26.4. Nucleic Acids http://www.ck12.org
thymine, and vice versa. Guanine and cytosine form another complementary pair. Mismatched bases will form
unfavorable interactions in the center of the helix.
FIGURE 26.17
Base pairing in DNA.If we know the sequence of one strand in a DNA double helix, we can predict the sequence of the opposite strand
based on the required pairings.
RNA
RNA is nearly identical to DNA, except that the sugar has an extra OH group and uracil is used instead of thymine.
Due to the additional hydrogen bonding opportunities generated by the extra OH group, RNA is found more often
as a single strand that is folded in on itself. However, RNA can still form a double helix with a strand of either DNA
or RNA if the bases form a complementary sequence.
RNA is sometimes classified based on the function that it is performing. The types most relevant to the production
of proteins are messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). We will look at the
role of each type of RNA in the following section.
Protein Synthesis
The process of protein synthesis is summarized in theFigure26.19. DNA produces an RNA template that directs
the amino acids to be introduced into the growing protein chain in the proper sequence. A specific transfer RNA
attaches to each amino acid and brings it to the RNA for incorporation.