Answer:
- RNA polymerase is always present in the cell, but sometimes present in viruses.
- tRNA is always present in the cell but never present in viruses.
- Ribosomes are always present in a cell but never present in viruses.
- Genes are always present in the cell, but always present in viruses.
Explanation:
- Viruses are acellular microorganisms that do not have a biochemical or gene expression of their own. They hijack the host's gene expression system.
- RNA polymerase is the enzymes that forms RNA primers during DNA replication and the mRNA transcript of template DNA during transcription. Therefore, RNA polymerase is always required in cells.
- Most viruses lack RNA polymerase except some RNA viruses such as polio viruses that contain an RNA dependent RNA polymerase, an enzyme that synthesizes mRNA from an RNA template.
- Viruses lack tRNA and ribosomes as they are not capable of translation on their own.
- Unlike the gene expression machinery, all organisms including viruses have a genome. Viruses can have both DNA and RNA genomes.
