The chemical components of ribosomes include proteins and ribosomal RNA (rRNA). Proteins are composed of amino acids, which are small molecules that consist of a central carbon atom bonded to various other atoms, including hydrogen, oxygen, carbon, nitrogen, and sulfur. Ribosomal RNA, on the other hand, is composed of ribonucleotides, which are molecules that consist of a pentose sugar (ribose), a phosphate group, and a nitrogenous base (adenine, uracil, guanine, or cytosine).