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Proteins and Genes
The mastermind behind the whole festival of life is DNA, a self-seeking molecular code. DNA expresses genes that direct the assembly of amino acids into proteins. Some of the proteins are enzymes that assemble molecules that are used to construct living cells. The human genome is a living text that continually edits and rewrites itself. Over half of the human genome is occupied by repeating sequences and a historical record of evolution.
The human genome is packaged into 23 pairs of chromosomes found in the nucleus of cells, half of each pair donated by each parent. We now appreciate that DNA sequences are part of an elaborate, dynamic process of expressing old information in new creatures. As a construction blueprint, genes appear to be autonomous and construct their organism according to a predetermined plan.
However, once an organism is constructed and living on planet earth, it needs a plan of interaction with its environment. The DNA plan must be flexible enough to adapt to changing circumstances, yet stable enough to keep a rose a rose, a sparrow a sparrow and a human a human. One human eats too much fat, another eats too much lean, and so DNA is read differently depending on circumstances.
Life is an exercise in molecular synthesis and control. The programs, which determine what we are and how we function, are coded in DNA molecules, housed in the nucleus of every cell. The DNA code consists of strings of 64 alphabet characters that specify amino acids in-groups of three characters (codones). A single character is a base pair that is visualized as the rung on a ladder, twisted into a helix. The entire range of cellular procedures of life consists of stringing amino acids together. The DNA alphabet (blueprint) is first translated into enzyme synthesis. Enzymes, in turn, orchestrate and control the synthesis of all molecules (construction procedures). This is an elegant, simple plan that permits the evolution of great complexity.
Molecular synthesis takes the form: DNA---->RNA---->Proteins
The amino acid sequence is read from the DNA molecule and transferred to the protein synthesis machinery in a cell by messenger RNA. Protein synthesis centers are known as Ribosomes. Ribosomes use messenger RNA as a template for the protein to be manufactured and draw amino acids attached to transfer RNA to the template. The ordered amino acids are then linked by enzymatic action to form a polypeptide or protein. The link between amino acids is as a peptide bond. The "Amino" of amino acids is a nitrogen-hydrogen group, NH2.
Protein shape is information. The shape may determine where the protein can go in a cell or which biological membrane will let it pass. The shape determines its structural role. The shape of a protein is also its identity. Shape ID is recognized and remembered by the immune system and is the basis of the body's immune defense. If a single gene, encoding the assembly instructions for a protein, is defective, the protein is missing or does not function properly.
Abnormal proteins can cause disease by not functioning and by doing something else, not the intended function. The idea of prions, for example, is that abnormally folded proteins act as ”infectious” agents that cause a cascading transformation of normally folded proteins. In the brain, the transformation of normal proteins into abnormally folded prions can produce neurodegenerative disease.
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