In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: In the liver both the content of RNA and the biosynthesis of ribosomal RNA increased while both the RNA content and ribosomal RNA biosynthesis were reduced in the gastrocnemius muscle .
### Output Text:
In the liver both the content of RNA and the biosynthesis of ribosomal RNA increased while both the RNA content and ribosomal RNA biosynthesis were reduced in the gastrocnemius muscle . 