Chapter 18Bacteria and

Viruses

What is a virus?

• Is an infectious particle made of up a protein capsid and DNA or RNA but never both

• It cannot replicate on its own but needs to be in a living host cell to be replicated

• Causes disease such as AIDS, Colds, Polio, Flu…

What are bacteria?• Are prokaryotic, unicellular microorganisms.• Like viruses, may be pathogens (disease causing

agents)• Causes diseases such as Lyme, Staph infections,

Strep throat, Syphilis,

What is the structure of a bacteriophage virus

• Like all viruses, it has a protein capsid, that houses either DNA or RNA

• It has tail fibers for attachment onto the surface of the host bacteria

Capsid

DNA or RNA

Tail fibers

Discuss the Lytic infection pathway• Virus gains entry, gets replicated then gets out• Colds, the flu,SARS, measles…

Discuss a Lysogenic infection pathway

• Viral DNA becomes incorporated into the host’s DNA, maybe forever or may come out at some time.

• HIV, Cold sores, Chickenpox/Shingles or any herpes virus like mono...

DNA enters DNA is replicatedDNA incorporates Cells reproduce

What is the difference between the Lytic and Lysogenic cycles?

• Lytic infection occurs immediately many times with the destruction of the host cell.

• Lysogenic infection does not ever have to progress past incorporation of the DNA. One can be HIV + forever or may never get Shingles

Vaccines, the magic shots!• Vaccines are substances that stimulate the immune

system to produce antibodies against a particular pathogen (disease causing agent)

• Using made from a weakened version of a virus or parts of the virus that cannot cause the disease.– Measles, mumps, rubella– Chicken pox/Shingles– HPV– Hepatitis– Rabies (for your pet, not you!)– West Nile– Flu (influenza)

What are the 3 shapes of bacteria?

Coccus - round Spirilla - spiralBacillus - rod

Label the main parts of a bacterial cell

Flagella

Ribosomes

DNA

Pili

Methods of reproduction in Bacteria

• Asexually– Binary fission – one round of mitosis– No genetic variation occurs– Every cell is a clone of the original

• “Sexually”– Conjugation – duplication and then transfer of

and extra piece of DNA– Endospores – specialized thick walled protective

cells to allow bacteria to survive adverse conditions like cold or drought• Tetanus bacteria is one of these

How are bacteria mutualistic symbionts in us

• Found along our entire digestive system

• Helps us to: – break down food– provide essential

vitamins and minerals– protecting us from other

harmful pathogens• They get a place to live

and food from us

Bacteria’s role in the ecosystem• Decomposers• Producers – photosynthetic

bacteria• Nitrogen fixation – in

legumes from nitrogen fixing bacteria to take atmospheric nitrogen and convert it into ammonia (NH3)

What are antibiotic & why won’t it work with the cold or flu?

• Antibiotics are chemicals that kill or slow down the growth of bacteria until the immune system can produce antibodies

• Produced by bacteria and fungus – Penicillin

• Stops the production of cell walls.

• Since viruses don’t have cell walls and aren’t living, antibiotics are useless on them.