Transcript protein coat

Viruses
THE MICROSCOPIC MENACE
Viruses are Pathogens

Viruses are incredibly abundant and can cause disease in not only humans,
but all living organisms including plants, fungi, and even bacteria.
FIRST THINGS FIRST!
Viruses Are Not Alive!

Viruses do not have the characteristics of
life and are not considered alive.

Viruses do not respond to their environment.

Viruses do not grow.

Viruses do not require energy

Viruses cannot reproduce on their own and
must reproduce in a host cell.
Virus Structure
Viruses are composed of a protein coat and a piece of
genetic material (DNA or RNA)
 The surface of the virus is covered in antigens

Antigens
Protein
Coat
Viral DNA
Learning Check

Make a t-chart showing the differences between
bacteria and viruses
Bacteria
Viruses
INFLUENZA a.k.a The Flu

The Influenza Virus affects respiratory systemthe nose, throat, and lungs.

Symptoms: Fever, aching muscles,
headache, cough, nasal congestion, and
fatigue.

Although it usually passes, it can be deadly
depending on the strain of the virus.

Young children and older adults have a
higher risk of facing complications from the
flu.
The Flu Pandemic of 1918

In 1918, a strain of flu virus carried by
American soldiers to Europe during
WWI became the deadliest flu in
human history.

Infected over 500 million people

Killed as many as 100 million
worldwide.
Human
Immunodeficiency Virus
a.k.a HIV

HIV infects T-cells and other white blood cells,
causing a failure of the immune system

It can be transmitted sexually or by sharing drug
needles.

Acquired Immunodefieciency Syndrome (AIDS)
results when the virus has weakened the immune
system allowing other diseases to infect the body.

The virus can be managed with various
medications.
Ebola Virus Disease

The virus is believed to be carried by African
fruit bats and other animals.

The Ebola Virus infects macrophages, liver
cells, and cells lining the blood vessels

Symptoms: Fever, Headache, Diarrhea,
Vomiting, and unexpected bleeding

Symptoms can appear between 2-21 days
after exposure to the virus.

Can be spread by direct contact with bodily
fluids and infected objects.

Survivors develop antibodies that last for at
least 10 years.
HOW DO WE STOP THEM?

Viruses are different than bacteria. Bacteria
can be killed by antibiotics, such as penicillin,
but viruses can’t.

Vaccines are injections of weakened or
inactive versions of the virus that can be
recognized by your immune system.

Vaccines kick start your immune system to
quickly create antibodies against the virus.

Memory cells remember how to create
necessary antibodies for the virus. This keeps
you safe from future infections.
Remember you cannot destroy viruses with antibiotics!
Viral Replication

Viruses replicate by invading a host cell and forcing it to make copies of
the virus. This process kills the host cell.
2 types of Viral Replication
• Lytic Cycle
• Lysogenic Cycle
Lytic Cycle

The virus attaches itself to a host cell.

The virus injects its DNA into the cell.

The viral DNA merges with the host
cell’s DNA

The viral DNA “hijacks” the cell
forcing it to make copies of the viral
DNA and viral Proteins.

The new viruses assemble and
destroy the cell.
Lytic Cycle
Viral DNA
Release
DNA and Proteins
 From This
To This 
Lysogenic Cycle
START
Virus Attaches
and Injects DNA
Releas
e
Viral DNA Replicates
Assembl
y
Cell divides with
Viral DNA inside
Lysogenic Cycle

The Lysogenic Cycle ends in the same way as
the Lytic Cycle.

The Lysogenic Cycle is usually longer than the
Lytic Cycle.

After the viral DNA is injected, the virus waits
until it is ready to enter the Lytic Cycle again
and kill the cell.
Learning Check #2
Describe the Lytic and the Lysogenic Cycle
Lytic Cycle
Lysogenic Cycle

1. Virus - non-living, disease-causing particle.

2. Bacteria - single-celled organism without a
nucleus.

3. Eukaryote - single or multicellular organism with
a nucleus.