Transcript Viruses

Viruses
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Is it living?
Shapes/Structure
Replication
Types of viruses
Are Viruses Living????
 Viruses are segments of nucleic acids enclosed in a protein
capsid
 Very, Very small
 Contain either RNA or DNA
 Considered to be non-living because they do not carry on
life process on their own for example movement and
reproduction. In addition they:
- do not grow
- do not have homeostasis
- do not metabolize
Structure
• Capsid: protein coat surrounding nucleic acid
• Envelope: membrane-like structure outside the capsid
(can have or not can an envelope)
• Glycoprotein: projections used to attach to a host cell.
Capsid
•
DNA/RNA
Glycoprotein
HIV virus
Envelope
Shapes of viruses
• 2 shapes
- Helical: Rod-like appearance, with capsid proteins winding around the core i
a spiral
EX:
Rabies Virus
Tobacco Mosaic virus
Shapes Con’t
Icosahedral
- 20 triangular faces: herpes, chickenpox, polio
Herpes Virus
Common Viruses to Humans
Viral group
Nucleic
Acid
Papovaviruses
Adenoviruses
Herpesvirues
Picornviruses
Myxovirues
Rhabdovirues
Retroviruses
DNA
DNA
DNA
RNA
RNA
RNA
RNA
Shape
Structure
I, NE
I, NE
I, E
I, NE
H,E
H, E
I, E
Diseases
Caused
Warts, Cancer
Respiratory, Intestinal Infection
herpes, chickenpox, shingle, Mono
Hepatitis, Cancer
Influenza A, B, C
Rabies
AIDS, Cancer
Virus Types
1. DNA: Works in 2 ways
- Virus enters the cell and directly produces RNA to make viral
proteins
- Viruses DNA joins with the host cell DNA to make new viruses
2. RNA
- RNA enters in the host cell’s cytoplasm . It then uses the
ribosomes to make new viral proteins .
3. Retroviruses
- Contain an enzyme called reverse transcriptase: causes DNA to be
made from RNA. The DNA becomes part of the host
DNA/Genes. Then new RNA is made from this new DNA. RNA
makes new viral proteins.
4. Viroid: short, single strand of RNA, no capsid. They interfere with
plant metabolism and has destroyed entire crops (potatoes,
cucumbers, oranges)
5. Prions: 250 amino acids and have no nucleic acid. Linked to brain
diseases such as scrapie (slow degeneration of nervous system in
sheep) and Mad Cow (brain disease in cows)
Replication:Bacteriophage
Bacteriophage:
- viruses that infect bacteria
- T-4 bacteriophage- Escherichia coli- found in human digestive
tract
- composed of icosahedral head contain
nucleic acids.
-Tail composed of the collar and
sheath; this helps to inject
Collar
nucleic acid into the host cell.
- Tail Fibers: attached to the
Tail
base plate help attach to host
cell
base
plate
Replication Cycles
 Lytic Cycle
- They are virulent: cause disease
- A virus invades a host cell, produces new viruses,
destroys the host cell, and releases new viruses.
 Lysogenic Cycle
- infects the cell without causing immediate harm.
- these viruses can stay in the host for a long period of
time.
- Called a temperate virus
- When the DNA is injected into the host cell, it does not start to
make new viral parts immediately, they will become part of the
host’s DNA. When the cell is replicated naturally by the host, the
virus is also being replicated.
- this can become virulent.
Lytic Cylce:
1. Attachment/Adsorption
• Adsorption of a Bacteriophage to the Cell Wall of the
Bacterium
• Attachment sites on the virus bind to corresponding
receptors on the host cell wall.
Lytic Cycle:
2. Injection/Penetration
• The bacteriophage injects its genome (DNA) into
the bacterium's cytoplasm
Lytic Cycle:
3. Viral Replication and Assembly
• The viral genome directs the host cell's metabolic
machinery (ribosomes, tRNA, nutrients, energy,
enzymes, etc.) to make viral enzymes and viral parts.
The capsids assemble around the viral genomes as the
viral tails assemble. (they are replicating viral parts)
Lytic Cycle
4. Release
• Release of the Bacteriophages by Lysis of the
Bacterium
• A bacteriophage-coded enzyme breaks down the
peptidoglycan in the bacterial cell wall causing osmotic
lysis.
Treatments
Antiviral Drugs
 Vaccines
 Animal Control: mosquitoes, rabies,
 Antibiotics are not a treatment for viruses
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