Define transcriptomics.

Transcriptomics is defined as the study of the complete set of RNA transcripts produced by the genome at any given moment. This encompasses all types of RNA molecules, including messenger RNA (mRNA), ribosomal RNA (rRNA), and non-coding RNAs. By analyzing these RNA transcripts, researchers can gain insights into gene expression patterns, how genes are regulated, and how these processes change in response to various conditions or treatments.

Understanding transcriptomics is crucial for various fields of biology, including developmental biology, cancer research, and systems biology, as it allows for a more dynamic view of the genome's expression rather than just its static structure. The analysis of RNA provides a deeper understanding of functional genomics, as RNA levels can reflect the activity of genes.

The other options focus on different aspects of molecular biology. The study of DNA structure and function pertains to genomics, while the analysis of protein structures and functions relates to proteomics. Investigating cellular metabolic pathways is connected to metabolomics. Each of these fields has its own distinct focus, but transcriptomics specifically pertains to RNA and gene expression, making it the correct choice in this context.