Bacterial Genetics Terms! - ruthur

[ArchivalUser]

Can someone please explain to me in very very basic terms what the following 4 terms mean. I have included a very basic definition for some:

1. Recombination- Only happens in segmented viruses?
2. Resortment- only happens in Influenza virus? Whole genomes get exchanged?
3. Complementation
4. Phenotype mixing

I have read First Aid and the Uworld explanations but find it rather difficult and tend to get these answers wrong.

Thanks for your help

[ArchivalUser]

Viral Replication and Genetics

Viruses are obligate intracellular parasites → require host cell to replicate.

Viruses receive protection (e.g. oxidative stress, acid-base extremes, the immune system), nutrients (amino acids, nucleotides), and enzymes (DNA polymerase, ribosomes) from host cells.
Viruses are small → viral genomes are small and viruses rarely contain proteins → degree to which a virus pirates host cell machinery depends on its size → smaller viruses use more host cell machinery, larger viruses contain or code more of their own machinery.
Lysogeny is when viral DNA integrates with host cell DNA.

Genes encoding bacterial exotoxins are often transmitted by bacteriophages in this way.

Transduction is the transfer of genes from one bacterium to another via viruses.

Viral genetic interactions include
• Recombination
• Reassortment
• Complementation
• Phenotypic mixing

Recombination is the exchange of genetic information between 2 chromosomes by crossing over within regions of significant base sequence homology.

Reassortment is when viruses with segmented genomes such as influenza and rotavirus exchange material. Most notably is the viral reassortment of genes from human, swine, and avian viruses that was the cause of the 2009 H1N1 influenza A pandemic.

Complementation is when 1 of 2 viruses that infect the cell has a mutation that results in a nonfunctional protein. The non-mutated virus "complements" the mutated one by making a functional protein that serves both viruses. An example of this can be seen in hepatitis D, where the presence of replicating hepatitis B provides HBsAg that serves as the envelope protein for HDV.

Phenotypic mixing is a form of interaction between two viruses, each of which holds its own unique genetic material. The genome of virus A can be partially or completely coated with the surface protein of virus B. The virus B protein coat determines the tropism (infectivity) of the resulting (hybrid) virus. However, the progeny from this infection will have a type A coat that is encoded by the type A genetic material.

Viral replication entails:
1. Penetration of the host cell
2. Virion uncoating
3. Transcription of viral mRNA
4. Translation of viral mRNA
5. Replication of the viral genome
6. Assembly of virions
7. Release of virions through budding or through cell lysis

Most RNA viruses replicate in the cytoplasm, with exception to retroviruses and segmented orthomyxoviruses.

Most DNA viruses replicate in the nucleus, with exception to poxviruses.

Enveloped viruses bud through a host membrane to acquire their envelope → do not lyse the cell.

Genetic mutations are common in viruses.

Viruses rely on bypassing normal safeguards of genomic integrity to replicate. Normal host mechanisms of genome protection and repair are deactivated to allow for viral replication. Viral infection thus increases the mutation rate in host DNA as well.

Many virions are defective → require high inoculation to infect.