PL1003 Cellular Respiration PDF

PL1003: Cellular Respiration Janine Coombes  Why is this important for pharmacists? Cellular respiration is an essential metabolic pathway used by cells to release energy from glucose (as ATP). Cells are flexible in their metabolism, shifting between glycolysis and oxida...

PL1003: Cellular Respiration Janine Coombes  Why is this important for pharmacists? Cellular respiration is an essential metabolic pathway used by cells to release energy from glucose (as ATP). Cells are flexible in their metabolism, shifting between glycolysis and oxidative phosphorylation depending on the Re-directing situation. energy metabolism in cells is an important therapeutic strategy. Shifting cancer cell metabolism from aerobic glycolysis to oxidative phosphorylation can inhibit growth of tumours. Shifting energy metabolism from oxidative phosphorylation to glycolysis can inhibit oxidative damage in ischemic injury. Activation of thermogenesis (where respiration in uncoupled from ATP synthesis) could be an important therapeutic strategy for obesity and T2D. 9 December 2 2 024  Cellular Respiration A series of reactions that break down glucose (the fuel) and produce ATP (the energy currency of the cell) Glycolysis Pyruvate oxidation Citric Acid Cycle (Kreb’s cycle) Oxidative Phosphorylation (electron transport chain and chemiosmosis) 9 December 2 3 024  ATP: The energy currency of the cell Adenosine triphosphate (ATP) is a nucleotide. Nucleotides consist of a nitrogenous base (nucleobase) a five-carbon sugar (pentose) and one to three phosphates Adenosine triphosphate provides energy to drive cellular processes. ATP 9 December 2 4 024  ATP: the energy currency of the cell Mediates the transfer of chemical energy from reactions that release energy (exergonic), to those that require energy (endergonic). ATP “stores” this energy in the form of a high energy phosphoanhydride bond. Hydrolysis of ATP splits the phosphoanhydride bond releasing energy. ATP + H2O  ADP + Pi + Energy The cell is constantly using this energy, so ATP energy stores need to be replaced! Energy released in an exergonic reaction can be used to add a phosphate group to ADP, regenerating ATP. 9 December 2 5 024 9 December 2 6 024  Mechanisms for generating ATP Substrate level phosphorylation Transfer of a phosphate from a substrate directly to ADP, forming ATP. Energy comes from the substrate which is converted from a higher to lower energy product in the process. Occurs in glycolysis and citric acid cycle. Oxidative phosphorylation Muessig, CC BY-SA 3.0 , via Wikimedia 9 December 2 Commons, https://commons.wikimedia.org/wiki/File:ADP_ATP_cycle.png 7 024  What type of “work” does ATP power? The phosphate group is transferred from the ATP to another molecule (helped by enzymes) The molecule that accepts the phosphate can now perform transport, Chapter 7: Concept 7.3 (mtchs mechanical or chemical “work” 9 December 2 8 024  Oxidation and Reduction Always coupled – one substance is oxidised, while another is reduced. Oxidation = “removal” of electrons (hydrogen) The hydrogen is picked up by coenzymes for transfer to another compound. Reduction = “gain” of electrons (hydrogen) Oxygen, carbon are more electronegative therefore “hog” the electrons from the incoming hydrogen. Oxidation and reduction review from biological point-of- view (video) | Khan Academy 9 December 2 9 024  NAD+ / NADH Nicotinamide adenine dinucleotide (NAD) is a coenzyme important in cellular respiration. High energy molecule It can exist in an oxidised (NAD+) Energy used and reduced (NADH) form. When NAD+ is reduced, energy is Energy STORED. released When NADH is oxidised, energy is RELEASED. Low energy molecule 9 December 2 10 024  NAD+ / NADH Functions as an electron carrier and, in doing so, acts as a carrier of energy, trapping and High energy molecule transporting electrons from one Energy used reaction to another (in the form of a hydride ion). When another molecule is Energy oxidised, 2 hydrogen atoms are released removed as a hydride ion (H-) and a hydrogen ion (H+). The H- is Low energy transferred to NAD+, and the H+ molecule is released into solution. 9 December 2 11 024  requiring Energy Glycolysis Occurs in the cytosol Begins with glucose (6 carbons) and ends with 2 x pyruvate (3 carbons). Energy-requiring and Energy- releasing Energy releasing phases Energy-releasing phase creates ATP and NADH. Concepts of Biology. Authored by: Open Stax. Located at: http://cnx.org/contents/[email protected]:1/ Concepts_of_Biology. License: CC BY: Attribution 9 December 2 12 024  Glycolysis: energy-requiring phase Phosphate group transferred from ATP to glucose Glucose-6-phosphate is converted into its isomer, fructose-6-phosphate. Phosphate group transferred from ATP to fructose-6-phosphate, Fructose-1,6-bisphosphate splits to form two three-carbon sugars: DHAP and glyceraldehyde-3-phosphate. These three carbon sugars are isomers. DHAP converts easily to glyceraldehyde-3-phosphate Glyceraldehyde-3-phosphate enters the Rozzychan, Public domain, energy-releasing via Wikimedia Commons phase. 9 December 2 13 024  Glycolysis: Energy releasing phase Glyceraldehyde-3-phosphate generated in the energy- requiring phase is turned into pyruvate, resulting in the creation of 4 x ATP and 2 x NADH Glyceraldehyde 3- A phosphate phosphate is group is oxidised, while donated to NAD+ is reduced. ADP this reaction is exergonic overall, and the extra energy generated is used to phosphorylate glyceraldehyde 3- phosphate. Glycolysis | Cellular respiration | Biology (article) | Khan Academy Image modified from " Glycolysis: Figure 2," by OpenStax College, Biology (CC BY 3.0) 9 December 2 14 024  Pyruvate Oxidation Pyruvate transported into mitochondria Pyruvate is decarboxylated (a carboxyl group is removed, releasing CO2). The two-carbon molecule generated is then oxidised to form an acetyl group. NAD+ is reduced to NADH. The acetyl group is attached to Coenzyme A: Acetyl-CoA Captures remaining energy from Access for free at https://openstax.org/books/biology/pages/1-introduction. Creative Commons — Attribution 4.0 International — CC BY 4.0 pyruvate molecules and generates a substrate for the citric acid cycle. 9 December 2 15 024 December 9, 2024 16  What if oxygen is limited? Anaerobic pathway. Pyruvate acid is reduced to lactic acid. Electrons come from NADH/H+ NAD+ is ready to be used in glycolysis again. 9 December 2 17 024  Citric Acid (Krebs) Cycle Occurs in the mitochondrial matrix A series of decarboxylation reactions  release CO2 oxidation-reduction reactions  Acetyl CoA derivatives are oxidised, NAD+ and FAD are reduced to NADH and FADH2. This transfers chemical energy to NADH and FADH2. ATP is generated. 9 December 2 18 024  Citric Acid (Krebs) Cycle For each complete turn of the citric acid cycle (stored energy!): 3 NADH/H+ Oxidation- 1 FADH reduction 1 ATP reactions Substrate level phosphorylatio n BUT each glucose generates 2 x acetyl CoA Access for free at https://openstax.org/books/biology/pages/1-introduction 9 December 2 19 024  Oxidative Phosphorylation Occurs in the inner mitochondrial membrane Uses the electron transport chain – a series of membrane protein complexes and other molecules that act as electron carriers. Carriers in the chain gain electrons (are reduced) and lose electrons (are oxidised). This Eventually oxygen is reduced, releases energy. and the reduced oxygen picks up hydrogen ions to make Where do these electrons come water. from?? What is the energy used for? Access for free at https://openstax.org/books/biology/pages/1-introduction 9 December 2 20 024  Oxidative Phosphorylation NADH is oxidised! (NADH  NAD+ + H+ + 2e-)* As electrons pass through the chain, energy is used by the electron carrier complexes to pump H+ ions (protons) across the mitochondrial membrane. Produces a concentration Access for free at https://openstax.org/books/biology/pages/1-introduction *Note that NADH cannot easily cross the mitochondrial gradient. membrane, so a shuttle system is used to deliver the electrons to the electron transport chain 9 December 2 21 024  Oxidative Phosphorylation Ions cannot diffuse freely through membranes – requires a channel. In the inner mitochondrial membrane, ATP synthase is used. The flow of H+ ions allows ATP synthase to catalyse the addition of phosphate to ADP, Access for free at generating ATP. https://openstax.org/books/biology/pages/1-introdu ction 9 December 2 22 024  Cellular Respiration A series of reactions that break down glucose (the fuel) and produce ATP (the energy currency of the cell) Glycolysis Pyruvate oxidation Citric Acid Cycle (Kreb’s cycle) Oxidative Phosphorylation (electron transport chain and chemiosmosis) 9 December 2 23 024  Brown adipocytesProtons are translocated across “Uncoupling Protein 1” instead of ATP Synthase. What happens to all the energy harvested in the earlier stages of respiration? 9 December 2 24 024  Brown adipocytes Pharmacological activation of thermogenesis in brown adipose tissue (i.e increased UCP1 expression / activity) is considered a promising strategy to treat obesity. 9 December 2 25 024  Glucose metabolism in tumour cells Glucos e Pyruva te Acetyl- CoA Lactate Citric Acid Cycle OXPH OSplentiful Oxygen Oxygen limited 9 December 2 26 024  Glucose metabolism in tumour cells Tumours take up huge amounts Glucos of glucose. e Even in the presence of Pyruva adequate oxygen, a lot of this te glucose in converted to lactate  Acetyl- “Warburg effect” CoA Lactate Why? Citric Acid Cycle OXPHO S plentiful Oxygen 9 December 2 27 024  Glucose metabolism in tumour cells Does glycolysis or oxidative Glucos phosphorylation produce more e ATP? Pyruva Is it faster to produce lactate or te to complete oxidative Acetyl- phosphorylation? CoA Lactate Citric Acid Cycle OXPHO S plentiful Oxygen 9 December 2 28 024  Glucose metabolism in tumour cells Does glycolysis or oxidative Glucos phosphorylation produce more e ATP? Pyruva X10-100 Is it faster to produce lactate or te speed to complete oxidative Acetyl- phosphorylation? CoA Lactate Citric Acid 4 ATP Cycle OXPHO S 36-38 ATP 9 December 2 29 024  Glucose metabolism in tumour cells Glucose to lactate is 10-100X faster than complete oxidation of glucose. So a cell can generate just as much ATP (and faster) by favouring aerobic glycolysis over complete oxidation of glucose (just needs more glucose…..). Provides additional glucose-derived metabolites for nucleotide, lipid or protein biosynthesis. DNA replication and RNA transcription Membrane production PROLIFERATION Protein translation !!! 9 December 2 30 024  Glucose metabolism in tumour cells So a cell can generate just as much ATP (and faster) by favouring aerobic glycolysis over complete oxidation of glucose. Provides additional glucose-derived metabolites for nucleotide, lipid or protein biosynthesis. High consumption of glucose limits availability to other cells, including immune cells. Production of lactate also benefits the tumour: lactate dampens immune responses, while acidification of the environment favours invasion. 9 December 2 31 024  Increased demand for NAD+ rel ative to ATP drives aerobic glyc olysis - ScienceDirect New Clarity on the Warburg Effect - NCI (cancer.go v) 9 December 2 32 024  Therapeutic targeting of glucose metabolism Fasentin, STF-31, Block glucos genistein e uptake Inhibit aerobic Lonidamine (selective inhibition of glycoly hexokinase in cancer sis cells – different isoforms) 9 December 2 33 024