Viruses and Monera

Microbiology – study of small life

Virus – “poison”

• Alive? – we are not sure. Consensus is they are not alive, they meet some but not all of the traits of life

Why study?

• They affect living things, also helps understand difference between life and non-life

Composition and Structure

Composition and Structure

• Nucleic acid – DNA or RNA, genetic material

Composition and Structure

• Protein coat - (capsid) surrounds and protects the nucleic acid

Composition and Structure

• Envelope – additional protective coating, contains spikes that bind to sites on a cell

Classification

Shape Host they infect

How they function

Shape – the arrangement of proteins in capsids

Helical

• RNA coils tightly inside the long, narrow capsid

Binal

• Two parts, polyhedral capsid and a helical tail

Polyhedral

• Multifaceted geometric appearance

Adenovirus is one that causes colds

Filovirus

• No distinct shape, threadlike or looped at end

What shape is it?

What shape is it?

What shape is it?

What shape is it?

Host – who they infect

Animal

• infect only animals

Plant

• Infect only plants

Bacteria

• (bacteriophages) Infect only bacteria

Other

• Can infect many different hosts or only certain species of that host

Function

• How they behave or work inside a host

Normal viruses and Retroviruses

Retrovirus

• “reverse” virus, turns its RNA to DNA

Discovery – found by surprise, looking for the cause of tobacco mosaic disease

Dmitri Ivanovsky

• Must be caused by unusually small bacteria or poisons from bacteria

Russian Biologist1892

Martinus Beijerinck

• Caused by something smaller than bacteria, an infectious agent he called virus

Dutch Biologist1897

Still unsure where viruses came from, but have discovered many diseases since that have been caused by viruses

Viral Diseases in Humans:

• Common cold

Viral Diseases in Humans:

• Measles

infection of the respiratory system, spread through air, fever, cough, red eyes, rash

Viral Diseases in Humans:

• Warts

Viral Diseases in Humans:

• AIDS

Auto immune deficiency syndrome – spread through body fluids or blood

Viral Diseases in Humans:

• Mono

Spread through saliva or mucus, fatigue, swollen lymph nodes, enlarged spleen

Viral Diseases in Humans:

• Polio

damage the nervous system and cause paralysisEnters mouth by contaminated hands with feces

Viral Diseases in Humans:

• Viral pneumonia

Inflammation of the lungs, cough with mucus, fever, chills

Viral Replication – do not reproduce,

no cell division, need a host

Host

• An organism that shelters and nourishes something

Lytic Life Cycle

• Virus rapidly kills the host cell (lyses = break apart)

Lytic Life Cycle

• Attachment – virus sticks to cell and enzymes eat a hole in host cell membrane

Lytic Life Cycle

• Entry – viral DNA enters host cell and takes control

Lytic Life Cycle

• Replication – viral DNA instructs host to make copies of itself and protein coats

Lytic Life Cycle

• Assembly – viral parts are put together to form new viruses

Lytic Life Cycle

• Release – host cell bursts releasing new viruses

Then it all starts again…

But sometimes…

Lysogenic cycle

• Virus doesn’t immediately kill the host cell

Lysogenic cycle

• Attachment – virus sticks to cell and enzymes eat a hole in host cell membrane

Lysogenic cycle

• Entry – viral DNA enters host cell and inserts into chromosomes

Lysogenic cycle

• Replication – host cell divides, replicating viral DNA with own DNA

Lysogenic cycle

• Stimulus – something causes the viral DNA to separate from chromosome and enter Lytic cycle

Without a stimulus, the viral DNA stays dormant in the cell’s chromosomes

Lysogenic cycle

• That’s how people with HIV can go years without showing symptoms of AIDS, and still pass the virus on to others

Non-viral Particles

• Recently discovered particles that act like viruses

VIROIDS PRIONS

Viroids

• Just a nucleic acid (no protein coat)

• Causes – plant diseases

Prions

• Just a protein (no nucleic acid)

• Causes – mad cows disease