Unit 12 Viruses & Bacteria

Learning Goals

Identify structures and characteristics of Viruses and Bacteria

Explain how viruses and bacteria reproduce

Recognize the importance of viruses and bacteria

Explain how the immune system fights infection

Viruses

Infectious particle made of only a strand of DNA or RNA surrounded by a protein coat.

Only contains information on how to reproduce the virus

Protein coat = capsid

Capsid sometimes surrounded by protective lipid envelope

Viruses

Smaller than bacteria

Non living – cannot reproduce on their own

Need living cells to help them reproduce

Viruses

Structure and shape play an important role in how they work

Each type can only infect certain hosts

Surface proteins on virus fit to receptor molecules on host cell

Virus Shapes - Polyhedral

Virus Shapes - Helical

Virus Shapes - Enveloped

Viruses that infect bacteria

Bacteriophage

Virus Life Cycles

Lytic cycle

Host cell bursts, releasing new viruses into the host's system, each of which infects another cell

STEP SUMMARY

1. ATTACHMENT - The lytic virus attaches itself to the

host cell.

2. ENTRY - The virus injects the nucleic acid into the cell.

3. REPLICATION – virus DNA breaks down host DNA and

takes over, instructing cell to make virus parts

4. ASSEMBLY – Virus parts are put together into new

viruses

5. RELEASE - When viruses are mature, they come out of

the cell (destroying it) and start to infect other cells.

Virus Life Cycles

Lysogenic cycle

virus combines its DNA into the host cell's DNA

Forms a provirus

Virus lays “dormant” as host cell reproduces (remember mitosis S phase)

Trigger can activate the provirus or it can remain a permanent gene

STEP SUMMARY

1. ATTACHMENT – The virus attaches itself to the host

cell.

2. ENTRY - The virus injects the nucleic acid into the cell.

3. INTEGRATION – virus DNA becomes part of host cell's

DNA

4. REPLICATION – host cell is replicated with viral DNA

Lytic vs. Lysogenic

Lytic – causes symptoms very quickly

New viruses are made and spread to other cells right away

Lysogenic – organism may have no symptoms for many years

Once virus is triggered to enter lytic stage symptoms will develop

Proviruses

Activated when lysogenic virus enters a lytic cycle

Chicken pox → shingles

Cold sores

Retroviruses

Lysogenic

Contain RNA

Forces host cell to make viral DNA

Viral DNA is added to host cell's DNA

Retroviruses

HIV

Virus infects white blood cells

AIDS: virus enters lytic cycle → white blood cells are destroyed → body cannot fight off other infections

Prions

Infectious particle made only of protein that can cause other proteins to fold incorrectly.

Misfolded proteins will not work

Can incubate for a long time with no symptoms

Once symptoms appear, they worsen quickly and are always fatal

Body has no immune response against a protein

Viroids

Cause disease in plants

Passed through seeds or pollen

Single stranded RNA without a protein coat

Major economic impact because they can stunt growth in plants

Bacteria and Archaea

Most abundant organisms on earth

Live in just about every habitat on earth

Prokaryotes

Archaea

Methanogens

Anaerobic

Produce methane gas

Found in

Marshes

Bottom of lakes

Digestive tracts of herbivores

Archaea

Halophiles

Anaerobic

Live in very salty environments

Dead sea, great salt lake

Thermoacidophiles

Anaerobic

Live in hot acidic environments

Sulfur springs

Ocean vents

Bacteria

Heterotrophs

Parasitic – feed on living organisms

Saprophytic – feed on dead organisms/waste

Bacteria

Autotrophs

Cyanobacteria – photosynthesizer

Usually blue green

Live in ponds, streams, or other moist areas

Chains of independent cells

Probably earth's 1st oxygen producers

Chemosynthesizers – energy comes from break down of inorganic compounds

Convert atmospheric nitrogen to usable compounds (nitrogen fixation)

Bacteria Structure

Identifying Bacteria

2 groups based on amount of peptidoglycan in cell wall

Gram negative – thin layer, stain red

Gram positive – thick layer, stain purple

Identifying Bacteria

Further classified by shape

Spherical (cocci)

Rod (basilli)

Spiral (spirilla)

Comma (vibrios)

Corkscrew (spirochates)

Reproduction

Binary fission

asexual

Bacteria cell copies its DNA

Both copes of DNA attaches to plasma membrane

Partition forms to create 2 identical new cells

Takes less than 20 minutes under ideal conditions

Reproduction

Conjugation

Sexual

One bacterium transfers part of its chromosome across a pilus

Offspring not genetically identical to parent

Bacterial Survival

Endospore – specialized cell with thick, protective wall

Helps cell survive harsh conditions

Can be killed by heating over 100 degrees Celsius

Importance of Bacteria

Nitrogen fixation

Digestive tract (probiotics)

Fermenation (cheese, yogurt, pickles)

Bioremediation (breaks down pollutants)