Genomes and Genetics: Virology

Flashcards covering key concepts from lecture notes on genomes and genetics in virology, including viral genome types, replication strategies, and historical discoveries.

Virology breakthrough in the 1950s

Discovery that the viral nucleic acid genome is the genetic code.

Hershey-Chase experiment

Demonstrated that DNA, not protein, is the genetic material in phage T4.

Fraenkel-Conrat's work with TMV

Confirmed that RNA was the genetic material by showing RNA specifies the coat protein.

Avery, McCleod & McCarthy (1944)

Experiment demonstrating bacterial transformation, suggesting DNA as the genetic material.

Watson & Crick (1953)

Discovered the double helix structure of DNA.

Wendell Stanley (1935)

Crystallized TMV, incorrectly believed protein was the infectious agent, but received a Nobel Prize.

Viral nucleic acid

The genetic material that specifies proteins in viruses.

Key rule for viral genomes

All viruses must make mRNA that can be read by a host ribosome.

David Baltimore

Discovered Reverse Transcriptase, proposed the classification of viruses, and worked on viral oncogenes.

Baltimore system (1970)

A classification system for viruses based on how they make mRNA, originally missed gapped dsDNA.

mRNA (messenger RNA)

Ribosome ready, always the positive (+) strand by convention, and can be translated.

DNA (+) strand

A DNA strand with equivalent polarity to mRNA, also known as the sense strand.

Negative (-) or antisense strand

RNA and DNA complements of positive (+) strands, which typically cannot be directly translated.

Gapped DNA virus

A viral genome type that must be repaired and made into double-stranded DNA first before it can be transcribed into mRNA.

dsDNA virus

A viral genome type that can be directly transcribed into mRNA.

ssDNA virus

A viral genome type that must be made into double-stranded DNA first before it can be transcribed into mRNA.

dsRNA virus

A viral genome type where the (-) strand is first copied into mRNA by a viral RNA-dependent RNA polymerase (RdRp) because the (+) strand in the duplex cannot be translated.

ss (+) RNA virus

A viral genome type whose genome can be immediately translated into protein by host ribosomes, and which uses viral RNA polymerase to make more mRNA.

ss (-) RNA virus

A viral genome type that cannot be translated directly and requires a viral RNA-dependent RNA polymerase (RdRp) to convert it to (+) strand mRNA.

ss (+) RNA with DNA intermediate

A viral genome type (Retroviridae) where the (+) RNA genome is converted to dsDNA by viral reverse transcriptase, integrated into the host genome, and then transcribed to make mRNA.

Seven classes of viral genomes

dsDNA, gapped dsDNA, ssDNA, dsRNA, ss (+) RNA, ss (-) RNA, and ss (+) RNA with DNA intermediate.

Viroid

Small, highly folded RNA molecules that are mainly plant pathogens, encode no proteins, and are considered relics of the RNA world.

Information encoded in a viral genome

Gene products and regulatory signals for protein synthesis (partially), genome replication, assembly/packaging, replication cycle regulation, host defense modulation, and spread.

Reverse Transcriptase

An enzyme (RNA-dependent DNA polymerase) that synthesizes DNA from an RNA template.

RNA-dependent RNA polymerase (RdRp)

An enzyme found in RNA viruses that synthesizes RNA from an RNA template.

Hepadnaviridae (e.g., Hepatitis B virus)

A family of viruses with gapped dsDNA genomes that cause serious human diseases like liver cancer, spread through sex and blood transfusion.

B19 parvovirus

An ssDNA human virus that causes fifth disease, a childhood illness.

Rotavirus (Reoviridae)

A dsRNA virus with a segmented genome that causes human gastroenteritis.

Picornaviridae (e.g., Poliovirus, Rhinovirus)

A family of ss (+) RNA viruses.

Coronaviridae (e.g., SARS, MERS, 2019-nCoV)

A family of ss (+) RNA viruses known for causing respiratory illnesses.

Retroviridae (e.g., HIV 1 & 2, HTLV)

A family of ss (+) RNA viruses that use a DNA intermediate in their replication, causing diseases like AIDS and certain cancers.

Orthomyxoviridae (e.g., Influenza virus)

A family of segmented ss (-) RNA viruses.

Reassortment

The mixing of genome segments when two genetically diverse segmented viruses infect the same cell, leading to new viral variants.

Ambisense RNA genome

A viral genome containing both (+) and (-) strand information on a single strand of RNA; officially classified as (-) strand viruses because they carry RNA polymerase to make mRNA.

Mutation

A change in DNA or RNA (nucleotide addition, deletion, rearrangement) that can lead to changes in amino acids or proteins.

Synthetic Virology

The process of chemically synthesizing entire viral genomes and transfecting them into cells to create infectious viruses, enabling experiments not previously possible.

NSABB (National Science Advisory Board for Biosecurity)

A federal advisory committee providing guidance on biosecurity oversight of dual-use research, like synthetic virology.