Download I. What is a virus?

I. What Is a Virus?
II. Viral Structures
A. DNA or RNA core
B. Capsid
III. Viral Infections
A. Lytic
B. Lysogenic
IV. Viruses and Living Cells
I. What is a virus?



A. Particles of nucleic acid (DNA or RNA),
protein, and in some cases, lipids.
B. Viruses reproduce by infecting living
cells and using the cell’s machinery to
produce more viruses.
C. Viruses are composed of core of DNA or
RNA surrounded by a protein coat.
II. Virus Structures-page 526
A. T4 Bacteriophage
B. Tobacco Mosaic
Virus
Capsid
proteins
C. Influenza
Virus
Capsid
RNA
Tail
sheath
Tail
fiber
Surface
proteins
Membrane
envelope
III. Viral Infections


A. Lytic infection occurs when a virus
enters a host cell, the cell makes and
assembles viral parts, and the new viruses
leave by exocytosis or causing the cell to
burst (lyse).
B. Lysogenic infection occurs when a virus
inserts its DNA into the DNA of the host
cell, replicate with the host cell’s DNA,
may remain dormant but is later activated
and begins the lytic cycle
Lytic vs. Lysogenic Cycle of Viruses
III. Viral Infections Continued


C. Prophage is viral DNA that is embedded
in the host cell’s DNA. It may remain part of
the host’s DNA for many generations before
becoming active. Any number of factors can
cause the prophage to activate.
D. Retroviruses are viruses with RNA as
their genetic material instead of DNA. Once
they invade a host cell, they make a DNA copy
of their RNA. This DNA copy is then inserted into
the host cell DNA, much like a prophage would.
E. Antibiotics won’t cure viral diseases!
(The Doctor can’t cure your cold!)
F. Vaccines can be given to help your own
immune system fight the disease
Some vaccines work by preventing viruses
from attaching to cells, and thus injecting their
DNA inside the host cell
Vaccines for smallpox, a deadly
virus, helped wipe it out.
Other diseases that can be
prevented by vaccines are:
Common cold is caused by virus,
but does not require vaccines
G. HIV, the virus that causes Aids, infects Tcells.
HIV (Human Immunodeficiency Virus) can hide for years
in the nucleus of T-cells (white blood cells that help fight
infection).
People can have no symptoms, yet be spreading the
disease to many partners.
HIV then begins the Lytic cycle and T-cells begin to die. The
patient eventually dies from another disease that the
immune system can’t control because there are no T-cells to
help fight infection.
Polio
Poliomyelitis is a communicable disease caused by viral infection and occurs
through direct contact with infected secretions. Polio is found worldwide, but
immunization has reduced the incidence. Clinical polio affects the central
nervous system (brain and spinal cord). Disability is more common than
death.
https://health.google.com/health/ref/Poliomyelitis
Influenza


Influenza is a viral infection that attacks
your respiratory system — your nose,
throat and lungs. Influenza, commonly
called the flu, is not the same as the
stomach viruses that cause diarrhea and
vomiting.
http://www.mayoclinic.com/health/influenza/DS00081
Measles is an infectious disease caused by a virus. It spreads easily from
person to person. The main symptom of measles is an itchy skin rash.
The rash often starts on the head and moves down the body.
http://www.nlm.nih.gov/medlineplus/measles.html
Mumps is a contagious disease that leads to painful swelling of the
salivary glands. The salivary glands produce saliva, a liquid that moistens
food and helps you chew and swallow.
https://health.google.com/health/ref/Mumps
IV. Viruses and Living Cells
Diseases Caused by Viruses
Are Viruses Living?




Based upon the characteristics of life- NO; but
borderline of living and non-living
Viruses are not made of cells-they’re particles of
cells
Viruses cannot reproduce WITHOUT infecting living
cells
Viruses do have some characteristics of life,
especially after infecting cells. They can reproduce,
regulate gene expression, and evolve.