Download Virus teacher notes Pre-AP 14-15

VIRUSES
I. VIRUSES (Latin for poison) text p.478
Viruses are not classified in any kingdom.
A. General Characteristics
1. A virus is an infectious agent made up of – nucleic acid (DNA or RNA), wrapped in protein coat
a. they have no nucleus, no organelles, no cytoplasm or cell membrane – non-cellular particle
b. viruses have either – DNA or RNA, but not both
c. viruses with RNA that transcribes into DNA (using enzyme reverse transcriptase) are called –
retroviruses
Ex: HIV, flu (influenza), cold
RNA viruses have a high rate of mutations – replication of RNA does not involve proofreading step
(as in DNA replication)
2. Viruses are - parasitic - organism that depends entirely upon another living organism
(host) for its existence in such way that it harms that organism.
B. Examples:
1. Bacteriophage – virus that infects a bacteria
capsid
(protein coat)
DNA
2. Flu (influenza), HIV
RNA
tail
fibers
envelope –
(has marker proteins
+ carbs derived from
host cell)
capsid
C. Replication (reproduction): How a virus spreads.
*** A virus cannot reproduce by itself – it must invade a cell and take over its activities.
1. Virus (bacteriophage) invading a bacterium (E. coli): Virus uses what it
needs from cell +
makes more virus
Virus attaches
to cell
DNA of virus
enters cell
Cell bursts, new
viruses are released
Cell divides, replicating
DNA of virus
2. During Lysogenic Cycle, it is possible for viral DNA to separate from host cell DNA and cause cell to
enter Lytic Cycle and replicate new viruses.
Virus DNA becomes part of cell’s DNA
Envelope of HIV
contains marker
proteins + carbs
derived from host cell
3. Virus invading an animal cell:
Ex: HIV invading human cell
Virus particle enters
human cell by
endocytosis
New virus buds off
RNA replicates
4. Capsid proteins of a virus bind to receptors on cell surface and “trick” cell into allowing it inside
5. Because of this fit between virus and cell receptors, most viruses are specific for cells they infect.
Ex: the rabies virus only infects brain or nervous cells
Virus
Cell
Receptor
Sites
D. Importance
1. Harmful
a. causes disease – pathogenic , disease producing agent – pathogen
b. human diseases - DNA: chicken pox, mono, cold sores, genital herpes, warts, hepatitis, smallpox
RNA: cold, influenza, polio, AIDS, rabies, Ebola
c. viruses disrupt the body’s normal equilibrium/balance (homeostasis)
d. viruses can be prevented with vaccines, but NOT treated with vaccines or antibiotics
2. Beneficial
a. genetic engineering – harmless virus carries good genes into cell nucleus
Use p.483 to compare viruses and living cells
Characteristic
Structure
VIRUS
Genetic material (DNA or RNA)
capsid
CELL
Cell membrane, cytoplasm,
genetic material, organelles
Reproduction
Copies itself only within host cell
Cell division – sexual or asexual
DNA or RNA
DNA and RNA
Growth and Development
No
yes
Obtain and use energy
Response to Environment
Change over time (evolve)
No
No
Yes
yes
yes
yes
Genetic Material
How many characteristics of life do viruses possess? 2 – change over time and contains genetic material
Are they then living? Non-living