Genomics and Proteomics

Core Concepts

Structural genomics: the genome as blueprint

Structural genomics maps and sequences whole genomes, locates genes, and compares genomes across species (comparative genomics). The logic is simple: genes that are conserved between distantly related species — bacteria, yeast, worms, flies, mice, humans — almost certainly do something important, and their function can often be studied in a convenient model organism. Commonly taught model organisms include E. coli, yeast, the nematode C. elegans, the fruit fly, zebrafish, and the mouse; their genes frequently have human counterparts whose jobs are easier to study in the lab.

Functional genomics: what genes actually do

Knowing a gene's sequence is not knowing its function. Functional genomics investigates activity. Transcriptomics measures which genes are transcribed into mRNA, using RNA-seq or DNA microarrays (chips with thousands of probes that detect specific mRNAs). Gene-disruption experiments — knockouts, or RNA interference to silence a gene — reveal what happens when a gene is missing. Large projects such as ENCODE have cataloged functional elements across the human genome, showing that much of the "noncoding" majority is active regulatory DNA (commonly taught finding).

From genome to transcriptome to proteome

Information flows DNA → RNA → protein, and each step adds complexity:

• The transcriptome is the complete set of mRNA molecules in a cell — which genes are switched on and how strongly.
• The proteome is the complete set of proteins — what was actually translated, modified, and allowed to persist.

Crucially, mRNA levels and protein levels are not perfectly correlated: an mRNA may be degraded before translation, or a protein may be modified or destroyed after synthesis. Regulation happens at every level, which is why "gene is transcribed" does not equal "protein is active."

Why the proteome is bigger than the genome

Humans have roughly 20,000–25,000 protein-coding genes (commonly taught estimate), yet the proteome is far larger, because one gene can generate many distinct proteins:

• Alternative splicing: during mRNA processing, different combinations of exons can be joined, so a single gene produces multiple mRNA variants and therefore multiple protein isoforms.
• Post-translational modifications (PTMs): after synthesis, proteins are chemically altered — commonly taught examples include phosphorylation, glycosylation, and acetylation — changing their activity, location, or lifetime.
• Interactions and complexes: proteins work in complexes, adding functional diversity beyond individual molecules.

The proteome also changes with cell type, developmental stage, and environment. It is a snapshot, not a constant — which is what makes it informative.

How proteomics is done

• Two-dimensional (2D) gel electrophoresis separates proteins in two passes — first by isoelectric point (charge), then by molecular mass — producing a field of spots; spots present in one sample but not another are candidates for further study.
• Mass spectrometry is the workhorse: it ionizes proteins or digested peptides and measures their mass-to-charge ratios, identifying proteins by mass and sequence with high sensitivity.
• Protein microarrays expose thousands of proteins or antibodies on a chip to detect expression or binding in parallel.
• Interaction screens such as the yeast two-hybrid method reveal which proteins physically interact (commonly taught technique).
• Structure databases such as the Protein Data Bank (commonly referenced) store experimentally determined 3D structures of proteins.

Applications

Proteomics compares healthy and diseased samples to find biomarker candidates — proteins whose abundance signals a condition — and catalogs the proteins of pathogens and tumors to propose drug targets. It also illuminates signaling: cascades of phosphorylation turn enzyme activity on and off, controlling everything from cell division to immune responses (commonly taught). Every candidate biomarker or target still requires rigorous validation before clinical or industrial use.

Common Confusions