What is Genetic code?
DNA is the genetic material of an organism since it carries genetic information from cell to cell and from generation to generation and encloses these hereditary messages in the form of a sequence of nitrogenous bases. DNA controls all the life processes by directing and controlling the synthesis of various kinds of proteins.
➤ We know that DNA is the blueprint of all genetic information. This genetic information can be expressed in the form of protein synthesis. A given DNA fragment may contain information for the synthesis of multiple proteins. That section or part of DNA, which carries the information about the formation of a protein (polypeptide), is called a gene.
➤ The Information about the formation of a particular protein (polypeptide) is written in DNA (or gene) in a coded language. This coded language is called Genetic code or genetic language. We also know that the DNA (or gene) contains only four types of nucleotides. These nucleotides act as four letters of the genetic language. These four types of nucleotides (letters) are arranged in peculiar sequences to form genetic words or codons.
➤ So the sequence of nucleotides acts like codes in which genetic information is stored. These codes are called genetic codes. These codes are the ultimate determiner of the type of protein to be synthesized.
➤ The existence of Genetic code was first proposed by FH.C. Crick. In the early 1960s, M.W. Nirenberg, J.H. Matthei, Severo Ochoa Holley, etc, played a significant role in deciphering genetic codes. Dr. Hargovind Khurana and coworkers finally accomplished this feat by synthesizing artificial genes using these genetic codes. For this outstanding work, Khorana, Nirenberg, and Holley were given the Nobel Prize in 1968.
➤ We know that DNA is the blueprint of all genetic information. This genetic information can be expressed in the form of protein synthesis. A given DNA fragment may contain information for the synthesis of multiple proteins. That section or part of DNA, which carries the information about the formation of a protein (polypeptide), is called a gene.
➤ The Information about the formation of a particular protein (polypeptide) is written in DNA (or gene) in a coded language. This coded language is called Genetic code or genetic language. We also know that the DNA (or gene) contains only four types of nucleotides. These nucleotides act as four letters of the genetic language. These four types of nucleotides (letters) are arranged in peculiar sequences to form genetic words or codons.
➤ So the sequence of nucleotides acts like codes in which genetic information is stored. These codes are called genetic codes. These codes are the ultimate determiner of the type of protein to be synthesized.
➤ The existence of Genetic code was first proposed by FH.C. Crick. In the early 1960s, M.W. Nirenberg, J.H. Matthei, Severo Ochoa Holley, etc, played a significant role in deciphering genetic codes. Dr. Hargovind Khurana and coworkers finally accomplished this feat by synthesizing artificial genes using these genetic codes. For this outstanding work, Khorana, Nirenberg, and Holley were given the Nobel Prize in 1968.
Codon - The group of nucleotides that contains the message or code for a single amino acid is called a codon. For example, AUG is the start codon.
Anticodon - The three-base group present in t-RNA, which is complementary to the codon present in m-RNA, is called anticodon.
Triple Code - Gamow (Gamow, 1954) revealed the possibility of a three-letter code. DNA and RNA contain a total of four nucleotides, and the code for the configuration of about 20 amino acids is based on their configuration. If it is assumed that each code is composed of only one nucleotide, there will be a total of four codes that can control the configuration of only 4 amino acids.
If each code is considered to be made up of two nucleotides, then (4×4) only 16 codes will be formed. These are also not sufficient for the 20 amino acids. The code made up of three nucleotides (4 x 4 x 4 = 64) makes 64 code words. These exceed the requirements for twenty amino acids, So Gamow's three-letter code is probably correct.
Read more: Forms of DNA
Developing of genetic code
There are 64 different codons. Each codon contains three bases, and nucleic acids hold four different types of bases. With this setup, there are 64 different ways the four bases can be combined into groups of three 4³ = 64.
➤ We do not know how this particular arrangement first developed. However, given that nucleic acids initially had only four bases, groups of three are the smallest units of equal length that provide enough codons for all 20 amino acids.
Read more: Forms of DNA
Developing of genetic code
There are 64 different codons. Each codon contains three bases, and nucleic acids hold four different types of bases. With this setup, there are 64 different ways the four bases can be combined into groups of three 4³ = 64.
➤ We do not know how this particular arrangement first developed. However, given that nucleic acids initially had only four bases, groups of three are the smallest units of equal length that provide enough codons for all 20 amino acids.
➤ If each of the four bases is coded for an amino acid (a codon of one), then only four amino acids (4) could be coded for, and that's not enough. If the codon were a doublet rather than a triplet, then 16 amino acids (4²) would be coded for, which is close to the number needed but not quite enough. While a triplet provides more than enough (4³ =64) codons, it is the minimum number of bases in a codon when four different kinds of these are used.
Having 64 codons for 20 amino acids means that some codons can be reserved for start (AUG) and stop signals (UAA, UAG, UGA), and many are synonyms of one another. They usually differ in only the third base. For example, GUU, GUC, GUA, and GUG are all codes for valine. This flexibility about the third base in a codon is known as the wobble effect.
Classification or Types of Codons
The codons are basically of three types-
(1) Initiating Codon - Also called a chain initiation codon. This is AUG, or sometimes it may be GUG. AUG code for methionine which initiates the polypeptide chain formation with methionine as the first residue.
(2) Termination Codon - These are also called Non-Sense codons as they do not code for any amino acid. These include UAA (known as ochre), UAG (called as amber) and UGA (called as opal). They cause the termination of the polypeptide chain, which would be released from the ribosome.
(3) General Codons - Except for these four codons (beginning and ending codons), the remaining 60 codons code for amino acids that specifically provide elongation to the polypeptide chain.
Read more - Nucleic Acids
Properties of Genetic Code
1. Genetic Codes are Triplet Nature - The genetic code is triplet code. Three different bases termed a codon specifies one amino acid. The first and second third bases represent the 5' to 3' direction.
2. Genetic Codes are Degeneracy - The code contains many synonyms, in that almost all amino acids are represented by more than one codon example, arginine, many of the synonym codons specifying the same amino acid, the first two bases of the triplet are constant whereas, third can vary e.g. all codons starting with CC specify proline (CCU CCC CCA, CCG) and all codons starting with AC specify theronine.
3. Genetic Codes are Non-Overlapping - The code is non-overlapping i.e., no single base takes part in the formation of the next codon in succession. (They do not share any base), CCU CAG is read only as CCU and CAG and not as CCU, CUC, UCA, or CAG. The code for a protein containing 100 aminoacid units consists of 300 nucleotides linked in linear order.
4. Genetic Codes are Ambibuity - Genetic code is ambiguous i.e., the same codon specifies more than one amino acid. For example, UUU usually codes for phenylalanine, but in the presence of streptomycin, it may code for Isoleucine and leucine acid serine.
5. Genetic Codes are Commaless - Genetic codes are Commaless i.e. no codon is reserved for punctuation.
6. Genetic Codes are Universality - The genetic code is universal, and the same code applies to all kinds of living systems.
7. Genetic Codes start Codon - AUG (in prokaryotes) and GUG (in eukaryotes) function in chain initiator codons because they initiate the synthesis of a polypeptide chain.
8. Genetic Codes are Nonsense Codons - UAA (called ochre), UAG (called amber), and UGA (called opal). These three codons (UAA, UAG, UGA) were initially called Nonsense codons since these codons did not code for any of the 20 essential amino acids. Later, it was discovered that they have a definite function of termination to perform. It would not be correct to call them Nonsense codons.
9. Genetic Codes are Collinearity- DNA is a linear polynucleotide chain, and a protein is a linear polypeptide chain that responds to the sequence of nucleotides base in the gene (DNA) that codes for it. A change in a specification in DNA produces a change of amino acids in the corresponding position.
10. Genetic Codes are Gene Polypeptide Parity - A specific gene transcribes a specific mRNA, which produces an exact polypeptide. On the basis that a cell can have only as many types of polypeptides as it has the type of genes.
FAQs
1. What is the genetic code for GCSE?
The genetic code for GCSE, which stands for General Certificate of Secondary Education, refers to a course or curriculum usually used to teach genetics at the secondary school level. It covers fundamental concepts in genetics and heredity, including the structure of DNA, the principles of inheritance, and genetic variation.
The genetic code contains instructions that tell the cell how to make proteins. It is a sequence of nucleotides that is found in DNA and RNA.
2. How many genetic codes are in A human?
Human beings have the same genetic code. The genetic code is a set of rules that control how information stored in DNA is translated into proteins. This genetic code occurs in all humans and most living organisms, meaning that only one genetic code is used in human biology.
3. Is genetic code DNA or RNA?
The genetic code is found in both DNA and RNA. DNA is the genetic material that is passed down from parents to offspring. RNA is a molecule that helps in the synthesis of proteins.
4. What is genetic code in biology?
The genetic code is a set of instructions that tell the cell how to make proteins. It is a sequence of nucleotides that is present in DNA and RNA. The set of three nucleotides is called a codon, which codes for a specific amino acid. 20 amino acids are used to make proteins, and 64 codons, so most amino acids are coded for by more than one codon. The genetic code is the same for all living organisms, with few exceptions.
5. What is the genetic code? Why is it important?
The genetic code is crucial because it tells the cell how to make proteins. Proteins are essential for life. They are involved in all activities of cells, including metabolism, growth, and reproduction. The genetic code also determines the traits of an organism, such as its eye color and hair color.
The genetic code is also necessary for biotechnology. Scientists can use the genetic code to create new products and medicines. For example, scientists can use the genetic code to make insulin for people with diabetes.
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