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 non-living?

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

ExamplesHost Virus Example

Bacteria Bacteriophage, T4

Plant Tobacco Mosaic Virus

Animal Adenovirus (cold)Influenza Virus (flu) Herpes Simplex Type I IISmall Pox MeaslesHuman Papilloma Virus (HPV)Cervical CancerEpstein-BarrEbollaHIVYellow FeverEtc…

HistorySmall 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

B

C

Head

Tail

DNA

Capsid

Tail Fibers

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

B

C

Infection

Replication & Assembly

Lysis

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 CyclePart 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

A

B

C

D

EF

Infection

Reproduction of host cells

(virus dormant)

ActivationReplication

Assembly

Lysis

Viral DNA inserted

G

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

B

C

Head

Tail

DNA

Capsid

Tail Fibers

Review A

B

C

Infection

Replication & Assembly

Lysis

Review

A

B

C

D

EF

Infection

Reproduction of host cells

(virus dormant)

ActivationReplication

Assembly

Lysis

Viral DNA inserted

G

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

ImmunityThere 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 (weakened form of the pathogen)

4

Acquired Immunity

Immunity Active (antibodies produced by one’s own body)

Passive (produced by other animals)

Natural 1. Exposure to the pathogen

3. Transferred from mother’s placenta or milk

Artificial 2.Vaccine (weakened form of the pathogen)

4

Acquired Immunity

Immunity Active (antibodies produced by one’s own body)

Passive (produced by other animals)

Natural 1. Exposure to the pathogen

3. Transferred from the mother’s placenta or milk

Artificial 2.Vaccine (weakened form of the pathogen)

4. Injected 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.