Enzymes 2022 PDF

What on earth are enzymes?  All proteins? High MW Catalyst ---- FAST AND FURIOUS Active outside cell Water soluble- amphoteric molecules Specificity  Molecules must collide in order to react. In order to effectively initiate a reaction, collisions must be sufficiently energe...

What on earth are enzymes?  All proteins? High MW Catalyst ---- FAST AND FURIOUS Active outside cell Water soluble- amphoteric molecules Specificity  Molecules must collide in order to react. In order to effectively initiate a reaction, collisions must be sufficiently energetic (kinetic energy) to break chemical bonds; this energy is known as the activation energy. As the temperature rises, molecules move faster and collide more vigorously, greatly increasing the likelihood of bond breakage upon collision.  Specificity of enzyme action-4 The Fischer “lock-and-key” hypothesis Fischer (1890) According to this model, structures do not change their shape during the binding process The Koshland “induced-fit” hypothesis Koshland (1958) X-ray diffraction analysis and NMR data have revealed differences in structure btw free and substrate-bound Conformational change Such mechanism could help to achieve high degree of specificity.... – e.g. yeast hexokinase D-hexose + ATP D-hexose-6-P + ADP Induced-fit  Factors affecting enzyme activity Temperature  Rise in temp ---- increase in kinetic energy Bring molecules closer for reaction Most enzymes optimal temp – 37o C Cold water fish dies at 30o C, thermophylic enzymes may have activity at 100oC Most enzymes denature at 70oC  Extreme pH causes denaturation Make and break intra and intermolecular bonds ------ active site distorted --- X fit for substrates Optimum pH varies ---- 5-9, ; pepsin pH 2, Vmax = rate of reaction (saturation point) Km = affinity of enzyme towards substrate (half of the enzymes filled)  Enzyme inhibitors Irreversible inhibitors: Combine with the functional groups of the amino acids in the active site, irreversibly. Examples: nerve gases and pesticides, containing organophosphorus, combine with serine residues in the enzyme acetylcholine esterase. SARIN  Reversible inhibitors: These can be washed out of the solution of enzyme by dialysis. There are two categories. Or overcome 1. Competitive: These compete with the substrate molecules for the active site. The inhibitor’s action is proportional to its concentration. Resembles the substrate’s structure closely. 2. Non-competitive: These are not influenced by the concentration of the substrate. It inhibits by binding irreversibly to the enzyme but not at the active site. Examples UPON BINDING TO ENZYMES, CHANGES THE BINDING SITE Cyanide combines with the Iron in the enzymes cytochrome oxidase. Heavy metals, Ag or Hg, combine with –SH groups. These can be removed by using a chelating agent such as EDTA. HALF OF VMAX IS KM Regulation of enzyme reactions  Enjoy the rest of the course and SEE you during the test!! Check spectrum from time to time for study reviews and test results in the coming weeks. All the best!