DNA viruses

twoeggfinnishΒιοτεχνολογία

14 Δεκ 2012 (πριν από 4 χρόνια και 8 μήνες)

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Viruses

Viruses are extremely small non
-
living parasites
that contain genetic material but lack all other
cell structures necessary for metabolism.


grow and develop in the cells of a host


Rely on host for respiration, nutrition and all
other functions


Viruses consist of:


Protein coat called a capsid


Genetic material




Capsid




Give the virus its
characteristic
shape


See Fig 12.14 on
pg

400 for
examples


Genetic Material


Can contain DNA or RNA

DNA viruses


Viruses can incorporate into the host cells genetic
information and are copied just as regular DNA

RNA viruses


Bypass the DNA portion of protein synthesis and
make proteins themselves

Retroviruses


Contain RNA which can be converted into DNA

Lytic Cycle


Virus injects it’s genetic material into the host
cell and immediately begins to replicate itself
using the host cells resources


Once hundreds of new viruses are synthesized
the cell breaks and all the new viruses spill out
to infect new cells


See Fig 12.16 on
pg

402

yc


Lysogenic Cycle


Virus infects cell and then inserts itself into
the host’s DNA to become part of the host’s
genetic material


As the host reproduces itself it also
reproduces the virus


This can continue for many generations until
the virus excises itself from the host DNA and
enters the lytic cycle


See Fig 12.17 on
pg

403


Genetic Engineering Using Viruses


Viruses can be used to inject needed genetic
information into a cell


Most often a virus is used that will infect a
bacteria


The bacteria grows and makes the required
protein which is then harvested


It is also possible to use this method to inject
DNA into a human cell to allow a new gene to be
expressed


See Fig 12.22 on
pg

410



Vaccines and Immunization


A vaccine is used to stimulate an individuals
immune response to produce
antibodies

against
a specific harmful organism (
pathogen
) and to
provide protection against later exposure

Pathogen
: something that causes disease

Antibodies
: protein molecules that recognize
specific sites on the pathogen (called antigens)


The antibody
-
antigen complex stimulates the
body’s immune response


Immunization/Vaccination: getting a vaccine
into the body either by injection or by some
other means


Immunity: possessing enough specific
antibodies to elicit an immune response
capable of destroying the pathogen


Natural Immunity: acquired by natural exposure to
a pathogen


Active Immunity: acquired by a vaccination