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Nucleic acids: the code of life • The next class of biological molecules, nucleic acids, are the information-bearing “code of life”. Like proteins, nucleic acid have specific linear sequence of subunits. This linear structure is called a special language of chemical letters. The letters spell out instructions both for characteristics passed on to offspring and for translating that hereditary message into proteins, which will be built into new cell parts, cells and organisms.
Structure of the nucleic acids • Nucleic acids are polymer chain made up of building blocks called nucleotides. Each nucleotide consists of a nitrogen –containing base, a five –carbon sugar, and a phosphate group. There are two types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). The main chemical difference is that the DNA contains sugar molecules with a five carbon monosaccharide called deoxyribose and the RNA contain a similar sugar called ribose. These sugars become bonded to the nitrogen containing bases through a condensation reaction, creating a nucleoside.
Nitrogen-containing bases These are five different nitrogen- containing bases in the nature – adenine A, guanineG, cytosineC, thymineT and uracil U. Each of them has a slightly different chemical composition. These are the “ letters” that make up the nucleic acid alphabet, and although they are fewer than the 20 amino acids in proteins, they are just as capable of encoding diversity. The addition of a phosphate group to the sugar by another condensation reaction yields a nucleotide.
Bio-molecule: Nucleic Acids.There are two main types of nucleic acids
DNA monomers use all bases but uracil. The DNA molecule itself consists of two polymer chains twisted around each other in a double helix. The outer spiral “rails” formed by deoxyribose sugars are connected by phosphate “bridges”, and the ladder rungs formed by pairs of bases (adenine and thymine, or guanine and cytosine) are attached by hydrogen bonds. The precise order of the “rings” carries information about the primary structure of enzymes and other proteins. In turn, enzymes act on row materials to build up all four types of biological molecules – carbohydrates, lipids, proteins and nucleic acids – as well as the cell part constructed of them, DNA responsible for the passing of hereditary information from one cell generation to the next.
DNA is the fundamental building block of genetic material. DNA makes the genes. The key how genes function lies in the unique double helix structure of DNA. DNA stores information in order of its bases. The order of the bases specifies the order of amino acids in polypeptides. The four bases can be in any order, so that each gene has a different – but specific – sequence. From this variability comes DNA’s remarkable capacity to store almost infinite amounts of information. Each of the four bases tends to form weak hydrogen bonds with only one of the other three bases.
Adenine joint with thymine, and cytosine joints with guanine. This phenomenon is called complementary base pairing. Because of it, the bases of the two – nucleotide chains bond to each other, holding the two chains together, with the bases facing inward. DNA in higher organisms is extremely long and must be packaged neatly so that it doesn’t tangle during cell division. It is would around spools of proteins called histones and coiled upon itself repeatedly. Because of base pairing, each chain acts as a template for the creation of a new copy of the other chain, thus, two new strands are created one from each half of the old chain in a process called semi-conservative replication.
RNA • RNA molecules are made up of single chains that may fold into complex shapes or remain stretched out as long threads. Because of their structural and functional features RNA can be divided into messenger RNA, transfer RNA, and ribosomal RNA. The base uracil replaces the base thymine. RNA molecules are also much shorter than DNA molecules because they tend to code only one or two genes. The mRNA acids are about 5% of the cell’s RNA. They translate the information from DNA and take part in protein’s building processes.
The tRNA translates the m RNA codons into amino acid sequence. The t RNA acids are about 15% from the cell’s RNA. They transport amino acids to the ribosomes where the proteins are built. There are 20 amino acids and 20 types of tRNA . Every tRNA can be paired with only one amino acid. Ribosomal RNA is 80% of cell’s RNA. They take part in building of cell’s organelle –ribosomes. Proteins are built in ribosomes.
The genetic code • Much of the genetic research in the mid-twenty century went to reveal that a gene is made of DNA and that it acts by specifying the amino acid sequence in a polypeptide chain. The next question arising from this work is : exactly how does the information in DNA become decoded and translated into protein structure? The answer unfolded over decades of research and can be summarized this way : genetic information within each cell flows from DNA to RNA to protein. Bulgarian /English dictionary acts as a sort of code when you translate a paragraph from Bulgarian into English.
In a similar way cells need a code for translating words from the language of nucleic acids (bases) to the language of proteins (amino acids). This code is called the genetic code. During protein synthesis, the translator is transfer RNA. The genetic code is identical in nearly all organisms. A group of three bases is a codon. Except for the start codon and the three stop codons, each codon specifies one amino acid. Several different codons may specify the same amino acid but no codon specifies more than one amino acid RNA.
