BIOL1XX8_2024_L17_Cellular Respiration.pdf

Cellular respiration Dr. Hong Dao Nguyen School of Life and Environmental Sciences Animations originally created by Prof. Danny Liu Learning objectives Differentiate between anabolism and catabolism with examples Describe glucose catabolism thro...

Cellular respiration Dr. Hong Dao Nguyen School of Life and Environmental Sciences Animations originally created by Prof. Danny Liu Learning objectives Differentiate between anabolism and catabolism with examples Describe glucose catabolism through the processes of glycolysis, the intermediate reaction, the Krebs Cycle and the Electron Transport Chain Analyse and predict the potential impacts on cellular respiration pathways under metabolic poisoning scenarios Last lecture… What we consume What can be absorbed Stored as glycogen Carbohydrates Monosaccharides (mostly starches) (mostly glucose) Broken down for the release of energy in the form of ATP (today’s lecture) Proteins Amino acids Energy can also be extracted from these Lipids (next lecture) Fatty acids (mostly triglycerides)  Metabolism The collection of all chemical reactions that occur in the body Cellular respiration: Synthesis of glycogen oxidation of glucose to from glucose CO2 Synthesis of peptides Breakdown of proteins to from amino acids peptides Anabolism is to Build Catabolism is to Destroy Image from Lewis & Keshari (2017) Imaging and Metabolism Energy carriers: ATP ATP is like a rechargeable battery Energy released for another activity ATP ADP Pi Adenosine diphosphate Adenosine triphosphate Energy extracted from another activity ATP ATP cannot be stored Holds energy temporarily in covalent bonds between phosphates Can be generated in the presence (aerobic respiration) or absence of oxygen (anaerobic respiration) ~1 billion ATP molecules are in a cell at any one time and this ATP is turned over every 1-2 minutes Adenosine triphosphate At rest we produce our body weight in ATP every day – At maximal exercise, this number can increase to 0.5-1kg per minute ATP is energy currency of the cell. It is used in multiple ways e.g. – active transport of molecules across cell membranes, – contraction of muscles – synthesising hormones, cell membranes, and other essential molecules, – cell division and growth Images: Wikimedia Commons; OCAL Cellular respiration: an overview Cellular respiration involves many oxidation-reduction reactions The breakdown of glucose to CO2 (over many steps!!) is an oxidation process C6H12O6 + 6O2 à 6CO2 + 6H2O + energy Free energy Glucose & O2 CO2 & H2O Molecules that are oxidised lose electrons (and therefore lose hydrogen) – Carbon is more electron poor when in the form of CO2 compared to glucose – Glucose is oxidised to carbon Molecules that are reduced gain electrons (and therefore gain hydrogen) – Oxygen is reduced to water  In biological rea Other energy carriers Throughout the process of cellular respiration, energy is captured by other energy carriers before ATP is generated. Nicotinamide adenine dinucleotide – NADH (reduced form): carries electrons and is a good electron donator – NAD+ (oxidised from): not carrying electrons and is a good electron acceptor Flavin adenine dinucleotide – FADH2: (reduced form): carries electrons and is a good electron donator – FAD (oxidised form): not carrying electrons and is a good electron acceptor OIL RIG p+ Oxidation is loss of H (H+ + e-) Reduction is gain of H (H+ + e-) e- Hydrogen atom Cellular respiration pathways Glycolysis – occurs in the cytoplasm – Does not require the presence of oxygen (anaerobic pathway) Intermediate reaction Occurs in the mitochondria Krebs Cycle Reliant on the presence of oxygen (aerobic pathways) Electron Transport Chain Mitochondrial matrix Matrix Inner mitochondrial Intermembrane membrane (IMM) space Outer membrane  Glycolysis Series of 10 reactions in the cytosol that produces 2 pyruvate molecules from 1 glucose molecule Does not use oxygen and occurs regardless of whether it is present or not Produces 4 ATP molecules (net 2 ATP) NAD+ picks up electrons and is reduced to NADH 2NAD+ 2x NADH 4ADP 4ATP Cytoplasm Glucose 2ATP 2ADP 2x Pyruvate Mitochondria image from Wikimedia Commons Intermediate reaction During the process of pyruvate converting to Acetyl CoA, electrons are removed and given to NADH electron basket Let’s follow the fate of one pyruvate molecule… CO 2 Outer mitochondrial membrane Inner mitochondrial membrane Matrix CO2 CoA Acetyl CoA Pyruvate NADH NAD+ Krebs cycle Mitochondria image from Wikimedia Commons  Series of 8 reactions in the mitochondrial matrix Krebs Cycle For every Acetyl CoA taking part, products are 2 x CO2, 3 x NADH, one FADH2, one ATP CoA Acetyl CoA NADH CO2 NAD+ NAD+ NADH ×2 FADH2 CO2 FAD ADP + Pi ATP  Electron transport chain Electrons donated by NADH & FADH2 move through protein complexes Protein complexes is reduced then oxidised, releasing energy which is used to actively pump and concentrate H+ against its electrochemical gradient in the intermembrane space Electrons eventually fall to O2 and combine with protons to form water OMM Intermembrane space ATP synthase IMM FAD ½ O2 + 2H+ H 2O FADH2 Matrix NADH2 NAD+ H 2O H+ + OH- ADP + Pi ATP Electron transport chain  ATP synthase harnesses potential energy to generate ATP H+ are concentrated in the intermembrane space creating an electrochemical gradient (potential energy) Energy is harvest from the flow of H+ down their electrochemical gradient through ATP synthase Energy is used by ATP synthase to combine ADP + Pi à ATP 28-32 molecules of ATP produced per glucose oxidised Intermembrane space Mitochondrial matrix IMM Matrix Inner mitochondrial Intermembrane membrane (IMM) space Outer membrane Matrix Matrix Video from http://www.youtube.com/watch?v=XI8m6o0gXDY Aerobic pathways are more efficient at producing ATP Efficiency here refers to the amount of ATP produced per molecule glucose Glycolysis is faster but only produces net 2 ATP per glucose molecule Electron transport chain takes longer but produces 28-34 molecules per glucose molecule – 3 ATP molecules are produced for every NADH oxidised – 2 ATP molecules are produced for every FAHD2 oxidised Cellular respiration summary Glucose + oxygen à carbon dioxide + water + energy 6 x NADH Cytoplasm 2 x NADH 2 x FADH2 Electron transport chain Glucose Intermediate reaction & Krebs Cycle Oxygen reduced to water 2 x NADH CO2 Acetyl-CoA CO2 Glycolysis IMM Intermembrane Matrix space Pyruvate Mitochondria ATP ATP ATP 28-34 ATP per ATPATP Net 2 ATP per ATP ATP ATP molecule of glucose ATP ATP ATP ATP glucose molecule Mitochondria image from Wikimedia Commons 2 ATP per glucose molecule Cellular respiration summary Glucose + oxygen à carbon dioxide + water + energy Cytoplasm IMM Intermembrane Matrix space Mitochondria ATP ATP Mitochondria image from Wikimedia Commons Head scratcher Someone accidentally consumes a poison known as DCCD and experiences extreme fatigue. Given the provided evidence, which stage of cellular respiration is mostly being disrupted by DCCD? O2 is present Lucas is only producing 4 ATP molecules per glucose molecule Pyruvate is present in the cytoplasm and acetyl-CoA is present in the mitochondria NADH is at normal levels A. Glycolysis B. Intermediate reaction C. Krebs Cycle D. Protein complexes of the electron transport chain E. ATP synthase