Enzymes PDF

AIU-PT Prof. Rasha Nassra Medical Biochemistry & Molecular Biology SUBJECTS Water TO BE Macromolecules COVERED (ECM) Enzymology Vitamins & Minerals Cell Membrane & Signal Transduction Molecular Biology...

AIU-PT Prof. Rasha Nassra Medical Biochemistry & Molecular Biology SUBJECTS Water TO BE Macromolecules COVERED (ECM) Enzymology Vitamins & Minerals Cell Membrane & Signal Transduction Molecular Biology SUBJECTS TO BE COVERED Enzymes Molecular Biology 1. Define terms used in enzymology 2. Describe the role of enzymes as biological catalysts 3. Explain enzyme specificity 4. Define Ribozymes and recognize their functions  Enzymes ✓ Act at very small concentrations, ✓ Increase the speed of chemical reactions Without changing the result. ✓ At the end of the reaction the structure of the enzyme Unchanged TERMS USED IN ENZYMOLOGY  Substrate: Is the organic substance on which the enzyme acts.  Product: Is the organic substance produced by the action of the enzyme  Coenzymes: Essential for the activity of enzymes and they are considered as second substrates or Co-substrate (Substrate)  SUBSTRATE  Molecule that enters a reaction to be transformed by the catalytic activity of an enzyme.  All molecules that enter an enzymatic reaction and are permanently modified are called substrates.  PRODUCT  Molecule that appears during an enzyme catalyzed reaction.  The new molecule that results from this transformation is called the product.  CATALYTIC SITE A special sequence of amino acids in the protein molecule of the enzyme to which the substrate is attached.  ACTIVE SITE A more general term which involves all sequences of amino acids which affect the activity of the enzyme Includes for example the catalytic site, the allosteric sites TERMS USED IN ENZYMOLOGY Catalytic site  ENZYMATIC REACTION  SUBSTRATE ENZYME PRODUCT  Enzymes are: Organic catalysts, Protein in nature RIBOZYME  Non-protein Organic catalysts ✓ Segments of RNA ✓ Display an enzyme activity in the absence of protein ✓ Acting on themselves or other RNA molecules ✓ Require divalent metal cations (eg. Mg2+ ) as cofactors GENERAL PROPERTIES OF ENZYMES: They are of high molecular weight, Thermolabile, (substance that is subject to destruction /decomposition or change in response to heat --------- lose their activity when the body temperature is high) NOMENCLATURE Enzymes which were discovered early were given general names: Example: ptyalin, pepsin, trypsin, cathepsin, emulsin etc......  Now a suffix (ase) is added to indicate enzyme The prefix may be: General nature of substrate e.g.: protease, lipase Name of substrate: urease, lactase Type of reaction e.g.: transaminase, dehydrogenase.  Combination: Name of substrate + type of reaction e.g.: Lactate Dehydrogenase Glycogen Synthase  1. Absolute (total) 2. Structural (group) 3. Relative (bond) ENZYME 4. SPECIFICITY Stereochemic al Absolute  amino group of an aromatic a.a. & carboxylic group of another amino acid carboxylic group of basic a.a. and amino group of another amino acid Structural Relative Alpha ester bonds at position 1 & 3 in Triglycerides Stereochemical 1. Absolute specificity(total) The enzyme acts only on a specific substrate  Lactase acts on lactose 2. GROUP SPECIFICITY (STRUCTURAL SPECIFICITY): Acts on a special type of bond at specific site and attached to specific groups A) Pepsin: peptide bonds between amino group of aromatic amino acid and carboxylic group of another amino acid B) Trypsin: peptide bonds between carboxylic group of basic amino acid and amino group of another amino acid 3. RELATIVE SPECIFICITY Acts at different rates on one type of bond in compounds chemically related Pancreatic lipase: hydrolyzes alpha ester bonds at position 1 & 3 in Triglycerides 4. STREOCHEMICAL SPECIFICITY A) Enzymes act on D or L isomers D - Amino acid oxidase acts only on D-amino acids L- Amino acid oxidase acts only on L-amino acids B) Enzymes act on specific type of linkages (α ou β) ❖ Amylase hydrolyses α-1.4 glycosidic linkage of starch. CLINICAL IMPORTANCE OF ENZYMES DIAGNOSIS OF DISEASES Enzymes are intracellular and when there is cellular damage, they are released into the circulation ENZYMES IN PLASMA A. FUNCTIONAL PLASMA ENZYMES Present normally in blood to perform certain physiological functions Synthesized in the liver. Present in blood in higher concentration than tissues. Their substrates are present in the circulation. Examples: ✓ Enzymes of blood clotting NON-FUNCTIONAL PLASMA ENZYMES  Present in a very low concentration in blood due to tissue turn over 1.Perform no physiological function in blood. 2. Their substrates, are absent from blood. 3. Their level is normally low and increase in tissue damage. Examples: 1. Alkaline phosphatase: increases in obstructive jaundice, and metastatic carcinoma to bone. NON-FUNCTIONAL PLASMA ENZYMES Some enzymes can be used as tumor markers II. TREATMENT OF DISEASES Digestiveenzymes in treatment of maldigestion. MECHANISM OF ENZYME ACTION: Most of the chemical reactions in the body fail to react rapidly because most of them possess insufficient kinetic energy to overcome the energy barrier for reaction. Enzymes may be considered to lower energy barriers for chemical reactions ✓ reduce activation energy MECHANISM OF ENZYME ACTION  Transition state Unstable arrangement of atoms in which chemical bonds are in the process of being formed or broken Activation energy The energy required to reach the transition state from the ground state of the reactants  MECHANISM OF ENZYMATIC CATALYSIS Enzymes Increase the rate of the reactions by lowering the activation energy (free energy of activation) REDUCE ACTIVATION ENERGY MODE OF ACTION OF ENZYME