Proteins are molecular machines, building blocks, and arms of a living cell. Theirmajor and almost sole function is enzymatic catalysis of chemical conversions inand around the cell. In addition, regulatory proteins control gene expression, andreceptor proteins (which sit in the lipid membrane) accept intercellular signals thatare often transmitted by hormones, which are proteins as well. Immuno proteins andthe similar histocompatibility proteins recognize and bind “foe” molecules as well as“friend” cells thereby helping the latter to be properly accommodated in the organism.Structural proteins form microfilaments and microtubules, as well as fibrils, hair, silkand other protective coverings; they reinforce membranes and maintain the structureof cells and tissues. Transfer proteins transfer (and storage ones store) other molecules.Proteins responsible for proton and electron transmembrane transfer provide for theentire bioenergetics, that is, light absorption, respiration, ATP production, etc. ByATP “firing” other proteins provide for mechano-chemical activities – they work inmuscles or move cell elements.The enormous variety of protein functions is based on their high specificity forthe molecules with which they interact, a relationship that resembles a key and lock(or rather, a somewhat flexible key and a somewhat flexible lock). Anyhow, thisspecific relationship demands a fairly rigid spatial structure of the protein. That’swhy the biological functions of proteins (and other macromolecules of the utmostimportance for life – DNA and RNA) are closely connected with the rigidity oftheir three-dimensional (3D) structures. Even a little damage to these structures, letalone their destruction, is often the reason for loss of or dramatic changes in proteinactivities.A knowledge of the 3D structure of a protein is necessary to understand howit functions. Therefore, in these lectures, the physics of protein function will bediscussed after protein structure, the nature of its stability and its ability to selforganize,that is, at the very end.Proteins are polymers: they are built up by amino acids that are linked into apeptide chain; this was discovered by E. Fischer as early as the beginning of the 20thcentury. In the early 1950s Sanger showed that the sequence of amino acid residues(a “residue” is the portion of a free amino acid that remains after polymerization) is
đang được dịch, vui lòng đợi..