How many codons are present in genetic code

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Genetic codons are the gene sequences which encodes specific amino acids that polymerize to form proteins. DNA is the heritable material that serves as a source of the hereditary unit, which transfers genetic information from one to the next generations. Therefore, in a cell, DNA is a director that mediates the synthesis of proteins. A protein is a polypeptide chain translated from the polynucleotide chain. Any changes in the polynucleotide chain (addition, deletion etc.) cause changes or mutation in the sequence of codons encoding specific amino acids. Content: Genetic Codons • • • • • • Definition of Genetic Code A genetic code can define either as the RNA or DNA codons, which are generally expressed in a pattern of triplet codons of nitrogenous bases. A genetic coding system has 64 sets of triplet codons, which encodes specific amino acid to form a functional protein. A triplet coding system has four different combinations of the nitrogenous bases, in which each encodes for one of the 20 essential amino acids. A genetic code is degenerative because of many codons code for similar amino acid. Three codons serve as termination or stop codons, and one functions as the initiation or start codon out of 64 nucleotide triplets. The termination codons, i.e. UAA, UAG and UGA, play a significant role in the cessation of translation, whereas initiation codon, i.e. AUG or ATG mediates the synthesis of proteins. Genetic codons hold the set of information or gene sequences, by using ...

Determining the Number of Codons Needed to Code for Three Amino Acids: Decoding the Genetic Code. Introduction The genetic code is the set of instructions that governs the synthesis of proteins in living organisms. This code is written in the sequence of nucleotides that make up DNA and RNA molecules. The code is composed of codons, which are three-nucleotide sequences that specify a particular amino acid. Amino acids are the building blocks of proteins, which are essential for the structure and function of all living cells. In this article, we will explore how many codons are needed to specify three amino acids and how they are used in the process of protein synthesis. How Many Codons Are Needed To Specify Three Amino Acids? There are 20 different amino acids that are used to build proteins. Each amino acid is specified by one or more codons. For example, the amino acid methionine is specified by the codon AUG, while the amino acid lysine is specified by the codons AAA and AAG. To specify three amino acids, we need to use three codons. There are 64 possible codons, but only 61 of them code for amino acids. The other three codons are stop codons, which signal the end of the protein chain. Each codon is read by the ribosome during protein synthesis, and the corresponding amino acid is added to the growing protein chain. The ribosome reads the codons in a specific order, starting at the beginning of the mRNA molecule and ending at the stop codon. The sequence of codons deter...

Cells decode mRNAs by reading their nucleotides in groups of three, called codons. Each codon specifies a particular amino acid, or, in some cases, provides a "stop" signal that ends translation. In addition, the codon AUG has a special role, serving as the start codon where translation begins. The complete set of correspondences between codons and amino acids (or stop signals) is known as the genetic code. Why was this a tricky problem? In one of the simplest potential codes, each nucleotide in an DNA or RNA molecule might correspond to one amino acid in a polypeptide. However, this code cannot actually work, because there are 20 20 2 0 20 amino acids commonly found in proteins and just 4 4 4 4 nucleotide bases in DNA or RNA. Thus, researchers knew that the code must involve something more complex than a one-to-one matching of nucleotides and amino acids. Gamow's reasoning was that even a doublet code ( 2 2 2 2 nucleotides per amino acid) would not work, as it would allow for only 16 16 1 6 16 ordered groups of nucleotides ( 4 2 4^2 4 2 4, squared ), too few to account for the 20 20 2 0 20 standard amino acids used to build proteins. A code based on nucleotide triplets, however, seemed promising: it would provide 64 64 6 4 64 unique sequences of nucleotides ( 4 3 4^3 4 3 4, cubed ), more than enough to cover the 20 20 2 0 20 amino acids. The cracking of the genetic code began in 1961, with work from the American biochemist Marshall Nirenberg. For the first time, Nirenberg...

Dedicated November 12, 2009, at the National Institutes of Health in Bethesda, Maryland. DNA consists of a code language comprising four letters which make up what are known as codons, or words, each three letters long. Interpreting the language of the genetic code was the work of Marshall Nirenberg and his colleagues at the National Institutes of Health. Their careful work, conducted in the 1960s, paved the way for interpreting the sequences of the entire human genome. Contents • • • • • • • • Modern genetics begins with an obscure Augustinian monk studying the inheritance of various traits in pea plants. Gregor Mendel’s laws of inheritance revealed the probabilities of dominant and recessive traits being passed from generation to generation. Mendel’s research received little recognition in his lifetime. The significance of Mendel’s laws was recognized only in the early 20th century. With that rediscovery came interest in how genetic information is transmitted. Oswald Avery, a bacteriologist at New York’s Rockefeller Institute, demonstrated that deoxyribonucleic acid, DNA, produced inheritable changes. This discovery was not well received: How could DNA, a substance containing only four different nucleotide building blocks, store genetic information? Others discovered that DNA varies from species to species. Then, in 1953, James Watson and Francis Crick at Cambridge University electrified the scientific world with their model of DNA, the double helix. Watson and Crick rec...

Examples of termination codons are UAG, UAA, or UGA. Translation stops when one of these codons is encountered by the ribosome (ribosomes are small particles in cells that serve as the sites of protein synthesis). Special release factors associate with the ribosome in response to these codons, and the newly synthesized protein, transfer RNAs (tRNAs), and mRNA dissociate. This article was most recently revised and updated by

Once it was determined that RNA ( mRNA) serves as a copy of chromosomal DNA and specifies the sequence of amino acids in proteins, the question of how this process is actually carried out naturally followed. It had long been known that only 20 amino acids occur in naturally derived proteins. It was also known that there are only four nucleotides in mRNA: adenine (A), uracil (U), guanine (G), and cytosine (C). Thus, 20 amino acids are coded by only four unique bases in mRNA, but just how is this coding achieved? The discordance between the number of nucleic acid bases and the number of amino acids immediately eliminates the possibility of a code of one base per amino acid. In fact, even two nucleotides per amino acid (a doublet code) could not account for 20 amino acids (with four bases and a doublet code, there would only be 16 possible combinations [4 2 = 16]). Thus, the smallest combination of four bases that could encode all 20 amino acids would be a triplet code. However, a triplet code produces 64 (4 3 = 64) possible combinations, or codons. Thus, a triplet code introduces the problem of there being more than three times the number of codons than amino acids. Either these "extra" codons produce redundancy, with multiple codons encoding the same amino acid, or there must instead be numerous dead-end codons that are not linked to any amino acid. Preliminary evidence indicating that the genetic code was indeed a triplet code came from an experiment by Francis Crick and S...

Skills to Develop • Explain the “central dogma” of protein synthesis • Describe the genetic code and how the nucleotide sequence prescribes the amino acid and the protein sequence The cellular process of transcription generates messenger RNA (mRNA), a mobile molecular copy of one or more genes with an alphabet of A, C, G, and uracil (U). Translation of the mRNA template converts nucleotide-based genetic information into a protein product. Protein sequences consist of 20 commonly occurring amino acids; therefore, it can be said that the protein alphabet consists of 20 letters (Figure \(\PageIndex_3^+\)), a carboxyl group (COO -), and a side chain (blue). The side chain may be nonpolar, polar, or charged, as well as large or small. It is the variety of amino acid side chains that gives rise to the incredible variation of protein structure and function. The Central Dogma: DNA Encodes RNA; RNA Encodes Protein The flow of genetic information in cells from DNA to mRNA to protein is described by the Central Dogma (Figure \(\PageIndex\): Instructions on DNA are transcribed onto messenger RNA. Ribosomes are able to read the genetic information inscribed on a strand of messenger RNA and use this information to string amino acids together into a protein. The Genetic Code Is Degenerate and Universal Given the different numbers of “letters” in the mRNA and protein “alphabets,” scientists theorized that combinations of nucleotides corresponded to single amino acids. Nucleotide doublets ...