Bacteria and Viruses

AP Biology

Bacteria

• Very diverse

• Most abundant

• Prokaryotic

• Single chromosome; some have a plasmid

• Usually a cell wall

• Prokaryotic fission

• Great diversity in metabolism

Three Shapes

• Coccus—pl. cocci spherical

• Bacillus—pl. bacilli rod

• Spirillum—pl. spirilla spiral

Three Shapes

Three Shapes

Three Shapes

Three Shapes

bacillus

coccus

Three Shapes

• Diplococcus: chain of two

• Streptococcus: chain of many

• Tetrad: ball of four• Sarcinae: larger ball• Staphylococci: bunch

of grapes

Three Shapes

Three Shapes

Three Shapes

Three Shapes

Typical Cell

Typical Cell

Gram Stain• Bacteria are often identified as gram positive or

gram negative• This refers to their reaction to a staining method

developed by Hans Christian Gram• The structure of the cell wall determines the

response

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Gram Stain

• Gram positive appears purple or blue because the cell wall contains more peptidoglycan, which holds the violet stain.

• Gram negative appears pink or red. These have less peptidoglycan, which does not hold the violet dye.

• After the violet stain, they are rinsed in a red dye. The gram negative pick up only the second color.

Gram Stain

Gram Stain

Prokaryotic Fission

• DNA is copied• New cell membrane

and new cell wall sections are made

• Cells separate

Prokaryotic Fission

Conjugation

• A tube connects the two bacteria

• The plasmid is replicated and transferred to the recipient cell

Classification

• Eubacteria: most abundant; now includes the blue-green algae and other monerans

• Archaebacteria: three groups based on metabolism

Viruses

• Are they alive?

• Do they exhibit the characteristics of life?

• What diseases do they cause?

Viruses

• Non-cellular• Infectious agent• Consist only of protein

coat surrounding genetic material; coat contains proteins that bind with a receptor protein

• Genetic material can be DNA or RNA

• Range from 4 genes to several hundred genes

Viruses

• 4 typical body plans• Helical• Polyhedral-many

sided coat• T-even• Enveloped • Page 356

Viruses• Cannot reproduce itself

• Must have a host cell

• Mutates frequently, outer protein coat changes

• That’s why we can’t make some vaccines and why we get some illnesses over and over again

RNA viruses are called retroviruses;

They must make cDNA from RNA and then proceed with replication

Viruses

• Viruses can attack animal cells, plant cells, and bacterial cells

• Viruses which attack bacteria are called bacteriophages, or phages

• Notice different types by shape

Viral reproduction in host cells

• Virus matches a receptor on host cell membrane

• Enters by endocytosis

• Directs replication of viral DNA and the manufacture of new viruses

• Damages or destroys the cell, resulting in symptoms

Viruses

• Replication in phages takes one of two pathways: lytic or lysogenic

• Lytic progresses right away

• Lysogenic may be latent and reactivated later

Viruses

• Lytic cycle in a human cell

Viruses

• Lyse means “to burst”• The lytic cycle always

results in the death of the host cell

• Page 358 in text

Computer generated picture of the polio virus

Smaller than Viruses

• Prions are small proteins that cause diseases of the nervous system—Mad Cow Disease

• Viroids are tightly folded strands or circles of RNA that resemble introns—mostly plant diseases

Prions

Viroid plant infections

Influenza virus