The GNC hypothesis or GNC-SNS primeval genetic code hypothesis refers to a hypothesis about the
origin of genes. It suggests the universal genetic code originated not from a three-amino acid system, but from a four-amino acid system. It is this GNC code encoding
ADVproteins which is the most primitive genetic code. This hypothesis was first proposed by Kenji Ikehara at Nara Women's University.
Details
While almost all of the
organism
In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...
s on Earth share the universal
genetic code
The genetic code is the set of rules used by living cells to translate information encoded within genetic material ( DNA or RNA sequences of nucleotide triplets, or codons) into proteins. Translation is accomplished by the ribosome, which links ...
, in the GNC hypothesis it is argued that two primeval genetic codes preceded the present genetic code as follows:
* First, there emerged
GN
C primeval genetic codes involving 4
codons
The genetic code is the set of rules used by living cells to translate information encoded within genetic material ( DNA or RNA sequences of nucleotide triplets, or codons) into proteins. Translation is accomplished by the ribosome, which links ...
(GGC, GCC, G
AC and G
UC), which code 4 GADV-
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...
s (
glycine
Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid (carbamic acid is unstable), with the chemical formula NH2‐ CH2‐ COOH. Glycine is one of the proteinogeni ...
,
alanine
Alanine (symbol Ala or A), or α-alanine, is an α-amino acid that is used in the biosynthesis of proteins. It contains an amine group and a carboxylic acid group, both attached to the central carbon atom which also carries a methyl group side c ...
,
aspartic acid
Aspartic acid (symbol Asp or D; the ionic form is known as aspartate), is an α-amino acid that is used in the biosynthesis of proteins. Like all other amino acids, it contains an amino group and a carboxylic acid. Its α-amino group is in the pro ...
and
valine
Valine (symbol Val or V) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH3+ form under biological conditions), an α- carboxylic acid group (which is in the deprotonat ...
).
* Second, GNC code evolved to SNS primeval genetic codes involving 16 codons (GGC, GGG, GCC, GCG, GAC, GAG, GUC, GUG, CUC, GUG, CCC, CCG, CAC, CAG, CGC and CGG), which code 10 amino acids (glycine, alanine, aspartic acid, valine,
glutamic acid
Glutamic acid (symbol Glu or E; the ionic form is known as glutamate) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can synt ...
,
leucine
Leucine (symbol Leu or L) is an essential amino acid that is used in the biosynthesis of proteins. Leucine is an α-amino acid, meaning it contains an α-amino group (which is in the protonated −NH3+ form under biological conditions), an α- ca ...
,
proline
Proline (symbol Pro or P) is an organic acid classed as a proteinogenic amino acid (used in the biosynthesis of proteins), although it does not contain the amino group but is rather a secondary amine. The secondary amine nitrogen is in the prot ...
,
histidine
Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated –NH3+ form under biological conditions), a carboxylic acid group (which is in the de ...
,
glutamine
Glutamine (symbol Gln or Q) is an α-amino acid that is used in the biosynthesis of proteins. Its side chain is similar to that of glutamic acid, except the carboxylic acid group is replaced by an amide. It is classified as a charge-neutral, ...
,
arginine
Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) and both the am ...
).
The GNC hypothesis is based on the following facts:
*
Protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s composed of GADV-amino acids coded by GNC primeval genetic code can form four fundamental structures found in proteins in present organisms, namely,
hydrophobic
In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, th ...
and
hydrophilic
A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press.
In contrast, hydrophobes are no ...
structures,
α-helices
The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-helix conformation in which every backbone N−H group hydrogen bonds to the backbone C=O group of the amino acid located four residues ear ...
,
β-sheets
The beta sheet, (β-sheet) (also β-pleated sheet) is a common motif of the regular protein secondary structure. Beta sheets consist of beta strands (β-strands) connected laterally by at least two or three backbone hydrogen bonds, forming a gen ...
, and
turns (or coils).
* Proteins composed of ten amino acids coded by SNS primeval genetic code can form six fundamental structures, namely, hydrophobic and hydrophilic structures, α-helices, β-sheets, turns,
acidic
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
and
basic
BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming languages designed for ease of use. The original version was created by John G. Kemeny and Thomas E. Kurtz at Dartmouth College ...
fragments.
Related literatures
{{Cite journal, first1 = Kenji, last1 = Ikehara, first2 = Yoko, last2 = Omori, first3 = Rieko, last3 = Arai, first4 = Akiko, last4 = Hirose, title = A Novel Theory on the Origin of the Genetic Code: A GNC-SNS Hypothesis, year = 2002, journal = Journal of Molecular Evolution, volume = 54, issue = 4, pages = 530–538, doi = 10.1007/s00239-001-0053-6, pmid=11956691, bibcode = 2002JMolE..54..530I
See also
*
GADV protein world
GADV-protein world is a hypothetical stage of abiogenesis. GADV stands for the one letter codes of four amino acids, namely, glycine (G), alanine (A), aspartic acid (D) and valine (V), the main components of GADV proteins. In the GADV-protein wor ...
Evolution
Genetics