Transcript Bacteria and Viruses

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
• Bacillus—pl. bacilli
• Spirillum—pl. spirilla
spherical
rod
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
+
-
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 bluegreen 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