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Bio II Exam 2: Viruses
Terms in this set (49)
Why are viruses not considered organisms?
They are not cells and are not made up of cells, and they cannot make their own ATP
How do viruses live and reproduce?
They enter a host cell, take over their biosynthetic machinery, and use that machinery to manufacture a new generation of viruses.
What kind of hereditary material do viruses possess?
DNA or RNA; single or double stranded
Do viruses have a plasma membrane?
Can viruses carry out transcription independently?
Can viruses carry out translation independently?
What metabolic capabilities do viruses possess?
Basic structure of a virus
Nucleic acid core, surrounded by a capsid
What are the most prevalent viruses around the world?
HIV, AIDS, and Spanish Flu
What are the two general categories of viruses?
What is a capsid?
Virus enclosed by just a shell of protein
What is an envelope?
Virus enclosed by both a capsid and a membrane like envelope
Viruses can remain latent for years
More kinds of viruses exist than organisms
What is virus called without a host cell?
How do viruses replicate inside the cell?
Viruses hijack the cell's transcription and translation machineries for the assembly and release of more viruses.
What are the 6 stages of viral replication?
1. attachment to host cell and entry into cytosol
2. transcription of the viral genome and production of viral proteins
3. replication of the viral genome
4. assembly of the new generation of virions
5. exit the infected cell
6. transmission to new host
1. Most single stranded
2. Replicated in the host cell's cytoplasm
3. Retroviruses (HIV) employ reverse transcriptase
1. Most double stranded
2. Replicated in the nucleus of the eukaryotic host cell
A viral enzyme that is an unusual DNA polymerase that can make DNA from from either RNA or DNA templates
How have viruses contributed to the diversity of life?
They introduce foreign genes into cellular genomes and thus promote lateral gene transfer
How much of the human genome consists of viral genome remnants?
Viruses that infect bacteria
What is replicative growth?
Virus kills the host cell -- lytic cycle
What is latent growth?
Virus incorporates into the cell's genome
What are lytic phages called?
What are lysogenic phages called?
What is induction?
When a virus switches from lysogenic to lytic
What is it called when a virus infects and animal cell and the genome resides in the cell without replicating or producing new virions.
Antiviral drugs are ineffective against viruses in a latent state
Why are lytic infections hard to treat?
The virus uses many of the host cell's enzymes and the drugs that disrupt these enzymes usually harm the host more than they harm the virus
What are the 6 steps of lytic replication?
1. Viral genome enters host cell
2. Viral genome is transcribed; proteins produced
3. Viral genome is replicated
4. particles assemble inside host
5. Particles exit the cell
6. Free particles transmit into new host
What are the 4 steps of lysogenic replication?
1. Viral genome enters host cell
2. Viral genome integrates into host cell genome
3. Host-cell DNA polymerase copies chromosome
4. Cell divides; virus is transmitted to daughter cell
How do HIV particles enter the cells?
Bind to the membrane protein CD4
How do enveloped viruses exit the cell?
They bud from a cell through the cell membrane and take part of the cell membrane with them including the envelope proteins that were inserted into the membrane
How do nonenveloped viruses exit the cell?
They burst out of the cell and enzymatically degrade the cell wall.
A disease that rapidly effects a large number of individuals
A worldwide epidemic
What was one of the most pandemic viruses, when did it occur, and why was it so bad?
The Spanish Flu (1918-1919) This strain of influenza was particularly virulent and killed 20-50 million people.
What is the "Escape" hypothesis pertaining to viruses
The viruses may have descended from clusters of genes like plasmids or transposons that physically escaped from bacterial or eukaryotic chromosomes long ago.
What is the "Degeneration" hypothesis pertaining to viruses
Organisms gradually degenerated into viruses by slowly losing the genes required to synthesize ATP, amino acids, etc.
What is the "Origin of Life" hypothesis pertaining to viruses
Viruses descended from the first, RNA-based life forms on earth
Where is there no phylogeny for viruses?
Viruses originated multiple times throughout the history of life
How are viruses organized?
The Baltimore scheme; grouped into 7 categories based on the nature of their genetic material
How much of cancer is made up of viruses?
How can viruses cause cancer?
Altering growth properties of human cells
1. Triggering expression of oncogenes
2. Disrupting tumor-suppressor genes
What are prions?
Proteinaceous infectious particles that cause TSEs
What are TSEs and examples
Transmissible spongiform encephalopathies:
EX: Mad cow, Scrapie in sheep, and Creutzfedlt-Jacobs disease in humans
What are viroids?
Tiny, naked molecules of circular RNA that cause disease in plants such as coconuts.
Recommended textbook explanations
Lehninger Principles of Biochemistry
David L Nelson, Michael M. Cox
Principles of Life
David E. Sadava, David M. Hillis, H. Craig Heller
Biocalculus: Calculus, Probability, and Statistics for the Life Sciences
Miller and Levine Biology
Joseph S. Levine, Kenneth R. Miller
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