Download Viruses

DO NOW
1.
Label the following as Totipotent,
Multipotent, or Pluripotent
A.
B.
C.
D.
Embryonic Stem Cells
Bone Marrow Cells
Umbilical Cord Stem Cells
Zygote
2.
During what embryonic phase do cells
differentiate?
3.
What is the role of morphogens in
embryo development?
Viruses
Chapter 19.4
What to Know about Viruses?
Characteristics
Structure
How they reproduce:
1.
2.
3.
◦
4.
The differences between lytic and
lysogenic cycles.
How we think they evolved
Bacteria vs. Viruses
Bacteria
Virus

Prokaryotic cell


Most are free-living (some
parasitic)
Not a living cell (genes
packaged in protein shell)

Intracellular parasite

Relatively large size

1/1000 size of bacteria

Antibiotics used to kill
bacteria

Vaccines used to prevent
viral infection

Antiviral treatment
Root Words

“phage” – Virus

Host – what the virus infects
Virus Characteristics
1.
2.
3.
4.
5.
6.
Not made of cells
Depend on other hosts (other living
things) for life functions, such as
reproduction & metabolism
Transmit DNA to other organisms
Infect all life forms (prokaryotes & eukaryotes)
Evolve independently of other
organisms
Cause most diseases
Structure of Virus
1. Nucleic acid: DNA or
RNA (double or singlestranded)
2. Capsid: protein shell
bacteriophage
Some viruses also have viral
envelopes that surround
capsid
Simplified viral replicative cycle
VIRAL
REPRODUCTION
Virulent: active
Lysogenic: inactive
Bacteriophage Reproduction
1.
Lytic Cycle:
◦ Virulent Phage reproduction
◦ Uses host cell to make more of itself
◦ Kills host cell by lysing (rupturing) & releasing
new viruses
2.
Lysogenic Cycle:
◦ Lysogenic Phage reproduction
◦ Prophage (Viral DNA) is incorporated into
host’s DNA and replicated along with it
Temperate Phage: uses both methods of replication
VIDEO: T4 PHAGE INFECTION
Lytic Cycle vs. Lysogenic Cycle
Animal viruses have a membranous
envelope
Host membrane
forms around
exiting virus
 Difficult for host
immune system to
detect virus

VIRAL
INFECTIONS
Bacteriophage

Virus that infects bacterial cells
Retrovirus
RNA virus that uses reverse transcriptase
(RNA  DNA)
 Newly made viral DNA inserted into
chromosome of host
 Host transcribes viral DNA (“provirus”) to
make new virus parts
 Example: HIV (Human Immunodeficiency
Virus)

HIV
◦ Infects white blood
cells
◦ HIV+: provirus (DNA
inserted)
◦ AIDS: active viral
reproduction
VIDEO: HIV LIFE CYCLE
HIV =
Retrovirus
Herpes virus
Smallpox
Herpes Simplex Virus 1 (HSV-1)
Herpes Simplex Virus 2 (HSV-2)
Eradicated in 1979 due to
worldwide vaccination campaigns
VACCINES
Vaccines

Consists of a weakened virus or
part of pathogen that triggers
immune system response
Emerging viruses = mutation of existing
viruses
Prions
Misfolded, infectious proteins that cause
misfolding of normal proteins
 Eg. mad cow disease (BSE),CreutzfeldtJakob disease (humans), scrapie
(sheep)

VIRUS EVOLUTION
Where did they come
from?
Viral Evolution

Viruses evolved many times from
many different cell (host) groups
1) Some are probably derived from
escaped genetic materials
2) Some probably evolved from highly
reduced parasites
EXIT QUIZ
1.
2.
3.
4.
What are the 2 common parts
that all viruses have?
What is the overall outcome of a
Lysogenic Cycle?
What is the overall outcome of a
Lytic Cycle?
Why do people have to get a flu
shot every year?
Viroids
Small, circular RNA
molecules that infect
plants
 Cause errors in
regulatory systems that
control plant growth
 Eg. coconut palms in
Philippines

Diseases caused by prions
Prions act slowly – incubation period of at
least 10 years before symptoms develop
 Prions are virtually indestructible (cannot be
denatured by heating)
 No known cure for prion diseases
