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A protein is a naturally occurring aliphatic compound, composed of amino acids (aa) and containing primarily at least the elements carbon (C), hydrogen (H), nitrogen (N), and oxygen (O). Many proteins also contain sulfur (S), occasionally phosphorus (P), and sometimes iron (Fe).

In biosynthesis, precursors are activated often by nucleotides, generally in the presence of a catalyst, oxidizing or reducing agent, to interconvert¹ biochemicals within living organisms.

Protein synthesis is the creation of proteins using DNA and RNA. Proteins can often be synthesized directly from genes by translating mRNA. When a protein is harmful and needs to be available on short notice or in large quantities, a protein precursor is produced. A proprotein is an inactive protein containing one or more inhibitory peptides that can be activated when the inhibitory sequence is removed by proteolysis during posttranslational modification. A preprotein is a form that contains a signal sequence (an N-terminal signal peptide) that specifies its insertion into or through membranes; i.e., targets them for secretion.² The signal peptide is cleaved off in the endoplasmic reticulum.². Preproproteins have both sequences (inhibitory and signal) still present.

For synthesis of protein, a succession of tRNA molecules charged with their appropriate amino acids have to be brought together with an mRNA molecule and matched up by base-pairing through their anticodons with each of its successive codons. The amino acids then have to be linked together to extend the growing protein chain, and the tRNAs, relieved of their burdens, have to be released. This whole complex of processes is carried out by a giant multimolecular machine, the ribosome, formed of two main chains of RNA, called ribosomal RNA (rRNA), and more than 50 different proteins. This evolutionarily ancient molecular juggernaut latches onto the end of an mRNA molecule and then trundles along it, capturing loaded tRNA molecules and stitching together the amino acids they carry to form a new protein chain.³

Process

Transcription - Protein synthesis starts in the nucleus, where the DNA is held. DNA structure is two chains of sugars and phosphates joined by pairs of nucleotides deoxyadenosine, deoxyguanosine, thymidine, anddeoxycytidine. Similar to DNA replication, the DNA is "unzipped" by the enzyme helicase, leaving the single nucleotide chain open to be copied. RNA polymerase reads the DNA strand, and synthesizes a single strand of messenger RNA (mRNA). This single strand of mRNA leaves the nucleus through nuclear pores, and migrates into the cytoplasm where it joins with ribosomes.Where protein synthesis occurs by the formation of peptide bonds and poly peptide chains.

• Note: in the new RNA strand, the nucleotide uridine takes the place of thymidine.

Translation - the process of converting the mRNA codon sequences into an amino acid polypeptide chain.

1. Initiation - A ribosome attaches to the mRNA and starts to code at the FMet codon (usually AUG, sometimes GUG or UUG).

2. Elongation - tRNA brings the corresponding amino acid to each codon as the ribosome moves down the mRNA strand.

3. Termination - Reading of the final mRNA codon (aka the STOP codon), which ends the synthesis of the peptide chain and releases it.

References

Biological and artificial methods for creation of proteins differ significantly.

• For biological protein synthesis, see protein biosynthesis
• For artificial protein synthesis, see peptide synthesis

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