O groups in the polypeptide backbone. They occur on widely separated domains of a polypeptide or between separate polypeptide chains. Small amino acids like glycine and alanine are favored in beta sheets. Antiparallel beta sheets are more common. Side groups stick above or below the beta sheets.
Most proteins contain both alpha helixes and beta sheets.
The nitrogenous bases are the most important component of nucleic acids. Pyrimidines are composed of 1 six membered ring. When the based are combined with sugars they are called a nucleoside. The sugar component of DNA is 2'-deoxyribose and the sugar component of RNA is ribose. When the bases are combined with sugars and phosphates it is referred to as a nucleotide.