Transcript 2.2 Viruses File

Viruses (2.2)
What are Viruses?
Viruses are non-living because…
①Acellular: lack a cell membrane
②No metabolic activity
③Lack an energy generating system
④They are obligate parasites – requires a
host cell to reproduce.
What are Viruses?
• Viral particles can be between 10 and
300 nm in size.
• The genetic material is surrounded in a
protein coat called a capsid.
What are Viruses?
• There may be a further layer referred to as
the envelope, which surrounds the capsid –
this is found in animal viruses and is derived
from the membrane of the host animal cell.
• Protein spikes may protrude from the viral
particle – these are involved in the
attachment of the particle to the host cell.
• Contain either DNA or RNA
Classification of Viruses
• Genetic material – either DNA or RNA
• Nucleic Acid either single stranded or
double stranded form
• Shape of the protein coat
• Nature of host (plant, animal or
bacteria)
• Presence or absence of envelope
Viral Shapes
Cylindrical
Spherical
Polyhedral
Irregular (bacteriophage)
Bacteriophage Structure
This bacteriophage (phage for short) is a virus that infects bacteria only!
Capsid (entire top part)
Nucleic acid
Tail (entire bottom part)
sheath
Tail fibres
Cell membrane
Viral RNA/DNA injected
into host cell
Infectious Cycles
• A virus infects a
cell by inserting
its nucleic acid
(DNA or RNA)
into it. The viral
nucleic acid then
enters 1 of 2
cycles:
1 – Lysogenic Cycle
1 – Lysogenic Cycle
1- Lysogenic Cycle
1 – Lysogenic Cycle
1 – Lysogenic Cycle
1 – Lysogenic Cycle
A virus can switch back and forth
between cycles and a virus may be in
lysogeny for many years.
Types of Viral Diseases
Types of Viral Diseases
Annual Influenza Rates Canada
•
•
•
•
•
•
5 million (1 in 6) infected per year
~50,000 hospitalizations
1% of those >65yrs; 0.5% of those <1yr
4,000 – 8,000 deaths (10 in children)
7% of children get otitis media
1.5 million work-days lost
Top 10 Infectious Diseases –
Ontario
source: Ontario Burden of Infectious Disease Study, 2010
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Hepatitis C virus
Streptococcus pneumoniae
Human papillomavirus (HPV)
Hepatitis B virus
E.coli
HIV/AIDS
Strap aureus
Influenza
C.difficile
Rhinoviruses (common cold)
Vaccinations
• Our immune
systems can create
a memory for
infections that we
have previously
fought-off.
(*excepting
mutations)
Previously encountered pathogens (like
viruses or bacteria) are much more easily
destroyed.
Vaccinations
A vaccination is a weakened pathogen
that our immune systems can easily fightoff.
After our bodies have learned how to
combat that particular pathogen, repeat
infections are more easily destroyed.
Immunization Schedule
Homework
• Read pg. 54-59
• Pg. 59 #6, 12 and 13
• Have you seen this movie?
• http://www.youtube.com/watch?v=4sYS
yuuLk5g