presentation on virus

If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

To log in and use all the features of Khan Academy, please enable JavaScript in your browser.

Biology library

Course: biology library   >   unit 24, intro to viruses.

• Bacteriophages
• Animal & human viruses
• Evolution of viruses
• The biology of Zika virus

Key points:

• A virus is an infectious particle that reproduces by "commandeering" a host cell and using its machinery to make more viruses.
• A virus is made up of a DNA or RNA genome inside a protein shell called a capsid . Some viruses have an external membrane envelope .
• Viruses are very diverse. They come in different shapes and structures, have different kinds of genomes, and infect different hosts.
• Viruses reproduce by infecting their host cells and reprogramming them to become virus-making "factories."

Introduction

What is a virus, how are viruses different from bacteria, the structure of a virus.

• A protective protein shell, or capsid
• A nucleic acid genome made of DNA or RNA, tucked inside of the capsid
• A layer of membrane called the envelope (some but not all viruses)

Virus capsids

• Icosahedral – Icosahedral capsids have twenty faces, and are named after the twenty-sided shape called an icosahedron.
• Filamentous – Filamentous capsids are named after their linear, thin, thread-like appearance. They may also be called rod-shaped or helical.
• Head-tail –These capsids are kind of a hybrid between the filamentous and icosahedral shapes. They basically consist of an icosahedral head attached to a filamentous tail. Diagram of icosahedral (roughly spherical), filamentous (rod-like), and head-tail (icosahedral head attached to filamentous tail) virus capsid shapes. Image modified from " Non-enveloped icosahedral virus ," " Non-enveloped helical virus ," and " Head-tail phage ," by Anderson Brito, CC BY-SA 3.0 . The modified image is licensed under a CC BY-SA 3.0 license.

Virus envelopes

Virus genomes, what is a viral infection.

• Attachment. Virus binds to receptor on cell surface.
• Entry. Virus enters cell by endocytosis. In the cytoplasm, the capsid comes apart, releasing the RNA genome.
• Replication and gene expression. The RNA genome is copied (this would be done by a viral enzyme, not shown) and translated into viral proteins using a host ribosome. The viral proteins produced include capsid proteins.
• Assembly. Capsid proteins and RNA genomes come together to make new viral particles.
• Release. The cell lyses (bursts), releasing the viral particles, which can then infect other host cells.
• Attachment. The virus recognizes and binds to a host cell via a receptor molecule on the cell surface. More about attachment Virus binding to its receptor on the cell surface. Image modified from " Viral attachment to host cell ," by ViralZone/Swiss Institute of Bioinformatics, CC BY-NC 4.0 . In attachment, a specific protein on the capsid of the virus physically "sticks" to a specific molecule on the membrane of the host cell. This molecule, called a receptor , is usually a protein. A virus recognizes its host cells based on the receptors they carry, and a cell without receptors for a virus can't be infected by that virus.
• Entry . The virus or its genetic material enters the cell. More about entry One typical route for viral entry is fusion with the membrane, which is most common in viruses with envelopes. Viruses may also trick the cell into taking them in by a bulk transport process called endocytosis. Some even inject their DNA into the cell! Routes of entry include endocytosis (in which the membrane folds inward to bring the virus into the cell in a bubble) and direct fusion of the viral particle with the membrane, releasing its contents into the cell. Image modified from " Virus entry ," by ViralZone/Swiss Institute of Bioinformatics, CC BY-NC 4.0 .
• Genome replication and gene expression. The viral genome is copied and its genes are expressed to make viral proteins. More about replication and protein synthesis The viral genome is copied, and its genes are also expressed to make viral proteins. Image modified from " Positive stranded RNA virus replication , by ViralZone/Swiss Institute of Bioinformatics, CC BY-NC 4.0 . This step involves copying the viral genome and making more viral proteins, so that new virus particles can be assembled. The materials for these processes (such as nucleotides to make new DNA or RNA) come from the host cell, not the virus. Most of the "machinery" for replication and gene expression is also provided by the host cell. For instance, the messenger RNAs (mRNAs) encoding viral genes are translated into viral proteins using the host cell's ribosomes. However, certain steps, such as the copying of an RNA virus's genome, cannot be performed by host cell enzymes. In such cases, the viruses must encode their own enzymes. The viral proteins produced vary from virus to virus. All viruses must encode capsid proteins, and enveloped viruses typically also encode envelope proteins (which often aid in host recognition). Viruses may also encode proteins that manipulate the host genome (e.g., by blocking host defenses or driving expression of genes to benefit the virus), help with viral genome replication, or play a role in other parts of the viral lifecycle.
• Assembly. New viral particles are assembled from the genome copies and viral proteins. More about assembly During assembly, newly synthesized capsid proteins come together to form capsomers, which interact with other capsomers to form the full-sized capsid. Some viruses, like head-tail viruses, first assemble an “empty” capsid and then stuff the viral genome inside. Other viruses build the capsid around the viral genome, as shown below. Proteins of the capsid assemble around the viral genome, forming a new viral particle with the genome on the inside (encased by the capsid). Image modified from " Cytoplasmic capsid assembly/packaging , by ViralZone/Swiss Institute of Bioinformatics, CC BY-NC 4.0 .
• Release. Completed viral particles exit the cell and can infect other cells. More about release Three actions inside a plasma membrane of a cell are shown. The first image shows a hexagon shaped structure outside a ruptured cell membrane and is labeled lysis. The second image shows the a hexagon shaped structure outside the plasma membrane and the plasma membrane has an inward facing indentation of the membrane. Below the membrane is a sketch of the golgi body and the endoplasmic reticulum and the image is labeled exocytosis. The third image shows a hexagon shaped structure inside the cell pushing the plasma membrane outward and is labeled budding. Image modified from " Virus exit ," by ViralZone/Swiss Institute of Bioinformatics, CC BY-NC 4.0 . The last step in the virus lifecycle is the release of newly made viruses from the host cell. Different types of viruses exit the cell by different routes: some make the host cell burst (a process called lysis), while others exit through the cell's own export pathways (exocytosis), and others yet bud from the plasma membrane, taking a patch of it with them as they go. In some cases, the release of the new viruses kills the host cell. (For instance, a host cell that bursts will not survive.) In other cases, the exiting viruses leave the host cell intact so it can continue cranking out more virus particles.

Works cited:

• Weitz, J. S., and Wilhelm, S. W. (2013, July 1). An ocean of viruses. In The scientist . Retrieved from http://www.the-scientist.com/?articles.view/articleNo/36120/title/An-Ocean-of-Viruses/ .
• Zimmer, C. (2013, Feb 20). An infinity of viruses. In The loom: A blog by Carl Zimmer . Retrieved from http://phenomena.nationalgeographic.com/2013/02/20/an-infinity-of-viruses/ .
• Suttle, C. A. (2007). Marine viruses - major players in the global ecosystem. Nat. Rev. Microbiol. ,. 5 (10), 801-12.
• Virus. (2016, May 4). Retrieved May 10, 2016 from Wikipedia: https://en.wikipedia.org/wiki/Virus .
• Pithovirus. (2016, March 26). Retrieved May 10,2016 from Wikipedia: https://en.wikipedia.org/wiki/Pithovirus .
• How big are genomes? (n.d.). Retrieved from http://www.weizmann.ac.il/plants/Milo/images/How%20big%20is%20the%20genome120112Clean.pdf .
• Pierson, T. C. (2012, November 2). The flavivirus lifecycle. In Labs at NIAID . Retrieved from https://www.niaid.nih.gov/research/ted-c-pierson-phd

Additional references:

Want to join the conversation.

• Upvote Button navigates to signup page
• Downvote Button navigates to signup page
• Flag Button navigates to signup page

8 Introduction to Viruses

Viruses are typically described as obligate intracellular parasites , acellular infectious agents that require the presence of a host cell in order to multiply. Viruses that have been found to infect all types of cells – humans, animals, plants, bacteria, yeast, archaea, protozoa…some scientists even claim they have found a virus that infects other viruses! But that is not going to happen without some cellular help.

Virus Characteristics

Viruses can be extremely simple in design, consisting of nucleic acid surrounded by a protein coat known as a capsid . The capsid is composed of smaller protein components referred to as capsomers . The capsid+genome combination is called a nucleocapsid .

Viruses can also possess additional components, with the most common being an additional membranous layer that surrounds the nucleocapsid, called an envelope . The envelope is actually acquired from the nuclear or plasma membrane of the infected host cell, and then modified with viral proteins called peplomers . Some viruses contain viral enzymes that are necessary for infection of a host cell and coded for within the viral genome. A complete virus, with all the components needed for host cell infection, is referred to as a virion .

Virus Genome

While cells contain double-stranded DNA for their genome, viruses are not limited to this form. While there are dsDNA viruses, there are also viruses with single-stranded DNA ( ssDNA ), double-stranded RNA ( dsRNA ), and single-stranded RNA ( ssRNA ). In this last category, the ssRNA can either positive-sense ( +ssRNA , meaning it can transcribe a message, like mRNA) or it can be negative-sense ( -ssRNA , indicating that it is complementary to mRNA). Some viruses even start with one form of nucleic acid in the nucleocapsid and then convert it to a different form during replication.

Virus Structure

Viral nucleocapsids come in two basic shapes, although the overall appearance of a virus can be altered by the presence of an envelope, if present. Helical viruses have an elongated tube-like structure, with the capsomers arranged helically around the coiled genome. Icosahedral viruses have a spherical shape, with icosahedral symmetry consisting of 20 triangular faces. The simplest icosahedral capsid has 3 capsomers per triangular face, resulting in 60 capsomers for the entire virus. Some viruses do not neatly fit into either of the two previous categories because they are so unusual in design or components, so there is a third category known as complex viruses . Examples include the poxvirus with a brick-shaped exterior and a complicated internal structure, as well as bacteriophage with tail fibers attached to an icosahedral head.

Virus Replication Cycle

While the replication cycle of viruses can vary from virus to virus, there is a general pattern that can be described, consisting of five steps:

• Attachment – the virion attaches to the correct host cell.
• Penetration or Viral Entry – the virus or viral nucleic acid gains entrance into the cell.
• Synthesis – the viral proteins and nucleic acid copies are manufactured by the cells’ machinery.
• Assembly – viruses are produced from the viral components.
• Release – newly formed virions are released from the cell.

Outside of their host cell, viruses are inert or metabolically inactive. Therefore, the encounter of a virion to an appropriate host cell is a random event. The attachment itself is highly specific, between molecules on the outside of the virus and receptors on the host cell surface. This accounts for the specificity of viruses to only infect particular cell types or particular hosts.

Penetration or Viral Entry

Many unenveloped (or naked ) viruses inject their nucleic acid into the host cell, leaving an empty capsid on the outside. This process is termed penetration and is common with bacteriophage, the viruses that infect bacteria. With the eukaryotic viruses, it is more likely for the entire capsid to gain entrance into the cell, with the capsid being removed in the cytoplasm. An unenveloped eukaryotic virus often gains entry via endocytosis , where the host cell is compelled to engulf the capsid resulting in an endocytic vesicle, allowing the virus access to the cell contents. An enveloped eukaryotic virus gains entrance for its nucleocapsid through membrane fusion , where the viral envelope fuses with the host cell membrane, pushing the nucleocapsid past the cell membrane. If the entire nucleocapsid is brought into the cell then there is an uncoating process to strip away the capsid and release the viral genome.

The synthesis stage is largely dictated by the type of viral genome, since genomes that differ from the cell’s dsDNA genome can involve intricate viral strategies for genome replication and protein synthesis. Viral specific enzymes, such as RNA-dependent RNA polymerases, might be necessary for the replication process to proceed. Protein production is tightly controlled, to insure that components are made at the right time in viral development.

The complexity of viral assembly depends upon the virus being made. The simplest virus has a capsid composed of 3 different types of proteins, which self-assembles with little difficulty. The most complex virus is composed of over 60 different proteins, which must all come together in a specific order. These viruses often employ multiple assembly lines to create the different viral structures and then utilize scaffolding proteins to put all the viral components together in an organized fashion.

The majority of viruses lyse their host cell at the end of replication, allowing all the newly formed virions to be released to the environment. Another possibility, common for enveloped viruses, is budding , where one virus is released from the cell at a time. The cell membrane is modified by the insertion of viral proteins, with the nucleocapsid pushing out through this modified portion of the membrane, allowing it to acquire an envelope.

Bacteriophage

Viruses that infect bacteria are known as bacteriophage or phage . A virulent phage is one that always lyses the host cell at the end of replication, after following the five steps of replication described above. This is called the lytic cycle of replication.

There are also temperate phage , viruses that have two options regarding their replication. Option 1 is to mimic a virulent phage, following the five steps of replication and lysing the host cell at the end, referred to as the lytic cycle. But temperate phage differ from virulent phage in that they have another choice: Option 2, where they remain within the host cell without destroying it. This process is known as lysogeny or the lysogenic cycle of replication.

A phage employing lysogeny still undergoes the first two steps of a typical replication cycle, attachment and penetration. Once the viral DNA has been inserted into the cell it integrates with the host DNA, forming a prophage . The infected bacterium is referred to as a lysogen or lysogenic bacterium . In this state, the virus enjoys a stable relationship with its host, where it does not interfere with host cell metabolism or reproduction. The host cell enjoys immunity from reinfection from the same virus.

Exposure of the host cell to stressful conditions (i.e. UV irradiation) causes induction , where the viral DNA excises from the host cell DNA. This event triggers the remaining steps of the lytic cycle, synthesis, maturation, and release, leading to lysis of the host cell and release of newly formed virions.

So, what dictates the replication type that will be used by a temperate phage? If there are plenty of host cells around, it is likely that a temperate phage will engage in the lytic cycle of replication, leading to a large increase in viral production. If host cells are scarce, a temperate phage is more likely to enter lysogeny, allowing for viral survival until host cell numbers increase. The same is true if the number of phage in an environment greatly outnumber the host cells, since lysogeny would allow for host cells numbers to rebound, ensuring long term viral survival.

Lysogens can experience a benefit from lysogeny as well, since it can result in lysogenic conversion , a situation where the development of a prophage leads to a change in the host’s phenotype. One of the best examples of this is for the bacterium Corynebacterium diphtheriae , the causative agent of diphtheria. The diphtheria toxin that causes the disease is encoded within the phage genome, so only C. diphtheriae lysogens cause diphtheria.

Eukaryotic Viruses

Eukaryotic viruses can cause one of four different outcomes for their host cell. The most common outcome is host cell lysis, resulting from a virulent infection (essentially the lytic cycle of replication seen in phage). Some viruses can cause a latent infection , inserting their viral DNA into the host cell genome, allowing them to co-exist peacefully with their host cells for long periods of time (much like a temperate phage during lysogeny). Some enveloped eukaryotic viruses can also be released one at a time from an infected host cell, in a type of budding process, causing a persistent infection . Lastly, certain eukaryotic viruses can cause the host cell to transform into a malignant or cancerous cell, a mechanism known as transformation .

Viruses and Cancer

There are many different causes of cancer, or unregulated cell growth and reproduction. Some known causes include exposure to certain chemicals or UV light. There are also certain viruses that have a known associated with the development of cancer. Such viruses are referred to as oncoviruses . Oncoviruses can cause cancer by producing proteins that bind to host proteins known as tumor suppressor proteins , which function to regulate cell growth and to initiate programmed cell death, if needed. If the tumor suppressor proteins are inactivated by viral proteins then cells grow out of control, leading to the development of tumors and metastasis, where the cells spread throughout the body.

virus, obligate intracellular parasite, capsid, bacteriophage, capsomere, nucleocapsid, envelope, peplomer, virion, dsDNA, ssDNA, dsRNA, +ssRNA, -ssRNA, helical viruses, icosahedral viruses, complex viruses, attachment, penetration, viral entry, synthesis, assembly, release, naked virus, endocytosis, membrane fusion, budding, bacteriophage, phage, virulent phage, lytic cycle, temperate phage, lysogeny, lysogenic cycle, prophage, lysogen, lysogenic bacterium, induction, lysogenic conversion, virulent infection, latent infection, persistent infection, transformation, oncovirus, tumor suppressor proteins.

Study Questions

• What are the general properties of a virus?
• What is the size range of viruses? How do they compare, size-wise, to bacteria?
• What is the general structure of viruses? What are the different components?
• What viral shapes exist?
• How do envelopes and enzymes relate to viruses?
• What types of viral genomes exist?
• What are the 5 basic steps of viral replication? What happens at each step? How do bacterial/archaeal viruses differ from eukaryotic viruses, in regards to replication details?
• What are the 2 types of viral infection found in Bacteria/Archaea ? What are the specific terms associated with viral infection of bacterial/archaeal cells?
• What are the 4 types of viral infection found in eukaryotes?
• How do some viruses cause cancer?

Exploratory Questions (OPTIONAL)

• What is the largest bacterium or archaean ever discovered? What is the smallest eukaryote ever discovered?

General Microbiology Copyright © 2019 by Linda Bruslind is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License , except where otherwise noted.

An Introduction to Viruses

Jul 24, 2014

1.02k likes | 1.96k Views

An Introduction to Viruses. Lecturer Dr Ashraf Khasawneh Department of Biomedical Sciences. Virus infections are Universal ……. Introduction to Virology. A virus is an obligate intracellular parasite containing genetic material surrounded by protein

Share Presentation

• california encephalitis viruscoronavirushantavirusinfluenza virus
• hav hepatitis b virus
• hiv human t
• capsid envelope
• step growth
• mosaic virus

Presentation Transcript

An Introduction to Viruses Lecturer Dr Ashraf Khasawneh Department of Biomedical Sciences

Virus infections are Universal …….

Introduction to Virology • A virus is an obligate intracellular parasite containing genetic material surrounded by protein • Virus particles can only be observed by an electron microscope

Introduction to Virology • Recognizing the shape, size, and structure of different viruses is critical to the study of disease • Viruses have an inner core of nucleic acid surrounded by protein coat known as an envelope • Most viruses range in sizes from 20 – 450 nanometers

Viral Properties • Viruses are inert (nucleoprotein ) filterable Agents • Viruses are obligate intracellular parasites • Viruses cannot make energy or proteins independent of a host cell • Viral genome are RNA or DNA but not both. • Viruses have a naked capsid or envelope with attached proteins • Viruses do not have the genetic capability to multiply by division. • Viruses are non-living entities

Virus vs. cells Property Viruses Cells Type of nucleic acid DNA or RNA DNA and RNA Proteins Few Many Lipoprotein membrane Enveloped Cell membrane present in present in some viruses all cells Ribosomes Absent Present Mitochondria Absent Present in eukaryotic cells Enzymes None or few Many Multiplication by binary fission No Yes (most cells)

Viruses are Ultramicroscopic Koneman et al. Color Atlas and Textbook of Microbiology 5th Ed. 1997

The size of viruses

VIRAL STRUCTURE – SOME TERMINOLOGY • virus particle = virion • protein which coats the genome = capsid • capsid usually symmetrical • capsid + genome = nucleocapsid • may have an envelope

Virion • The complete infectious unit of virus particle • Structurally mature, extracellular virus particles.

Nucleic acid Capsid Envelope protein Membrane protein Viral envelope** Nucleocapsid Viral Structure - Overview Spike protein Fig 1. Schematic overview of the structure of animal viruses ** does not exist in all viruses

Distinguishing characteristics of viruses • Obligate intracellular parasites • Extreme genetic simplicity • Contain DNA or RNA • Replication involves disassembly and reassembly • Replicate by "one-step growth”

Naming viruses • No taxa above Family (no kingdom, phylum, etc) • Classified based on structures, size, nucleic acids, host species, target cells. • 19 families of animal viruses (6 DNA, 13 RNA) • Family name ends in – viridae • Subfamily ends in — virinae • Genus name ends in – virus • Species • Example • Family – Herpesviridae • Subfamily - Herpesvirinae • Genus – Simplex virus • Common name – herpes virus (Herpes simplex virus I (HSV-I) • Disease – fever blisters, cold sores

How are viruses named? • Based on: - the disease they cause poliovirus, rabies virus - the type of disease murine leukemia virus - geographic locations Sendai virus, Coxsackie virus - their discovers Epstein-Barr virus - how they were originally thought to be contracted dengue virus (“evil spirit”), influenza virus (the “influence” of bad air) - combinations of the above Rous Sarcoma virus

Virus particle = virion

5 BASIC TYPES OF VIRAL STRUCTURE nucleocapsid icosahedralnucleocapsid lipid bilayer ICOSAHEDRAL ENVELOPED ICOSAHEDRAL helicalnucleocapsid COMPLEX nucleocapsid lipid bilayer glycoprotein spikes = peplomers HELICAL ENVELOPED HELICAL

Viral Structure • Varies in size, shape and symmetry • 3 types of capsid symmetry: • Cubic (icosahedral) • Has 20 faces, each an equilateral triangle. Eg. adenovirus • Helical • Protein binds around DNA/RNA in a helical fashion eg. Coronavirus • Complex • Is neither cubic nor helical eg. poxvirus

VIRAL STRUCTURE (virion) Protect genome during passage from one cell to another Aid in entry process Package enzymes for early steps of infection

CAPSID STRUCTURE Morphological types 1. Helical capsid • Rod-shaped capsomers • Coil around hollow center • Nucleic acid is kept inside – wound-up within tube (Helix )

Morphological types Helical – capsid surrounds DNA like hollow tube Ex: Influenza , measles, rabies (enveloped)

Helical symmetry

Helical symmetry How to assemble

Helical symmetry In 1955, Fraenkel, Conrat, and Williams demonstrated that tobacco mosaic virus (TMV) spontaneously formed when mixtures of purified coat protein and its genomic RNA were incubated together. TMV, a filamentous virus

Morphological types 2. icosahedral • 20-sided with 12 corners • Vary in the number of capsomers • Each capsomer may be made of 1 or several proteins • Some are enveloped PROTOMER

Icosahedral capsids a) Crystallographic structure of a simple icosahedral virus. b) The axes of symmetry

Cubic or icosahedral symmetry

5-FOLD 3-FOLD 2-FOLD ICOSAHEDRAL SYMMETRY

ICOSAHEDRAL SYMMETRY

CAPSOMER ICOSAHEDRAL SYMMETRY = PENTON (pentamer)

CAPSOMER CAPSOMER = HEXON ICOSAHEDRAL SYMMETRY = PENTON

12 PENTONS 240 HEXONS Adenovirus

Enveloped helical virus Enveloped icosahedral virus

Helical • California Encephalitis VirusCoronavirusHantavirusInfluenza Virus (Flu Virus)Measles Virus ( Rubeola)Mumps VirusPara influenza VirusRabies VirusRespiratory Syncytial Virus(RSV)

Adeno-associated Virus (AAV)AdenovirusB19Coxsackievirus - ACoxsackievirus - BCytomegalovirus (CMV)Eastern Equine Encephalitis Virus (EEEV)EchovirusEpstein-Barr Virus (EBV)Hepatitis A Virus (HAV)Hepatitis B Virus (HBV)Hepatitis C Virus (HCV)Hepatitis Delta Virus (HDV)Hepatitis E Virus (HEV) Herpes Simplex Virus 1 (HHV1)Herpes Simplex Virus 2 (HHV2)Human Immunodeficiency Virus (HIV)Human T-lymphotrophic Virus (HTLV)Norwalk VirusPapilloma Virus (HPV)Polio virusRhinovirusRubella VirusSaint Louis Encephalitis VirusVaricella-Zoster Virus (HHV3)Western Equine Encephalitis Virus (WEEV)Yellow Fever Virus Icosahedral

Complex viruses • Have additional or special structures • Examples: • Poxviruses – lack normal capsid – instead, layers of lipoprotiens and fibrils on surface cross section surface view

A bacteriophage • A 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. The genetic material can be ssRNA, dsRNA, ssDNA, or dsDNA ('ss-' or 'ds-' prefix denotes single-strand or double-strand) along with either circular or linear arrangement.

Phage - viruses have a polyhedral head, helical tail and fibers for attachment.

Classification of viruses • Nucleic acid • Capsid • Presence of envelope • Replication strategy

CLASSIFICATIONNUCLEIC ACID • RNA or DNA • segmented or non-segmented • linear or circular • single-stranded or double-stranded • if single-stranded RNA • is genome mRNA (+) sense or complementary to mRNA (-) sense

ENVELOPE • OBTAINED BY BUDDING THROUGH A CELLULAR MEMBRANE (except poxviruses) • POSSIBILITY OF EXITING CELL WITHOUT KILLING IT • CONTAINS AT LEAST ONE VIRALLY CODED PROTEIN • ATTACHMENT PROTEIN • LOSS OF ENVELOPE RESULTS IN LOSS OF INFECTIVITY

Properties of naked viruses • Stable in hostile environment • Not damaged by drying, acid, detergent, and heat • Released by lysis of host cells • Can sustain in dry environment • Can infect the GI tract and survive the acid and bile • Can spread easily via hands, dust, fomites, etc • Can stay dry and still retain infectivity • Neutralizing mucosal and systemic antibodies are needed to control the establishment of infection

Naked viruses( Non Enveloped ) • Adeno-associated Virus (AAV)AdenovirusB19Coxsackievirus - ACoxsackievirus - BEchovirusHepatitis A Virus (HAV)Hepatitis E Virus (HEV)Norwalk Virus

The Baltimore classification system Based on genetic contents and replication strategies of viruses. According to the Baltimore classification, viruses are divided into the following seven classes: 1. dsDNA viruses 2. ssDNA viruses 3. dsRNA viruses 4. (+) sense ssRNA viruses (codes directly for protein) 5. (-) sense ssRNA viruses 6. RNA reverse transcribing viruses 7. DNA reverse transcribing viruses where "ds" represents "double strand" and "ss" denotes "single strand".

Virus Classification - the Baltimore classification • All viruses must produce mRNA, or (+) sense RNA • A complementary strand of nucleic acid is (–) sense • The Baltimore classification has + RNA as its central point • Its principles are fundamental to an understanding of virus classification and genome replication, but it is rarely used as a classification system in its own right

Viral genome strategies • dsDNA (herpes, papova, adeno, pox) • •ssDNA (parvo) • •dsRNA (reo, rota) • •ssRNA (+) (picorna, toga, flavi, corona) • •ssRNA (-) (rhabdo, paramyxo, orthomyxo, • bunya, filo) • •ssRNA (+/-) (arena, bunya) • •ssRNA (+RTase) (retro, lenti)

Sub-viral agents • Satellites • Contain nucleic acid • Depend on co-infection with a helper virus • May be encapsidated (satellite virus) • Mostly in plants, can be human e.g. hepatitis delta virus • If nucleic acid only = virusoid • Viroids • Unencapsidated, small circular ssRNA molecules that replicate autonomously • Only in plants, e.g. potato spindle tuber viroid • Depend on host cell polII for replication, no protein or mRNA • Prions • No nucleic acid • Infectious protein e.g. BSE

Viroids & Prions • Viroids • ss RNA genome and the smallest known pathogens. • Affects plants • Prions • Infectious particles that are entirely protein. • No nucleic acid • Highly heat resistant • Animal disease that affects nervous tissue • Affects nervous tissue and results in • Bovine spongiform encepahltits (BSE) “mad cow disease”, • scrapie in sheep • kuru & Creutzfeld-Jakob Disease (CJD) in humans

• More by User

An Introduction to the Viruses

An Introduction to the Viruses. Viral Components. All viruses have capsids- protein coats that enclose & protect their nucleic acid Viruses may have a membrane envelope Nucleic acid genome: may be dsDNA, ssDNA, ssRNA, dsRNA. Size Comparison of Viruses. Viral Taxonomy.

325 views • 14 slides

INTRODUCTION TO VIRUSES AND THEIR STRUCTURE:

INTRODUCTION TO VIRUSES AND THEIR STRUCTURE: . PETER H. RUSSELL, BVSc, PhD, FRCPath, MRCVS Department of Pathology and Infectious Diseases, The Royal Veterinary College, Royal College Street, London NW1 OTU. E-mail Web site. Objectives Students should be able to:.

263 views • 15 slides

Introduction to Herpes Viruses

Introduction to Herpes Viruses. Hugh B. Fackrell Filename: Herpes1.ppt [email protected]. Herpes Viruses. Group characteristics Herpes simplex 1 Herpes simplex 2. VP26 Assembly in HSV-1 Capsid. Herpes Virus Outline. Structure Classification Multiplication Clinical manifestations

1.33k views • 41 slides

INTRODUCTION TO VIRUSES

INTRODUCTION TO VIRUSES . Viruses They are the non-cellular form of life. A virus is an obligate intracellular parasite containing genetic material surrounded by protein. Virus particles can only be observed by an electron microscope

527 views • 25 slides

An Introduction to Marine Viruses

An Introduction to Marine Viruses . What Is a Virus?. Virus Size & Structure. 1 Micron. Chlamydia. Pox virus. Herpes virus. Influenza Virus. Bacterium ( Staphyllococcus aureus ). Picornavirus (polio). Relative size of viruses and bacteria. Microbial Loop. CO2. DOC.

1.49k views • 16 slides

AN INTRODUCTION TO:

TECHNICAL. GUIDELINES. from the leading resource for education and information in the repair industry. ICRI Technical Guideline No. 210.4-2009. AN INTRODUCTION TO:. Evaluation.

176 views • 6 slides

An Introduction to Viruses. Chapter 6. 6.1 The Search for elusive viruses. Leeuwenhoek’s microscope was extremely important in discovering small life forms But there was a limit to magnification

757 views • 59 slides

Introduction to the Viruses:

Introduction to the Viruses:. General properties of viruses: 1-They are very small in size , from 20-300  m . 2-They contain one kind of nucleic acid ( RNA or DNA ) as their genome . 3-They are metabolically inert because they do not possess

946 views • 17 slides

VIROLOGY An Introduction to the Viruses

VIROLOGY An Introduction to the Viruses. By Prof. Mohamed I. Bassyouni. General properties of viruses.

780 views • 50 slides

Virology Introduction to viruses

418 views • 19 slides

TECHNICAL. GUIDELINES. from the leading resource for education and information in the repair industry. ICRI Technical Guideline No. 320.6-2012. AN INTRODUCTION TO:. Repair Materials and Methods . Guide for Evaluation and Repair of Unbonded Post-Tensioned Concrete Structures .

461 views • 6 slides

TECHNICAL. GUIDELINES. from the leading resource for education and information in the repair industry. ICRI Technical Guideline No. 210.3-2004. AN INTRODUCTION TO:. Evaluation. Guideline for Using In-Situ Tensile Pull-Off Tests to Evaluate Bond of Concrete Surface Materials. Formerly 03739.

224 views • 6 slides

R1 Introduction to Viruses

Section R Viruses R1 Introduction to Viruses R2 Bacteriophages R3 DNA Viruses R4 RNA Viruses. R1 Introduction to Viruses. Viruses Virus genomes Replication strategies Virus Virulence. Viruses-I.

663 views • 33 slides

TECHNICAL. GUIDELINES. from the leading resource for education and information in the repair industry. ICRI Technical Guideline No. 120.1-2009. AN INTRODUCTION TO:. Safety. Guidelines and Recommendations for Safety in the Concrete Repair Industry.

385 views • 6 slides

An Introduction to the Viruses. Chapter 6. The Search for the Elusive Virus. ______________ postulated that rabies was caused by a virus (1884) Ivanovski and Beijerinck showed a disease in tobacco was caused by a virus (1890s) 1950s virology was a multifaceted discipline

952 views • 74 slides

Introduction to Viruses

Introduction to Viruses. The student should be able to. Define the structure of viruses Describe the importance of structure for transmission Classif y the viruses List the steps in viral replication List at least two virus attachment protein and receptor

909 views • 75 slides

BioEd Online. Introduction to Viruses. By Christine Herrmann, PhD. Courtesy of B.V.V. Prasad. BioEd Online. What Are Viruses?. Viruses are very small (10 – 400nm). not cells. a genome surrounded by a protective protein coat. infectious.

450 views • 18 slides

An Introduction to

An Introduction to. Washington Green Schools. Is a voluntary, statewide, web-based program your school can use to: Reduce its carbon footprint Reduce campus operating costs Provide students with hands-on experience & education about the environment. The Mission.

456 views • 24 slides

TECHNICAL. GUIDELINES. from the leading resource for education and information in the repair industry. ICRI Technical Guideline No. 130.1R-2009. AN INTRODUCTION TO:. Procurement Methods. Guide for Methods of Measurement and Contract Types for Concrete Repair Work. Formerly 03735.

174 views • 6 slides

206 views • 18 slides

177 views • 15 slides

Got any suggestions?

We want to hear from you! Send us a message and help improve Slidesgo

Top searches

Trending searches

11 templates

solar eclipse

25 templates

26 templates

kinesiology

23 templates

8 templates

Coronavirus Presentation templates

Raise awareness about one of the hottest topics of the 21st century by downloading and editing our free ppt templates and google slides themes about coronavirus..

Omicron COVID-19 Variant Clinical Case

A new variant of COVID-19 has been notified by the World Health Organization and has been named the Omicron variant. Questions and doubts start to arise and to solve them, there is no better idea than a clinical case with real examples to illustrate any doubt you may have. For...

Premium template

Unlock this template and gain unlimited access

Perinatal Death Caused COVID-19 Case Report

This template for a case report about perinatal death caused by COVID-19 is as elegant and tasteful as its serious subject deserves. Its green, yellow and white color scheme is understated without being dour, and several photos and illustrations add a visual component to the subjects of pregnancy, disease and...

Stop The Virus! Distance Learning Escape Room

If you are a fan of escape rooms you will love this template that we have created in Slidesgo. It is inspired by these games and features a virus that you have to escape from. The design is creative, with purple background, fun illustrations and sans serif typography. Go solving...

COVID-19 Vaccine Breakthrough

Aren't you tired of COVID-19? Great news: vaccines are already here! Use this new editable template to tell your audience all the latest discoveries on the matter. Since blue is the color of safety, we've used it to set the right atmosphere. We've used other resources, such as illustrations of...

Flu vs. COVID-19 Infographics

How to tell the difference between the flu and other diseases such as COVID-19? Some of their symptoms are similar, so we think a lot of healthcare workers will agree that people should be informed about this. Help patients or society in general by using these editable infographics. The variety...

COVID-19 Vaccine Breakthrough: Case Investigation and Reporting

The COVID-19 vaccine has improved the pandemic situation. We are gradually returning to our pre-COVID-19 lifestyle. All this has been achieved thanks to the enormous efforts of the scientific community, which has not rested until a remedy has been found. However, new variants of COVID-19 continue to emerge and we...

Norwalk Virus Clinical Case

The best way to understand a disease is through a clinical case. Your knowledge about Norwalk virus, which causes acute gastroenteritis, occurs in outbreaks and is easily transmitted, will be key to prevent it. And this template, with its modern, yet professional and functional design, will be your best ally...

National Influenza Vaccination Week

National Influenza Vaccination Week is a week in December when the importance of getting vaccinated against the flu is emphasized, especially for older people and those who are at more risk for any medical condition. Most people get through the flu just fine, but it can also have dire consequences....

Immunology Breakthrough

The scientific world is continuously making strides in medical research, particularly in the field of immunology. Highlight these achievements with a Google Slides and PowerPoint presentation! Designed with clear blue hues, this template offers a professional and compelling way to share your groundbreaking research, data findings, and innovative treatments. Fully...

Arbovirus Disease: Dengue

Download the Arbovirus Disease: Dengue presentation for PowerPoint or Google Slides. Taking care of yourself and of those around you is key! By learning about various illnesses and how they are spread, people can get a better understanding of them and make informed decisions about eating, exercise, and seeking medical...

Diseases Related to Stomach: Gastritis

Descarga la presentación Diseases Related to Stomach: Gastritis para PowerPoint o Google Slides. Es fundamental cuidarse y cuidar a los que te rodean. Al aprender sobre diversas enfermedades y cómo se contagian, la gente puede comprenderlas mejor y tomar decisiones informadas sobre alimentación, ejercicio y búsqueda de atención médica. Este...

Infection by Microorganisms Case Report

Download the Infection by Microorganisms Case Report presentation for PowerPoint or Google Slides. A clinical case is more than just a set of symptoms and a diagnosis. It is a unique story of a patient, their experiences, and their journey towards healing. Each case is an opportunity for healthcare professionals...

Download the Arbovirus presentation for PowerPoint or Google Slides. Healthcare goes beyond curing patients and combating illnesses. Raising awareness about diseases, informing people about prevention methods, discussing some good practices, or even talking about a balanced diet—there are many topics related to medicine that you could be sharing with everyone....

COVID-19 High School Lesson

It's true that COVID-19 has been around for almost a year now, but it's never too late to explain all about this virus and the prevention measures. This new template will be useful for high schools, as it's been designed with an educational purpose in mind. With a color palette...

Immunology - Bachelor of Science in Human Biology

Download the Immunology - Bachelor of Science in Human Biology presentation for PowerPoint or Google Slides. As university curricula increasingly incorporate digital tools and platforms, this template has been designed to integrate with presentation software, online learning management systems, or referencing software, enhancing the overall efficiency and effectiveness of student...

COVID-19 Outbreak Thesis

Several fields of study can benefit from interesting dissertations on how COVID-19 has spread all around the world. Your thesis is about this matter and you need to defend it in front of the assessment committee? Use this presentation during your speech and have your data on the screen while...

COVID-19 Explained for Middle School

The pandemic has completely changed the way we live. The youngest have had to adapt without understanding what was going on. If you want to make COVID-19 understandable for your middle school students, we recommend using this editable template from Slidesgo. With it you can explain the symptoms, prevention measures,...

Hospital Acquired Infection Case Study

Download the Hospital Acquired Infection Case Study presentation for PowerPoint or Google Slides. A clinical case is more than just a set of symptoms and a diagnosis. It is a unique story of a patient, their experiences, and their journey towards healing. Each case is an opportunity for healthcare professionals...

• Page 1 of 9

New! Make quick presentations with AI

Slidesgo AI presentation maker puts the power of design and creativity in your hands, so you can effortlessly craft stunning slideshows in minutes.

Register for free and start editing online