds am from Uganda
am studying nursing/midwifery n kampala
I'm Gum Joseph Kakuu from Ghana,I'm studying RGN in nursing Jirapa.
I'm Hellen from Kenya studying applied biology
I live in india
am studying biotechnology
am maryjoy uwaoma from Nigeria,I am studying microbiology in NSUKKA NIGERIA
Nice meeting You people hear
thanks you.
can someone in there own words in the simplest way breakdown what aerobic respiration anaerobic respiration and fermentation means please and not from the dictionary version...!
what are the cultivation and identification of microorganisms
Algel Reply
ransport media.basic culture media.enriched media..differential media .indetification media
algel th above are some v th basic medias for bacterial growth
factors that can Prone the host to get disease
Linda Reply
what are the factors that prones host to get disease
Not sure about it, can you tell us Linda?
please I want to know the factors that prones host to get disease
please Linda we have internal and external factors. internal factors are within our body cavities.eg mother having TB giving it to her child,and the others. external factors are within our surrounding environment which include our daily activities(bathing, buying food and the others)
I don't understand aerobic respiration anaerobic respiration and fermentation. Can someone that do give me a short & simple breakdown.
pliz kisha ..aerobic respiration is th typ v repiration whre organisms use oxgyen for survival while anaerobic respiration is whre organisms survive without oxgyen at all.these use carbondioxide

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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