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    Lecture 2 Virology

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    Nawaz
    This document discusses the structure of viruses. It begins by describing the electron microscopes and techniques used to study viruses. Viruses can range from 10-400 nm in diameter, with Tobacco Mosaic Virus first observed under electron microscope in the 1950s. There are four main types of viral capsids: helical, icosahedral/polyhedral, complex, and enveloped. Helical viruses like TMV are spiral-shaped, while icosahedral viruses have spherical capsomeres. Complex viruses like pox have intricate internal structures. Enveloped viruses are bounded by a host-derived envelope containing glycoproteins.

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    Lecture 2 Virology

    Uploaded by

    Nawaz
    17 views15 pages
    This document discusses the structure of viruses. It begins by describing the electron microscopes and techniques used to study viruses. Viruses can range from 10-400 nm in diameter, with Tobacco Mosaic Virus first observed under electron microscope in the 1950s. There are four main types of viral capsids: helical, icosahedral/polyhedral, complex, and enveloped. Helical viruses like TMV are spiral-shaped, while icosahedral viruses have spherical capsomeres. Complex viruses like pox have intricate internal structures. Enveloped viruses are bounded by a host-derived envelope containing glycoproteins.

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    1639590005970_Lecture 2 Virology

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    This document discusses the structure of viruses. It begins by describing the electron microscopes and techniques used to study viruses. Viruses can range from 10-400 nm in diameter, with Tobacco Mosaic Virus first observed under electron microscope in the 1950s. There are four main types of viral capsids: helical, icosahedral/polyhedral, complex, and enveloped. Helical viruses like TMV are spiral-shaped, while icosahedral viruses have spherical capsomeres. Complex viruses like pox have intricate internal structures. Enveloped viruses are bounded by a host-derived envelope containing glycoproteins.

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    17 views15 pages

    Lecture 2 Virology

    Uploaded by

    Nawaz
    This document discusses the structure of viruses. It begins by describing the electron microscopes and techniques used to study viruses. Viruses can range from 10-400 nm in diameter, with Tobacco Mosaic Virus first observed under electron microscope in the 1950s. There are four main types of viral capsids: helical, icosahedral/polyhedral, complex, and enveloped. Helical viruses like TMV are spiral-shaped, while icosahedral viruses have spherical capsomeres. Complex viruses like pox have intricate internal structures. Enveloped viruses are bounded by a host-derived envelope containing glycoproteins.

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    of 15

    Structure of the Viruses

    Lecture # 2

    1
    • For the study of the viruses, there are two electron
    microscopes.
    • Scanning electron microscope (SEM) & Transmission
    electron microscope (TEM)
    • Besides these 2 methods, different techniques like X-
    rays diffraction and biochemical analysis are also
    used for the study of viruses.
    • Virus morphology has been extensively studied
    during the last decades due to importance of viruses
    and their simple structure.

    2
    Virion Size

    • Viral particles range from 10-400 nm in diameter.


    • The smallest viral particle is little larger than
    ribosome whereas pox viruses are have same size as
    the smallest bacteria and can be seen by light
    microscope at the highest resolution.
    • In the 1950’s, Tobacco mosaic virus (TMV) and other
    viruses were finally observed with electron
    microscope.

    3
    • Smallest virus = 17 nanometers in diameter.
    • Largest virus = 1000 nanometers (1 micrometer) in
    the greatest dimension.
    • Few are barely visible at light microscope level.
    • Some filoviruses have a total length of up to
    1400 nm; their diameters are only about 80 nm.

    4
    Different Viruses Size and Shapes

    5
    Morphology of Viruses
    • Rod like
    • Spiral
    • Spherical
    • Tadpole
    • All virions or viral particles consist of nucleocapsid.
    Each capsid is enclosed DNA or RNA. Therefore,
    morphologically there are four types of capsids.
    1. Helical Viruses
    2. Icosahedral / Polyhedral Viruses
    3. Complex viruses
    4. Enveloped Viruses
    6
    1. Helical Viruses

    • These are spiral shaped. Tobacco mosaic virus (TMV)


    is the best example of helical viruses.
    • A single type of protomer associate together in a
    spiral or helical arrangement to form a hollow tube
    like structure which is 10-15 nm in diameter and 300
    nm in length.
    • The genetic material, RNA, is present in spiral form in
    this tube. The size of capsid is influenced by both of
    its protomers and nucleic acid. The nucleic acid
    determines the capsid length because capsid cannot
    extend beyond the RNA.
    7
    8
    2. Icosahedral / Polyhedral Viruses

    • Some viruses are icosahedral in shape and


    icosahedral is a regular polyhedron with 20
    equilateral triangular phases and 12 vertices.
    • Icosahedral viruses can be seen under transmission
    electron microscope and these look like a knob like
    structure and their capsid is made up of about 5-6
    capsomeres or protomers. Protomers join together
    through non-covalent bonding. e.g., Vaccinia.

    9
    10
    3. Complex Viruses

    • Although most of the viruses are helical or


    icosahedral but many viruses do not fit in these
    categories. e.g., Pox viruses and Bacteriophages are
    two examples of complex viruses.
    • These have complex internal structure with an ovoid
    or brick shape exterior.
    • Nucleic acid is present in a region that is known as
    nucleoid.

    11
    12
    4. Enveloped Viruses
    • Many animal viruses and some plant viruses are bounded
    by some outer membranes known as envelop.
    • The envelopes are typically derived from portions of the
    host cell membranes (phospholipids and proteins), but
    include some viral glycoproteins.
    • These envelops may help viruses avoid the host immune
    system.
    • Glycoproteins on the surface of the envelope serve to
    identify and bind to receptor sites on the host's membrane.
    The viral envelope then fuses with the host's membrane,
    allowing the capsid and viral genome to enter and infect
    the host. 13
    • All enveloped viruses also have a capsid, another
    protein layer, between the envelope and the genome

    Schematic of a Cytomegalovirus, coat = envelope


    14
    Thanks

    15

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