Download viruses - My CCSD

IN:
► Discuss
the following two questions with
your group.
What is a virus?
(Come up with a definition.)
Are viruses alive?
(Be prepared to defend your answer.)
Characteristics of Life
►Are
made of one or more cells
►Reproduce
►Grow and develop
►Obtain and use energy
►Respond to their environment
Viruses = “poison” (Latin);
infectious particles
Viruses
► Not
living (???) organisms; not in 6 kingdoms
► Lack cell structures for growth and
reproduction
► Must replicate in a living host
► Smaller than bacteria; need electron
microscope to see
Structure
► Nucleic
Acid: DNA or RNA, single or double
stranded
► Wrapped in a protein coat called a capsid
► Some have an envelope (taken from host cell
membrane)
Symmetry
► Icosahedral
– 20 + sides
► Helical (Spiral)
► Complex (e.g. head & tail or
enveloped)
Classification
►Based
on…
►1. RNA or DNA
►2. Capsid
(size, symmetry, presence of envelope)
DNA Viruses
1.
2.
DNA
RNA
proteins
Join to host DNA
RNA
proteins
RNA Viruses
1.make proteins directly from RNA
2.RNA (reverse transcriptase) DNA
-
seen in retroviruses
RNA
proteins
► Obligate
Reproduction
intracellular parasites, gain control of
host cell’s machinery
1.Lytic Cycle (all viruses)
-virus attaches to host cell, injects nucleic acid
-DNA/RNA replicates utilizing host cell’s
enzymes
-host ruptures, releasing 100’s of viruses.
The Lytic cycle
Lysogenic Cycle
(some viruses – HIV, herpes)
 Virus attaches to host cell, injects nucleic
acid
 Viral nucleic acid inserts into host’s
DNA (provirus)
 Provirus replicates whenever the host cell
reproduces
 No new viruses are produced at this time
 The provirus does not harm the host cell
 Upon “activation” (e.g. radiation,
weakened state, chemicals), provirus
takes over the cell and resumes lytic cycle.
The Lysogenic Cycle
►
►
►
►
►
►
►
Diseases
Spread by air, human contact, insects, animals,
and food
Common diseases: flu, cold, chickenpox, measles,
herpes, hepatitis A
Serious Diseases: Smallpox, polio, AIDS, hepatitis C
Some Viruses (e.g. hepatitis B, human
papillomavirus)
 1. Carry oncogenes (genes that cause cancer) or
 2. Stimulate host oncogenes
Few antiviral drugs
Immune system provides protection; e.g. white
blood cells, lymohocytes, fever, interferons (interfere
with synthesis of viral proteins)
Vaccines are made from weakened form of virus;
stimulate immune response
Viral Diseases
► Warts
chickenpox
► Herpes
► Chicken
pox
► Smallpox
► The Common Cold
► Influenza (flu)
► Rabies
► AIDS
► Cancer
shingles
herpes
smallpox
Viroids
Recently isolated
Viroids = naked RNA segments with no protein coat or
envelope, smallest known particles to replicate; infect
plants
Prions
► Prions
= infectious proteins with no nucleic
acid, clump together inside of cell and eventually
destroy it;
► Cause slow, progressive disease; e.g. kuru, “mad
cow” disease, Creutzfelt-Jakob disease
Remember Viruses !!!!
► Not
►1.
►2.
►3.
►4.
►5.
considered living things by many
scientists…….
No Growth
No Homeostasis
No Metabolism
Reproduce only in a host cell
Only Protein and Nucleic Acid
Studying Viruses
1.
Virus: “poison”
Latin); infectious
particles
2.
Wendell Stanley was
the first to isolate a
virus in 1935 by
crystallization