Date post: | 10-May-2015 |
Category: |
Health & Medicine |
Upload: | rmasterson |
View: | 1,302 times |
Download: | 7 times |
CHAPTER 13: VIRUSES, VIROIDS, AND PRIONS
Exam 4 material
GENERAL CHARACTERISTICS OF VIRUSES
Virus is the Latin word for “poison”
1935Wendell Stanley isolated the Tobacco Mosaic virus for the first time
DEFINITION OF LIFE
A complex set of processes resulting from the actions of proteins specified by nucleic acids
“Viruses are not living things. Viruses are complicated assemblies of molecules, including proteins, nucleic acids, lipids, and carbohydrates, but on their own they can do nothing until they enter a living cell. Without cells, viruses would not be able to multiply. Therefore, viruses are not living things.”
Viruses are “alive” (able to multiply) when they enter a host organism
We will say that viruses are living, but they are not.
Obligate Intracellular parasite-must have a living host cell in order to multiply
ALL VIRUSES ARE O.I.Ps
FEATURES OF VIRUSES
Only one type of nucleic acidDNA or RNA (not both)
A protein coatMade of lipids, carbohydrates, proteins
• Must have a host cell• Uses the cells machinery to copy itself
• Makes specialized structures that can transfer the viral information to other cells
• Lack personal enzymes
• http://www.youtube.com/watch?v=s-HThHRV4uo
COMPARING PROKARYOTES & VIRUSES (P 387)
Prokaryotes Viruses
HOST RANGE
Viruses can have a host rangeA spectrum of host cells the virus can infect Viruses that infect bacteria are bacteriophages (phages)Outer surface of virus must chemically interact with specific receptor site on host cell
VIRAL SIZE
Viruses are very small compared to bacterial cells
Need an electron scanning microscope to view
VIRAL STRUCTURE
Virion = complete, fully developed, infectious viral particle composed of nucleic acid and surrounded by a protein coast that protects it from the environment
NUCLEIC ACID
Prokaryotes and Eukaryotes use RNA and DNA as genetic information
Viruses use RNA or DNA-not both It is single or double stranded
CAPSID AND ENVELOPE
Protein coat = capsid
Combination of lipid, proteins, and carbohydrates that convers the capsid = envelope
Capsids without envelopes = nonenveloped viruses
When a virus enters a host cell, the host antibodies are produced
An interaction between antibodies and virus’ should inactivate the virus
Some viruses escape antibodies and are able to change their surface proteins
Surface proteins are called spikes
This is why you can get the flu many different times
GENERAL MORPHOLOGY
Compare with prokaryotic morphology
Helical : long rods, hollow and cylindrical spirals
Polyhedral : many sided viruses
Complex : complicated structureMany bacteriophages
TAXONOMY OF VIRUSES
A viral species is a group of viruses sharing the same genetic information and ecological niche.
GROWING VIRUSES
Nonliving: needs a host cell
Difficult and expensive to
maintain cultures
Usually learn from
bacteriophages
plaque = clearing within a media
VIRAL MULTIPLICATION
http://www.youtube.com/watch?v=Rpj0emEGShQ
A virus must be able to invade a host
A virus must take over a host’s machinery
BACTERIOPHAGES
LYTIC CYCLE
1. attachment to receptor site
2. injects DNA/RNA into cell
3. host cell starts making viral copies of nucleic acid
4. bacteriophages are assembled inside host cell
5. host cell is lysed
LYSOGENIC CYLE
Process where cell is not lysed and is able to stay alive
FAMILIES OF VIRUSES PAGE 392-3
Paroviridae
Adenoviridae
Papovaviridae
Poxviridae
Herpesviridae
Hepadnaviridae
Picornaviridae
Orthomyxoviridae
Bunyaviridae
Arenaviridae
Retroviridae
Reoviridae
• Rhabdoviridae• Filoviridae• Paramyxoviridae• Deltaviridae• Caliciviridae• Togaviridae• Flaviviridae• Coronaviridiae
VIRUSES AND CANCER
Almost anything that can alter the genetic material of a eukaryotic cell has the potential to make a normal cell cancerous
HPV
Hepatitis B
Leukemia, Feline leukemia
VIRUSES AND INFECTIONS
Latent infection = infection capable of staying dormant until stimulus is applied
Chronic viral infection = long lasting viral infection that occurs over a gradual time period (usually fatal)
HerpesFever blisters/cold sores
Chicken poxshingles
PRIONS ????????
A prion is a proteinaceous infectious particle A protein that infects like a virus
These diseases run in families; however, they can’t be totally inherited
There is a lot that is not known about prions
• Mad Cow disease• Kuru• Creutzfeldt-Jakob disease• Fatal familial insomnia• Gerstmann-Straussler-Scheinker
syndrome
VIROIDS
Viroids are short pieces of RNA with no protein coat that does not code for any protein
They cause plant diseases
Much is still to be learned about these particles