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Protein biosynthesis

Protein biosynthesis is the process in which cells build protein. The term is sometimes used to refer only to protein translation, but more often it refers to a multi-step process, beginning with transcription and ending with translation:

Table of contents
1 Transcription
2 Translation
3 Events following biosynthesis
4 External link

Transcription

Transcription only desires one side of the DNA double helix. This strand is called the coding strand. The transcription starts with initiation. RNA polymerase, an enzyme, binds to a specific region on the DNA, marking the starting point, called the promoter. As the RNA polymerase binds on to the promoter, the DNA strands are beginning to unwind.

As the RNA polymerase travels through the strand that is opposite to the coding strand (the cell wants copy of the coding strand, so it needs to copy that from the DNA that is opposite of the coding strand), it matches corresponding mRNA nucleotides to the DNA. The mRNA is elongated as the polymerase proceeds. This process is known as elongation.

As the polymerase reaches the termination, modifications are required for the newly transcribed mRNA to be able to travel to the other parts of the cell, including cytoplasm and ER. A 5 cap is added to the mRNA to protect is from degradation. A poly-A tail is added on the 3 end as a protection and template for further process.

Translation

During translation, the message of mRNA is decoded to make proteins. Translation includes initiation, elongation, translocation, and termination.

Initiation and elongation occur when the ribosome recognizes the starting codon on the mRNA strand and binds to it. The ribosome has sites, which allow another enzyme, tRNA to bind to the mRNA. On tRNA, there is an anticodon that is used to match the codon on the mRNA. tRNA also has a single unit of amino acid attaches to it.

As the ribosome travels down the mRNA one codon at a time, another tRNA is attached to the mRNA at one of the ribosome site. The first tRNA is released, but the amino acid that is attached to the first tRNA is now moved to the second tRNA, and binds to its amino acid. This translocation continues on, and a long chain of amino acid (protein), is formed.

When the entire unit reaches the end codon on the mRNA, it falls apart and a newly form protein is released. This is the termination.

It is important to know that during this process, many enzymes are used to either assist or facilitate the whole procedure.

Events following biosynthesis

During and after its synthesis, a polypeptide chain begins to coil and fold spontaneously and sometimes with the assistance of chaperone proteins to assume secondary and tertiary structure.

Post-translational modification may involve the formation of disulfide bridges and attachment of any of a number of biochemical functional groups, such as acetate, phosphate or various lipids or carbohydrates. Enzymes may also remove one or more amino acids from the leading (amino) end of the polypeptide chain, leacing a protein made up by two polypeptide chains connected by disulfide bonds. In other cases, two or more polypeptides that are synthesized separately may join to become subunits of a protein with quaternary structure.

See also: Gene expression -- genetics -- biochemistry

External link