Enzymes (Lecture 1) PDF

University of Diyala/ College of Science Department of Biotechnology 4nd stage Enzymes (Lecture 1) Edited by Dr. Zeyad Khalouf Enzymes: are protein molec...

University of Diyala/ College of Science Department of Biotechnology 4nd stage Enzymes (Lecture 1) Edited by Dr. Zeyad Khalouf Enzymes: are protein molecules , produced by all living organisms. Act as highly efficient catalysts in biochemical reactions, that is, they help a chemical reaction take place quickly and efficiently. Enzymes are highly efficient in increasing the reaction rate of biochemical processes that otherwise proceed very slowly, or in some cases, not at all. Enzymes are excellent catalysts, speeding up reactions 105 to 1020 fold. They speed up reactions without being used up or consumed it. The human body uses thousands of enzymes to carry out a myriad of biochemical processes. One clear example of an enzyme-assisted process is digestion. Enzymes help break down carbohydrates, fats and proteins into simple compounds that the body can absorb and burn for energy or use to build or repair tissue. These include: - Amylase and lipase in saliva break down carbohydrates and fats. - Proteases (pepsin) released in the stomach aid in digestion of proteins; Lipases, amylases, and proteases are secreted in the small intestine and play a pivotal role in completing the digestive process. Enzymes efficiency include three major ways: 1- Catalytic power: Catalysts increase the rate of chemical reactions without being used up in the process. Enzymes act like many other catalysts by lowering the activation energy of a reaction, allowing it to achieve equilibrium more rapidly. The catalyst is able to reduce the activation energy by forming a transition state in a more favorable manner, and create a more "comfortable" fit for the substrate of a reaction to progress to a transition state. Enzymes can end up the reaction in seconds than it might take hours or weeks under laboratory. 2- Specificity: enzymes are highly specific in the reactions they catalyze. An enzyme with stereochemical specificity catalyzes the reaction of only one of two possible enantiomers (D-amino acid oxidase catalyzes the reaction of D-amino acids, but not L-amino acids). In general, there are four distinct types of specificity: 1- Absolute specificity - the enzyme will catalyze only one reaction. 2- Group specificity - the enzyme will act only on molecules that have specific functional groups, such as amino, phosphate. 3- Linkage specificity - the enzyme will act on a particular type of chemical bond regardless of the rest of the molecular structure. 4- Stereochemical specificity - the enzyme will act on a particular steric or optical isomer. 3- Regulation: enzymes activity as catalysts can be regulated, the catalytic behavior of enzymes can be regulated. A relatively small number of all of the possible reactions which could occur in a cell actually take place, because of the enzymes which are present. The cell controls the rates of these reactions and the amount of any given product formed by regulating the action of the enzymes. Cofactors (Coenzyme and activator) Some enzymes require an additional non-protein component for its optimum activity. This additional component is called cofactor which may be either loosely or tightly bound to the protein of the enzyme. These cofactors may be: Organic compounds, called coenzymes Inorganic ions, called activators. Enzyme without its cofactor is referred to as an apoenzyme; the complete catalytically active enzyme is called holoenzyme. Apoenzyme + cofactor = holoenzyme Enzymes, like other proteins, have molecular weights ranging from about 12,000 to more than 1 million. Some enzymes require no chemical groups for activity other than their amino acid residues. Others require an additional chemical component called a cofactor—either one or more inorganic ions, such as Fe2+ _, Mg2+ _, Mn+2 _, or Zn+2_, or a complex organic or metalorganic molecule called a coenzyme Some enzymes require both a coenzyme and one or more metal ions for activity.