BS1040 TOPIC 8: VIRUS GENOMES (LECTURE 2)

What is the size range of viral genomes?

From about 1,750 nucleotides (e.g., Circovirus) to about 2.5 Mb pairs (e.g., Pandora viruses).

What is the maximum size of RNA genomes?

30 kb.

Why are viral RNA genomes generally smaller than DNA genomes?

Viral RNA polymerases are error-prone compared to DNA polymerases, which may limit replication fidelity and size.

Where do viruses with RNA genomes typically replicate?

In the cytoplasm.

Where do viruses with DNA genomes typically replicate?

In the nucleus.

What types of nucleic acids can viral genomes be composed of?

DNA or RNA.

What are the structural forms of viral genomes?

Single-stranded (ss), double-stranded (ds), linear, circular, or segmented.

What are the three types of single-stranded RNA based on polarity?

Positive-sense, negative-sense, and ambisense.

baltimore classification

Very condensed genomes

Genomes that are tightly packed with genetic information.

Overlapping genes

Genes that share some of the same nucleotide sequences.

Different reading frames

Using alternative ways to read the same DNA sequence to produce different proteins.

Reading both strands

Utilizing both the forward and reverse strands of DNA for gene expression.

Differential RNA splicing

The process by which different combinations of exons are joined together to produce multiple RNA variants from a single gene.

What is a key event in viral replication?

Synthesis of viral proteins by the host cell.

What must a virus present to the host cell for replication?

mRNA that the cell can translate and its genome for packaging by viral proteins.

What is a constraint for viral RNA genomes in animal cells?

RNA is made in the nucleus, not in the cytoplasm.

Why can't animal cells replicate RNA genomes without viral factors?

Cells cannot make DNA or RNA from an RNA template.

What is a constraint for DNA genomes in viral replication?

Enzymes for replicating and transcribing DNA are present in the nucleus.

What must a virus do to utilize the enzymes for DNA replication?

Either get the DNA genome to the nucleus or make their own polymerases.

what are the four most common viral groups

- +RNA genome virus replication

- -RNA genome replication

- DNA genomes

- Retroviruses

plus-sense, single-strnaded RNA virus and minus-sense, single stranded RNA virus

DNA genomes

retroviruses and reverse transcription