Lecture 10/11: Viruses Flashcards
Virus notes
- Not considered “living”
- incapable of making ATP
- No metabolism
- Cannot replicate without host
- infectious agents, not organisms
Virus
- Gene delivery system that contains genes encoding for structural components and facilitate it’s reproduction
- Viral surfaces are only compatible with the surfaces of certain types of cell
Virus classifications
- Classified by the type of cell they infect: Eukaryotic or prokaryotic
- Bacteriophages: Infect prokaryotes, eats bacteria
- Classified by viral genome too: either DNA OR RNA, genome is linear OR circular, double OR single stranded
Viral genome components
- DNA or RNA
- Single or Doubled stranded
- Capsid
- Some have envelope
Capsid
Protective coating made out of protein that all viruses have AKA nucleocapsid if it has nucleus acid
- Carries enzymes
- Composed of identical subunits called capsomeres
Envelope
Surrounds the capsid and is made of lipid and protein, only some viruses have this
Viral reproduction
Viruses hijack ribosomes and polymerases to make copies of themselves
Virus reproduction components
- Make more viral proteins like capsid
- Make viral genomes like DNA or RNA
Virus characteristics
- Super small: 10 nanometers to 800 nanometers
- Smallest one is 10 nanometers with 10 genes
Virion (viral particle)
- Virus without a host
- Has capsid, matrix proteins
Enveloped virus
Have lipid bilayer envelope and mateix proteins between the nucleocapsid and envelope
Non envelope (naked) viruses
Lack envelope
Simplified viral life cycle
1) virus endocytose or fuses with cell
2) uncoats
3a) transcription of viral genes
3b) translation
3c) replication for more viral DNA
4) assembly of new viruses
5) leaves cell via budding or lyse
Viral entry into cell
- Must be able to recognize and bind to cell’s surface
- Recognize membrane proteins of host cells
- Uses capsid or envelope for recognizing
- Viruses cannot infect all cells
RNA viruses example
Rotaviruses, norovirus, polioviruses, rubella, hepatitus C
Lyric phage infection w/ T4 phage
1) Attachment to cell wall
2) penetration via tail and leaves phage coating outside
3) transcription
4) Replication
5) Assembly
6) Release of viral particles
General transduction
- Transfer of DNA from one cell to another via a virus
- Generalized transduction results from an error in DNA package
Temperate phage infections w/ lambda
1) Virus binds to bacterium
2) Injects linear phage DNA that turns into circle
3) phage DNA enters lysogenic cycle
4a) phage DNA that is integrated into the bacterial chromosome and is called prophage
4b) Bacterial DNA with phage DNA is called lysogen
5) cell division and remains dormant until there are extreme conditions
6) phage DNA separates from bacterial DNA
7) phage DNA replicates
8) Lyses from host cell
Lysogen
- Becomes immune to superinfection (cannot be infected by the same phage)
- Lysogenic conversion: lysogen’s phenotype changes due to prophage
Microorganisms encoded by prophage EX
- Clostridium botulinum is encoded by botulinum toxic and causes botulism
- Corynebacterium diphtheriae is encoded by diphtheria and causes diphtheria
Specialized transduction
- Transfer of DNA from one cell to another view of virus
- Specialized transduction results from an error in DNA excision of a prophage
Bacterial defense against phages
- Bacteria produces proteins to cover surface proteins and prevents phage attachment
- Bacteria produce capsule or biofilm
- Restriction modification systems
- CRISPR system
Restriction-modification systems
- Many bacteria encode restriction enzymes such as endonuclease
- Each restriction enzyme cuts a unique sequence EX if bacteria R. Enzyme scans GAATTC in a viral genome, it will cut it or degrade which means virus will degrade
- Modification: bacterial DNA protection from restriction enzyme
Modification
Bacteria protects own bacterial DNA by either not containing the R. Enzyme-recognizing gene sequence or methylation of own DNA
Methylation
Enzyme called methylase methylates host chromosome that has the R. Enzyme-recognized sequence
CRISPR system
- Clusters of regularly Interspersed short palindromic repeats
Studying bacteriophages
Melt agar
Inoculate with bacteria
Pour agar over tsa plate
Lawn of bacterial cells
Animal virus enveloped virus
1) attachment
2) membrane fusion
3a) necleocapsid released
4a) in coating
3b) virus enters
4b) bacteria forms vesicles around virus
5) synthesis
Animal virus synthesis
Expression of viral genes (transcription) to produce viral structure and catalytic proteins such as capsule proteins and enzymes required for replication
Synthesis by (genome type)
DNA viruses
(+)ssRNA viruses
(-)ssRNA viruses
Reverse transcribing RNA viruses
Double stranded DNA virus
1) viral gene
2) gene is transcribed from DNA into mRNA
3) ribosome translates mRNA into viral proteins
Single stranded DNA virus
1) synthesis of complementary strand
2) normal DNA genome and protein synthesis
Single stranded RNA virus
Viral proteins are made through translation
Viral genome is made by synthesizing the RNA
