A series of codons in part of a mRNA molecule. Messenger ribonucleic acid ( mRNA) is a molecule of RNA encoding a chemical "blueprint" for a Protein product Each codon consists of three nucleotides, representing a single amino acid. Nucleotides are Organic compounds that consist of three joined structures a nitrogenous base a Sugar, and a Phosphate group In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this

The genetic code is the set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins (amino acid sequences) by living cells. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Ribonucleic acid ( RNA) is a Nucleic acid that consists of a long chain of Nucleotide units Translation is the first stage of Protein biosynthesis (part of the overall process of Gene expression) Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called Specifically, the code defines a mapping between tri-nucleotide sequences called codons, and amino acids; every triplet of nucleotides in a nucleic acid sequence specifies a single amino acid. Nucleotides are Organic compounds that consist of three joined structures a nitrogenous base a Sugar, and a Phosphate group Because the vast majority of genes are encoded with exactly the same code (see #RNA codon table), this particular code is often referred to as the canonical or standard genetic code, or simply the genetic code, though in fact there are many variant codes; thus, the canonical genetic code is not universal. History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance For example, in humans, protein synthesis in mitochondria relies on a genetic code that varies from the canonical code. In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells.

It is important to know that not all genetic information is stored as the genetic code. All organisms' DNA contain regulatory sequences, intergenic segments, chromosomal structural areas, which can contribute greatly to phenotype but operate using a distinct sets of rules which may or may not be as straightforward as the well-defined codon-to-amino acid paradigm which underlies the genetic code. A phenotype is any observable characteristic of an Organism, such as its morphology, Development, biochemical or physiological properties

Cracking the genetic code

The genetic code

After the structure of DNA was deciphered by James Watson, Francis Crick, Maurice Wilkins and Rosalind Franklin, serious efforts to understand the nature of the encoding of proteins began. Francis Harry Compton Crick OM FRS (8 June 1916 – 28 July 2004 Ph Maurice Hugh Frederick Wilkins CBE FRS ( 15 December 1916 – 5 October 2004) was a New Zealand -born British Rosalind Elsie Franklin ( 25 July, 1920 Notting Hill, London – 16 April, 1958 Chelsea London) was an George Gamov postulated that a three-letter code must be employed to encode the 20 different amino acids used by living cells to encode proteins (because 3 is the smallest n such that 4ⁿ is at least 20). George Gamow (pronounced as ˈgamof ( March 4, 1904 &ndash August 19, 1968), born Georgiy Antonovich Gamov (Георгий Антонович In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this The fact that codons did consist of three DNA bases was first demonstrated in the Crick, Brenner et al. experiment. The Crick Brenner et al experiment was a Scientific experiment performed in 1961 by Francis Crick and Sydney Brenner. The first elucidation of a codon was done by Marshall Nirenberg and Heinrich J. Matthaei in 1961 at the National Institutes of Health. Marshall Warren Nirenberg (born April 10, 1927) is a US Biochemist and geneticist. J Heinrich Matthaei (* 1929 is a German Biochemist. He is best known for his unique contribution to solving the Genetic code on May 15, 1961 "NIH" redirects here For other meanings of NIH see NIH (disambiguation. They used a cell-free system to translate a poly-uracil RNA sequence (or UUUUU. A cell-free system is a widely-used In vitro tool used to study biological reactions that happen within a cell with less of the complex interactions found Translation is the first stage of Protein biosynthesis (part of the overall process of Gene expression) . . in biochemical terms) and discovered that the polypeptide they had synthesized consisted of only the amino acid phenylalanine. Peptides (from the Greek πεπτίδια, "small digestibles" are short Polymers formed from the linking in a defined order of α- Amino Phe redirects here For the BitTorrent feature see PHE. For the constellation see Phoenix (constellation. They thereby deduced from this poly-phenylalanine that the codon UUU specified the amino-acid phenylalanine. Extending this work, Nirenberg and his coworkers were able to determine the nucleotide makeup of each codon. In order to determine the order of the sequence, trinucleotides were bound to ribosomes and radioactively labeled aminoacyl-tRNA was used to determine which amino acid corresponded to the codon. Nirenberg's group was able to determine the sequences of 54 out of 64 codons. Subsequent work by Har Gobind Khorana identified the rest of the code, and shortly thereafter Robert W. Holley determined the structure of transfer RNA, the adapter molecule that facilitates translation. Har Gobind Khorana, or Hargobind Khorana (born January 9, 1922) is an Indian-American molecular biologist Robert William Holley ( January 28, 1922 &ndash February 11, 1993) was an American Biochemist, he was awarded the Nobel Prize Transfer RNA (abbreviated tRNA) is a small RNA (usually about 74-95 nucleotides that transfers a specific Amino acid to a growing polypeptide chain at This work was based upon earlier studies by Severo Ochoa, who received the Nobel prize in 1959 for his work on the enzymology of RNA synthesis. Severo Ochoa de Albornoz ( September 24, 1905 &ndash November 1, 1993) was a Spanish - American biochemist In 1968, Khorana, Holley and Nirenberg also received the Nobel Prize in Physiology or Medicine for their work. The Nobel Prize (Nobelpriset (Nobelprisen is a Swedish prize established in the 1895 will of Swedish chemist Alfred Nobel; it was first awarded in Peace, Literature

Transfer of information via the genetic code

The genome of an organism is inscribed in DNA, or in some viruses RNA. In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Ribonucleic acid ( RNA) is a Nucleic acid that consists of a long chain of Nucleotide units The portion of the genome that codes for a protein or an RNA is referred to as a gene. History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance Those genes that code for proteins are composed of tri-nucleotide units called codons, each coding for a single amino acid. Each nucleotide sub-unit consists of a phosphate, deoxyribose sugar and one of the 4 nitrogenous nucleotide bases. A phosphate, an Inorganic chemical, is a salt of Phosphoric acid. Deoxyribose, also known as D-Deoxyribose and 2-deoxyribose, is an Aldopentose &mdash a Monosaccharide containing five Carbon Nucleotides are Organic compounds that consist of three joined structures a nitrogenous base a Sugar, and a Phosphate group The purine bases adenine (A) and guanine (G) are larger and consist of two aromatic rings. Purine ( 1) is a heterocyclic Aromatic Organic compound, consisting of a Pyrimidine ring fused to an Imidazole ring Adenine is a Purine with a variety of roles in Biochemistry including Cellular respiration, in the form of both the energy-rich Adenosine Guanine is one of the five main Nucleobases found in the Nucleic acids DNA and RNA, the others being Adenine, Cytosine, The pyrimidine bases cytosine (C) and thymine (T) are smaller and consist of only one aromatic ring. Pyrimidine is a Heterocyclic Aromatic Organic compound similar to Benzene and Pyridine, containing two Nitrogen Atoms Cytosine is one of the five main bases found in DNA and RNA. It is a Pyrimidine derivative with a Heterocyclic Aromatic ring Thymine is one of the four bases in the Nucleic acid of DNA that make up the letters ATGC In the double-helix configuration, two strands of DNA are joined to each other by hydrogen bonds in an arrangement known as base pairing. In Molecular biology, two Nucleotides on opposite complementary DNA or RNA strands that are connected via Hydrogen bonds are called These bonds almost always form between an adenine base on one strand and a thymine on the other strand and between a cytosine base on one strand and a guanine base on the other. This means that the number of A and T residues will be the same in a given double helix as will the number of G and C residues. In RNA, thymine (T) is replaced by uracil (U), and the deoxyribose is substituted by ribose. Uracil is a common and naturally occurring Pyrimidine derivative Ribose (ɹˈaɪbəʊs ɹˈaɪbəɹʊs primarily seen as D-ribose, is an Aldopentose — a Monosaccharide containing five Carbon

Each protein-coding gene is transcribed into a template molecule of the related polymer RNA, known as messenger RNA or mRNA. Transcription is the synthesis of RNA under the direction of DNA Messenger ribonucleic acid ( mRNA) is a molecule of RNA encoding a chemical "blueprint" for a Protein product This in turn is translated on the ribosome into an amino acid chain or polypeptide. Translation is the first stage of Protein biosynthesis (part of the overall process of Gene expression) Ribosomes ( from ribo nucleic acid and "Greek soma ( meaning body") are complexes of RNA and Protein that In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this Peptides (from the Greek πεπτίδια, "small digestibles" are short Polymers formed from the linking in a defined order of α- Amino The process of translation requires transfer RNAs specific for individual amino acids with the amino acids covalently attached to them, guanosine triphosphate as an energy source, and a number of translation factors. Transfer RNA (abbreviated tRNA) is a small RNA (usually about 74-95 nucleotides that transfers a specific Amino acid to a growing polypeptide chain at Guanosine-5'-triphosphate ( GTP) is a Purine Nucleotide. One role is as substrate for the synthesis of RNA during transcription. tRNAs have anticodons complementary to the codons in mRNA and can be "charged" covalently with amino acids at their 3' terminal CCA ends. Individual tRNAs are charged with specific amino acids by enzymes known as aminoacyl tRNA synthetases which have high specificity for both their cognate amino acids and tRNAs. An aminoacyl tRNA synthetase ( aaRS) is an Enzyme that catalyzes the Esterification of a specific Amino acid or its precursor to one of all its compatible The high specificity of these enzymes is a major reason why the fidelity of protein translation is maintained.

There are 4³ = 64 different codon combinations possible with a triplet codon of three nucleotides. In reality, all 64 codons of the standard genetic code are assigned for either amino acids or stop signals during translation. If, for example, an RNA sequence, UUUAAACCC is considered and the reading-frame starts with the first U (by convention, 5' to 3'), there are three codons, namely, UUU, AAA and CCC, each of which specifies one amino acid. In Biology, a reading frame is a contiguous and non-overlapping set of three- Nucleotide Codons in DNA or RNA. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known This RNA sequence will be translated into an amino acid sequence, three amino acids long. A comparison may be made with computer science, where the codon is the equivalent of a word, which is the standard "chunk" for handling data (like one amino acid of a protein), and a nucleotide for a bit. Computer science (or computing science) is the study and the Science of the theoretical foundations of Information and Computation and their In Computing, " word " is a term for the natural unit of data used by a particular computer design A bit is a binary digit, taking a value of either 0 or 1 Binary digits are a basic unit of Information storage and communication

The standard genetic code is shown in the following tables. Table 1 shows what amino acid each of the 64 codons specifies. Table 2 shows what codons specify each of the 20 standard amino acids involved in translation. These are called forward and reverse codon tables, respectively. For example, the codon AAU represents the amino acid asparagine, and UGU and UGC represent cysteine (standard three-letter designations, Asn and Cys respectively). Asparagine (abbreviated as Asn or N; Asx or B represent either asparagine or Aspartic acid) is one of the 20 most common natural Not to be confused with Cystine, its oxidized dimer Cysteine (abbreviated as Cys or C) is an α- Amino acid with

RNA codon table

Salient features

Reading frame of a sequence

Note that a codon is defined by the initial nucleotide from which translation starts. Phe redirects here For the BitTorrent feature see PHE. For the constellation see Phoenix (constellation. Leucine (abbreviated as Leu or L) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH2CH(CH32 Serine (abbreviated as Ser or S) is an Organic compound with the formula H[[oxygen O]]2 CCH NH sub>2CH2OH Tyrosine (abbreviated as Tyr or Y) or 4-hydroxyphenylalanine, is one of the 20 Amino acids that are used by cells to synthesize Not to be confused with Cystine, its oxidized dimer Cysteine (abbreviated as Cys or C) is an α- Amino acid with Tryptophan (abbreviated as Trp or W) is one of the 20 standard amino acids, as well as an Essential amino acid in the Human diet Proline (abbreviated as Pro or P) is an α- Amino acid, one of the twenty DNA -encoded amino acids Histidine (abbreviated as His or H) is one of the 20 standard Amino acids present in Proteins In the Nutritional sense in Glutamine (abbreviated as Gln or Q; the abbreviation Glx or Z represents either glutamate or Glutamic acid) is one of the 20 Arginine (abbreviated as Arg or R) is an α- Amino acid. The L-form is one of the 20 most common natural amino acids Isoleucine (abbreviated as Ile or I) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH(CH3CH2CH3 Methionine ( abbreviated as Met or M) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH2CH2SCH3 Threonine (abbreviated as Thr or T) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH(OHCH3 Asparagine (abbreviated as Asn or N; Asx or B represent either asparagine or Aspartic acid) is one of the 20 most common natural Lysine (abbreviated as Lys or K) is an α- Amino acid with the Chemical formula HO2CCH(NH2(CH24NH2 Valine (abbreviated as Val or V) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH(CH32 Alanine (abbreviated as Ala or A) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH3 Aspartic acid (abbreviated as Asp or D; Asx or B represent either aspartic acid or Asparagine) is an α- Amino acid Glutamic acid (abbreviated as Glu or E) is one of the 20 Alpha Amino acids It is not among the human Essential amino acids Its Glycine (abbreviated as Gly or G) is the Organic compound with the formula NH2CH2COOH The genetic code is the set of rules by which information encoded in genetic material ( DNA or RNA sequences is translated into Proteins For example, the string GGGAAACCC, if read from the first position, contains the codons GGG, AAA and CCC; and if read from the second position, it contains the codons GGA and AAC; if read starting from the third position, GAA and ACC. Partial codons have been ignored in this example. Every sequence can thus be read in three reading frames, each of which will produce a different amino acid sequence (in the given example, Gly-Lys-Pro, Gly-Asp, or Glu-Thr, respectively). In Biology, a reading frame is a contiguous and non-overlapping set of three- Nucleotide Codons in DNA or RNA. With double-stranded DNA there are six possible reading frames, three in the forward orientation on one strand and three reverse (on the opposite strand). In Biology, a reading frame is a contiguous and non-overlapping set of three- Nucleotide Codons in DNA or RNA.

The actual frame in which a protein sequence is translated is defined by a start codon, usually the first AUG codon in the mRNA sequence. ATG and AUG denote sequences of DNA and RNA respectively that are the Start codon or initiation Codon encoding the Amino acid Mutations that disrupt the reading frame by insertions or deletions of a non-multiple of 3 nucleotide bases are known as frameshift mutations. A frameshift mutation (also called a framing error) is a genetic Mutation caused by Indels ie These mutations may impair the function of the resulting protein, if it is formed, and are thus rare in in vivo protein-coding sequences. In vivo ( Latin: within the living means that which takes place inside an organism. Often such misformed proteins are targeted for proteolytic degradation. Proteolysis is the directed degradation ( digestion) of Proteins by cellular Enzymes called Proteases or by intramolecular digestion In addition, a frame shift mutation is very likely to cause a stop codon to be read which truncates the creation of the protein (example [2]). One reason for the rareness of frame-shifted mutations being inherited is that if the protein being translated is essential for growth under the selective pressures the organism faces, absence of a functional protein may cause lethality before the organism is viable.

Start/stop codons

Translation starts with a chain initiation codon (start codon). ATG and AUG denote sequences of DNA and RNA respectively that are the Start codon or initiation Codon encoding the Amino acid Unlike stop codons, the codon alone is not sufficient to begin the process. Nearby sequences and initiation factors are also required to start translation. Initiation factors are proteins that bind to the small subunit of the Ribosome during the initiation of translation, a part of Protein biosynthesis. The most common start codon is AUG, which codes for methionine, so most amino acid chains start with methionine.

The three stop codons have been given names: UAG is amber, UGA is opal (sometimes also called umber), and UAA is ochre. In the Genetic code, a stop codon (or termination codon) is a Nucleotide triplet within Messenger RNA that signals a termination of translation "Amber" was named by discoverers Richard Epstein and Charles Steinberg after their friend Harris Bernstein, whose last name means "amber" in German. The other two stop codons were named 'ochre" and "opal" in order to keep the "color names" theme. Stop codons are also called termination codons and they signal release of the nascent polypeptide from the ribosome due to binding of release factors in the absence of cognate tRNAs with anticodons complementary to these stop signals. The release factor is a Protein that recognizes the Termination codon or stop Codon in a MRNA sequence on the ribosome ^[2]

Degeneracy of the genetic code

The genetic code has redundancy but no ambiguity (see the codon tables above for the full correlation). For example, although codons GAA and GAG both specify glutamic acid (redundancy), neither of them specifies any other amino acid (no ambiguity). The codons encoding one amino acid may differ in any of their three positions. For example the amino acid glutamic acid is specified by GAA and GAG codons (difference in the third position), the amino acid leucine is specified by UUA, UUG, CUU, CUC, CUA, CUG codons (difference in the first or third position), while the amino acid serine is specified by UCA, UCG, UCC, UCU, AGU, AGC (difference in the first, second or third position). Glutamic acid (abbreviated as Glu or E) is one of the 20 Alpha Amino acids It is not among the human Essential amino acids Its Leucine (abbreviated as Leu or L) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH2CH(CH32 Serine (abbreviated as Ser or S) is an Organic compound with the formula H[[oxygen O]]2 CCH NH sub>2CH2OH

A position of a codon is said to be a fourfold degenerate site if any nucleotide at this position specifies the same amino acid. For example, the third position of the glycine codons (GGA, GGG, GGC, GGU) is a fourfold degenerate site, because all nucleotide substitutions at this site are synonymous, i. Glycine (abbreviated as Gly or G) is the Organic compound with the formula NH2CH2COOH e. they do not change the amino acid. Only the third positions of some codons may be fourfold degenerate. A position of a codon is said to be a twofold degenerate site if only two of four possible nucleotides at this position specify the same amino acid. For example, the third position of the glutamic acid codons (GAA, GAG) is a twofold degenerate site, so is the first position of the leucine codons (UCA, UCC, CCU, CCC, CCA, CCG). Glutamic acid (abbreviated as Glu or E) is one of the 20 Alpha Amino acids It is not among the human Essential amino acids Its Leucine (abbreviated as Leu or L) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH2CH(CH32 In twofold degenerate sites, the equivalent nucleotides are always either two purines (A/G) or two pyrimidines (C/U), so only transversional substitutions (purine to pyrimidine or pyrimidine to purine) in twofold degenerate sites are nonsynonymous. Purine ( 1) is a heterocyclic Aromatic Organic compound, consisting of a Pyrimidine ring fused to an Imidazole ring Pyrimidine is a Heterocyclic Aromatic Organic compound similar to Benzene and Pyridine, containing two Nitrogen Atoms A position of a codon is said to be a non-degenerate site if any mutation at this position results in amino acid substitution. There is only one threefold degenerate site where changing three of the four nucleotides has no effect on the amino acid, while changing the fourth possible nucleotide results in an amino acid substitution. This is the third position of an isoleucine codon: AUU, AUC, or AUA all encode isoleucine, but AUG encodes methionine. Isoleucine (abbreviated as Ile or I) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH(CH3CH2CH3 Methionine ( abbreviated as Met or M) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH2CH2SCH3 In computation this position is often treated as a twofold degenerate site.

There are three amino acids encoded by six different codons: serine, leucine, arginine. Serine (abbreviated as Ser or S) is an Organic compound with the formula H[[oxygen O]]2 CCH NH sub>2CH2OH Leucine (abbreviated as Leu or L) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH2CH(CH32 Arginine (abbreviated as Arg or R) is an α- Amino acid. The L-form is one of the 20 most common natural amino acids Only two amino acids are specified by a single codon; one of these is the amino-acid methionine, specified by the codon AUG, which also specifies the start of translation; the other is tryptophan, specified by the codon UGG. Methionine ( abbreviated as Met or M) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH2CH2SCH3 Tryptophan (abbreviated as Trp or W) is one of the 20 standard amino acids, as well as an Essential amino acid in the Human diet The degeneracy of the genetic code is what accounts for the existence of silent mutations. Silent mutations are DNA Mutations that do not result in a change to the Amino acid sequence of a Protein.

Degeneracy results because a triplet code designates 20 amino acids and a stop codon. Because there are four bases, triplet codons are required to produce at least 21 different codes. For example, if there were two bases per codon, then only 16 amino acids could be coded for (4²=16). Because at least 21 codes are required, then 4³ gives 64 possible codons, meaning that some degeneracy must exist.

These properties of the genetic code make it more fault-tolerant for point mutations. A point mutation, or single base substitution, is a type of Mutation that causes the replacement of a single base nucleotide with another nucleotide of the genetic For example, in theory, fourfold degenerate codons can tolerate any point mutation at the third position, although codon usage bias restricts this in practice in many organisms; twofold degenerate codons can tolerate one out of the three possible point mutations at the third position. Codon usage bias refers to differences among organisms in the frequency of occurrence of Codons in Protein -coding DNA sequences ( Genes. Since transition mutations (purine to purine or pyrimidine to pyrimidine mutations) are more likely than transversion (purine to pyrimidine or vice-versa) mutations, the equivalence of purines or that of pyrimidines at twofold degenerate sites adds a further fault-tolerance. Not to be confused with the evolutionary concept of a Transitional fossil. In Molecular biology, transversion refers to the substitution of a Purine for a Pyrimidine or vice versa

Grouping of codons by amino acid residue molar volume and hydropathy.

A practical consequence of redundancy is that some errors in the genetic code only cause a silent mutation or an error that would not affect the protein because the hydrophilicity or hydrophobicity is maintained by equivalent substitution of amino acids; for example, a codon of NUN (where N = any nucleotide) tends to code for hydrophobic amino acids. Hydrophile, from the Greek (hydros "water" and φιλια (philia "friendship" refers to a physical property of a Molecule In Chemistry, hydrophobicity (from the combining form of water in Attic Greek hydro- and for fear phobos) refers to the physical property of NCN yields amino acid residues that are small in size and moderate in hydropathy; NAN encodes average size hydrophilic residues; UNN encodes residues that are not hydrophilic. ^{[3] [4]}

Even so, single point mutations can still cause dysfunctional proteins. For example, a mutated hemoglobin gene causes sickle-cell disease. Hemoglobin ( also spelled haemoglobin and abbreviated Hb or Hgb) is the Iron -containing Oxygen -transport Metalloprotein Sickle-cell disease or sickle-cell anaemia (or anemia) is a Blood disorder characterized by Red blood cells that assume an abnormal rigid In the mutant hemoglobin a hydrophilic glutamate (Glu) is substituted by the hydrophobic valine (Val), which reduces the solubility of β-globin. Glutamic acid (abbreviated as Glu or E) is one of the 20 Alpha Amino acids It is not among the human Essential amino acids Its Valine (abbreviated as Val or V) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH(CH32 Beta globulins are a group of Globular proteins in plasma that are more mobile in Alkaline or electrically charged solutions than Gamma globulins In this case, this mutation causes hemoglobin to form linear polymers linked by the hydrophobic interaction between the valine groups causing sickle-cell deformation of erythrocytes. Hemoglobin ( also spelled haemoglobin and abbreviated Hb or Hgb) is the Iron -containing Oxygen -transport Metalloprotein Sickle-cell disease is generally not caused by a de novo mutation. In biology mutations are changes to the Nucleotide sequence of the Genetic material of an organism Rather it is selected for in malarial regions (in a way similar to thalassemia), as heterozygous people have some resistance to the malarial Plasmodium parasite (heterozygote advantage). Malaria is a vector -borne Infectious disease caused by Protozoan Parasites It is widespread in tropical and subtropical regions including Thalassemia (from Greek θαλασσα thalassa sea + αίμα haima blood British spelling "thalassaemia" is an inherited Autosomal recessive Zygosity refers to the genetic condition of a Zygote. In genetics zygosity describes the similarity or dissimilarity of DNA between Homologous A plasmodium is also the macroscopic form of the Protist known as a Slime mould. A heterozygote advantage ( heterozygous advantage) describes the case in which the heterozygote genotype has a higher relative fitness than either the

These variable codes for amino acids are allowed because of modified bases in the first base of the anticodon of the tRNA, and the base-pair formed is called a wobble base pair. Transfer RNA (abbreviated tRNA) is a small RNA (usually about 74-95 nucleotides that transfers a specific Amino acid to a growing polypeptide chain at The modified bases include inosine and the Non-Watson-Crick U-G basepair. Inosine is a Nucleoside that is formed when Hypoxanthine is attached to a Ribose ring (also known as a Ribofuranose) via a β-N9-

Variations to the standard genetic code

While slight variations on the standard code had been predicted earlier,^[5] none were discovered until 1979, when researchers studying human mitochondrial genes discovered they used an alternative code. Mitochondrial genetics is the study of the Genetics of the DNA contained in Mitochondria. Many slight variants have been discovered since,^[6] including various alternative mitochondrial codes,^[7] as well as small variants such as Mycoplasma translating the codon UGA as tryptophan. Mycoplasma is a Genus of bacteria which lack a Cell wall. Without a cell wall they are unaffected by many common Antibiotics such In bacteria and archaea, GUG and UUG are common start codons. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have However, in rare cases, certain specific proteins may use alternative initiation (start) codons not normally used by that species. ^[8]

In certain proteins, non-standard amino acids are substituted for standard stop codons, depending upon associated signal sequences in the messenger RNA: UGA can code for selenocysteine and UAG can code for pyrrolysine as discussed in the relevant articles. Selenocysteine is an Amino acid that is present in several Enzymes (for example Glutathione peroxidases tetraiodothyronine 5' deiodinases Pyrrolysine is a naturally occurring genetically coded Amino acid used by some Methanogenic Archaea in Enzymes that are part of their Methane Selenocysteine is now viewed as the 21st amino acid, and pyrrolysine is viewed as the 22nd. A detailed description of variations in the genetic code can be found at the NCBI web site.

Notwithstanding these differences, all known codes have strong similarities to each other, and the coding mechanism is the same for all organisms: three-base codons, tRNA, ribosomes, reading the code in the same direction and translating the code three letters at a time into sequences of amino acids.

Theories on the origin of the genetic code

Despite the variations that exist, the genetic codes used by all known forms of life on Earth are very similar. Since there are many possible genetic codes that are thought to have similar utility to the one used by Earth life, the theory of evolution suggests that the genetic code was established very early in the history of life, with phylogenetic analysis of transfer RNA suggests that tRNA molecules evolved before the present set of aminoacyl-tRNA synthetases. eVolution is the third Album by eLDee, it was due to be released in 2008 An aminoacyl tRNA synthetase ( aaRS) is an Enzyme that catalyzes the Esterification of a specific Amino acid or its precursor to one of all its compatible ^[9]

The genetic code is not a random assignment of codons to amino acids. ^[10] For example, amino acids that share the same biosynthetic pathway tend to have the same first base in their codons,^[11] and amino acids with similar physical properties tend to have similar codons. ^[12][13]

There are three themes running through the many theories that seek to explain the evolution of the genetic code (and hence the origin of these patterns). ^[14] One is illustrated by recent aptamer experiments which show that some amino acids have a selective chemical affinity for the base triplets that code for them. Aptamers are oligonucleic acid or Peptide molecules that bind a specific target molecule ^[15] This suggests that the current, complex translation mechanism involving tRNA and associated enzymes may be a later development, and that originally, protein sequences were directly templated on base sequences. Transfer RNA (abbreviated tRNA) is a small RNA (usually about 74-95 nucleotides that transfers a specific Amino acid to a growing polypeptide chain at Another is that the standard genetic code that we see today grew from a simpler, earlier code through a process of "biosynthetic expansion". Here the idea is that primordial life 'discovered' new amino acids (e. g. as by-products of metabolism) and later back-incorporated some of these into the machinery of genetic coding. Although much circumstantial evidence has been found to suggest that fewer different amino acids were used in the past than today,^[16] precise and detailed hypotheses about exactly which amino acids entered the code in exactly what order has proved far more controversial. ^[17][18] A third theory is that natural selection has led to codon assignments of the genetic code that minimize the effects of mutations. Natural selection is the process by which favorable Heritable traits become more common in successive Generations of a Population of In biology mutations are changes to the Nucleotide sequence of the Genetic material of an organism ^[19].

References

See also

• Crick, Brenner et al. experiment
• Anticodon
• Protein biosynthesis
• Operon
• Lac operon
• Epigenetic code
• Degenerate bases

Further reading

• Griffiths, Anthony J. The Crick Brenner et al experiment was a Scientific experiment performed in 1961 by Francis Crick and Sydney Brenner. Transfer RNA (abbreviated tRNA) is a small RNA (usually about 74-95 nucleotides that transfers a specific Amino acid to a growing polypeptide chain at Protein biosynthesis (synthesis is the process in which cells build Proteins The term is sometimes used to refer only to protein translation but more An operon is a functioning unit of key Nucleotide sequences including an operator, a common Promoter, and one or more structural Genes, The lac operon is an Operon required for the transport and Metabolism of Lactose in Escherichia coli and some other The epigenetic code is hypothesized to be a defining code in every Eukaryotic cell consisting of the specific Epigenetic modification in each cell Degenerate base symbols in Biochemistry are a IUPAC representation for a position on a DNA sequence that can be have multiple possible alternatives F. ; Miller, Jeffrey H. ; Suzuki, David T. ; Lewontin, Richard C. ; Gelbart, William M. (1999). Introduction to Genetic Analysis (7th ed.). New York: W. H. Freeman & Co. ISBN 0-7167-3771-X
• Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter. (2002). Molecular Biology of the Cell (4th ed.). New York: Garland Publishing. ISBN 0-8153-3218-1
• Lodish, Harvey; Berk, Arnold; Zipursky, S. Lawrence; Matsudaira, Paul; Baltimore, David; Darnell, James E. (1999). Molecular Cell Biology (4th ed.). New York: W. H. Freeman & Co. ISBN 0-7167-3706-X

External links

• The Genetic Codes → Genetic Code Tables
• Online DNA → Amino Acid Converter
• Online DNA Sequence → Protein Sequence converter
• Online DNA to protein translation (6 frames/17+ genetic codes)
• The Codon Usage Database → Codon frequency tables for many organisms