Starting translation at the authentic (correct) start codon is essential for translation of the correct polypeptide. Errant translation starting at the wrong codon, or even at the wrong nucleotide of the start codon, may produce an abnormal polypeptide and result in a nonfunctional protein. Compare and contrast the mechanisms used by bacteria and eukaryotes to identify the authentic start codon during translation initiation.

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Explanation:

A codon is a sequence of nucleotide triplets of messenger ribonucleic acids, or deoxyribonucleic acid. The start codon is defined as the first codon of a messenger ribonucleic acid transcript that is being translated by the ribosomes.

The ability to initiate the right AUG codon determines the correctness of translation. In eukaryotes, this is accomplished by scanning mechanism. In the scanning mechanism, the ribosomal subunit attached to the five prime end of the messenger ribonucleic acid and inspects base to base for an AUG using complementarity with the anticodon of methionyl indicator transfer RNA as the key to identifying AUG.

The start codon always code for a modified methionine in bacteria and codes for methionine in eukaryotes. Alternate start codons are found in bacteria and eukaryotes . They are different from standard AUG codon and are initiated by a separate transfer ribonucleic acid. They are rare in eukaryotes but common in bacteria.

The method of identifying the correct codon for transcription is by means of the control STOP codons, which are those that face point mutations of the second, third or first position (the third position is the most imperceptible and usually goes unnoticed) they generate a STOP or stop of the process, causing a premature termination of the translation which causes an incomplete protein to be translated and, in most cases, not functional ... There are also start codons that are those that are in charge of start said process.

The start codon is not only a signal to start the translation, but it is translated effectively, so that, at least before their proteolytic processing, all eukaryotic proteins have a methionine at their amino terminus, which is the amino acid corresponding to the codon according to the genetic code. In prokaryotes, said methionine is modified as N-formylmethionine. This does not mean that all the components of the proteome possess said methionine at its end, since it is common for it to be enzymatically cleaved

Explanation:

Although AUG is the most widely used start codon in eukaryotes, there are other codons that are also valid as the start of translation. Such exceptions are much more common in prokaryotes, where GUG and UUG can be used as alternative translation start codons. For example, Escherichia coli, a bacterium in the Enterobacteriaceae family, uses ATG (AUG in RNA) in 83% of cases, GTG in 14% (GUG in the transcript) and TTG in 3% (UUG in RNA) and still someone else.

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light dependent reactions:

light independent reactions:

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