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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
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
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

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

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

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

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:
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?
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
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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