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
An organism is any life, living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have be ...
s on Earth share the universal
genetic code
Genetic code is a set of rules used by living cell (biology), cells to Translation (biology), translate information encoded within genetic material (DNA or RNA sequences of nucleotide triplets or codons) into proteins. Translation is accomplished ...
, 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
Genetic code is a 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 pro ...
(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 over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...
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. Glycine is one of the proteinogenic amino acids. It is encoded by all the codons starting with GG (G ...
,
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 sid ...
,
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. The L-isomer of aspartic acid is one of the 22 proteinogenic amino acids, i.e., the building blocks of protei ...
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 deproton ...
).
* 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; known as glutamate in its anionic form) 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 ...
,
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-Car ...
,
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 p ...
,
histidine
Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an Amine, α-amino group (which is in the protonated –NH3+ form under Physiological condition, biological conditions), a carboxylic ...
,
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 guanidinium, guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) a ...
).
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 residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
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 chemical property of a molecule (called a hydrophobe) that is seemingly repelled from a mass of water. In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, thu ...
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 n ...
structures,
α-helices
An alpha helix (or α-helix) is a sequence of amino acids in a protein that are twisted into a coil (a helix).
The alpha helix is the most common structural arrangement in the secondary structure of proteins. It is also the most extreme type of l ...
,
β-sheets, 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
An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen cation, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid.
The first category of acids are the ...
and
basic
Basic or BASIC may refer to:
Science and technology
* BASIC, a computer programming language
* Basic (chemistry), having the properties of a base
* Basic access authentication, in HTTP
Entertainment
* Basic (film), ''Basic'' (film), a 2003 film
...
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
Evolution
Genetics