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Why is it advantageous for viruses to possess different shapes?
RNA
DNA
Capsomere
Membranous
envelope
RNA
Head
DNA
Capsid
Capsomere
of capsid
Glycoproteins
Glycoprotein
18  250 nm
70–90 nm (diameter)
80–200 nm (diameter)
20 nm
(a) Tobacco mosaic
virus
50 nm
(b) Adenoviruses
50 nm
(c) Influenza viruses
True or False. Bacteria have the ability to infect viruses.
Tail
sheath
Tail
fiber
80  225 nm
50 nm
(d) Bacteriophage T4
Obligate
intracellular
parasite life cycle
VIRUS
1 Entry and
DNA
uncoating
Capsid
3 Transcription
and manufacture
of capsid proteins
2 Replication
HOST CELL
Viral DNA
How do viruses
identify their
host cells?
mRNA
Viral DNA
Many viruses are
species specific and
most will target one
type of cell
Capsid
proteins
4 Self-assembly of
new virus particles
and their exit from
the cell
What are the advantages and disadvantages of each cycle?
What does lysogenic mean?
Phage
DNA
Daughter cell
with prophage
The phage injects its DNA.
Cell divisions
produce
population of
bacteria infected
with the prophage.
Phage DNA
circularizes.
Phage
Bacterial
chromosome
Occasionally, a prophage
exits the bacterial
chromosome,
initiating a lytic cycle.
Lytic cycle
Lysogenic cycle
The bacterium reproduces,
copying the prophage and
transmitting it to daughter cells.
The cell lyses, releasing phages.
Lytic cycle
is induced
or
Lysogenic cycle
is entered
New phage DNA and proteins
are synthesized and
assembled into phages.
Temperate phage = λ phage that is used for research
Why might humans utilize this type of phage?
Prophage
Phage DNA integrates into
the bacterial chromosome,
becoming a prophage.
What are some harmful
examples of a bacteria
containing prophages?
Phage
DNA
The phage attaches to a
host cell and injects its DNA
Bacterial
chromosome
Lytic cycle
• Virulent or temperate phage
• Destruction of host DNA
• Production of new phages
• Lysis of host cell causes release
of progeny phages
Prophage
Lysogenic cycle
• Temperate phage only
• Genome integrates into bacterial
chromosome as prophage, which
(1) is replicated and passed on to
daughter cells and
(2) can be induced to leave the
chromosome and initiate a lytic cycle
Capsid and viral genome
enter the cell
Capsid
The host cell digests the
capsid releasing RNA into
the host cell
RNA
HOST CELL
Envelope (with
glycoproteins)
Viral genome (RNA)
Template
There are single stranded
and double stranded
viruses containing either
DNA or RNA
mRNA
Capsid
proteins
ER
Glycoproteins
Copy of
genome (RNA)
RNA viruses have higher
mutation rates because they
lack replication error checking
New virus
Viral envelope
Glycoprotein
Capsid
Reverse
transcriptase
HIV
RNA (two
identical
strands)
HIV
How is this different from
the previous slide?
Membrane of
white blood cell
Why is HIV called
a retrovirus?
HOST CELL
Reverse
transcriptase
Viral RNA
RNA-DNA
hybrid
0.25 µm
DNA
HIV entering a cell
NUCLEUS
Provirus
Chromosomal
DNA
RNA genome
for the
next viral
generation
New virus
New HIV leaving a cell
mRNA
Which cells are
targeted by HIV?
Viral Phylogenetics
Fimbriae
Cell wall
Why are bacteria so
successful?
Circular chromosome
Capsule
Sex pilus
What is the role
of each of these
components?
Internal
organization
Flagella
True or False. Bacteria are
unable to create proteins.
Gram staining is used to determine
which type of cell wall is present in
the bacteria
What are the major
differences?
Carbohydrate portion
of lipopolysaccharide
Cell
wall
Peptidoglycan
Cell
wall
layer
Outer
membrane
Peptidoglycan
layer
Plasma membrane
Plasma membrane
Protein
Protein
Grampositive
bacteria
(a) Gram-positive: peptidoglycan traps
crystal violet.
Staphylococcus aureus,,
Streptococcus pneumoniae
Gramnegative
bacteria
20 µm
(b) Gram-negative: crystal violet is easily rinsed away,
revealing red dye.
Eschericiacoli, Klebsiella pneumoniae,
Neiserria gonorrhea, Vibrio cholera
Phage DNA
Transduction
A+ B+
A+
A bacteria is infected
with bacteriophage DNA
B+
Donor
cell
The virus undergoes either the lytic
cycle or the lysogenic cycle
A+
Recombination
A+
A– B–
Recipient
cell
A+ B–
Recombinant cell
If bacteria acquires DNA from its
environment (i.e. not from a
virus) it changes its genome
through transformation
Plasmids – extracellular
chromosomes that can give
bacteria new traits
F plasmid
F factor is present in the F
plasmid to form the sex pilus
Bacterial chromosome
F+ cell
F+ cell
Mating
bridge
F– cell
F+ cell
Bacterial
chromosome
(a) Conjugation and transfer of an F plasmid
Hfr cell
A+
A+
F factor
F– cell
A+
A+
A–
Recombinant
F– bacterium
A–
A–
A+
A–
(b) Conjugation and transfer of part of an Hfr bacterial chromosome
R plasmid – provides resistance
to certain antibiotics
How does conjugation differ from
transformation or transduction?
A+
Uptake of K by plants (mg)
1.0
0.8
0.6
0.4
0.2
0
No
Strain 1 Strain 2
bacteria
Soil treatment
Strain 3
Euryarchaeotes
Crenarchaeotes
UNIVERSAL
ANCESTOR
Domain Archaea
Korarcheotes
Domain
Eukarya
Eukaryotes
Nanoarchaeotes
Proteobacteria
Spirochetes
Cyanobacteria
Gram-positive
bacteria
Domain Bacteria
Chlamydias
Halophiles,
thermophiles, and
methanogens belong to
which Domain?
What is a
facultative
anaerobe?
True or False. All
bacteria is harmful.