What is a Virus
a cellular microorganism, consisting of proteins and genetic material (DNA or RNA), that can replicate itself by infecting a host cell
What is a Prion
a cellular infectious particle consisting of just proteins that can cause progressive diseases in animals and humans
What did D.Ivanoski find?
Found the Tobacco Mosaic Disease (TMD) caused by a filterable component (TMVirus)
What is Bacteriophages?
Viruses that infect bacteria
What are some of the causes of Viruses?
- Abnormal Growth of the Cell
- Cell Death
- Alter the Cell’s Genome
- Physiological Effect in the Cell
What is the structure of Viruses?
Capsid: protein coat surrounding the genome of the virus
Capsomere: individual protein subunits that make up the capsid
Sheath: part of the tail on a bacteriophage that contracts to introduce the viral DNA into the bacterium
Naked Virus: Virus composed of a nucleic acid core, either DNA or RNA, surrounded by a capsid
Spike: Viral glycoprotein embedded within the viral capsid or envelope used for attachment to host cells.
Enveloped Virus: a virus formed with a nucleic-acid packed capsid surrounded by a lipid layer
Viral Envelope: Lipid membrane obtained from phospholipid membranes of the cell that surrounds the capsid
Who classified Viruses?
David Baltimore
Lytic Cycle
Virulent phages typically lead to the death of the cell through cell lysis
Lysogenic Cycle
Temperate phages can become part of the host chromosome and are replicated with the cell genome until such time as they are induced to make newly assembled viruses/progeny viruses
Process of the Lytic Cycle
Attachment: the phage attaches to the surface of the host through receptor
Penetration: Viral DNA enters host cell, tail sheath acts as needle & inject genome through cell wall & membrane
Biosynthesis: Phage DNA replicates and phage proteins are made, hijacks host cell to replicate. transcribe, and translate.
Maturation: New phage particles are assembled
Lysis: The cell lyses, releasing the newly made phages
What does the Lysogenic Cycle do compared to Lytic Cycle
does not kill the host, phage genome integrates into the bacterial chromosome and becomes part of host
Prophage (Lysogenic)
- Integrated phage genome
Lysogen (Lysogenic)
- Bacterial host with a prophage
Lysogeny (Lysogenic)
- The process in which bacterium is infected by a temperate phage
Temperate Phages
- Remains latent (inactive). As the bacterium replicates chromosomes, also replicates the phages DNA and passes it on to new daughter cells during reproduction.
Lysogenic/Phage Conversion
- The presence of the phage may alter the phenotype of the bacterium, since it can bring on extra genes.
Generalized Transduction v.s Specialized Transduction
Generalized Transduction: A random piece of bacterial DNA is transferred by the phage during the lytic cycle
Specialized Transduction: At the end of the lysogenic cycle, when the prophage is excised and the bacteriophage enters the lytic cycle
Life Cycle of the Flu (Influenza)
- Influenza virus becomes attached to a target epithelial cells
- The cell engulfs the virus by endocytosis
- Fusion and uncoating: Viral RNA released
- Viral RNA enters the nucleus where it is replicated by the viral RNA polymerase
- Viral mRNA is used to make viral proteins
- New viral particles are made and released into the extracellular fluid. The cell, which is not killed in the process, continues to make new virus.
Life Cycle of HIV
- HIV fuses with host cell
- HIV RNA, reverse transcriptase, integrase, and other viral proteins enter the host cell.
- Viral DNA is formed by reverse transcription
- Viral DNA is transported across the nucleus and integrates into the host DNA
- New viral RNA is used as genomic RNA and to make viral proteins.
- New viral RNA and proteins move to the cell surface and a new immature HIV forms.
- The virus matures when protease releases the proteins that form the mature HIV.
Eclipse Phase (bacterial growth curve)
- Viruses bind and penetrate the cells with no virions detected into the medium
Inoculation (bacterial growth curve)
- Inoculum of virus binds to the cells
Burst (bacterial growth curve)
- Host cells release many viral particles
Burst size (bacterial growth curve)
- Number of virions released per bacterium
