Protein_synthesis

Protein synthesis is the creation of proteins using DNA and RNA. 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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Stages of Protein Synthesis

Transcription - Protein Synthesis starts off in the nucleus, where the DNA lies. The DNA is structured as a double stranded helix. It is composed of a chain of nucleotides; Adenine, Guanine, Cytosine, and Thymine. Similarly in DNA replication, the DNA unzips. One strand of the DNA is used as a template to create an RNA strand. To create this strand, new complementary nucleotides fit into place by complementary base pairing. RNA polymerase is the enzyme which aids this process among the nucleotides. The nucleotides Adenine always pair with Thymine, and and Cytosine always pair with Guanine.

• Note: in the new RNA strand, Uracil replaces Thymine!

Now the new RNA strand is created. This strand is now called the Messenger RNA (mRNA). Since DNA itself cannot leave the cell, this process of transcription can send out the mRNA.

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

There are 3 steps involved.

1. Initiation. The addition of an active ribosome and the reading of the first mRNA codon (always methionine - AUG. Very rarely, GUG & UUG)

2. Elongation. The amino acid that corresponds to the codon will keep attaching and elongating itself in a chain.

3. Termination. Reading of the final mRNA codon (aka the STOP codon). The completion of polypeptide (chain of amino acids) that now detaches itself.

In more detail: The mRNA strand travels outside of the nucleus into the cytoplasm via nuclear pores. A ribosome then attaches itself onto the mRNA chain and moves along the chain until it\'s in place. Now, a tRNA(found floating in cytoplasm) attaches itself onto the mRNA. The tRNA is made up of an anticodon that corresponds to the codon (3 nucleotides)of mRNA. The other end of the tRNA has an amino acid attached to it based on the codon. The translation now occurs, one reading of codon-anticodon at a time. The corresponding amino acids attach to the next amino acid of the tRNA every codon-anticodon reading. They will start to form a chain. The process can go on after many nucleotides have been translated, until it reads the stop codon. The chain of amino acids (polypeptide) now gets released.

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