 Welcome to biomolecules, the proteins. Proteins do most of the work in cells, including DNA replication, transportation of molecules, and providing structure to cells. They're also some of the largest biomolecules, because they're made up of long chains of building blocks called amino acids. Proteins comprise 10 to 30% of cell mass and have many physiological functions. All enzymes, blood proteins, hemoglobin, and antibodies are examples of proteins. All proteins contain carbon, oxygen, hydrogen, and nitrogen, and they may have other elements as well. Differences in the R group identify the various amino acids. Amino acids are organic compounds that are distinguished by their attached R group. The simplest one, glycine, has only one hydrogen molecule in its R group. Some of the more complex ones, such as arginine and histidine, have larger compounds in this position. The sequence of amino acids determines the protein molecule's primary structure. These are connected by peptide bonds and form a polypeptide chain. The information to construct the amino acid sequence is in the DNA molecule. Some proteins have as few as 100 amino acids, while others have several thousand. Depending on a protein's amino acid sequence, the chain may use hydrogen bonding to form a secondary structure of coils or pleats. Still, more bonding and folding can create a three-dimensional shape or confirmation of the protein. The confirmation determines the protein's function. The confirmation of protein is vulnerable to destruction by high temperatures, the wrong pH, radiation, and chemicals. Many proteins are denatured this way. Animal protein molecules contain repeated use of all 20 amino acids and are complete proteins. Most plant proteins are incomplete because not all 20 amino acids are used in building each type of plant protein molecule. Vegetarians, therefore, eat a variety of plant materials to get all of the amino acids they need for their own protein synthesis. Congratulations! You have completed biomolecules, the proteins.