Anjali Mishra Content Writer-SME
Content Writer-SME
Genetic code is the information of all the morphological and physiological features of organisms in the coded form encrypted on the genetic molecule called DNA (Deoxyribose nucleic acid). The transfer of this information from parents to offspring is the basis for the heredity of characters.The importance of genetic code is also seen in all the three stages of gene regulation- replication, transcription, and translation.
- DNA replication is a first step that is marked by the duplication of DNA molecules.
- The process of copying information from DNA to mRNA is called transcription.
- The process of conversion of information from mRNA into an amino acid is called translation.
What is a Genetic Code?
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The instructions provided in the form of code for synthesis of proteins is called a genetic code. Four nucleotide bases (Adenine, Guanine, Cytosine, and Uracil) are required for coding all the essential and non essential amino acids. Genetic code is the total information about a protein encrypted on the messenger RNA. The change in the sequence of nucleotide base pairs leads to a change in the sequence of amino acids, which in turn leads to a change in the protein molecule itself.
- The genetic code is almost identical in all organisms from bacteria to humans due to their common ancestors.
- The structure of a protein can be identified by the amino acid sequence which is pre-determined by the genetic code.
- A single amino acid is coded for by a triplet codon and the protein formed by the group of amino acids has important functions in the body.
Genetic Code
What are Codons?
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Codon is a group of three nucleotides of four nitrogenous bases each. Since it is a group of three codons, it is also called the triplet codon. There are two types of codons that participate in the process of gene regulation: start codons & stop codons.
Start Codons & Stop Codons
Start Codons in Genetics
Codons that are responsible for initiating the process of protein synthesis are called as initiation or start codons. AUG acts as a start codon and the genetic code codes for a specific amino acid called methione in eukaryotes and archaebacteria. On the other hand in bacteria, and prokaryotes, the genetic code AUG codes for N-formyl methionine.
Stop Codons in Genetics
George Gamow’s concept suggests a possibility of 4 x 4 x 4 = 64 amino acids. However, in nature, there are only 20 amino acids. In total, it is believed that there are 64 codons that code for different amino acids. Out of these 64 codons, 3 codons are called stop codons and the remaining 61 codons actually code for specific amino acid molecules.
- The stop codons are essential to stop the process of translation.
- They can also be referred to as termination codons since they terminate the process of protein synthesis.
- The three genetic codes that act as stop codons are UAA, UAG and UGA.
Genetic Code Table
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The pattern of arrangement of nucleotides bases on mRNA and its conversion into a protein molecule can be explained through a concept of permutations and combinations put forth by George Gamow. According to him, each genetic code consists of three nucleotide bases. According to him, there are about 20 amino acids that together manufacture different proteins.
Genetic Code Table
Properties of Genetic Code
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The important features of genetic code are given below:
- The genetic code is a triplet codon made up of three nitrogenous bases.
- The genetic code is universal in all organisms.
- The genetic code has a polarity from 5’ to 3’ end.
- Some amino acids are coded by more than one triplet codon. This is called degeneracy.
- Each triplet codon generally codes for one amino acid. Thus, the genetic code is unambiguous.
- The genetic code is non-overlapping. Adjacent codons do not supersede over the nearby codons.
- The genetic code is commaless. There is no punctuation between two successive codons.
- The initiation codon is 5′ AUG in mRNA. Here, the polypeptide synthesis is started.
- The three termination codons or stop codons, or nonsense codons are UAA, UAG, and UGA. Here, the polypeptide synthesis is ended.
Things to Remember
- Genetic code is the information of all features of organisms in the coded form on DNA or genes.
- The process of copying information from DNA to mRNA is called transcription.
- The process of conversion of information from mRNA into an amino acid is called translation.
- A codon is a group of three nucleotides of four nitrogenous bases each.
- Amino acids are coded by triplet codons.
- Some amino acids are coded by more than one codon. This is called degeneracy.
Sample Questions
Ques. What is a genetic code? (2 Marks)
Ans. Genetic code is the information of all the morphological and physiological features of all organisms in the coded form encrypted on the genetic molecule called DNA or in genes on the chromosome. The code encrypted on genes or codons is the genetic code.
Ques. What are the three genetic processes that run genetic code? (3 Marks)
Ans. The process of transformation of the genetic code into proteins involves three important steps - replication, transcription, and translation.
- Replication - The process in which exact copies of DNA are being made is called replication.
- Transcription - The process by which DNA is converted to RNA is called transcription.
- Translation - The process by which mRNA molecule is converted to a protein is called translation.
These three processes take place on DNA and mRNA. It ultimately results in the formation of protein molecules from amino acids.
Ques. Define the terms replication, transcription, and translation? (2 Marks)
Ans. The process of the creation of DNA copies is called replication. The process of copying information from DNA to mRNA is called transcription. The process of conversion of information from mRNA into an amino acid is called translation. All three processes occur in succession.
Ques. How are the nucleotide base pairs arranged in the genetic code? (2 Marks)
Ans. In the genetic code, the nucleotide base pairs are arranged in a sequence that will be decoded into a chain of amino acids of particular properties. The change in the sequence of nucleotide base pairs leads to a change in the sequence of amino acids, which in turn leads to a change in the protein molecule itself.
Ques. What is a codon? What is George Gamow’s concept? (3 Marks)
Ans. A codon is a group of three nucleotides of four nitrogenous bases each. It is also called the triplet codon in genetics. The pattern of arrangement of nucleotides bases on mRNA and its conversion into a protein molecule can be explained through a concept of permutations and combinations put forth by George Gamow. George Gamow’s concept suggests a possibility of 4 x 4 x 4 = 64 amino acids. But, in nature, there are only 20 amino acids.
Ques. What are amino acids? How are they coded to make a protein? (3 Marks)
Ans. The simple organic compounds that contain both carboxyl (—COOH) and amino (—NH2) groups are called amino acids. The building blocks of proteins are amino acids. Each amino acid is coded by a triplet codon. 64 triplet codons code for 20 amino acids in nature. The sequence of amino acids decides the kind of protein produced. Amino acids combine to form a number of proteins during the process of translation.
Ques. What determines the genetic code? (2 Marks)
Ans. The sequence of the nitrogen bases adenine (A), cytosine (C), guanine (G) and thymine (T), in DNA, determines the genetic code. The sequence of these bases provides the information for producing a chain of amino acids or a protein molecule. The mRNA and ribosomal complex reads the DNA code in groups of three bases or triplet codons.
Ques. Write important features of the genetic code? (5 Marks)
Ans. The important features of genetic code are:
- The genetic code is a triplet code with three codons. It is universal for all organisms.
- Each triplet codon generally codes for one amino acid. Some amino acids are coded by more than one triplet codon. This is called degeneracy.
- There is no punctuation used between two successive codons.
- The genetic code is unambiguous.
- The polypeptide synthesis starts at the initiation codon and stops at the termination codon.
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