Viruses Are Not Cells There are several structural and functional differences between cells and viruses The structural differences include No nucleus No cell membrane No organelles The functional differences include ID: 439144
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Slide1
VIRUSESSlide2
Viruses Are Not Cells!
There are several structural and functional differences between cells and viruses
The structural differences include:
No nucleus
No cell membrane
No organelles
The functional differences include:
Do not grow
Do not respire
Do not develop
Do not reproduceSlide3
Viral Structure
Viruses are made up of 2 parts:
Capsid
—a protein coat which enables the virus to bind to a cell
Nucleic
acid
—either DNA or RNA
Some viruses have an additional protective coating called an
envelopeSlide4
Replication vs. Reproduction
Viruses do not reproduce
Viruses replicate
Reproduction requires cell division and replication does not
A virus requires a
host
for it to replicate
A host is a living cell that provides all the materials a virus needs to replicateSlide5
Classification of Viruses
Shape
: allows viruses to attach to only a few kinds of cells; like two pieces of a jigsaw puzzle
Filovirus
—has no distinct shape
Ebola-
Zaire Ebola Virus
, has the highest case-fatality rate, up to 90%. Massive blood loss leads to death.
Polyhedral
virus—multifaceted geometric shapeHerpesvirus- Cold sores, shingles, virus lays dormant along nerve fibersSlide6
Binal
virus
—has a polyhedral capsid and a helical tail
Bacteriophage T4- virus which infects E.Coli. for molecular biology research
Helical
virus
—tightly coiled DNA or RNA inside a long, narrow capsid
Tobacco Mosaic Virus-infect members of nine plant families, 125 individual speciesSlide7
Classification of Viruses (cont.)
Host
:
Plant virus
Animal virus
Bacterial
virus
—these are also called
bacteriophagesSlide8
Lytic Cycle
Bacteriophage
DNA or RNA
Attachment
Bacterial host cell
Bacterial chromosome
Entry
Replication
Assembly
Lysis and
ReleaseSlide9
Lysogenic Cycle
Prophage
Entry:
Replication:
Lysis &
Release:
Assembly:
Not picturedSlide10
Retrovirus
Contains an RNA core that is replicated by 1
st
transcribing its RNA into DNA
Ex: HIV—
the virus that infects white blood cells and causes AIDS
1. RNA & reverse transcriptase enter the host cell
2. Enzymes copy the viral RNA into DNA
3. Viral DNA attaches to cell DNA
4.Viral DNA produces new virusesSlide11
Nonviral Particles
Viroid:
No capsid
Contains RNA
Cause plant diseases
Prion:
Protein molecule with no RNA or DNA
Cause animal diseases (
i.e. mad cow disease
)