Virology Basics: DNA vs RNA Viruses

Viruses can have either RNA or DNA genomes, which can be single-stranded or double-stranded, and positive or negative sense.

Viruses are composed of a genetic material (RNA or DNA) encased in a protein coat.

The primary objective of a virus is to replicate itself and spread to new host cells.

Virology began in 1899 with the work of Martinus Beijerinck, who studied plant diseases, like mosaic tobacco virus.

Early research into the structure of viruses focused on determining whether the core was protein or ribonucleoprotein. Crucial experiments were done by Stanley and Bawden.

RNA is typically single-stranded, uses uracil, and has an OH group at the 2' ribose position. DNA is typically double-stranded, uses thymine, and has an H at the 2' ribose position.

RNA is found in both the nucleus and cytoplasm, whereas DNA is mainly found in the nucleus.

RNA has less intrinsic stability than DNA due its single stranded nature.

A collection of genetically diverse viral strains within a population, arising from mutations.

Viral mutations drive selection; most mutations don't affect fitness, negative mutations are lost, positive mutations are selected.

A process of gradual antigenic change in viral populations due to accumulation of small mutations.

RNA and DNA viruses can have significantly different genome sizes, but the size of the genome is not directly determined by its type (RNA or DNA)

Accuracy of a DNA polymerase enzyme in replicating DNA. RNA polymerase typically has lower fidelity, leading to higher mutation rate.

The process where advantageous traits become more common in a population over time due to their benefit in survival and reproduction.

Changes in the SARS-CoV-2 spike protein can affect its ability to bind to human cells, evade antibodies, and potentially increase infectivity.

A mutation in the SARS-CoV-2 spike protein that enhances its binding to the ACE2 receptor, potentially leading to increased infectivity.

An escape mutation that allows the virus to evade certain antibodies, making it harder for the immune system to fight off infection.

A virus with a genome that is divided into multiple segments of genetic material.

The influenza virus genome is made up of 8 segments of RNA.

The Rift Valley fever virus genome is made up of 3 segments of RNA.

All segments of a segmented virus's genome must be present for the virus to be infectious. This is because each segment carries different genetic information that is essential for its function.

A state where a virus exists within a host cell without actively replicating, often hiding from the immune system.

The process where a virus's DNA inserts itself into the host cell's genome, allowing for long-term persistence.

RNA viruses mutate and evolve much faster than DNA viruses due to their unstable genome.

Some RNA viruses divide their genome into multiple segments, allowing for greater genetic diversity.

DNA viruses have a larger storage capacity for genetic information compared to RNA viruses.

DNA viruses can establish persistent infections by entering a latent state, hiding from the immune system.

RNA viruses can quickly adapt to changing environments, making them effective at evading immune responses.

DNA viruses have more stable genomes and can establish long-lasting infections through latency.

The mixing of genetic material from different viruses with segmented genomes, resulting in a new viral strain with a novel combination of genes. This is a major mechanism for antigenic shift.

Exchange of genetic material between viruses or with the host, leading to new or altered proteins. This process can significantly alter a virus's characteristics and contribute to antigenic shift.

Genetic exchange between similar DNA sequences, often occurring during DNA replication. This process can lead to subtle variations in viral genomes.

A DNA repair mechanism that joins broken DNA ends, even if those ends are not perfectly complementary. This can lead to insertions, deletions, or other mutations in the viral genome.

Viruses can evolve to mimic host proteins, like receptors or signaling molecules, to evade the immune system and gain entry into cells.

A viral protein produced by cytomegalovirus (CMV) that mimics MHC molecules, preventing natural killer cells from recognizing and attacking infected cells.

Viruses can use mimicry and other strategies to evade the immune system, like producing decoys that bind to immune cells, preventing them from attacking infected cells.