Enzymes Lecture Notes PDF

Almaaqal University Enzymes Dr/ Wael Sobhy Darwish Biochemistry PhD Lec-3  Enzymes  Enzymes are a type of protein that acts as a catalyst, speeding up chemical reactions without undergoing any change themsel...

Almaaqal University Enzymes Dr/ Wael Sobhy Darwish Biochemistry PhD Lec-3  Enzymes  Enzymes are a type of protein that acts as a catalyst, speeding up chemical reactions without undergoing any change themselves.  All enzymes are proteins.  Enzymes are required in very small quantities.  Each enzyme is very specific and only attaches to one type of molecule.  Enzymes possess active site, at which interaction with substrate take place.  The molecule the enzyme acts upon is called its substrate.  Our bodies naturally synthesize enzymes The properties of enzymes Catalytic property A small amount of enzyme is enough to break large molecules down into smaller molecules. Specificity Enzymes are very specific in action, with one enzyme acting only on a particular substrate. Reversibility Most reactions that are catalyzed by enzymes are reversible. Sensitivity to temperature Enzymes are thermos-liable or very sensitive to heat and temperature. Specificity to pH Enzymes show maximum activity at an optimum pH of 6 – 8.  Function of enzymes  They are essential for respiration, digestion of food, DNA replication, muscle contraction and nerve function.  Store and release energy (ATP).  Create larger molecules from smaller ones  Hormone production  Transporting materials around a cell Sources of enzymes  Endoenzymes: enzymes that function within the cells, most of enzymes are these types. Ex: metabolic oxidase.  Exoenzymes: enzymes that are liberated by cells and catalyze reactions outside the cell. Ex: digestive enzymes (amylase, lipase, protease).  Chemical composition of enzymes:  Enzymes classified according to their chemical composition into.  1. Enzyme consist of protein only. Ex: pepsin, trypsin  2. Enzyme conjugated protein, it is called holoenzyme  A. Enzyme consist of : protein + Co - Enzyme  B. Enzyme consist of: Protein + prosthetic group  C. Enzyme consist of: Protein + metal  Coenzymes: are organic non-protein molecules. They bind to the enzyme and also participate in the reaction by carrying electrons or hydrogen atoms.  Cofactors: are non-proteinous substances that associate with enzymes. A cofactor is essential for the functioning of an enzyme.  Holoenzyme : enzyme consist of Apoenzyme + prosthetic group  Apoenzyme: term refers to the protein part of enzyme.  Prosthetic groups: These are cofactors tightly bound to an enzyme at all times. FAD  Zymogen: the active form of enzyme.  Ex: pepsinogen Hcl pepsin (active)  Enzyme Conjugated Enzyme(Holoenzyme) Simple Enzyme  Enzyme nomenclature (Naming): 1. Trivial name: such as trypsin and pepsin. 2. Adding suffix ase to the substrate such as maltase and lactase. 3. To standardize enzyme nomenclature, the International Union of Biochemistry (IUB) made a systemic name to each enzyme that can indicate: a- The substrate acted upon. b- The coenzyme involved in the reaction. c- The type of reaction catalyzed  Classification of Enzymes Oxidoreductases These catalyze oxidation and reduction reactions, e.g. pyruvate dehydrogenase, catalysing the oxidation of pyruvate to acetyl coenzyme A. Isomerases They catalyze the formation of an isomer of a compound.  Transferases These catalyze transferring of the chemical group from one to another compound. An example is a transaminase, Hydrolases They catalyze the hydrolysis of a bond. For example, the enzyme pepsin hydrolyzes peptide bonds in proteins. Lyases These catalyze the breakage of bonds without catalysis, e.g. aldolase. Ligases Ligases catalyze the joining of two molecules. For example, DNA ligase catalyzes the joining of two fragments of DNA by forming a phosphodiester bond.