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If the results of the present study on the chemical nature of the transforming principle are confirmed, then nucleic acids must be regarded as possessing biological specificity, the nature of which is as yet undetermined.
O.T. Avery, C. MacLeod, and M McCarty, "Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types", Journal of Experimental Medicine 1944, Volume 79, p. 155.

In 1944, when Avery, MacLeod and McCarty published the work quoted above, the structure of nucleic acids was still unknown. But their work was one of the more important bits of evidence indicating that nucleic acids contained important biological information. We now know a lot more about the information content, and, thanks to the work of Watson and Crick a few years after this statement was published, we know how the structure of nucleic acids is related to the function of information storage, We know that nucleic acids are the most important macromolecules for the continuity of life. They carry the genetic blueprint of a cell, and carry instructions for the functioning of the cell.

Dna and rna

The two main types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) . DNA is the genetic material found in all living organisms, ranging from single-celled bacteria to multicellular mammals. It is found in the nucleus of eukaryotes and in the organelles, chloroplasts, and mitochondria. In prokaryotes, the DNA is not enclosed in a membranous envelope.

The entire genetic content of a cell is known as its genome , and the study of genomes is genomics. In eukaryotic cells but not in prokaryotes, DNA forms a complex with histone proteins to form chromatin , the substance of eukaryotic chromosomes. A chromosome may contain tens of thousands of genes. Many genes contain the information to make protein products; other genes code for RNA products. DNA controls all of the cellular activities by turning the genes “on” or “off.”

The other type of nucleic acid, RNA, is mostly involved in protein synthesis. The DNA molecules never leave the nucleus but instead use an intermediary to communicate with the rest of the cell. This intermediary is the messenger RNA (mRNA) . Other types of RNA—like rRNA, tRNA, and microRNA—are involved in protein synthesis and its regulation.

DNA and RNA are made up of monomers known as nucleotides . The nucleotides combine with each other to form a polynucleotide , DNA or RNA. Each nucleotide is made up of three components: a nitrogenous base, a pentose (five-carbon) sugar, and a phosphate group ( [link] ). Each nitrogenous base in a nucleotide is attached to a sugar molecule, which is attached to one or more phosphate groups. Some nucleotides such as ATP (Adenosine Triphosphate) are a short term energy source for all cells and is called the "Energy currency of the cell."

The molecular structure of a nucleotide is shown. The core of the nucleotide is a pentose whose carbon residues are numbered one prime through five prime. The base is attached to the one prime carbon, and the phosphate is attached to the five prime carbon. Two kinds of pentose are found in nucleotides: ribose and deoxyribose. Deoxyribose has an H instead of OH at the two prime position. Five kinds of base are found in nucleotides. Two of these, adenine and guanine, are purine bases with two rings fused together. The other three, cytosine, thymine and uracil, have one six-membered ring.
A nucleotide is made up of three components: a nitrogenous base, a pentose sugar, and one or more phosphate groups. Carbon residues in the pentose are numbered 1′ through 5′ (the prime distinguishes these residues from those in the base, which are numbered without using a prime notation). The base is attached to the 1′ position of the ribose, and the phosphate is attached to the 5′ position. When a polynucleotide is formed, the 5′ phosphate of the incoming nucleotide attaches to the 3′ hydroxyl group at the end of the growing chain. Two types of pentose are found in nucleotides, deoxyribose (found in DNA) and ribose (found in RNA). Deoxyribose is similar in structure to ribose, but it has an H instead of an OH at the 2′ position. Bases can be divided into two categories: purines and pyrimidines. Purines have a double ring structure, and pyrimidines have a single ring.

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Source:  OpenStax, Principles of biology. OpenStax CNX. Aug 09, 2016 Download for free at http://legacy.cnx.org/content/col11569/1.25
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