Keratin. Any of a group of fibrous proteins occuring in hair, feathers, hooves, and horns. Keratins have coiled polypeptides linked by disulphide bonds between adjacent cysteine amino acids.

Aggregates of these super coils from microfibrils, which are embedded in a protein matrix. This produces a strong but elastic structure.

Ketose. A monosa ccharide with a ketonic structure.

Kidney. Organ excretion and/or water regulations in vertebrates, consisting of numerous nephrons and their blood supply.

Krebs Cycle.
(Citric acid cycle). A series in oxidation of carbohydrates. Complex cycle enzyme-controlled reactions by which, from pyruvic acid provided by glycolysis, carbon dioxide is produced, and, through formation of reduced NAD, ATP, a source of energy, is synthesized. Pyruvic acid is fed source of energy, is synthesized. Pyruvic acid is fed into this cycle after combination with CoA as acetyl CoA.
The first step in the cycle is citric acid, and the final step is the reconstitution of citric acid by combination of oxalo acetic acid with acetyl CoA. The cycle is also concerned with the synthesis of some amino acids. This system is situated in the mitochondria.