Ribosomal Law and Order for Protein Synthesis
How Ribosome Structure Influences and Directs Protein Synthesis
Oct 9, 2009
The 2009 Nobel Prize in Chemistry was awarded for determinations on the detailed atomic structure of the ribosome of prokayotes. These discoveries contributed to a better understanding of how accuracy and precision in protein synthesis is obtained and maintained, and how antibiotics interfere with these processes.
Importance of Amino Acid Sequence and Types
When polypeptides and proteins are synthesized, the order and arrangement of the constituent amino acids are critical. A protein that has the wrong amino acid in a critical position – and almost all positions in a protein are critical – that protein, can be inactivated, or become dysfunctional. Cells need proteins to thrive and survive. Incorrectly aligned amino acids may lead to injury or death of cells and, ultimately, the organism. All this indicates the importance of rigid application of law and order when synthesizing proteins. See here how this protein policing works at those special sites where ribosomes, mRNA and tRNA meet and interact.
The Universal Code of Life and Overview of Protein Coding
DNA---->RNA------>proteins
The DNA of the nucleus directs the synthesis of 3 kinds of RNA:
- mRNA - messenger RNA, contains the instructions for the precise number and order of amino acids and the termination point of synthesis. Codon trios of nucleotides specify each of 20 amino acids, and 3 specific stops or termination-stop signals.
- tRNA - transfer RNA, carries amino acids to the codon trio site, and each tRNA contains an anticodon that matches up with the right codon.
- rRNA - ribosomal RNA complexes with special ribosomal proteins to form the ribosome, composed of 1 small unit and 1 large unit .These 2 unit combine to make the whole ribosome (see photos below).
- polypeptide and proteins peal off when termination signal codes are reached during synthesis.
The Ribosome, How It is Structured and Organized to Control and Police Protein Synthesis
- The paired codons and anti-codons alone do not guarantee amino acid precision. Dr. Venkatraman Ramakrishnan’s research of the small subunit of the ribosome identified a molecular ruler. Nucleotides in the small sub-unit’s rRNA help determine the distance between the codon and the anticodon. Incorrect distances cause the tRNA molecule to fall off the ribosome. Ribosomes double-check these distances, and errors only occur about once per 100, 000 amino acids.
- The large subunit in the ribosome is organized to assist synthesis of new protein and promotes peptide bond formation between amino acids. Almost 20 peptide bonds can be formed every second – a very fast sequencing. Thomas Steitz, of Yale has noted specific ribosome atom sites and sequences of these peptide reactions.
- Knowledge of the bacterial ribosome's specific atomic structure should be useful in the search for new antibiotics. Many antibiotics kill bacteria by blocking ribosomal functions. Since bacteria can become antibiotic resistant, an understanding of the physical and chemical nature of the ribosome and its functions may well help in the design new antibiotics and drugs.
- The 2009 Chemistry Nobel Laureates have shown how different antibiotics bind to the ribosome and interfere with: 1. growing protein channels (this blocks protein release). 2. peptide bond formation. 3. translation of the mRNA.
In the future, synthetic antibiotics will be designed to exploit and target vulnerable sites of bacterial ribosomes. See more about basic ribosome activities and the Nobel Prize for Chemistry in 2009.
Sources
Lodish, H. et al. 2000. Molecular Cell Biology. Fourth Ed., W. H. Freeman and Co., New York, N.Y.
Nobelprize.org. 2009. Chemistry Award for 2009.
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