Enzymes and Protein Functions PDF

👽 Topic 11 - Enzymes + Protein Functions Enzymes What are enzymes Enzymes are catalysts that speed up RoR by lowering activation energy Enzymes regulate the rate of metabolic pathways in the...

👽 Topic 11 - Enzymes + Protein Functions Enzymes What are enzymes Enzymes are catalysts that speed up RoR by lowering activation energy Enzymes regulate the rate of metabolic pathways in the body Topic 11 - Enzymes + Protein Functions 1  Substrate & Product Concentration for Enzymes Rate of Reaction Allosteric Regulation (R + T States) Allosteric activators/inhibitors are compounds that bind to the active catalytic site (allosteric site) and regulate the enzyme through conformational changes that affect the catalytic site. T = Tense - Low Affinity R = Relaxed - High Affinity Topic 11 - Enzymes + Protein Functions 2  Allosteric regulation – PFK1 Adenosine diphosphate (ADP) or adenosine monophosphate (AMP) are allosteric activators of PFK1 When the concentration of ATP in a muscle cell begins to decrease, AMP activates PFK1. The precise regulation of PFK1 prevents glycolysis and gluconeogenesis from occurring simultaneously. ATP Build Up —> inhibits PFK1 Enzymes - Covalent Modification Enzyme activity may also be regulated by a covalent modification such as phosphorylation of an a.a. residue by a protein kinase Most common form of covalent modification: phosphorylation, glycosylation, methylation, acetylation Glycosylation is a post-translational modification Topic 11 - Enzymes + Protein Functions 3  Covalent modification - Phosphorylation Phosphorylation by a protein kinase dephosphorylation by a protein phosphatase - removes phosphate by hydrolysis Protein kinases transfer a phosphate from ATP to the hydroxyl group of a specific serine, threonine or tyrosine (a.a.) on the target enzyme, conformational change makes certain enzymes more/less active This effect is reversed by a specific protein phosphatase that removes the phosphate by hydrolysis Why is phosphorylation so effective? Adds two negative charges A phosphoryl group can make H-bonds Define Zymogens Enzymes are often made in an inactive form known as zymogens. What is Proteolytic Cleavage/Proteolysis zymogens (inactive enzymes) become active through a process of proteolysis (protein cleavage). This activation is irreversible Topic 11 - Enzymes + Protein Functions 4  helps prevent these enzymes from prematurely breaking down other proteins during their production or release. The blood clotting cascade (don’t need to remember everything) Serine proteases play a role by activating proenzymes + procofactors in the cascade through limited proteolysis. PROTHROMBIN —> THROMBIN The protease function (the thrombin part) is contained in the C-terminal domain. The two Kringle (K1 +K2) domains help keep prothrombin in the inactive form Gla domains target prothrombin to appropriate sites for its activation The Role of γ-Carboxyglutamate (Gla) Residues Addition of COOH groups to glutamate residues to form carboxyglutamate (Gla), Topic 11 - Enzymes + Protein Functions 5  Vitamin K dependent (warfarin [anticoagulant] inhibits this!) Allows interaction with sites of damage and brings together clotting factors Prothrombin binds calcium ions via Gla residues FIBRINOGEN → FIBRIN (by Thrombin) cleavage of small polypeptide chains, releasing fibrinopeptides (by the Thrombin Enzyme) polypeptides chains come together → form crosslinks —> fibrin mesh —> crosslinked Haemophilia A Haemophilia A (most common, classic haemophilia) Defect in factor VIII Topic 11 - Enzymes + Protein Functions 6  Leads to reduced thrombin activation Treatment for haemophilia A is via recombinant factor VIII Haemophilia B Deficient in factor IX (intrinsic) Treatment for haemophilia B is via recombinant factor IX Protein Functions Kinases [….] substrates Kinases phosphorylates substrates What are Defensive Proteins Example: Antibodies inactivate and help destroy viruses and bacteria. Immunoglobin Structure Constant, Variable, Hinge Regions. They consist of 2 heavy chains (440 amino acids) and 2 light chains (220 amino acids). Unique variability in immunoglobulin regions allows them to target specific antigens, B cells have antibodies with antigen binding sites on their surfaces, which bind to pathogenic cell epitopes, leading to antibody dissociation from the B cell. Topic 11 - Enzymes + Protein Functions 7  Types of Antibodies Phagocytosis Phagocytosis occurs when macrophages engulf viruses recognized by antibody-bound receptors. Storage Proteins Topic 11 - Enzymes + Protein Functions 8  Transport Proteins Function: Transport of substances Examples: Haemoglobin Membrane transporters transport molecules across membranes. Receptor Proteins Membrane-bound receptors bind to signals and trigger cascades of actions. Tyrosine Kinase Homodimer - 2 same types of protein, becomes activated when a growth factor binds When homodimer proteins activated by Growth factor, they phosphorylate each other’s a.a. from the kinase domain Signal Transduced from the membrane to the signal transducer protein Topic 11 - Enzymes + Protein Functions 9  JAK-STAT Receptors Heterodimers - 2 different proteins bind + close togther Only becomes activated when a cytokine attaches JAK kinases bind to heterodimers & phosphorylate each protein Signal Transduced from the membrane to the signal transducer protein Serine-Threonine Kinase Receptors Cytokine Dimer binds to Heterodimers one heterodimer proteins phosphorylates another, and that protein phosphorylates a Signal Transducer Protein Topic 11 - Enzymes + Protein Functions 10  Hormonal proteins Function: Coordination of an organism’s activities Example: Insulin Contractile and motor proteins Function: Movement Examples: Actin and myosin proteins are responsible for the contraction of muscles. Structural proteins 3 types of Structural Proteins Topic 11 - Enzymes + Protein Functions 11  What is the consequence of Misfolding and what do Chaperone Proteins do in this case? Misfolded proteins can clump together, potentially harming cells. Chaperone proteins aid in correct folding, by providing the right environment for proper folding. How are amyloid fibrils formed and what can they lead to Misfolding can create amyloid fibrils, leading to diseases like Alzheimer's and Parkinson's. Amyloids result from misfolding, affecting normal protein functions and forming disruptive deposits. What are Prions = misfolded proteins that are responsible for neurodegenerative disorders Topic 11 - Enzymes + Protein Functions 12 Topic 11 - Enzymes + Protein Functions 13