Download Treatment of Viruses

Bio 1010
Dr. Bonnie A. Bain
CHAPTER 10
DNA Structure and Function
Part 3
Viruses
Don't Forget: Exam 3
November 21
Bring Scantron and #2 Pencil
Point Mutations:
A change in a single nucleotide
Frameshift Mutations:
An insertion or deletion of 1 or 2 nucleotides
Remember:
Mutations are the ultimate source of diversity of
life on our planet
Figure 10.23
Figure 10.24
Viruses:
Genes
in
Packages
Why talk about viruses here?
Answer: Virus is “DNA in a Box”
A Virus consists of a protein coat (the box)
plus either a strand of DNA or RNA
Fig. 10-24
Protein coat
DNA
Characteristics of Viruses
1. Has genes (DNA or RNA)
2. Reproduces by infecting other cells and
hijacking their molecular machinery to make
more viruses
3. Has a complex structure
Figure 10.24
Adenovirus
These cause respiratory infections in humans
Figure 10.25
Bacteriophage
200 nm
high
or
0.0002 mm
Infect Bacteria
Fig. 10-26c
Phage lambda
E. coli
Bacteriophage Reproduction
1. Inject their DNA into the “host” bacterium
2. The injected DNA forms a circle. The circle of
DNA then hijacks the cell's machinery and
makes lots more copies of itself as well as
copies of the protein coat “parts”
3. New phages are assembled and then leave
the bacterium (by lysing it, usually)
Fig. 10-26-2
Phage
Phage
attaches
to cell.
Cell lyses,
releasing
phages.
Phage DNA
Bacterial
chromosome (DNA)
Phage injects DNA
Many cell divisions
Occasionally a
prophage
may leave the bacterial
chromosome.
LYTIC CYCLE
Phages assemble
Phage DNA
circularizes.
LYSOGENIC
CYCLE
Prophage
Lysogenic bacterium
reproduces normally,
replicating the prophage
at each cell division.
OR
New phage DNA and
proteins are synthesized.
Phage DNA is inserted into
the bacterial chromosome.
Bacteriophage Life Cycles
Lytic Cycle
– After lots of viral copies made,
– they escape the cell by lysing it
– (breaking it open)
Lysogenic Cycle
– Viral DNA replication occurs,
– but no phage are produced
– and the cell doesn't die
Figure 10.28
Influenza Virus
Causes the Flu
Figure 10.30a
Question: Are viruses alive??
Characteristics of living organisms (page 4):
1. Organization and complexity
2. Regulation (physiology)
3. Growth and development
4. Utilize Energy
5. Respond to environment
6. Reproduce
7. Evolve (change over time)
How are viruses related to living organisms??
Figure 14.26
Origin of viruses
1. Regressive Theory:
Viruses originated from bacteria that became
intracellular parasites
These became dependent upon a host
Then lost most of their genetic information
Origin of Viruses
2. Run-away RNA:
Viruses arose from host RNA or DNA that
gained a self-replicative, but parasitic existence
and acquired the ability to replicate
independently of their host
Origin of Viruses
3. Co-evolution:
Viruses originated and evolved along with the
most primitive molecules
(the first ones able to self-replicate)
Some molecules were packaged into
membranes and eventually became cells
Others became packaged into protein coats and
became virus particles that co-evolved with cells
and parasitized them
Many Viruses cause disease
Animal viruses:
Adenovirus
HIV
Ebola
Polio
Mumps
West Nile
Avian flu
SARS
Etc.
Many Viruses cause disease
Plant Viruses:
Tobacco Mosaic virus
infects lots of agricultural crops (tomato,
squash, cantaloupe, etc.)
Papaya ringspot potyvirus (PRSV)
Kills papaya plants
Fig. 10-27
RNA
Protein
Tobacco mosaic virus
Treatment of Viruses
Very hard to treat viral diseases
Antibiotics do NOT work on viral infections
(only work on bacteria)
Treatment of Viruses
Many treatments that kill viruses will also kill the host
Antiviral Drugs:
Some focus on enzymes that the virus uses
High mutation rates in viruses
Best treatments are vaccinations
Your own immune system attacks viruses
on contact
Figure 10.29
Mumps Virus
Life Cycle
(p. 191)
Virus Life Cycle (Enveloped RNA virus)
This type of virus has RNA covered with protein
First, the virus attaches to the cell with its protein
spikes
Virus Life Cycle (Enveloped RNA virus)
Then:
1. Viral envelope fuses with cell membrane;
allowing the viral RNA to enter the cytoplasm
2. Enzymes remove the protein covering around
the viral RNA
3. Using the viral RNA as a template, a viral
enzyme makes copies of the viral RNA
Figure 10.29
Mumps Virus
Life Cycle
(p. 191)
Virus Life Cycle (Enveloped RNA virus)
4. Two functions for the viral RNA copies:
a. Act as mRNA to make new viral proteins
(using the host cell's ribosomes)
b. Act as templates for making more virus RNA
Virus Life Cycle (Enveloped RNA virus)
5. The newly made viral proteins assemble
around the newly made copies of the virus RNA,
forming lots more new viruses
6. The new virus copies leave the cell
Figure 10.29
Mumps Virus
Life Cycle
(p. 191)
Lots of variations on the viral life cycle
Viruses can replicate in the nucleus or the
cytoplasm of the host cell
Some viruses (Herpes simplex 1, 2; Polio virus)
replicate inside nerve cells only
Lots of variations on the viral life cycle
Some are DNA viruses
Some are RNA viruses
Some reproduce like the Mumps virus
Others use Reverse Transcriptase (HIV virus)
Figure 10.30c
HIV virus
Causes AIDS
Life Cycle:
1. Virus attaches to a white blood cell (T cell)
and injects its RNA into the cell
2. The viral enzyme, Reverse Transcriptase,
makes two copies of DNA using the RNA as a
template
Figure 10.30a
HIV virus life cycle (con't)
3. The newly made viral DNA goes into the
nucleus and inserts itself into the host cell's DNA
4. This is then transcribed and the mRNA is used
to make new viral proteins (using the cell's
ribosomes)
5. Newly formed viral particles leave the cell
7. Viruses bud
from host cell
1. Attachment
2. Penetration
6. Viral proteins
and RNA
assembled into
new virus
3. Viral RNA
to Viral DNA
4. Viral DNA
incorporated into host DNA
5. Viral proteins
and RNA synthesized
by host cell
Figure 10.00a
Anti-HIV Drugs
1. AZT
Function: inhibits Reverse Transcriptase
2. Protease Inhibitors
Function: block the formation of the HIV
viral proteins
This “drug cocktail” keeps the virus in check and
extends people's lives, but it is NOT A CURE
Figure 10.1
How AZT
works
Next Chapter: Chapter 11
How Genes are Controlled
(Gene Regulation)
Don't Forget: Exam 3
November 21
Bring Scantron and #2 Pencil