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Molecular Basis of Heredity: Part 1. Nucleic Acids

Author(s): Raye L. Alford, PhD

The DNA and RNA Strand

DNA and RNA nucleotides join, through a single phosphate, to form a string of DNA or RNA nucleotides, or a strand of DNA or RNA. When deoxyribose sugar nucleotides join, they make a DNA strand, as shown in the drawing on the left. When ribose sugar nucleotides join, they make an RNA strand.

When nucleotides join together to form a strand of DNA or RNA, the terminal two phosphates of the phosphate group are cleaved off and the remaining phosphate of one nucleotide is joined to the 3' carbon of the last nucleotide of the existing strand. The 5′ to 3′ orientation of the nucleotides in the diagrams indicate the relative positions of the 5′ and 3′ carbons of the pentose sugars. Nucleotides are always linked 3′ carbon to 5′ carbon, through a phosphate group.

DNA strands are synthesized by an enzyme called DNA polymerase. RNA strands are synthesized by enzymes called RNA polymerases.