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Lecture 35

BIOA01H3 Lecture 35: Module 3 Lecture 35.docx

Biological Sciences
Course Code
Effiette Sauer

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What is a virus?
Non- living infectious agents
Consisting of nucleic acid genome in a protein coat (capsid)
The genome consist of DNA or RNA
How do they reproduce?
They enter host cells and direct cellular machinery to make new same particles
Why are Viruses not on the tree of life?
They don’t have the 7 basic rules of life
Viral Structure
Helical Viruses
oProtein subunits from in a rod like structure around the genome (i.e.
Polyhedral Viruses
oProteins form triangles that bond and create a geodesic sphere
oSome proteins have spikes
These infect plants, animals and bacteria
Enveloped viruses
oHelical or polyhedral virus covered by membrane derived from host cell
oContains protein spikes extended for host to cell recognition and adhesion
Complex polyhedral Viruses
oPolyhedral head plus complex tail
oGenome in head, injected into host cell through sheath
E-coli’s Bacteriophage
Virulent bacteriophage kills host cell during each cycle of infection
Temperate bacteriophage have inactive phases of DNA replication with host cells
T-even bacteriophage
oMost valuable in e-coli
oLinear molecule of DNA
oTail attaches to E-coli
Infection of Bacteria
The Lytic cycle: Events that occur from Infection to progeny release
1. Phage attacks the host cell
2. Lysozyme digests hole in cell wall
3. Phage DNA enters the bacterium
4. Phage genes expressed to direct phage replication
a. Proteins are synthesized
b. DNA is replicated
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