Title: Microbiology 6/e
1Chapter 1
2Lecture content
- Background cases
- General characteristics
- Terminologies
- Viral structures
- Host range
- Antigenic shift
3Virus
Small particles in nanometres (10 -9)
Viruses are not cell!
4In 2003, an outbreak of chicken flu
necessitated killing tens of millions of birds
5An outbreak of swine flu (Influenza A)
originated in Mexico in March 2009 caused by H1N1
virus
6General characteristics
7General 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
8How 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.
9The 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.
10terminologies
11Components 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
12Terminology
- 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
15Virus structures
161. 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
17Viral sizes and shapes Variations in shapes and
sizes of viruses compared with a bacterial cell,
an animal cell, and a eukaryotic ribosome
181. 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
19Capsid and envelope
202. 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
21Host Range
- Infect all cellular life form
- Host specific eg. Virus that infects potato do
not infect human.
22Antigenic 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
23Thank you