Enzymes: Building Blocks of Cells Part 2 PDF

Introduction to Medical Sciences 1 Building Blocks of Cells Part 2 Enzymes Copyright © Brunel University London v.3 2024. All rights reserved Building Blocks of Cells Dr Ricardo Carnicer Hijazo 2024 Version 3 [email protected]...

Introduction to Medical Sciences 1 Building Blocks of Cells Part 2 Enzymes Copyright © Brunel University London v.3 2024. All rights reserved Building Blocks of Cells Dr Ricardo Carnicer Hijazo 2024 Version 3 [email protected] Copyright © Brunel University London v.3 2024. All rights reserved 5  Proteins as enzymes Metabolism: all the chemical reactions that maintain the living state of cells. Enzymes are catalysts, proteins that accelerate chemical reactions. Copyright © Brunel University London v.3 2024. All rights reserved Image of several cellular metabolic routes from iPath. Public domain 6 Properties of enzymes: Active site The enzyme only reacts with a few Substrate closely related Products substrates Active site Enzyme Image created by TimVickers. Wikipedia public domain. Copyright © Brunel University London v.3 2024. All rights reserved 7 Properties of enzymes: Specificity The enzyme only reacts with a few Substrate closely related Products substrates Enzyme Image created by TimVickers. Wikipedia public domain. Copyright © Brunel University London v.3 2024. All rights reserved 8 Properties of enzymes: Cofactors The enzyme only reacts with a few closely related substrates Products Cofactor: is a non-protein chemical compound that is required for the enzyme’s biological activity. Cofactors can be ions or organic Cofactor molecules (e.g. Vitamin C in collagen synthesis). The enzyme is not consumed during the reaction Copyright © Brunel University London v.3 2024. All rights reserved 9 Properties of enzymes The enzyme only reacts with a few Substrate closely related Products substrates Active site Enzyme The enzyme is not consumed during the reaction Copyright © Brunel University London v.3 2024. All rights reserved 10  Enzymes are able to Properties of enzymes decrease the energy of activation required Transition state to start a reaction. consumed Energy Enzymes do not affect the energy level of substrates or products (free energy released released remains the same). Graph created by Jerry Cison. Wikipedia, CC BY-SA Product Reaction time Copyright © Brunel University London v.3 2024. All rights reserved 11 Summary Enzymes are proteins that speed up reactions by reducing the activation energy. Each enzyme typically binds only one substrate (Specificity). Enzymes are not consumed during a reaction. Copyright © Brunel University London v.3 2024. All rights reserved Isoenzymes Isoenzymes are variants of the same enzyme that differ in amino acid sequence but catalyse the same chemical reaction. Isozymes are usually regulated differently, and therefore, allow the fine- tuning of metabolism to meet the particular needs of a given tissue or developmental stage.(e.g. Lactate dehydrogenase, creatine kinase) Copyright © Brunel University London v.3 2024. All rights reserved 13 Regulation of enzyme activity Substrate concentration Temperature pH Copyright © Brunel University London v.3 2024. All rights reserved Regulation of enzyme activity Substrate concentration Vmax The activity of an enzyme increases with increasing substrate concentration. The activity will cease to rise regardless of any further increases in substrate levels after a certain point. Graph created by GYassineMrabetTalk. Wikimedia, Public Domain Copyright © Brunel University London v.3 2024. All rights reserved 15 Regulation of enzyme activity Temperature The activity of enzymes varies with temperature, increasing until an ‘optimum’ and then falling away due to thermal denaturation. Body temperature is very tightly regulated over a very narrow range, and is therefore rarely controlling enzyme activity in vivo. Temperature may however be a significant issue when a person suffers hypothermia or fever. Copyright © Brunel University London v.3 2024. All rights reserved 16 Regulation of enzyme activity pH Each enzyme has a specific optimal pH at which it achieves maximum activity (Usually pH between 6 and 8). The pH decides the charge on the amino acid residues at the active site. Example: Pepsin works best in the acidic environment of the stomach (pH ∼1.5) and it is inactivated in the small intestine (pH > 7). Alterations in pH cause denaturation of enzymes. Copyright © Brunel University London v.3 2024. All rights reserved 17 Regulation of enzyme activity Regulation Gene Enzyme expression activity Enzyme Covalent Allosteric production modification regulation Diagram created by RCH. Public Domain Control enzyme Enzyme On/Off kinetics Copyright © Brunel University London v.3 2024. All rights reserved 18  Regulation of enzyme activity Regulation Gene Enzyme expression activity Enzyme Covalent Allosteric production modification regulation Diagram created by RCH. Public Domain Control enzyme Enzyme On/Off kinetics Copyright © Brunel University London v.3 2024. All rights reserved 19 Regulation of enzyme activity Regulation Gene Enzyme expression activity Enzyme Covalent Allosteric production modification regulation Diagram created by RCH. Public Domain Control enzyme Enzyme On/Off kinetics Copyright © Brunel University London v.3 2024. All rights reserved 20 Covalent modification: 1) Proteolysis Many proteins are synthesised in a ‘pro’ or inactive form (zymogen). The active form of the protein is only liberated following proteolytic cleavage of parts of the initial amino acid sequence. Why? To ensure that a protein is only active: - under appropriate conditions or in response to correct stimuli. - in the correct location (e.g. trypsin and chymotrypsin). Copyright © Brunel University London v.3 2024. All rights reserved 21 Covalent via chemical modification 2) Phosphorylation Amino acids containing –OH functional groups accept the covalent addition of a phosphate from ATP via the action of specific protein kinases. The modification is rapid and reversible, being removed by phosphatases. Chemical structures from wikipedia Copyright © Brunel University London v.3 2024. All rights reserved 22 Phosphorylation Phosphorylation introduces a bulky and negatively charged moiety. Phosphorylation introduces large conformational changes due to electrostatic repulsion/attraction. These conformational changes can alter substrate binding or intra- protein communication. Protein kinase Chemical structures from wikipedia Copyright © Brunel University London v.3 2024. All rights reserved 23 Phosphorylation Phosphorylation introduces a bulky and negatively charged moiety. Phosphorylation introduces large conformational changes due to electrostatic repulsion/attraction. These conformational changes can alter substrate binding or intra- protein communication. Protein kinase Protein phosphatase Copyright © Brunel University London v.3 2024. All rights reserved 24 Phosphorylation cascades Phosphorylation is often associated with intracellular signalling events that result in rapid amplification of signals. Some examples of signal transduction: - Cell cycle. - Glycogen breakdown. - Cell growth and development. Copyright © Brunel University London v.3 2024. All rights reserved 25 Allosteric control (non-covalent) Inhibition or activation of an enzyme by a small regulatory molecule that interacts at a site (allosteric site) other than the active site at which catalytic activity occurs. Substrate Active site Allosteric site Image created by TimVickers. Wikipedia public domain. Inhibitor Copyright © Brunel University London v.3 2024. All rights reserved 26 Allosteric control Allosteric binding will modulate enzyme activity by either inhibiting or promoting substrate binding or formation/release of products. Substrate Products Substrate Enzyme Enzyme Enzyme Enzyme Image created by TimVickers. Wikipedia public domain. Copyright © Brunel University London v.3 2024. All rights reserved 27 To complete this session, please read: Textbook of Biochemistry for medical students 9th Ed. DM Vasudevan Chapter 4, pages 72-76. Copyright © Brunel University London v.3 2024. All rights reserved 28 To contact me: [email protected] Copyright © Brunel University London v.3 2024. All rights reserved