Monomers Of Dna And Rna

Nucleic Acids

Nucleic Acids and Nucleotides

Nucleic acids, which are relatively stiff acids found in the nuclei of cells, were get-go isolated in 1869. The nucleic acids are polymers with molecular weights as high as 100,000,000 grams per mole. They can exist broken downward, or digested, to form monomers known as nucleotides. Each nucleotide contains iii units: a sugar, an amine, and a phosphate, as shown in the figure below.

Classes of Nucleic Acids

Nucleic acids are divided into classes on the footing of the sugar used to form the nucleotides. Ribonucleic acid (RNA) is built on a b-D-ribofuranose ring. Deoxyribonucleic acid (Dna) contains a modified ribofuranose in which the -OH grouping on the second carbon atom has been removed, equally shown in the fiugre below.

Purines and Pyrimidines

The amines that form nucleic acids fall into two categories: purines and pyrimidines. There are three pyrimidines cytosine, thymine, and uracil and two purines adenine and guanine, equally shown in the figure below.

DNA and RNA each contain four nucleotides. Both contain the same purines adenine and guanine and both also contain the pyrimidine cytosine. But the fourth nucleotide in Dna is thymine, whereas RNA uses uracil to complete its quartet of nucleotides.

Polynucleotides

The carbon atoms in the sugar at the center of a nucleotide are numbered from 1� to 5�. The -OH group on the three� carbon of one nucleotide can react with the phosphate fastened to the v� carbon of another to form a dinucleotide held together by phosphate ester bonds. Every bit the chain continues to grow, it becomes a polynucleotide. A brusk segment of a DNA chain is shown in the figure beneath.

structure

Reading from the 5� end of this chain to the 3� end, this DNA segment contains the following sequence of amine substituents: adenine (A), cytosine (C), guanine (G), and thymine (T).

Role of Nucleic Acids in Living Systems

For many years, the role of nucleic acids in living systems was unknown. In 1944 Oswald Avery presented evidence that nucleic acids were involved in the storage and transfer of the genetic information needed for the synthesis of proteins. This proffer was actively opposed by many of his contemporaries, who believed that the structure of the nucleic acids was too regular and therefore too dull to carry the information that codes for the thousands of dissimilar proteins a cell needs to survive.

In hindsight, the first clue about how nucleic acids office was obtained by Erwin Chargaff, who institute that Dna ever contains the same amounts of certain pairs of bases. There is always only as much adenine as thymine, for example, and just as much guanine as cytosine.

In 1954, James Watson and Francis Crick proposed a structure for DNA that explained how Dna could be used to shop genetic information. Their structure consisted of ii polynucleotide chains running in reverse directions that were linked by hydrogen bonds between a specific purine (A or 1000) on i strand and a specific pyrimidine (C or T) on the other, every bit shown in the figure below. These strands grade a helix that is not quite as tightly coiled equally the a-helix Pauling and Corey proposed for proteins.

This structure must be able to explain 2 processes. In that location must exist some style to brand perfect copies of the Dna that tin be handed down to time to come generations (replication). At that place as well must be some style to decode the data on the Dna concatenation (transcription) and translate this information into a sequence of amino acids in a protein (translation).

Replication is piece of cake to understand. According to Watson and Crick, an adenine on one strand of DNA is ever paired with a guanine on the other, and a cytosine is always paired with a thymine. The 2 strands of DNA therefore complement each other perfectly; the sequence of nucleotides on one strand can always exist predicted from the sequence on the other. Replication occurs when the two strands of the parent DNA molecule divide and both strands are copied simultaneously. Thus, one strand from the parent Deoxyribonucleic acid is nowadays in each of the daughter molecules produced when a jail cell divides.