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Living or Non-living?. Viruses. 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

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Viruses

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Living or non living

Living or Non-living?

Viruses


Viruses

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

Are Viruses Living?

Living Characteristics:

  • contain DNA or RNA

  • have protein ( therefore Carbon)

  • contain small amounts of enzymes


Are viruses living1

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

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 nonlivingthings


What is a virus

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

Examples


History

History

Small Pox

  • Prior to the 1700s this disease meant certain death

  • Edward Jennerobserved 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

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 viruses1

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

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


Viruses

Sizes


Shapes

Shapes


Structure of a virus

Structure of a Virus

A typical virus is composed of:

  • Nucleic Acid (DNA)

  • Capsid (protein coat to protect DNA)

  • BacteriophageT4 is a complex virus with a tail and tail fibers


Bacteriophage structure

Bacteriophage Structure

A

DNA

Head

Capsid

B

C

Tail Fibers

Tail


Electron microscope

Electron Microscope


Viruses1

VIRUSES

Life Cycle


Viral life cycles

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

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 cycle1

Lytic Cycle

A

Infection

C

B

Lysis

Replication & Assembly


Lytic cycle2

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 cycle3

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

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 cycle1

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 cycle2

Lysogenic Cycle

Viral DNA inserted

A

Lysis

Infection

B

Reproduction of host cells

(virus dormant)

G

C

F

E

Assembly

D

Activation

Replication


Interchangeable viral cycles

Interchangeable Viral Cycles


Retro viruses

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

Review

What cycle is this? What evidence do you see?


Review1

Review

B: What cycle is this?

A: What cycle is this?


Group activity

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 activity1

Group Activity

  • Your presentation must be ~ 5 minutes long

  • You must include the following:


Review2

Review:

A

DNA

Head

Capsid

B

C

Tail Fibers

Tail


Review3

Review

A

Infection

C

B

Lysis

Replication & Assembly


Review4

Review

Viral DNA inserted

A

Lysis

Infection

B

Reproduction of host cells

(virus dormant)

G

C

F

E

Assembly

D

Activation

Replication


Defense against viruses

Defense against VIRUSES

Our Immune System


Our immune system

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 system1

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

White Blood Cells

B – Lymphocytes (B-cells)

  • mature in our bone marrow and make antibodies


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 cells1

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

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


Immunity1

Immunity

There are different types of immunity:

  • Innate  born with it

  • Acquired  achieved in four ways:


Acquired immunity

Acquired Immunity


Acquired immunity1

Acquired Immunity


Acquired immunity2

Acquired Immunity


Acquired immunity3

Acquired Immunity


Questions page 976

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 viruses1

Defense against VIRUSES

Part II: Immune System


Our immune system2

Our Immune System:

  • Consists of specific and nonspecific defenses against infection

  • Nonspecificdefenses are the body’s primary line of defense against all pathogens

  • Specific defensemechanisms involve the production of antibodies against particular pathogens (discussed last class)


Nonspecific defenses

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 defenses1

Nonspecific Defenses

  • First-line defences arebarriers to keep pathogens from entering the body, including:

    • Skin

    • Oil & sweat

    • Tears & saliva

    • Mucus & cilia

    • Stomach acid

    • Beneficial bacteria


Nonspecific defenses2

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 defenses3

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

Inflammatory Response


Nonspecific defenses4

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.


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