Protein structures

If any class of molecules contains the essential building blocks of mammalian life, it is the protein. This category of very large organic molecules regulates, enables and delivers energy derived from food, water, and oxygen to bodily parts such as cells, muscles, nerves, components of organs and all fluids. Proteins are polymers of amino acids, which are joined by peptide bonds (Sect. 11.2). The sequence of amino acids in a protein molecule is genetically-coded for a specific function. Egg white, technically called hen lysome, is an animal protein consisting of about 100 amino acids. The largest protein molecule contains about 27,000 amino acids. However, the monomer units in proteins are chosen from only 20 different amino acids, and not all are used in any particular protein.

Proteins perform their functions in part by "folding" into a tight compact mass not unlike a ball of yarn. Under certain conditions, a folded protein can "unfold" into a flexible one-dimensional structure that resembles a vine. The folded state is also called native, and the unfolded state is often termed denatured. Only the folded state is biologically active. Figure 11.6 is a highly-simplified sketch of the structure of the two states of a generic protein molecule. The unfolded state is a floppy chain of regularly-repeating amino acids. In the folded configuration, the interwoven mass of the amino-acid chains are held together by a variety of interactions, including hydrogen bonds5 and ionic bonds.

The protein in an aqueous solution is in one of two states, which are in equilibrium. This situation, with the protein designated by P, is described by:

with f and u meaning folded and unfolded, respectively. The equilibrium constant is

5 The type of bond responsible for many of the properties of water. The bond joins the O atom of one water molecule to the H atom of another. The bond energy is due to electrostatic attraction of H and O atoms rather than that of a true covalent bond.

Unfolded Folded

Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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