Systems to Cells 2024 Lecture 1 - Clare Rollie PDF

Systems to Cells Introduction Dr Clare Rollie [email protected]  What is “Systems to Cells”? Study of key molecular and cellular mechanisms that operate across various tissues Maintenance of physiological homeostasis Disruption can cause disease Ro...

Systems to Cells Introduction Dr Clare Rollie [email protected]  What is “Systems to Cells”? Study of key molecular and cellular mechanisms that operate across various tissues Maintenance of physiological homeostasis Disruption can cause disease Roadmap to investigate, understand and ultimately treat complex diseases Glucose Metabolism and Diabetes 4.7 million people in the UK have currently have diabetes Urgent unmet medical need to: Understand the biological mechanisms involved Understand the factors that contribute to disease risk Develop novel and effective treatments  Block overview Systems, Cells, Genetic and Exercise in Molecules and environmental Diabetes Genes interactions in Management disease 5 lectures 1 lecture 2 lectures Dr Clare Rollie Prof Kevin O’Dell Dr Stephen Leckey  Course Delivery Overview During lectures: ask questions anonymously via Padlet or just shout out! After lectures: post questions, ideas, comments to the Moodle forum Reading list Use the ‘study guide’ and ‘what you can do’ Come and talk to me Most importantly have fun!  Systems, Cells, Molecules and Genes (and back again) Lecture 1 Carbohydrate Metabolism, Diabetes, and Molecular Cell Biology Dr Clare Rollie [email protected]  Aims - 1 Understand the important role of glucose in metabolism Compare the roles of insulin and glucagon Understand the reciprocally regulated reactions involved in glycogen synthesis and breakdown Explain the different ways enzymes are regulated - Post-translational modification, e.g. phosphorylation  Whole body energy First law of thermodynamics (“energy can be transformed from one form to another but cannot be created or destroyed”) applies to all organisms. Lectures will focus mainly on humans, but other organisms will be considered as many show interesting adaptations (e.g. hibernating brown bears; migrating birds) Energy balance Energy needed for… Cell growth and division Building new molecules/replacing old ones Movement (muscle contraction is ATP-dependent) Breathing, thinking (yes, even now…), speaking etc. Energy currency is ATP ATP formed by substrate-level and oxidative phosphorylation (Level-1 lectures/textbook)  ATP Average human body has 100-250g ATP Daily requirement is 50-75 kg! You make >your body weight of ATP every day…. ATP is re-formed from ADP ~ 1000x each day Essential for life We need to keep replenishing this energy – It’s neither created or destroyed: where does it come from? Oxidative phosphorylation of glucose  Glucose.. Glucose is an excellent fuel; complete oxidation DG= -2840 kJ/mol Broken down to pyruvate by glycolysis. Under aerobic conditions the pyruvate is converted to Acetyl-CoA and this enters the TCA/Krebs cycle. Under anaerobic conditions, its converted into lactate. Can be efficiently stored (starch; glycogen)  Glucose.. Glucose is an excellent fuel; complete oxidation DG=-2840 kJ/mol Can be efficiently stored (starch; glycogen) Involved in many biosynthetic reactions, e.g. all amino acids, membrane lipids, nucleotides in DNA and RNA, etc.  Glucose.. Glucose is an excellent fuel; complete oxidation DG=-2840 kJ/mol Can be efficiently stored (starch; glycogen) Involved in many biosynthetic reactions, e.g. all amino acids, membrane lipids, nucleotides in DNA and RNA, etc. Glucose is a key energy source Brain and nerves have an absolute requirement for glucose for energy. So do erythrocytes, testes and kidney medulla.  Whole body glucose homeostasis Blood sugar levels kept constant by a range of homeostatic mechanisms. When in excess, glucose stored as glycogen (liver, muscle) or triglycerides (adipose). When levels low, these tissues become net exporters of glucose/fatty acids. Hyperglycaemia - high blood glucose Hypoglycaemia - low blood glucose  Whole body glucose homeostasis Metabolic pathways, such as those involved in glucose metabolism, are organised at multiple levels: System e.g. human, migrating bird, hibernating brown bear…. Tissue/Organ e.g. brain, liver, gut Cellular e.g. liver and muscle respond differently to high or low glucose Subcellular e.g. mitochondria, lipid droplet, cytosol Genetic. Cells/tissues can change patterns of gene expression in response to nutritional status.  This presents challenges! How is food intake regulated? Brain, Gut… How is it sensed? Circulation, mechanical, other.. How does the body respond/communicate between tissues? Produce ‘signals’ (hormones) How is this response identified and integrated by specific organs/tissues? Signal perception How is this transduced into changes in cellular metabolism? Signal transduction, cellular mechanisms of control What happens in disease? Defect is…? Therapy? How does genetics influence this? Why are some people more prone to a disease than others?  Blood glucose is carefully controlled by complex mechanisms. Insulin – released from pancreatic b-cells when blood glucose increases. Glucagon – released from pancreatic α-cells when blood glucose levels fall. Opposing actions!  A tale of two hormones… Insulin Glucagon Increases glucose uptake Stimulates into fat and muscle gluconeogenesis Increases glycogen Inhibits glycogen synthesis synthesis in the liver in the liver Inhibits gluconeognesis in Triggers lipid breakdown liver Insulin signals the fed Glucagon signals the state and the removal of release of glucose into the glucose from the blood blood  A tale of two hormones… Insulin Glucagon Increases glucose uptake into fat and muscle Increases glycogen synthesis in the liver Inhibits gluconeognesis in liver Insulin signals the fed state and the removal of glucose from the blood Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactate or amino acids.  A tale of two hormones… Insulin Glucagon Increases glucose uptake Stimulates into fat and muscle gluconeogenesis Increases glycogen Inhibits glycogen synthesis synthesis in the liver in the liver Inhibits gluconeognesis in Triggers lipid breakdown liver Insulin signals the fed Glucagon signals the state and the removal of release of glucose into the glucose from the blood blood Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactate or amino acids.  Questions to discuss Other sources of fuel in the body? Why is glucose such a good fuel? Glucose storage All organisms store food within their cells. Sugar stored as glucose subunits in the polymer glycogen (mainly in liver and muscle cells) Synthesis and degradation of glycogen is rapidly regulated by need.  Glucose High circulating glucose – the fed state Glycogen Acetyl-CoA  Glucose Low circulating glucose Fasted state Glycogen Acetyl-CoA Glucose-6-phosphatase hexokinase These two steps represent quite distinct reactions catalysed by very different enzymes and different Glycolysis mechanisms. They are regulated reciprocally: when one is active, the other is not, and vice versa.  Glucose Flux through any Hexokinase Glucose-6-phosphatase metabolic pathway is controlled by one (or Glucose-6-phosphate more) key regulatory enzymes. Phosphoglucomutase Glucose-1-phosphate Controlling the activity of these key enzymes allows careful integration of metabolism. Glycogen Synthase Glycogen Phosphorylase Glycogen Key: this process can be switched very quickly from one direction to the other  INSULIN Glucose-1-phosphate ON OFF Glycogen Synthase Glycogen Phosphorylase Glycogen  Glucagon Glucose-1-phosphate OFF ON Glycogen Synthase Glycogen Phosphorylase Glycogen Both reactions are energetically favourable – they happen spontaneously Reciprocal regulation of enzymes needed Allow the system to quickly react to changes in blood sugar levels  Regulation of Enzymes Mammalian enzymes are regulated by many mechanisms. These include: Changing rate of biosynthesis/degradation LEVELS Changing ACTIVITY Changing LOCATION  Regulation of Enzymes Mammalian enzymes are regulated by many mechanisms. These include: Changing rate of biosynthesis/degradation LEVELS Changing ACTIVITY Changing LOCATION  Reversible Covalent Modification Regulates Key Mammalian Enzymes A commonly used way to quickly regulate enzyme activity in response to a signal (e.g.hormone) is to use reversible covalent modification. Although this can include many forms (prenylation, ubiquitination, glycosylation, etc.) by far the most common is PHOSPHORYLATION  Reversible Covalent Modification Regulates Key Mammalian Enzymes Phosphorylation involves the covalent addition of a phosphate, transferred from ATP by the action of a class of enzymes called KINASES. This is reversible, and the removal of the phosphate is catalysed by a group of enzymes called PHOSPHATASES.  Reversible Covalent Modification Regulates Key Mammalian Enzymes Phosphorylation may turn an enzyme on or off. Alters the 3D conformation of the target protein because of the high charge density of the protein-bound phosphoryl group, -2 at physiological pH. These often make salt bridges with nearby Arginine or Lysine residues (+vely charged)  Reversible Covalent Modification Regulates Key Mammalian Enzymes Changes to the enzyme induced by phosphorylation can be rapidly reversed by virtue of the kinase/phosphatase system. Two main classes of kinase: those that phosphorylate TYROSINE residues, and those that phosphorylate SERINE/THREONINE residues.  Summary – where have we got to? Insulin and glucagon regulate carbohydrate metabolism reciprocally They do this by coordinating the flux through metabolic pathways – E.g. The formation and breakdown of glycogen – Next time: molecular detail which underpins that Homework question – other examples of reciprocal regulation?