The procedure is used when a woman with genetically defective mitochondria wishes to procreate and produce offspring with healthy mitochondria. The need to develop formal guidelines for human gene For example, our (vertebrate) mitochondrial code is different from the one yeast uses. Every sequence can, thus, be read in its 5' 3' direction in three reading frames, each producing a possibly distinct amino acid sequence: in the given example, Lys (K)-Trp (W)-Thr (T), Asn (N)-Glu (E), or Met (M)-Asn (N), respectively (when translating with the vertebrate mitochondrial code). Find the intersecting box of A row and C column in the table. [63][64][65] Because viruses must use the same genetic code as their hosts, modifications to the standard genetic code could interfere with viral protein synthesis or functioning. Surprisingly, variations in the interpretation of the genetic code exist also in human nuclear-encoded genes: In 2016, researchers studying the translation of malate dehydrogenase found that in about 4% of the mRNAs encoding this enzyme the stop codon is naturally used to encode the amino acids tryptophan and arginine. 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 proteinogenic amino acids in an order specified by messenger RNA (mRNA), using transfer RNA (tRNA) molecules to carry amino acids and to read [36][37], Missense mutations and nonsense mutations are examples of point mutations that can cause genetic diseases such as sickle-cell disease and thalassemia respectively. [8], Across all organisms, there are six main genome types found in mitochondrial genomes, classified by their structure (i.e. Endosymbiotic gene transfer, the process by which genes that were coded in the mitochondrial genome are transferred to the cell's main genome, likely explains why more complex organisms such as humans have smaller mitochondrial genomes than simpler organisms such as protists. The histone code is a hypothesis that the transcription of genetic information encoded in DNA is in part regulated by chemical modifications (known as histone marks) to histone proteins, primarily on their unstructured ends. [56] Both selenocysteine and pyrrolysine may be present in the same organism. In 1999 it was reported that paternal sperm mitochondria (containing mtDNA) are marked with ubiquitin to select them for later destruction inside the embryo. The mRNA below can be translated into three totally different orders of amino acids, depending on the frame in which its read. If the codons are changed, the amino acids and thus the proteins that are synthesized will not be the ones coded for in the original gene sequence. A ketogenic amino acid is an amino acid that can be degraded directly into acetyl-CoA, which is the precursor of ketone bodies and myelin, particularly during early childhood, when the developing brain requires high rates of myelin synthesis. She has taught science courses at the high school, college, and graduate levels. [2] Seven out of the nine possible single-nucleotide substitutions at the AUG start codon of dihydrofolate reductase are functional as translation start sites in mammalian cells. Later during evolution, this matching was gradually replaced with matching by aminoacyl-tRNA synthetases. For example, lets say you know the sequence of one DNA strand that is as follows:DNA (coding strand): 5-TTG ACG ACA AGC TGT TTC-3Using the complementary base pairing rules, you can conclude that the complementary strand is:DNA (template strand): 3-AAC TGC TGT TCG ACA AAG-5RNA strands are also complimentary with the exception that RNA uses U instead of T. Therefore, you can also infer the mRNA strand that would be produced from the first DNA strand. The genetic code is a code for proteins made within cells. How do our cells know which of these proteins to make? Under this hypothesis, any model for the emergence of the genetic code is intimately related to a model of the transfer from ribozymes (RNA enzymes) to proteins as the principal enzymes in cells. A codon table can be used to translate a genetic code into a sequence of amino acids. In 2021, the largest, UK Biobank-based, genome-wide association study of mitochondrial DNA unveiled 260 new associations with phenotypes including lifespan and disease risks for e.g. A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds.They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA and RNA.Dictated by specific hydrogen bonding patterns, "WatsonCrick" (or "WatsonCrickFranklin") base pairs That scheme is often referred to as the canonical or standard genetic code, or simply the genetic code, though variant codes (such as in mitochondria) exist. AJOG's Editors have active research programs and, on occasion, publish work in the Journal. On the other hand, the substitution rate of mt-proteins is very low, thus amino acid changes accumulate slowly (with corresponding slow changes at 1st and 2nd codon positions) and thus they provide information about the genetic distances of distantly related species. ThoughtCo, Aug. 26, 2020, thoughtco.com/table-of-mrna-codons-genetic-code-603871. The copy from DNA to RNA is simple: following the complementary base pairing rule. The 20% discount cannot be combined with an additional "% off your total purchase" offer running at the same time. VIII", "Establishing the Triplet Nature of the Genetic Code", https://en.wikipedia.org/w/index.php?title=DNA_and_RNA_codon_tables&oldid=1119137944, Creative Commons Attribution-ShareAlike License 3.0, As of Nov. 18, 2016: absent from the NCBI update. Nevertheless, changes in the first position of the codons are more important than changes in the second position on a global scale. RNA contains the nucleotides adenine, guanine, cytosine and uracil (U). Genome types 4 and 6 each range from 1200 kbp in size. [19] The other two stop codons were named "ochre" and "opal" in order to keep the "color names" theme. Three other triplets (UAA, UAG, and UGA) are stop sequences. Mutations cause changes in the genetic code that lead to genetic variation and a variety of effects. Experimental evidence indicates the genetic code is. Male mitochondrial DNA inheritance has been discovered in Plymouth Rock chickens. )", "Ban on scientists trying to create three-parent baby", "First 'three person baby' born using new method", "Is there more to aging than mitochondrial DNA and reactive oxygen species? The impetus of the membership remains research-based academic surgery, and to promote the shared vision of research and academic pursuits through the exchange of ideas between senior surgical residents, junior faculty and established academic When the number of amino acids adds up (usually > 30 units) and the polypeptide chain folds into a 3D structure, we call it a protein. For example, UGA can code for selenocysteine and UAG can code for pyrrolysine. During transcription, the tRNAs acquire their characteristic L-shape that gets recognized and cleaved by specific enzymes. Find the A on the axis of the left side, which refers to the first letter of the codon triplet. Several arthropods translate the codon AGG as lysine instead of serine (as in the invertebrate mitochondrial genetic code) or arginine (as in the standard genetic code) (Abascal et al., 2006). mtDNA is conserved across eukaryotic organism given the critical role of mitochondria in cellular respiration. type 2 diabetes.[117][118]. Another standard codon table, wheel view, with each amino acid and amino acid class highlighted. [8]In Fungi, however, there is no single gene shared among all mitogenomes. Certain proteins called transcription factors unwind the DNA strand and allow the enzyme RNA polymerase to transcribe only a single strand of DNA into a single stranded RNA polymer called messenger RNA (mRNA). The experiment at the time supported Alexander Oparin's and J. DNA consists of the four nucleotide bases: adenine (A), guanine (G), cytosine (C) and thymine (T). [88] Thus oxidative damage to mtDNA of motor neurons may be a significant factor in the etiology of ALS. Reading the table, if uracil (U) is in the first codon position, adenine (A) in the second, and cytosine (C) in the third, the codon UAC specifies the amino acid tyrosine. Two more recent studies have independently shown that 17 or more non-AUG start codons may initiate translation in E. Amino acids are linked together to form proteins. [50][51] Note in the table, below, eight amino acids are not affected at all by mutations at the third position of the codon, whereas in the figure above, a mutation at the second position is likely to cause a radical change in the physicochemical properties of the encoded amino acid. RNA contains the nucleotides adenine, guanine, cytosine and uracil (U). In addition, higher breakpoint densities were consistently observed within GC-skewed regions and in the close vicinity of the degenerate sequence motif YMMYMNNMMHM.[94]. Helmenstine, Anne Marie, Ph.D. "Table of mRNA Codons and Properties of the Genetic Code." More than half of all human mRNAs have at least one AUG codon upstream (uAUG) of their annotated translation initiation starts (TIS) (58% in the current versions of the human RefSeq sequence). Editor/authors are masked to the peer review process and editorial decision-making of their own work and are not able to access this work in the online manuscript submission system. [13], In many unicellular organisms (e.g., the ciliate Tetrahymena and the green alga Chlamydomonas reinhardtii), and in rare cases also in multicellular organisms (e.g. References for the image are found in Wikimedia Commons page at: Fllen G, Youvan DC (1994). Amino acids that share the same biosynthetic pathway tend to have the same first base in their codons. [79] Extensive research is being conducted to further investigate this link and methods to combat aging. The main points related to genetic code are given below: ADVERTISEMENTS: 1. Because the translation only begins at the start codon (AUG) and continues in successive groups of three, the position of the start codon ensures that the mRNA is read in the correct frame (in the example above, in Frame 3). Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. From a gene to a protein, there are two steps, transcription and translation. [4][5], Candida albicans uses a CAG start codon. AJOG's Editors have active research programs and, on occasion, publish work in the Journal. However, naturally occurring non-AUG start codons have been reported for some cellular mRNAs. The within-cell and between-cell distributions of heteroplasmy dictate the onset and severity of disease[68] and are influenced by complicated stochastic processes within the cell and during development. The standard genetic code is traditionally represented as an RNA codon table, because when proteins are made in a cell by ribosomes, it is messenger RNA (mRNA) that directs protein synthesis. Table of mRNA Codons and Properties of the Genetic Code. Moreover, nuclear DNA genes involved in aerobic respiration and in mitochondrial DNA replication and transcription were either absent or present only as pseudogenes. The genetic code is often summarized in a codon chart (or codon table), where codons are translated to amino acids. A gene mutationis an alteration in the sequence of nucleotides in DNA. Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. [17][18] For example, in 1981, it was discovered that the use of codons AUA, UGA, AGA and AGG by the coding system in mammalian mitochondria differed from the universal code. High blood pressure is common, affecting 1 in 3 people in the U.S. We discuss natural ways to reduce blood pressure, including diet, exercise, and supplements. Optimality: the genetic code continued to evolve after its initial creation, so that the current code maximizes some, Chemical principles govern specific RNA interaction with amino acids. You may also notice that all ACU, ACC, ACA, and ACG encode the same amino acid. Moreover, different species have their own versions of mitochondrial codes. There is more than one code for most amino acids. The heavy strand is rich in guanine and encodes 12 subunits of the oxidative phosphorylation system, two ribosomal RNAs (12S and 16S), and 14 transfer RNAs (tRNAs). (Y-chromosomal DNA, paternally inherited, is used in an analogous way to determine the patrilineal history.) Anabolic steroids, also known more properly as anabolicandrogenic steroids (AAS), are steroidal androgens that include natural androgens like testosterone as well as synthetic androgens that are structurally related and have similar effects to testosterone. Error rates are typically 1 error in every 10100million basesdue to the "proofreading" ability of DNA polymerases. In eukaryotes, ORFs in exons are often interrupted by introns. The genetic code is degenerate, which means there is more than one triplet code for many of the amino acids. Genetic coding. Anabolic steroids, also known more properly as anabolicandrogenic steroids (AAS), are steroidal androgens that include natural androgens like testosterone as well as synthetic androgens that are structurally related and have similar effects to testosterone. [43], Although most mutations that change protein sequences are harmful or neutral, some mutations have benefits. The first tablethe standard tablecan be used to translate nucleotide triplets into the corresponding amino acid or appropriate signal if it is a start or stop codon. DNA is translated into RNA. Mutations are the major cause of cancers and many genetic disorders.Even a single base pair altered (called point mutation) can cause a significant consequence. In the cells of extant organisms, the vast majority of the proteins present in the mitochondria (numbering approximately 1500 different types in mammals) are coded for by nuclear DNA, but the genes for some, if not most, of them are thought to have originally been of bacterial origin, having since been transferred to the eukaryotic nucleus during evolution. Any of the four nucleotides in RNA may occupy one of three possible codon positions. It is fully viable and grows 1.6 slower than its wild-type counterpart "MDS42".[29][30]. Some plant species have enormous mitochondrial genomes, with Silene conica mtDNA containing as many as 11,300,000 base pairs. [23], First codon of a messenger RNA transcript translated by a ribosome, Brenner S. A Life in Science (2001) Published by Biomed Central Limited, "Dual functions of codons in the genetic code", "Identification of evolutionarily conserved non-AUG-initiated N-terminal extensions in human coding sequences", "Translation initiation at non-AUG triplets in mammalian cells", "Molecular biology. [7], E. coli uses 83% AUG (3542/4284), 14% (612) GUG, 3% (103) UUG[8] and one or two others (e.g., an AUU and possibly a CUG). This is the first multicellular organism known to have this absence of aerobic respiration and lives completely free of oxygen dependency.[17][18]. Specifically, documented occurrences exist for mice,[46][47] where the male-inherited mitochondria were subsequently rejected. If you are not familiar with mitochondria, click here to learn more about mitochondria.The mitochondrial code is slightly different from the standard genetic code. The 20% discount cannot be combined with an additional "% off your total purchase" offer running at the same time. To receive the 20% discount enter Coupon Code PICKUP20 at checkout. [2] Soviet-American physicist George Gamow was the first to give a workable scheme for protein synthesis from DNA. For example, although codons GAA and GAG both specify glutamic acid (redundancy), neither specifies another amino acid (no ambiguity). Three bases (combinations of adenine, uracil, guanine, and cytosine) code for an amino acid. High blood pressure is common, affecting 1 in 3 people in the U.S. We discuss natural ways to reduce blood pressure, including diet, exercise, and supplements. Nirenberg did so in a test tube of cytoplasm from burst. With the mitochondrial RNA processing, individual mRNA, rRNA, and tRNA sequences are released from the primary transcript. In order to understand these secret messages, we would need to know the code and apply the same set of rules, in reverse, to decode it. ; A similar level of deficiency of factor VIII or IX results in clinically indistinguishable disease because the [34] Among the 12 tissues examined the highest level of expression was observed in heart, followed by brain and steroidogenic tissue samples. Efforts to understand how proteins are encoded began after DNA's structure was discovered in 1953. Ala: Alanine Arg:ArginineAsn:AsparagineAsp: Aspartic acid, Cys: CysteineGlu:Glutamic acidGln:GlutamineGly:Glycine, His:HistidineIle:IsoleucineLeu:LeucineLys:Lysine, Met:MethioninePhe: Phenylalanine Pro:ProlineSer:Serine, Thr:ThreonineTrp:TryptophanTyr:TyrosineVal: Valine. [64] Moreover, mitochondria evolved a unique mechanism which maintains mtDNA integrity through degradation of excessively damaged genomes followed by replication of intact/repaired mtDNA. [41] These mutations may impair the protein's function and are thus rare in in vivo protein-coding sequences. Only 22 alpha amino acids appear in the genetic code.. Amino acids can be classified according to the locations of the core structural functional groups, as DNA is translated into RNA. : codon 3mRNA DNA31 [76] Once, there was thought to be a positive feedback loop at work (a 'Vicious Cycle'); as mitochondrial DNA accumulates genetic damage caused by free radicals, the mitochondria lose function and leak free radicals into the cytosol. [38][39][40] Clinically important missense mutations generally change the properties of the coded amino acid residue among basic, acidic, polar or non-polar states, whereas nonsense mutations result in a stop codon. The first type is a circular genome that has introns (type 2) and may range from 19 to 1000 kbp in length. Leder and Nirenberg were able to determine the sequences of 54 out of 64 codons in their experiments. have published studies tracing the matrilineal descent of domestic dogs from wolves. When close to the 3' end they act as terminators while in internal positions they either code for amino acids as in Condylostoma magnum[71] or trigger ribosomal frameshifting as in Euplotes. This is the RNA world hypothesis. The prefix has the following meaning: map Arginine and proline metabolism 00340 M Histidine metabolism 00350 M N Tyrosine metabolism Genetic Information Processing 2.1 Transcription. Mutations (changes in DNA sequences) may derail the genetic information and cause cells to make the wrong proteins. DNA to protein translation (6 frames/17 genetic codes) Tablas del cdigo gentico The Genetic Codes Genetic Code Tables; Revisiones Niremberg y Khorana, los hackers del ADN Archivado el 20 de agosto de 2011 en Wayback Machine., en el Museo Virtual Interactivo sobre la Gentica y As an example for addressing stop codon evolution, it has been suggested that the stop codons are such that they are most likely to terminate translation early in the case of a, This page was last edited on 20 October 2022, at 16:02. "[5], In 1954, Gamow created an informal scientific organisation the RNA Tie Club, as suggested by Watson, for scientists of different persuasions who were interested in how proteins were synthesised from genes. Together with similar modifications such as DNA methylation it is part of the epigenetic code. [61] Also, naked mole rats, rodents about the size of mice, live about eight times longer than mice despite having reduced, compared to mice, antioxidant defenses and increased oxidative damage to biomolecules. ; A similar level of deficiency of factor VIII or IX results in clinically indistinguishable disease because the The three consecutive DNA bases, called nucleotide triplets or codons, are, Alternative codons in other translation tables, Each stop codon has a specific name: UAG is, The major difference between DNA and RNA is that, International Union of Pure and Applied Chemistry, Mold, protozoan, and coelenterate mitochondrial + Mycoplasma / Spiroplasma, Candidate division SR1 and Gracilibacteria, "Molecular Mechanism of Scanning and Start Codon Selection in Eukaryotes", "Generation of protein isoform diversity by alternative initiation of translation at non-AUG codons", "The Information in DNA Determines Cellular Function via Translation", "The genome of bacteriophage T4: an archeological dig", "Abbreviations and Symbols for Nucleic Acids, Polynucleotides and Their Constituents", "Evolutionary changes in the genetic code", "Recent evidence for evolution of the genetic code", "Case for the genetic code as a triplet of triplets", "Synthetic polynucleotides and the amino acid code. Mutations of mitochondrial DNA can lead to a number of illnesses including exercise intolerance and KearnsSayre syndrome (KSS), which causes a person to lose full function of heart, eye, and muscle movements. [58], An IVF technique known as mitochondrial donation or mitochondrial replacement therapy (MRT) results in offspring containing mtDNA from a donor female, and nuclear DNA from the mother and father. ", "Mathematica function for # possible arrangements of items in bins? The key discoverers, English biophysicist Francis Crick and American biologist James Watson, working together at the Cavendish Laboratory of the University of Cambridge, hypothesied that information flows from DNA and that there is a link between DNA and proteins. [67] Particularly in the context of disease, the proportion of mutant mtDNA molecules in a cell is termed heteroplasmy. Codons in an mRNA are read by a ribosome during translation. 714-X (PDQ): Integrative, alternative, and complementary therapies - Health Professional Information [NCI] The mitochondrial code is slightly different from the standard genetic code. Some ciliates, such as Paramecium bursaria, use unusual genetic code.Another exception is mitochondrial DNA. The start codon always codes for methionine in eukaryotes and Archaea and a N-formylmethionine (fMet) in bacteria, mitochondria and plastids. If amino acids were randomly assigned to triplet codons, there would be 1.51084 possible genetic codes. The start codon is the first codon of a messenger RNA (mRNA) transcript translated by a ribosome.The start codon always codes for methionine in eukaryotes and Archaea and a N-formylmethionine in bacteria, mitochondria and plastids.The most common start codon is AUG (i.e., ATG in the corresponding DNA sequence). First, environmental factors such as chemicals, radiation, and ultraviolet light from the sun can cause mutations. In the mid-1950s, physicist George Gamow predicted that the genetic code is likely composed of triplets of nucleotides because the possible combination of duplet is not enough (44 = 16), and that of quadruplet is too many (4x4x4x4 = 256), to cover 20 kinds of amino acids.The actual experiments to pinpoint the genetic code began in 1961 by American biochemist Marshall Nirenberg. Learn About Nucleic Acids and Their Function, Translation: Making Protein Synthesis Possible, DNA Definition: Shape, Replication, and Mutation, Amino Acids: Structure, Groups and Function, Har Gobind Khorana: Nucleic Acid Synthesis and Synthetic Gene Pioneer. Using various copolymers most of the remaining codons were then determined. So, altogether mtDNA encodes for two rRNAs, 22 tRNAs, and 13 protein subunits, all of which are involved in the oxidative phosphorylation process. [29][30], Between most (but not all) protein-coding regions, tRNAs are present (see the human mitochondrial genome map). [In this image] The examples of showing the consequence of missense mutation and nonsense mutation.Photo credit: NIH. The development of a new genetic tool to selectively deplete or modify group 2 innate lymphoid cells (ILC2s) addresses the debate regarding the non-redundant functions of this immune cell type. A codon table can be used to translate a genetic code into a sequence of amino acids. GUG may possibly function as an initiator in Drosophila (Clary and Wolstenholme, 1985; Gadaleta et al., 1988). Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). The prefix has the following meaning: map Arginine and proline metabolism 00340 M Histidine metabolism 00350 M N Tyrosine metabolism Genetic Information Processing 2.1 Transcription. [34], As demonstrated by the effect of the trophic hormone ACTH on adrenal cortex cells, the expression of the mitochondrial genes may be strongly regulated by external factors, apparently to enhance the synthesis of mitochondrial proteins necessary for energy production. [86] Mutant huntingtin protein promotes oxidative damage to mtDNA, as well as nuclear DNA, that may contribute to Huntingtons disease pathology.[87]. Genome-wide association studies can reveal associations of mtDNA genes and their mutations with phenotypes including lifespan and disease risks. Altering nucleotide sequences most often results in non-functioning proteins. [42] Frameshift mutations may result in severe genetic diseases such as TaySachs disease. Selenocysteine came to be seen as the 21st amino acid, and pyrrolysine as the 22nd. When RNA polymerase transcribes the DNA, guanine pairs with cytosine and adenine pairs with uracil. Many models belong to one of them or to a hybrid:[88], Hypotheses have addressed a variety of scenarios:[92], Rules by which information encoded within genetic material is translated into proteins, "Codon" redirects here. For other uses, see, Expanded genetic codes (synthetic biology). Because of this and because the mutation rate of animal mtDNA is higher than that of nuclear DNA,[95] mtDNA is a powerful tool for tracking ancestry through females (matrilineage) and has been used in this role to track the ancestry of many species back hundreds of generations. The genetic code is the code our body uses to convert the instructions contained in our DNA the essential materials of life. In a broad academic audience, the concept of the evolution of the genetic code from the original and ambiguous genetic code to a well-defined ("frozen") code with the repertoire of 20 (+2) canonical amino acids is widely accepted. [27] In contrast, the cells of the inner cell mass restrict mtDNA replication until they receive the signals to differentiate to specific cell types. This is an essential part of the translation process, and it is surprising how few errors of translation occur. [13] They thereby deduced that the codon UUU specified the amino acid phenylalanine. ThoughtCo. Editor/authors are masked to the peer review process and editorial decision-making of their own work and are not able to access this work in the online manuscript submission system. DNA to protein translation (6 frames/17 genetic codes) Tablas del cdigo gentico The Genetic Codes Genetic Code Tables; Revisiones Niremberg y Khorana, los hackers del ADN Archivado el 20 de agosto de 2011 en Wayback Machine., en el Museo Virtual Interactivo sobre la Gentica y In addition, UGA and AUA change from stop codon and Isoleucine (Ile) to Methionine (Met) and Tryptophan (Trp), respectively, in mitochondria.The same situation also happens in the plants chloroplast and plastid codes. They used a cell-free system to translate a poly-uracil RNA sequence (i.e., UUUUU) and discovered that the polypeptide that they had synthesized consisted of only the amino acid phenylalanine. [66] In bacteria and archaea, GUG and UUG are common start codons. [55] Unlike selenocysteine, pyrrolysine-encoded UAG is translated with the participation of a dedicated aminoacyl-tRNA synthetase. The smallest mitochondrial genome sequenced to date is the 5,967 bp mtDNA of the parasite Plasmodium falciparum.[23][24]. mtDNA can be used to estimate the relationship between both closely related and distantly related species. Gene mutations can be generally categorized into two types: point mutations and base-pair insertions or deletions. There are three different mitochondrial genome types found in plants and fungi. However, it is now agreed that the genetic code evolves,[18] resulting in discrepancies in how a codon is translated depending on the genetic source. The genetic code is the sequence of nucleotide bases in nucleic acids (DNA and RNA) that code for amino acid chains in proteins. It has also been found in sheep,[48] and in cloned cattle. For example, changing from UCU to UGU will turn Serine (Ser) to Cysteine (Cys). The other 15 amino acids are coded by two, three, and four triplets. The mtDNA GC% and resting metabolic rate explain the differences in animal species maximum life spans in a multiplicative manner (i.e., species maximum life span = their mtDNA GC% * metabolic rate). [1], Alternate start codons (non-AUG) are very rare in eukaryotic genomes. https://www.thoughtco.com/genetic-code-373449 (accessed November 4, 2022).