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Viruses and Bacteria

the lytic and lysogenic cycles of viruses and binary fission of bacteria
by

Jean Battinieri

on 17 April 2012

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Transcript of Viruses and Bacteria

Binary fission in bacteria
type of cell division that prokaryotes use to reproduce
most genes on bacteria are on 1 single circular DNA molecule/chromosome
Bacteria
Binary Fission
chromosome begins to replicate
while replication occurs the cell grows
the copies of the first replicated region - called the origin of replication - move apart rapidly to the opposite sides of the cell
replication finishes
the plasma membrane grows inward, and a new cell wall is deposited
two new daughter cells are formed
What is a virus?
it is the simplest genetic system
they are infectious particles consisting of nucleic acids enclosed in a protein coat and, in some cases, a membranous envelope
it was first discovery in 1883 when a german scientist was seeking the cause of the tobacco mosaic disease
those studying the disease found that it could not be grown in a petri dish but could be transferred from plant to plant
in 1935 American scientist crystallized the infectious particle - was seen by electron microscope
Viruses
Viruses
a noncellular particle made up of genetic materal that is surrounded by a protective coat of protein called a CAPSID
some viruses have an ENVELOPE made mostly of lipids
the surface of the envelope are projections made of glycoproteins - proteins containing carbohydrate chains that the virus uses to attach to a host cell
its genetic material can be either DNA or RNA not both
it is closely related to prokaryotes because the DNA is not surrounded by a nucleus but is not classified as a prokaryote
it does not metabolize energy or undergo cellular respiration
it is NOT a cell
it can have many shapes
How do viruses survive?
viruses are parasites
they can only reproduce within a host cell
they depend on the host cell for respiration, nutrition and other functions for survival
viruses can only infect a limited range of host cells
they get into a cell through a receptor site on the surface of the cell
There are 3 basic shapes of bacteria
rod shaped - bacillus
round - cocci
spiral - spirillus
How do viruses reproduce?
there are two possible ways
1) the lytic cycle
2) the lysogenic cycle
Viral Shape
icosahedron - 20 triangular faces
includes those that cause herpes simplex, chickenpox, and polio
helical - coiled spring
includes rabies, measles, and tobacco mosiac viruses
The Lytic Cycle
a virus invades a host cell, produces new viruses, destroys the host cell, and releases new viruses
viruses that undergo this cycle are VIRULENT because they cause disease
The 5 step process
Attachment
attaches tail fibers to a receptor sites
can't infect if there is no receptor site
Entry
releases an enzyme that weakens a spot in the cell wall/membrane of the host
injects its (viral) DNA (or RNA) into the host cell
capsid is left outside the cell
Replication
the virus takes control of the host's protein synthesizing mechanisms, transcribing mRNA from the viral DNA
ribosomes make viral proteins and enzymes in the host cell that form capsids
viral DNA is also replicated
Assembly
the replicated DNA are enclosed in the newly created capsids
Release
an enzyme created by the virus cause the host cell to disintegrate therefore releasing new viruses
the newly created viruses leave the host cell but take a piece of the host cell's cell membrane which becomes the viral envelope
Viral Reproduction
The Lysogenic Cycle
viruses that infect a host cell without causing its immediate destruction this type of virus is called a TEMPERATE virus
viruses that stay in their host cell for an extended period of time - days, months, or years - use this type of replication
The Process
Attachment
attaches tail fibers to a receptor sites
can't infect if there is no receptor site
Injection
releases an enzyme that weakens a spot in the cell wall/membrane of the host
injects its (viral) DNA (or RNA) into the host cell
capsid is left outside the cell
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Integration
the viral DNA is integrated (becomes part of) into the host cells DNA
the site of integration of the viral DNA into the host cells genome is called a PROPHAGE
each time the host cell replicates its DNA the prophage replicates as well and is passed on to the new cells that are formed.
the prophage does not harm the host cell however an outside factor can cause the prophage to become VIRULENT and then the virus will enter the lytic cycle at replication
____________________________________________________________________________________________________________________
Replication
the virus takes control of the host's protein synthesizing mechanisms, transcribing mRNA from the viral DNA
ribosomes make viral proteins and enzymes in the host cell that form capsids
viral DNA is also replicated
Assembly
the replicated DNA are enclosed in the newly created capsids
Release
an enzyme created by the virus cause the host cell to disintegrate therefore releasing new viruses
the newly created viruses leave the host cell but take a piece of the host cell's cell membrane which becomes the viral envelope
Lytic vs. Lysogenic
Is a virus living?
Lytic vs. Lysogenic
Genetic recombination
the combining of DNA from two sources
3 mechanisms can bring together prokaryotic DNA from different sources
transduction
transformation
conjugation
DNA cloning
modify plasmid by recombining with another source
plasmid returned to bacteria and allowed to reproduce
use gene or proteins for our benefit
Restriction enzymes protect bacteria cells by cutting up foreign DNA
recognize self DNA to to addition of methyl groups (CH3)
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