GADV-protein world is a hypothetical stage of

abiogenesis In biology, abiogenesis (from a- 'not' + Greek bios 'life' + genesis 'origin') or the origin of life is the natural process by which life has arisen from non-living matter, such as simple organic compounds. The prevailing scientific hypothes ...

. GADV stands for the one letter codes of four

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 a ...

s, namely,

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 proteinog ...

(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 side ...

(A), aspartic acid (D) 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 deprotona ...

(V), the main components of GADV

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, res ...

s. In the GADV-protein world hypothesis, it is argued that the prebiotic chemistry before the emergence of

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

s involved a stage where GADV-proteins were able to pseudo-replicate. This hypothesis is contrary to the

RNA world The RNA world is a hypothetical stage in the evolutionary history of life on Earth, in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins. The term also refers to the hypothesis that posits the existen ...

hypothesis.

Description

The GADV-protein world hypothesis was first proposed by Kenji Ikehara at

Nara Women's University is a national women's university located in Nara, Nara Prefecture, Japan. It is one of two national women's universities in the country, the other being Ochanomizu University.For more about the legal status of "national universities" in Japan, s ...

. It is supported by GNC-SNS primitive gene code hypothesis (

GNC hypothesis 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 ...

) also formulated by him. In the GNC hypothesis, the origin of the present standard

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 ...

is considered to be the GNC genetic code that includes the codons G GC, G CC, G AC, G UC, respectively coding

, aspartic acid, and

; it also follows the SNS primitive genetic code that codes ten amino acids, where N denotes arbitrary four

RNA base Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides, which, in turn, are components of nucleotides, with all of these monomers constituting the basic b ...

s and S denotes

guanine Guanine () ( symbol G or Gua) is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine (uracil in RNA). In DNA, guanine is paired with cytosine. The guanine nucleoside is c ...

(G) and

cytosine Cytosine () ( symbol C or Cyt) is one of the four nucleobases found in DNA and RNA, along with adenine, guanine, and thymine (uracil in RNA). It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an ...

(C). The GADV hypothesis proposes these mechanisms: * Analysis on present proteins and simulation using chemical factors of amino acid shows GADV-proteins that contains almost the same amount of the four amino acids can form four basic structures of protein, 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, t ...

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 ...

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 ...

and β-sheets. * Therefore, GADV-proteins polymerized from randomly chosen amino acids from the four choices, probably becoming globular and water-soluble like some present proteins. * Proteins generated like this have different

primary structures Primary Structures: Younger American and British Sculptors was an exhibition presented by the Jewish Museum in New York City from April 27 to June 12, 1966. The show was a survey of recent work in sculpture by artists from the Northeast United Sta ...

. However, their simple composition leads to the formation of similar spherical and water-soluble proteins that have bulky and hydrophobic valines inside and hydrophilic aspartic acids outside. * GADV-peptides can polymerize by simple cycles of evaporation and hydration. This gives a rationale for the production of GADV-peptides in

tide pool A tide pool or rock pool is a shallow pool of seawater that forms on the rocky intertidal shore. Many of these pools exist as separate bodies of water only at low tide. Many tide pool habitats are home to especially adaptable animals that ...

s on the

early Earth The early Earth is loosely defined as Earth in its first one billion years, or gigayear (Ga, 109y). The “early Earth” encompasses approximately the first gigayear in the evolution of our planet, from its initial formation in the young Solar Sy ...

. Moreover, GADV-peptides randomly polymerized as above have the catalytic activity to

hydrolyze Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis ...

peptide bonds In organic chemistry, a peptide bond is an amide type of covalent chemical bond linking two consecutive alpha-amino acids from C1 (carbon number one) of one alpha-amino acid and N2 (nitrogen number two) of another, along a peptide or protein cha ...

in bovine

serum albumin Serum albumin, often referred to simply as blood albumin, is an albumin (a type of globular protein) found in vertebrate blood. Human serum albumin is encoded by the ''ALB'' gene. Other mammalian forms, such as bovine serum albumin, are chemica ...

. Therefore, they can catalyze the formation of peptide bonds as the reverse reaction. * GADV-proteins can multiply by pseudo-replication in the absence of genes, considering the features above.

References

Related literatures

* *

External links

Kenji Ikehara's GADV-protein world laboratory
(only in Japanese) {{Origin of life Origin of life Amino acids Prebiotic chemistry

Description

See also

References

Related literatures

External links