The Cell's Protein Factory in Action
Emily Carlson, National Institutes of Health | December 11, 2013 07:50am ET
What looks like a jumble of rubber bands and twisty ties is the ribosome, the cellular protein factory. The ribosome is made up of proteins and strands of RNA, a chemical relative of DNA. It has two interlocked parts that behave as a single molecular machine to assemble all of the cell's protein molecules. Some 30,000 different types of proteins enable us to think, move, eat, play and do so much more.
Because the ribosome is central to so many cellular activities in all life forms, it's the target of many drugs, including antibiotics. For example, some antibiotics block bacterial ribosomes — and thus the microorganisms' ability to make the proteins they need to function. A challenge in developing antibiotics is targeting the ribosomes of only the harmful bacteria, not our own ribosomes or those of beneficial bacteria living on and in our bodies.
Since each of our cells has about 10 billion proteins, making them is a 24/7 job. To build proteins, the ribosome's two halves — in the image, blue and purple — ratchet along a chain of messenger RNA (mRNA), reading its genetic instructions and, along the way, adding protein building blocks called amino acids with the help of transfer RNA (tRNA). Once the amino acids are in the right order, the proteins are essentially complete and released into the cell. In bacteria, ribosomes can stitch together 20 amino acids in 1 second.
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http://www.livescience.com/41863-ribosomes-protein-factory-nigms.html
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The rate of protein synthesis is about seven and fifteen amino acids per second, in the eukaryotic and the bacterial ribosome, respectively. Hence, a few minutes is required to synthesize a polypeptide of an average length. This is much longer than the time needed for the hydrophobic collapse (folding) to take place. So a polypeptide gets enough time to form its local secondary to tertiary structures cotranslationally and put such segments in proper order while in association with the ribosome, unless something prevents its entire length from folding. As reported earlier, ribosomes from prokaryotes, eukaryotes, and mitochondria act as molds for protein folding, and each mold has a set of recognition sites for all proteins.
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http://onlinelibrary.wiley.com/doi/10.1002/ijch.201000004/full
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hemoglobin
 It selected 4: an ingenious device with 574 components, including 4 magnetised platforms to capture oxygen and enable it to be distributed equally within a liquid, which is otherwise an impossible task. 280 million of these precisely manufactured devices are inside every red blood cell. There are about 5.5 trillion red blood cells in a litre of blood, meaning the total number of hemoglobin assemblies in the body can be more than 9 followed by 21 zeroes (roughly equivalent to the number of stars in the universe). Interestingly, the number of oxygen molecules taken in with each breath is also about this figure!
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