Transcript Viruses - WordPress.com

Living or Non-living?
Viruses

Viruses are the smallest organisms in
biology; however, the debate is still on
whether to classify them as living.

What makes something living or nonliving?

Are viruses living?
Are Viruses Living?
Living Characteristics:
contain DNA or RNA
 have protein ( therefore Carbon)
 contain small amounts of enzymes

Are Viruses Living?
Non Living Characteristics
Non cellular
 Do not respire (breathe), respond to
stimuli, or “grow”
 Reproduce only within living cells, and
are assembled in parts which join
together.

Cell Theory by Schleiden & Schwann

All living things are composed of cells

The cell is the basic living unit of
organization

All cells arise from pre-existing cells

Cells do not come from nonliving
things
What is a Virus?

A virus is a noncellular particle made up
of genetic material and protein that can
invade living cells

Viruses use the living host cells to
reproduce their viral DNA

Viruses are considered to be nonliving
Examples
Host
Virus Example
Bacteria
Bacteriophage, T4
Plant
Tobacco Mosaic Virus
Animal
Adenovirus (cold)
Influenza Virus (flu)
Herpes Simplex Type I II
Small Pox
Measles
Human Papilloma Virus (HPV)
Cervical Cancer
Epstein-Barr
Ebolla
HIV
Yellow Fever
Etc…
History
Small Pox
 Prior to the 1700s this disease meant
certain death
 Edward Jenner observed that milkmaids
would survive this disease
 Jenner Hypothesized that cow pox
provided protection
 Proved this by injecting his own son and
named this technique vaccination (Latin
for “pertaining to the cow)
Discovery of Viruses

First identified was the tobacco mosaic viruses

Adolf Meyer (1883) - discovered the disease could
be spread via juice from an infected plant.

Dmitri Ivanowski (1893)- Passed sap through
bacteria filters – small bacteria or chemical toxin?
Discovery of Viruses

Martinus Beijerinick (1890s)- Diluted filtered sap
and found it was still toxic

Concluded that a extremely small pathogen was at
work (virus = dutch for poison)

Wendell Stanley (1930s) -Used the electron
microscope to identify TMV
Viral Diversity

Viruses come in many
shapes and sizes

Viruses are much too
small to be seen with
any light microscope.
The smallpox virus is more
than 5 times smaller than
the bacterium E. coli

Sizes
Shapes
Structure of a Virus
A typical virus is composed of:
Nucleic Acid (DNA)
 Capsid (protein coat to protect DNA)


Bacteriophage T4 is a complex virus
with a tail and tail fibers
Bacteriophage Structure
A
Head
DNA
B Capsid
C Tail Fibers
Tail
Electron Microscope
VIRUSES
Viral Life Cycles
There are two cycles for viral reproduction:

Lytic Cycle

Lysogenic Cycle

These two cycles should not be seen as separate, but
rather interchangeable.
Lytic Cycle

This type of viral infection follows the pattern of
infection, replication, and lysis.

Viral infection can spread quickly in a multicellular
organism as the lytic cycle is repeated over and
over again destroying hundreds of host cells at an
exponential rate in a matter of hours.

Viruses that produce a lytic cycle are said to be
virulent.
Lytic Cycle
A
Infection
C
Lysis
B
Replication
&
Assembly
Lytic Cycle
Part A: Infection
virus attaches to specific cell 
cell specificity

Part B: Replication & Assembly


cell is opened by enzymes
virus DNA or RNA enters into the cell, remaining
structures stay outside.
Lytic Cycle
Part B Continued


virus DNA is inserted into host DNA causing the
replication of more virus DNA and parts.
Virus parts and DNA are assembled
Part C: Lysis

Viruses burst out of the host cell  lysis
1 virus in  up to 300 viruses out!

Host cell is destroyed

Lysogenic Cycle

In this pattern of infection, the viral DNA is
incorporated into the host cell’s chromosome and
remains dormant while it is mass-produced as the
host cell divides.

A virus that exists in the cell but does not lyse out
of the cell is called latent.

The latent period can last for years. Ex: HIV
latent period can be 10-25 years.
Lysogenic Cycle

When conditions trigger activation of the viral
chromosome, replication and lysis follow the
lytic cycle.

Activation of dormant viruses can be caused by
UV radiation, stress, temperature, nutrients, etc
Lysogenic Cycle
Viral DNA
inserted
A
Lysis
Infection
B
G
C
F
E
Assembly
Reproduction of
host cells
(virus dormant)
D Activation
Replication
Interchangeable Viral Cycles
Retroviruses

Some viruses contain RNA instead of DNA

A retrovirus assembles its code into the host
cell’s DNA

HIV is a retrovirus

Cancer causing viruses are also retroviruses
Review
What cycle is this?
What evidence do
you see?
Review
B: What cycle is
this?
A: What
cycle is
this?
Group Activity

In groups of 5-6, you will demonstrate
your knowledge of the lysogenic cycle in
one of the following creative formats:
Skit
 News Broadcast
 Rap
 Other?

Group Activity
Your presentation must be ~ 5 minutes
long
 You must include the following:

Criteria
Incomplete
Somewhat
Completely
Creativity Wow Factor
wow
wow wow
wow wow wow
Covers all of the steps
1
2
3
Steps clearly
explained/labeled/identified
1
2
3
Review:
A
Head
DNA
B Capsid
C Tail Fibers
Tail
Review
A
Infection
C
Lysis
B
Replication
&
Assembly
Review
Viral DNA
inserted
A
Lysis
Infection
B
G
C
F
E
Assembly
Reproduction of
host cells
(virus dormant)
D Activation
Replication
Defense against VIRUSES
Our Immune System:
 is the most complex system in our body

is our primary defense against infection from
pathogens

effectively responds to antigens (foreign
substances on pathogens like viruses & bacteria)
in a number of different ways
Our Immune System

is controlled by our white blood cells:

Phagocytes = white blood
cells that engulf and destroy
antigens

Lymphocytes = B and T Cells
White Blood Cells
B – Lymphocytes (B-cells)

mature in our bone marrow and make
antibodies
Antibodies

Antibodies are special proteins that bind to
specific antigens on the surface of a pathogen
and help destroy it by poking holes in its structure.
White Blood Cells
T - Lymphocytes :

function by identifying & presenting the antigen
to the B – cells to activate antibody production.

Low T - Cell counts
are implicated in cancers.
Immunity

The production of antibodies from the first
exposure to an antigen is called the primary
immune response

Once the body has been exposed to an antigen, a
large number of B and T- Cells (memory cells)
remain capable of producing a more powerful and
faster secondary immune response to the same
antigen
Immunity
There are different types of immunity:

Innate  born with it

Acquired  achieved in four ways:
Immunity
Active (antibodies
produced by one’s
own body)
Passive (produced
by other animals)
Natural
1,
3.
Artificial
2,
4.
Acquired Immunity
Immunity
Active (antibodies
produced by one’s own
body)
Passive (produced by other
animals)
Natural
1.
Exposure to the
pathogen
3.
Artificial
2.
4
Acquired Immunity
Immunity
Active (antibodies
produced by one’s own
body)
Passive (produced by other
animals)
Natural
1.
Exposure to the
pathogen
3.
Artificial
2.Vaccine
4
(weakened form of
the pathogen)
Acquired Immunity
Immunity
Active (antibodies
produced by one’s own
body)
Passive (produced by other
animals)
Natural
1.
Exposure to the
pathogen
3. Transferred
Artificial
2.Vaccine
4
(weakened form of
the pathogen)
from
mother’s placenta or
milk
Acquired Immunity
Immunity
Active (antibodies
produced by one’s own
body)
Passive (produced by other
animals)
Natural
1.
Exposure to the
pathogen
3. Transferred
2.Vaccine
4. Injected
Artificial
(weakened form of
the pathogen)
from
the mother’s
placenta or milk
antibodies
Questions Page 976

What is an antigen? Why are antigens important to
the immune system?

What are the two main types of lymphocytes?
What roles do they play in the immune system?

Compare and contrast active and passive
immunity. Give examples of each.

Do you think vaccines are good for children? Why
or why not?
Defense against VIRUSES
Our Immune System:

Consists of specific and nonspecific defenses
against infection

Nonspecific defenses are the body’s primary line
of defense against all pathogens

Specific defense mechanisms involve the
production of antibodies against particular
pathogens (discussed last class)
Nonspecific Defenses

Nonspecific defenses provide physical and
chemical barriers against infection

Non-specific defense mechanisms can be divided
into first-line and second-line defenses
Nonspecific Defenses

First-line defences are barriers to keep
pathogens from entering the body, including:
• Skin
• Oil & sweat
• Tears & saliva
• Mucus & cilia
• Stomach acid
• Beneficial bacteria
Nonspecific Defenses
With a partner, answer the following questions:

How do these barriers defend the body? Make a list.

What is the most important nonspecific defense?
Nonspecific Defenses

If pathogens get passed the first line of defense,
then the a secondary line of defense begins
called the Inflammatory Response:

Phagocytes engulf and destroy bacteria and other
antigens near wounds or infected areas which
become inflamed

If the infection spreads, a fever and swollen
lymph nodes may result
Inflammatory Response
Nonspecific Defenses

Another nonspecific defence is the interferon

An Interferon is a protein that is produced by
host cells that have become infected by a virus

Once produced by infected cells,
interferons attach to nearby healthy
cells, preventing replication of the
virus particles in those cells.