Anticodon- Definition, Principle, Functions, Examples

What is Anticodon?

Anticodonis a trinucleotide sequence present on one arm of the tRNA (transfer RNA) which is complementary to the sequence or codon present on mRNA (messenger RNA).

• The anticodon sequence is present on the anticodon loop of the tRNA and is involved in the process of translation.
• Theamino acidbinds to the 3` adenosine end of the tRNA which yields an aminoacyl tRNA.

AnticodonPrinciple

• The arrangement of mRNA and tRNA is antiparallel.
• The first base of the codon on mRNA (5` to 3`) binds with the third base of anticodon on the tRNA to initiate the翻译过程.

• 每个tRNA都带有特定的氨基酸，并结合原核生物中30S亚基的mRNA互补密码子和真核生物中的40S亚基。
• During this process the first anticodon is accepted by the A site, then it binds to the P site on mRNA where the growing polypeptide of the protein is held together.
• Once the amino acid carried by the tRNA is transferred the anticodon moves 3 nucleotides further to the E site (Exit).
• If it is considered that perfect paring occurs between codon and anticodon, then unique tRNA will be required for every amino acid.
• However, this is not the case. Some tRNAs include anucleotideinosinate（i）包含一个不常见的碱，称为“低黄嘌呤”。

• This inosinate can form hydrogen bonds with three different nucleotides – U, C and, A.
• inosinate与这些核苷酸结合较弱hydrogen bondsleading to weaker pairings as compared to the normal pairings between the nucleotides.
• As some tRNAs include this different nucleotide approximately 32 tRNAs can code for 61 amino acids.
• This imperfect pairing of inosinate with other nucleotides is known as theWobble hypothesis其中两个核苷酸之间有完美的配对，但第三个核苷酸之间不完美或弱配对。

AnticodonFunctions

• An anticodon is responsible for the process of translation in which a protein polypeptide is formed.
• An anticodon determines the amino acid specificity.
• 反od子负责翻译过程的启动和终止。
• The first anticodon in prokaryotes and eukaryotes is UAC which binds to the sequence AUG on the mRNA.
• The initiator anticodon of the tRNA binds with a complementary codon on mRNA which adds the first amino acid of the protein polypeptide. The first amino acid in prokaryotes is N-formyl-methionine, whereas the one in eukaryotes is unmodified methionine.
• 由于tRNA反密码子负责翻译过程的启动，因此它也负责翻译的终止。
• 当tRNA上的反密码子是AUU，AUC和ACU时，可以实现这三个序列终止之一。

AnticodonExamples

基于与氨基酸代码的密码子的遗传密码，可能的二刺激物可能如下：

• The anticodons for amino acid Phenylalanine are – AAA, AAG
• 氨基酸亮氨酸的反火成岩是AAU，AAC，GAA，GAG，GAU，GAC
• The anticodons for amino acid Isoleucine are – UAA, UAG, UAU
• The anticodon for amino acid Methionine is – UAC
• The anticodons for amino acid Valine are – CAA, CAG, CAU, CAC
• The anticodons for amino acid Serine are – AGA, AGG, AGU, AGC, UCA, UCG
• 氨基酸脯氨酸的反火成岩是 - GGA，GGG，GGU，GGC
• The anticodons for amino acid Threonine are – UGA, UGG, UGU, UGC
• The anticodons for amino acid Alanine are – CGA, CGG, CGU, CGC
• The anticodons for amino acid Tyrosine – AUA, AUG
• 氨基酸组氨酸的反火成岩是GUA，GUG
• 氨基酸谷氨酰胺的盘子是 - GUU，GUC
• The anticodons for amino acid Asparagine are – UUA, UUG
• 氨基酸赖氨酸的反火成岩是UUU，UUC
• The anticodons for amino acid aspartic acid are – CUA, CUG
• The anticodons for amino acid Glutamine acid are – CUU, CUC
• The anticodons for amino acid Cysteine are- ACA, ACG
• The anticodons for amino acid Tryptophan are – AGU, ACC
• 氨基酸精氨酸的反火成岩是 - GCA，GCG，GCU，GCC，GCC，UCU，UCC
• 氨基酸甘氨酸的反火成岩是CCA，CCG，CCU，CCC

参考

1. Cell_ A Molecular Approach, Fourth Edition, The – Geoffrey M. Cooper & Robert E. Hausman.
2. Lehninger Principles of Biochemistry – 6th ed- c2013.
3. Cell Biology，T Devasena，牛津大学出版社。