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THE GENETICS OF VIRUSES
Daniela, Shanayah, Nisma
Virus- a small infectious agent that replicates only inside the living cells of other organisms
• Viruses are acellular organisms• Consist of: -Genetic material (double or single-stranded DNA/RNA) -Capsid (protein shell)
General
• “Obligate intracellular parasites” (Fox, 2011)
(Carter, 1997)
• Can only reproduce with a host cell
• Don’t have cell machinery
Viruses• Composed of a capsid, genetic material, a tail, and base
fibers (BBC, 2014
• Bacteriophages- virus that infects bacteria specifically
(BBC, 2014)
Bacteriophages
• Lytic cycle: early & late stages
• Uses promoter for transcription
• Turns off host gene expression
• Replicates viral genes• Viral genes transcribed
and release (Hillis et al., 2012)
(Kometani & Matsui, 2005)
Common Viruses: HIV (Al-Aulfi, 2011) • Human Immunodeficiency Virus
• Retrovirus• Causes AIDS• Attacks T-helper cells• Uses reverse transcriptase to turn
RNA into DNA• Opportunistic infections (Hillis et al., 2012)
Common Viruses: Rhinovirus(Virology, 2014)
•Common Cold•Attacks respiratory tract•Many different strains•Symptoms: Runny nose Sneezing Congestion Cough Sore throat
Overview of Viral Replication
Two Processes: Lytic Cycle and Lysogenic Cycle
• Lytic cycle is faster than Lysogenic
Lytic cycle, lysogenic cycle, or both can be used for viral replication
Lytic Cycle
• Lytic Cycle- viruses are made within a host cell, which then bursts open, releasing new viruses
• Destruction of host cell and membrane lysis
• Viral products released• Millions of copies in hours• Viral genetic material stays
in cytoplasm
Lysogenic Cycle
• Lysogenic –viral DNA is added to the host cell's DNA and is copied along with the host cell's DNA
• Genetic recombination• Viral DNA passed on to
daughter cells • Doesn’t kill host cell
Matching
1. Bacteriophage 2. Capsid3. Lytic cycle4. Lysogenic cycle5. Acellular6. Retrovirus7. Opportunistic
infections
A. Single-celled B. A virus that infects and
replicates within a bacterium C. The protein shell of a virusD. Possesses reverse transcriptaseE. infections that usually do not
cause disease in a healthy hostF. a viral reproductive cycle in
which copies of a virus are made and released in lysis
G. a viral reproductive cycle in which the viral DNA genetically recombines to the host cell's DNA