Viruses & Bacteria
What Do You Already Know?
• What are the differences between bacteria
and viruses?
• Are all bacteria harmful?
• Are bacteria and viruses living?
• If you have a cold, should you take an
antibiotic? Why or why not?
• What is the best/easiest way to avoid
getting sick?
Viruses
• Tiny particles containing DNA and RNA
• Requires a host cell to survive
• Have SOME (not ALL) characteristics of
life!
Virus Structure
• All viruses have the same basic structure!
– Inner core made up of nucleic acid.
– Capsid  protein coat surrounding the inner
core
Examples
• Bacteriophage – virus
that infect bacteria
• Influenza, HIV
How Do Viruses Work?
https://www.youtube.com/watch?v=Rpj0emEGShQ
Must have a host cell (can be any living cell, but
viruses are specific!)
1. Attach  Capsid of a virus binds to receptors on
surface of host cell
2. Inject  Injects its DNA/RNA into host
3. Assemble  host cell begins making viruses (it’s
been HIJACKED!)
4. Repeat  host cell eventually bursts, releasing
hundreds of newly formed viruses to infect
surrounding cells
Lytic Cycle
• Virus enters host cell.
• Virus destroys cell’s DNA.
• “Tricks”/”reprograms” cell to make virus
parts.
• New viruses are built/assembled inside
cell.
• Cell bursts (dies) releasing viruses!
Lysogenic Cycle
(longer name, longer cycle)
• Virus enters host cell.
• Virus inserts its genetic information into the
host’s DNA molecule.
– At this point, it doesn’t interfere with the cell’s
function, it is copied along with the cell’s DNA, and
passed on to future cells.
• Virus DNA can be activated and enter the lytic
cycle at any time. (reproducing viruses and
killing the cell.)
Viruses can cause disease too!
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Common Cold
Hepatitis A, B, C
Herpes
Mononucleosis
Warts
Chickenpox
Flu
AIDS
Ebola
The good news is…
There are vaccines to protect us against
some viruses!
https://www.youtube.com/watch?v=rb7TVW77ZCs&app=desktop
Viruses in the News…
Zika Virus
http://www.cdc.gov/media/dpk/2016/dpk-zika-virus.html
http://www.wdrb.com/story/31436597/first-case-of-zika-virus-reported-in-kentucky
Viruses in the News…
Ebola
https://www.youtube.com/watch?v=XCrOde-JYs0
https://www.youtube.com/watch?v=sRv19gkZ4E0
Review!
https://www.youtube.com/watch?v=PHp6iYD
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Viroids & Prions
• Infectious agents! (non-living)
• Viroids  short strands of circular RNA with
no protein coat, typically affect plants
• Prions  small, misfolded proteins, affect
animals (one causes Mad Cow disease)
Bacteria
https://www.youtube.com/watch?v=kxM_9DL2GYw
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Prokaryotic
Unicellular
Contain DNA and ribosomes
Have ALL the characteristics of living things!
Reproduce through binary fission
Evolution
• Bacteria reproduce very quickly (via binary
fission).
– This means evolution can occur very quickly!
Bacteria can exchange genetic info in 3
ways:
Basic Structure of Bacteria
• Cell wall – for protection,
support, rigidity, made of
peptidoglycan (sugars and
amino acids)
• Cell membrane
• Cytoplasm
• Ribosome
• Plasmids – circular DNA,
used to exchange DNA
between bacteria
• Capsule – covers outside
cell wall
• May have pili, flagella, etc.
Bacteria have 3 distinct shapes:
• Spherical (cocci)
• Rod-shaped (bacilli)
• Spiral (spirilla)
Gram Staining of Bacteria
• Process used to separate bacteria into 2 large
groups, based on chemical and physical properties of
their cell wall, for medical diagnosis purposes.
• Gram positive bacteria: Those bacteria when they
are stained in gram stain results in purple color 
(more peptidoglycan in cell wall)
• Gram negative bacteria: Those bacteria when they
are stained in gram stain results in pink color.
• MOST pathogenic bacteria are gram negative!
Uses of Bacteria
• Food (buttermilk, yogurt, cheese, sauerkraut, pickles,
olives, etc…)
• Decompose organic matter (recycle nutrients from
dead organisms; break down sewage into simple
compounds)
• Nitrogen fixation (chemically changes nitrogen gas
into a usable form for plants)
• Human health (bacteria on skin help prevent infection,
bacteria in gut aid digestion)
• Biotechnology (used to make antibiotics, insulin,
human growth hormone, vitamins)
Pathogenic Bacteria
• Bacteria typically cause disease by:
– Releasing toxins  bacteria release a toxin
(poison) into the bloodstream and it travels
throughout the body
Pathogenic Bacteria…
Less than 1% of bacteria cause
disease in humans, animals, & plants!
…BUT they cause a variety of diseases!
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Food poisoning
Tuberculosis
Cholera
Syphilis
Ulcers
Strep Throat