1.
Nucleic acids
SCH 305: AMINO ACIDS, PEPTIDES, PROTEINS, CARBOHYDRATES AND
NUCLEIC ACIDS
1.0 Nucleic Acids
Nucleic acids are substituted polymers of the aldopentose ribose that carry an
organism’s genetic information. A tiny amount of DNA in a fertilizedegg cell
determines the physical characteristics of the fully developed animal. The difference
between a frog and a human being is encoded in a relativelysmall part of this DNA.
Each cell carries a complete set of genetic instructions that determine the type of cell,
what its function will be, when it will grow and divide, and how it will synthesize all the
proteins, enzymes, carbohydrates, and other substances the cell and the organism
need to survive.
The two major classes of nucleic acids are ribonucleicacids (RNA) and
deoxyribonucleicacids (DNA). In a typical cell, DNA is found primarilyin the
nucleus, where it carries the permanentgenetic code. The molecules of DNA are
huge, with molecularweights up to 50 billion. When the cell divides, DNA replicates to
form two copies for the daughter cells. DNA is relativelystable, providing a medium
for transmission of genetic informationfrom one generation to the next.
RNA molecules are typicallymuch smaller than DNA, and they are more easily
hydrolyzed and broken down. RNA commonlyserves as a working copy of the nuclear
DNA being decoded. Nuclear DNA directs the synthesis of messenger RNA, which
leaves the nucleus to serve as a templatefor the construction of protein molecules in
the ribosomes. The messenger RNA is then enzymaticallycleaved to its component
parts, which become available for assembly into new RNA molecules to direct other
syntheses.