VirusesViruses

Is it living?Is it living? Shapes/StructureShapes/Structure ReplicationReplication Types of virusesTypes of viruses

Are Viruses Living????Are Viruses Living????

Viruses are segments of nucleic acids enclosed in a Viruses are segments of nucleic acids enclosed in a protein capsidprotein capsid

Very, Very smallVery, Very small Contain either RNA or DNAContain either RNA or DNA Considered to be non-living because they do not Considered to be non-living because they do not

carry on life process on their own for example carry on life process on their own for example movement and reproduction. In addition they: movement and reproduction. In addition they:

- do not grow- do not grow

- do not have homeostasis- do not have homeostasis

- do not metabolize- 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 in a spiralEX: Rabies Virus

Tobacco Mosaic virus

Shapes Con’t

Icosahedral

- 20 triangular faces: herpes, chickenpox, polio

Herpes Virus

Common Viruses to Humans

Viral group Nucleic Shape Diseases

Acid Structure Caused

Papovaviruses DNA I, NE Warts, Cancer

Adenoviruses DNA I, NE Respiratory, Intestinal Infection

Herpesvirues DNA I, E herpes, chickenpox, shingle, Mono

Picornviruses RNA I, NE Hepatitis, Cancer

Myxovirues RNA H,E Influenza A, B, C

Rhabdovirues RNA H, E Rabies

Retroviruses RNA I, E AIDS, Cancer

Virus TypesVirus Types1.1. DNA: DNA: Works in 2 ways Works in 2 ways

- Virus enters the cell and directly produces RNA to make viral - Virus enters the cell and directly produces RNA to make viral

proteinsproteins- Viruses DNA joins with the host cell DNA to make new viruses- Viruses DNA joins with the host cell DNA to make new viruses

2. 2. RNARNA - RNA enters in the host cell’s cytoplasm . It then uses the - RNA enters in the host cell’s cytoplasm . It then uses the

ribosomes to make new viral proteins .ribosomes to make new viral proteins .3. 3. RetrovirusesRetroviruses - Contain an enzyme called reverse transcriptase: causes DNA - Contain an enzyme called reverse transcriptase: causes DNA

to be made from RNA. The DNA becomes part of the host to be made from RNA. The DNA becomes part of the host DNA/Genes. Then new RNA is made from this new DNA. RNA DNA/Genes. Then new RNA is made from this new DNA. RNA makes new viral proteins. makes new viral proteins.

4. Viroid: short, single strand of RNA, no capsid. They interfere 4. Viroid: short, single strand of RNA, no capsid. They interfere with plant metabolism and has destroyed entire crops with plant metabolism and has destroyed entire crops (potatoes, cucumbers, oranges)(potatoes, cucumbers, oranges)

5. Prions: 250 amino acids and have no nucleic acid. Linked to 5. Prions: 250 amino acids and have no nucleic acid. Linked to brain diseases such as scrapie (slow degeneration of nervous brain diseases such as scrapie (slow degeneration of nervous system in sheep) and Mad Cow (brain disease in cows)system in sheep) and Mad Cow (brain disease in cows)

Replication:BacteriophageBacteriophage:

- 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 CyclesReplication Cycles Lytic CycleLytic Cycle - They are virulent: cause disease- They are virulent: cause disease - A virus invades a host cell, produces new viruses, - A virus invades a host cell, produces new viruses, destroys the host cell, and releases new viruses.destroys the host cell, and releases new viruses.

Lysogenic CycleLysogenic Cycle- infects the cell without causing immediate harm. - infects the cell without causing immediate harm. - these viruses can stay in the host for a long period of - these viruses can stay in the host for a long period of

time. time. - Called a temperate virus- Called a temperate virus- When the DNA is injected into the host cell, it does not - When the DNA is injected into the host cell, it does not start to make new viral parts immediately, they will become start to make new viral parts immediately, they will become part of the host’s DNA. When the cell is replicated naturally part of the host’s DNA. When the cell is replicated naturally by the host, the virus is also being replicated. by the host, the virus is also being replicated. - this can become virulent. - 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 Cycle4. 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.

TreatmentsTreatments

Antiviral DrugsAntiviral DrugsVaccinesVaccinesAnimal Control: mosquitoes, rabies, Animal Control: mosquitoes, rabies, Antibiotics are not a treatment for viruses Antibiotics are not a treatment for viruses