Microbiology 6/e - PowerPoint PPT Presentation

1 / 23
About This Presentation
Title:

Microbiology 6/e

Description:

Title: Microbiology 6/e Author: Jacquelyn G. Black Last modified by: edaranadmin Created Date: 12/24/2002 1:08:46 AM Document presentation format – PowerPoint PPT presentation

Number of Views:33
Avg rating:3.0/5.0
Slides: 24
Provided by: jacqu6
Category:

less

Transcript and Presenter's Notes

Title: Microbiology 6/e


1
Chapter 1
  • INTRODUCTION

2
Lecture content
  • Background cases
  • General characteristics
  • Terminologies
  • Viral structures
  • Host range
  • Antigenic shift

3
Virus
Small particles in nanometres (10 -9)
Viruses are not cell!
4
In 2003, an outbreak of chicken flu
necessitated killing tens of millions of birds
5
An outbreak of swine flu (Influenza A)
originated in Mexico in March 2009 caused by H1N1
virus
6
General characteristics
7
General Characteristics of Viruses
  • Viruses are infectious agents that are too
  • small to be seen with a light microscope and
    that are not cells
  • When they invade susceptible host cells, viruses
    display some properties of living organisms and
    so appear to be on borderline between living and
    nonliving NOT CELL.
  • Viruses can replicate, or multiply, only inside a
    living host cell (obligate intracellular
    parasites)
  • Size 20 to 1000 nm in length

8
How to answer..
  • 1. Living characteristics of viruses
  • a. They reproduce at a fantastic rate, but only
    in living host cells.
  • b. They can mutate.
  • 2. Nonliving characteristics of viruses
  • a. They are acellular, that is, they contain no
    cytoplasm or cellular organelles.
  • b. They carry out no metabolism on their own and
    must replicate using the host cell's metabolic
    machinery. In other words, viruses don't grow and
    divide. Instead, new viral components are
    synthesized and assembled within the infected
    host cell.
  • c. The vast majority of viruses possess either
    DNA or RNA but not both.

9
The Best description
  • 3. Criteria used to define a virus
  • a. The vast majority of viruses contain only one
    type of nucleic acid DNA or RNA, but not both.
  • b. They are totally dependent on a host cell for
    replication. (They are strict intracellular
    parasites.)
  • c. Viral components must assemble into complete
    viruses (virions) to go from one host cell to
    another.

10
terminologies
11
Components of Viruses
  • Nucleic Acid Core (DNA or RNA)
  • Capsid Surrounding protein coat
  • Envelope Some viruses have this additional
    surrounding lipid
  • bilayer membrane
  • Virion A complete virus particle infectious

The Components of an Animal Virus
12
Terminology
  • Nucleocapsid Nucleic Acid (genome) capsid
  • Spikes attachment proteins(glycoproteins), aid
    in attachment to the host cell
  • Naked viruses with a nucleocapsid and no
    envelope

13
  • Viruses use their nucleic acids (genome) to
    replicate themselves in host cells
  • Capsids also play a key role in the attachment of
    some viruses. Each capsid is composed of protein
    subunits called capsomeres.
  • Enveloped viruses have a typical bilayer membrane
    outside their capsids and acquire their envelope
    after they are assembled in a host cell and bud
    through hosts membrane lipid composition from
    host, proteins from virus
  • Nucleocapsid comprises the viral genome together
    with the capsid

14
  • Naked viruses with a nucleocapsid only
  • Spikes projections that extend from the viral
    envelope that may aid in attachment to the host
    cell
  • Glycoprotein these surface projections serve to
    attach virions to specific receptor sites on
    susceptible host cell surfaces
  • Envelopes help the virus in evading detection by
    the hosts immune system
  • Complex virus complicated structure such as
    bacteriophage/poxviruses head, tail, pin, plate

15
Virus structures
16
1. Capsid
  • Some viruses are variable in shape, but most have
    a specific shape that is determined by the
    capsomeres or envelope
  • Francis Crick James Watson (1956), were the
    first to suggest that virus capsids are composed
    of numerous identical protein sub-units arranged
    either in helical or cubic (icosahedral)
    symmetry.
  • Helical capsid consists of a ribbonlike protein
  • that forms a spiral around the nucleic acid
  • Polyhedral capsid many-sided, and one of the
  • most common polyhedral capsid shapes is the
  • icosahedron
  • Some viruses have a bullet-shaped and some are
    spherical - envelope

17
Viral sizes and shapes Variations in shapes and
sizes of viruses compared with a bacterial cell,
an animal cell, and a eukaryotic ribosome
18
1. envelope
  • 2 types envelope and non-enveloped viruses
  • Envelope virus released from host cell by an
    extrusion process.
  • May/ may not covered by spikes
  • Most virus related to clumping of blood contain
    spikes
  • For non-enveloped viruses, the capsid itself a
    best protector
  • However, the gene of certain virus can manipulate
    the surface protein frequent changes

19
Capsid and envelope
20
2. Nucleic acid / genetic material
  • Virus can have either DNA / RNA never both
  • Each differ by single / double stranded
  • Classified by Baltimore classification technique
  • Proportion of genetic materials to the protein
    are varies depending on types of virus
    resulting of antigenic shift

21
Host Range
  • Infect all cellular life form
  • Host specific eg. Virus that infects potato do
    not infect human.

22
Antigenic shift
  • Always happen in influenza virus
  • Examples
  • -when a pig infected by avian virus (H7N7) at the
    same time of infection from human virus (H3N2)
    producing new pig virus (H1N1) which further
    infecting human.
  • Combination and transformation can occur in virus
    due to the host type changes

23
Thank you
Write a Comment
User Comments (0)
About PowerShow.com