What Are the Two Basic Kinds of Nucleic Acids?

Nucleic acids such as DNA pass traits from generation to the next.

Human beings have known since the discovery of agriculture that living things pass traits to their offspring. However, the mechanism for passing traits remained a mystery until the 19th and 20th centuries. Discovered in 1869 by biochemist Johann Friedrich Miescher, nucleic acids are organic compounds found in all living things. In the 20th century, scientists began unraveling the important roles these compounds play in the storage, replication and expression of hereditary information.

Deoxiribonucleic Acid (DNA)

Deoxyribonucleic acid, or DNA, is like a blueprint containing the instructions for building a life form instead of an office building. It consists of a long chain of organic substances called nucleotides linked together in a shape called a double helix. Nucleotides consist of a sugar, a phosphate group and one of four nitrogen bases: adenine, guanine, thymine and cytosine. The order of these bases controls which instructions are included in a particular strand of DNA.

Discovery

Miescher isolated a substance he called nuclein in 1869, which is now known as DNA. However, it wasn't until the 1950s that scientists discovered its significance in genetics and heredity. Rosalind Franklin and Maurice Wilkins at London's King's College photographed DNA's physical structure using X-rays while James Watson and Francis Crick at Cambridge University discovered that the DNA strands are linked together as a double helix. The discovery of DNA's structure revealed how it is copied, transferred and stored.

DNA Replication

DNA's helical structure means the connected strands are complementary to each other. If a researcher knows the order of bases in one strand, he knows the order of bases in the other. Adenine always pairs off with thymine and cytosine always pairs off with guanine. Strings of complete nucleotides form units called genes that are tightly packed into structures called chromosomes. A full set of chromosomes is contained in the nucleus of every cell in the body except for the red blood cells, eggs and sperm. As an embryo develops, its cells divide millions of times. During a process called replication, DNA strands unwind and separate. An enzyme called a DNA polymerase scans the old DNA strands and then creates complementary new strands. The new strands pair off with the old strands, creating new DNA molecules. Mistakes during replication lead to cancer or genetic disorders.

Ribonucleic Acid (RNA)

Ribonucleic acid, or RNA, is similar to DNA and contains nucleotides that are complementary to the nucleotides in DNA. However, RNA contains a different sugar and substitutes a base called uracil for the thymine. During a process called transcription, an enzyme called a RNA polymerase reads the DNA and creates an RNA copy. The RNA then carries the DNA's information to tiny "machines" in the cells called ribosomes that generate the proteins that function as the basic building blocks of the body's tissues.

References

• National Human Genome Research Institute: DNA
• "UXL Encyclopedia of Science"; Nucleic Acids; 2002
• "The Columbia Encyclopedia"; Nucleic Acid; 2008
• Genetics Home Reference: What is DNA?
• National Institute of General Medical Science: How Genes Work
• NCBI Science Primer: What is a Genome?