Enzymes: Definitions & Classifications (PDF)

 Understand & Enjoy Bio ] 1st Year: Foundation Module - En y e[ Enzymes § Definition : - Enzymes are biological protein catalyst that increase rate of reaction Protein may by nucleic acids called ribozyme - Enzymes incre...

 Understand & Enjoy Bio ] 1st Year: Foundation Module - En y e[ Enzymes § Definition : - Enzymes are biological protein catalyst that increase rate of reaction Protein may by nucleic acids called ribozyme - Enzymes increase rate by lowering energy barriers separating substrates from products  Classification of enzyme 1. Oxidoreductase: - Def: enzyme catalyze oxidation reduction reactions. ❑ Oxidation: means gain of oxygen or loss of hydrogen or electron. ❑ Reduction: means gain of hydrogen or electron or loss of oxygen. 2. Transferase: DEF: Enzymes catalyzing transfer functional groups (other than H) between two substrates one donor and other acceptor Ex: Transaminase : transfer amino group (NH2) ex: ALT , AST 3. Hydrolase: DEF: Enzymes catalyzing hydrolysis of a bond by addition of water Ex: Digestive enzymes : peptidases and proteinases 4. Lyase: DEF: Enzymes catalyzing group elimination to form double bonds Ex: (fumarase). L-malate → fumarate + H2O 5. Isomerase: DEF: Enzymes catalyzing interconversion of isomers by rearrangement of atomic groupings without altering molecular weight or number of atoms. Ex: epimerase Dr. Mostafa El-Fallaha  Understand & Enjoy Bio ] 1st Year: Foundation Module - En y e[ 6. Ligase: DEF: Enzymes catalyzing bond formation coupled with ATP hydrolysis. Ex: ATP + L-glutamate + NH4 ADP+ Pi + L-glutamine. (glutamine synthase) Cofactor and coenzymes § Enzymes may be: 1. Simple protein 2. Compound protein ( holo enzyme) Ex: Lipase and - Metal amylase Amino acid + Group - Organic: Coenzymes Co factor (loosely attached) § Types of coenzymes: Organic Inorganic Coenzymes transfer group rather than Coenzymes transfer hydrogen group hydrogen: (hydrogen carrier): - Plp Pyredoxyl phosphate ( ): a. (from niacin): Ex: NAD & NADP b. (from Riboflavin): Ex: FAD & FMN Isoenzymes § Def: Multi physical form of a given enzymes catalyse the same reaction but differ in chemical structure in different cells. and may differ in affinity to substrate and electrophoretic mobility. Examble: Creatine kinase: Diamar formed of 2 subunit M&B 3 isomers: CK1(BB): CK2(BM): CK3(MM): present in brain in blood in in heart in blood in in muscle in blood in brain infarction myocardial infarction muscle disease Dr. Mostafa El-Fallaha  Understand & Enjoy Bio ] 1st Year: Foundation Module - En y e[ Mechanism of enzyme action For substrates to react and form products energy needed this energy called activation energy The transition state is the transitory of molecular structure in which the molecule is no longer a substrate but not yet a product S→ X → P, X is the transition state, which is located at the peak of the curve  Active site: Restricted region on surface of enzyme at which catalysis occour as it is richin active chemical groups.  2 models for active site: Lock & Key (Fischer’s theory): Induced fit model (Koshland theory): Enzyme is rigid like lock and Substrate induce conformational not changeable changes in enzyme active site is complementary to subs. (fixed) Regulation of enzyme A. Amount (long term): B. Activity (short term) Synthesis Degradation Allosteric Covalent Limited effecttor Modification Proteolysis B. Regulation of enzyme activity: 1. Allosteric effectors Def: low molecular weight compounds that modulate activity of enzyme no similarity to substrate bind enzyme at other site (allosteric site) Allosteric enzymes: enzymes can regulate by allosteric activator Feedback back inhibition: Inhibition of enzyme in pathway by its products A B C D Dr. Mostafa El-Fallaha Understand & Enjoy Bio ] 1st Year: Foundation Module - En y e[ 2. Covalent modification Def: covalent binding phosphate group (in mammals) or nucleotide (in bacteria) to enzyme called Interconvertible as they are present in 2 form active and inactive 3. Limited proteolysis: Def: Cut part of surface of enzyme creak active site Pro enzyme active enzyme Ex: ✓ digestive enzyme pepsinogen ✓ Blood clotting enzymes ✓ Blood coagulation enzymes AD EL DEEP A B D E L R A H M A N Dr. Mostafa El-Fallaha Practical Understand & Enjoy Bio ] 1st Year: Foundation Module - En y e[ Questions Ü Enzyme : biochatalyst increase rate of reaction up to 1020 folds Ü Ribozyme : some nucleic acids with enzyme activity Ü Oxidoreductase : enzymes catalyze oxidation reduction reactions Ü transferases : enzymes catalyze transfer of chemical group rather than hydrogen to acceptor molecule Ü Hydrolases :enzymes catalyze hydrolytic cleavage of bond by addition of water. Ü Lyases : enzymes catalyze addition of group on double bond or removal of group to form double bond. Ü Isomerases : enzymes catalyze interconversion between isomers (Enzymes that reform the shape of compound) Ü Ligase : enzymes catalyze joining 2 molecules together Ü Holoenzyme : conjugated protein part (Apoenzyme) with cofactor group Ü Apoenzyme : conjugated protein part of enzyme without cofactor group. Ü cofactor : substrates needed for enzyme to be active. It is either organic or inorganic. Ü Coenzyme : organic substance loosely attached to apoenzyme part Ü activation energy : energy barrier needed for substrates to reach transition state. Ü active site : restricted region of enzyme at which catalysis takes place where active chemical groups are present. Ü Lock and key model (Fisher theory) : theory states that enzyme is complementary to shape of substrate like lock and key. Ü Induced fit model (Koshland theory) : it states that when substrates bind enzyme they induce conformational changes in the enzyme. Ü Isoenzymes : physical distinct forms of same enzyme catalyze same reaction but differ in chemical structure in different tissues. Dr. Mostafa El-Fallaha Understand & Enjoy Bio ] 1st Year: Foundation Module - En y e[ Ü allosteric effectors : low molecular weight compounds that regulates activity of enzyme by binding allosteric site Ü allosteric site : other site rather than active site Ü allosteric enzyme : enzyme can be regulated by allosteric effectors Ü Feed back inhibition : inhibition of pathway by its product Ü covalent modification : attachment of phosphate or nucleotide to enzyme by covalent bond Ü limited proteolysis : cut part of surface of enzyme creating active site Enumerate 1. classes of enzymes 5. theories of active site 2. types of oxidoreductases 6. factors affecting enzyme activity 3. types of cofactors 7. types of enzyme inhibitors 4. types of isoenzymes MCQ 1. All the following describes enzymes except ? A) they are protein catalyst that accelerate reactions B) they undergo chemical changes during the reaction C) they lower free energy barrier that separates reactants and products 2. Which one of the following enzymes catalyze hydrolysis of bond by addition of water? A) Transferases b) Lyases c) Ligases d) Hydrolases 3. Which one of the following catalyze group elimination to form double bond ? A) Transferase B) Lyases c) Ligases d) isomerases 4. which one of the following catalyze bond formation ? a) Transferase B) Lyases C) ligase d) isomerase 5. all of the following describe the active site of enzyme except ? a) wide region on enzyme surface B) it it a pocket or groove in the surface of the enzyme c) Functional groups that mediate catalytic events are present adjacent to the active site Dr. Mostafa El-Fallaha Understand & Enjoy Bio ] 1st Year: Foundation Module - En y e[ 6. All the following statements describes allosteric enzymes except ? A) Their catalytic activity modulated by allosteric effectors B) They bind effector at catalytic site C) They bind the effector at a site distict from catalytic site 7. which one of the following statements describes interconvertible enzymes ? A) Their activity modulated by covalent attachment of PO4 group only B) Their activity modulated by covalent attachment of nucleotide only C) They exist in 2 states , one of high and other of low catalytic activity 8. enzyme which catalyze addition of phosphate group is ? a) Transaminase b) kinase c) phosphatase d) hydratase 9. esterase is an example of ? a) oxidoreductase b) hydrolase c) Lyase d) ligase 10. enzyme without its cofactor or coenzyme called? a) holoenzyme b) apoenzyme c) proenzyme 11. feischer theory says that ? a) enzyme like key b) enzyme is changeable in conformation c) enzyme is rigid 12. brain specific creatine kinase is A-CK1 b-CK2 c-CK3 13. kinase and pohosphatase A) Belong to same class b) catalyze the same reaction C) have opposite function 14. class of enzyme that reform the structure of enzyme is a) Oxidoreductase b-isomerase c-ligase d-lyase Compare 1- Functional and non functional plasma enzymes (very important) 2- lock and key and induced fit model theories AD EL DEEP A B D E L R A H M A N Dr. Mostafa El-Fallaha