Counting atoms.

Mass Spectrometry is a widespread technique that measures atomic mass, a very informative property of matter.

Biological molecules, like DNA and proteins, are so diverse that few of these molecules share the same mass. In other words, you can use the mass to identify a bio-molecule (like hemoglobin or the COVID spike protein).

Additional tools, like fragmenting the molecule into smaller pieces, narrows down the list of possible candidates and bolsters confidence in the protein ID.

In the cell, proteins work together by forming complexes that perform specific functions, such as transcription, protein degradation or oxygen transport. However, the exact composition of many of these machines remains unknown. Thanks to recent improvements in mass spec technology, proteomics researchers are analyzing these protein machines and identifying their components. For example, researchers are using mass spec to identify the proteins involved in cancer and the specific antibodies that recognize COVID. Specifically, they match their experimental measurements with the proteins’ theoretical masses predicted in the DNA sequence.

Unexpectedly at first, this effort revealed the presence of ‘modifications’ : changes to the atomic structure of proteins that were not predicted in the genome (e.g., addition of metals, sugars, carbon atoms). These changes alter enzymatic function and play a role in virtually all cellular processes, including metabolism, Epigenetics and signaling. Currently, there is a major scientific effort to catalogue and assert the function of these protein modifications.

Below is a video that simulates the journey of a molecule traversing through a mass spectrometer.