3.5 Amino Acids

Amino acids are building blocks that join together to form proteins

Basic structure of an amino acid.

Amino acid molecules have a central carbon-hydrogen molecule attached to three parts:

  1. the carboxylic acid group, containing carbon and oxygen
  2. the amino group, containing nitrogen and hydrogen
  3. the side chain (the R group), which varies by amino acid and contains one or more of the following: hydrogen, carbon, oxygen, nitrogen, sulfur, phosphorus, sulfur, and selenium. The 21 common amino acids with their various side chains are depicted below.
The 21 amino acids used by living organisms as building blocks for proteins. By OrgoGuy2theRescue – Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=55068925

The amino acids pictured above combine to form proteins when the carboxyl group from one amino acid and the amino group from another chemically react and form a bond.  RNA helps guide the amino acid assembly to create a chain of amino acids called a polypeptide or a protein.  This chain of amino acids folds into a functional protein based on the properties of the amino acid side chains.  The resulting proteins can have a variety of functions in an organism based on each protein’s shape.  Watch this short video describing the function of various proteins:

Video 1. The functions of various proteins

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The Evolution and Biology of Sex by Sehoya Cotner and Deena Wassenberg is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.