Peptides are tiny. To picture them, it helps to climb a ladder of sizes, one step at a time.
At the bottom are atoms. Most atoms in living things, such as carbon, hydrogen, oxygen and nitrogen, are roughly 0.1 to 0.3 nanometres across. A nanometre is one billionth of a metre. A carbon atom is about 0.2 nm wide.
One step up are amino acids. Each amino acid is a small molecule built from 10 to 27 atoms. It measures less than one nanometre. Amino acids are the building blocks of every peptide and protein.
Link a few dozen amino acids into a chain, let the chain fold, and you get a compact shape a few nanometres across. Large proteins made of hundreds of amino acids reach ten nanometres or more. These molecules are far too small to see with a light microscope. Scientists study their shapes with X-ray crystallography, NMR and electron microscopy.
At the top of our ladder is the cell. A typical animal cell is roughly 10 to 20 micrometres wide, which is about ten thousand times wider than a small peptide. A single cell holds billions of protein molecules. Keeping these scales in mind makes the rest of this course easier. When we talk about bonds, side chains and folding, we are describing events at the nanometre level.
References
- Alberts B et al. Molecular Biology of the Cell, 4th ed., The Chemical Components of a Cell (2002)
- Berg JM, Tymoczko JL, Stryer L. Biochemistry, 5th ed., Section 3.1: Proteins Are Built from a Repertoire of 20 Amino Acids (2002)
- RCSB PDB-101, Guide to Understanding PDB Data: Protein Hierarchical Structure (n.d.)
Educational content about laboratory research. Not medical advice. All Orion compounds are for laboratory research use only.
