BIOL111 Lectures 5 and 6 2024 PDF

3/25/24 What you should know at the end of these lectures (5 and 6) Aerobic respiration is the oxidation of glucose to CO2 and H2O Electrons are removed from glucose (hence it is oxidised) Elect...

3/25/24 What you should know at the end of these lectures (5 and 6) Aerobic respiration is the oxidation of glucose to CO2 and H2O Electrons are removed from glucose (hence it is oxidised) Electrons are added to O2 (hence it is reduced) forming H2O Glucose is converted to 2 molecules of pyruvate in a metabolic pathway called glycolysis Pyruvate enters the mitochondrion and is converted to acetyl coA Acetyl Co A enters the citric acid cycle Electrons pass from the metabolites in glycolysis and the citric acid cycle to NAD+ and FAD which pass them to O2 via large protein complexes in the mitochondrial inner membrane O2 is electronegative – electrons lose energy as the move to an electronegative atom 1 What you should know at the end of these lectures The energy is passed to the large protein complexes enabling them to change shape (only slightly) The shape change enables them to act as H+ pumps creating a H+ gradient across the inner mitochondrial membrane H+ move through ATP synthase a rotational enzyme which couples H+ movement to the production of ATP Much of the above can also occur through the oxidation of fats and proteins If O2 is absent fermentation occurs 2 1  3/25/24 Respiration Glucose oxidised to carbon dioxide C6H12O6 + 6O2 6CO2 + 6H2O Oxygen reduced to water 3 Transforming energy – lecture 2 Food – chemical energy (potential energy) Used to create a H+ gradient across the membrane of mitochondria (potential energy) H+ cause ATP synthase to rotate (kinetic energy) Rotation makes ATP (potential energy) ATP drives many processes such as muscle contraction (kinetic energy) 4 2  3/25/24 Respiration Exergonic reaction DG = -686 kcal mol-1 Exergonic as the electrons are moved from glucose to oxygen 5 Respiration Electrons lose potential energy as they move to an electronegative atom In cells they are moved through various steps – initially to electron carriers (NADH and FADH2) then proteins in the electron transport chain then to oxygen The energy is used to fuel a H+ gradient that is used to synthesise ATP 6 3  3/25/24 Reduction of NAD+ and terminology NAD+ + 2H+ + 2e- NADH + H+ “NAD” “Reduced NAD” 7 Aerobic Respiration – when O2 present Glycolysis, pyruvate oxidation, citric acid cycle and oxidative phosphorylation Occurs in cytosol and mitochondria (eukaryotes) Occurs in the cytosol and plasma membrane (prokaryotes) 8 4  3/25/24 Mitochondria 9 Glycolysis – a catabolic pathway Occurs in cytosol 10 reactions 1 glucose converted to 2 pyruvates Yield of 2 ATPs per glucose Yield of 2 NADH per glucose Energy investment phase (5 reactions) Glucose converted to 2 glyceraldehyde 3-phosphates Energy payoff phase (5 reactions) 2 glyceraldehyde 3-phosphates converted to 2 pyruvates 10 5  3/25/24 Glycolysis – energy investment phase 11 Glycolysis – energy payoff phase 12 6  3/25/24 Substrate level phosphorylation 13 Control of respiration 14 7  3/25/24 Control of respiration –allosteric regulation of an enzyme Phosphofructokinase activated by AMP (cell low in energy) inhibited by ATP, citrate (cell high in energy) 15 Pyruvate If O2 present Pyruvate enters mitochondria Converted to Acetyl CoA Pyruvate dehydrogenase complex Multienzyme complex 16 8  3/25/24 Citric acid cycle 17 Citric acid cycle: Summary Krebs cycle/ TCA cycle 8 reactions Start with Acetyl CoA Produce 3 NADH (thus 6 per original glucose) Produce 1 FADH2 (2 per original glucose) Produce 1 GTP = 1 ATP (2 per original glucose) 2 CO2 (4 per original glucose) 18 9  3/25/24 Citric acid cycle http://www.csulb.edu/~cohlberg/ Songs/krebs.mp3 http://www.youtube.com/watch?v =FgXnH087JIk&feature=PlayList &p=4143AA8F3DD1B435&index =14 19 What happens next? Glucose oxidised to carbon dioxide n C6H12O6 + 6O2 6CO2 + 6H2O Electrons have been passed to NADH and FADH2 These are then passed onto O2 via the electron transport chain ~90% of O2 that you breath in is used for this 20 10  3/25/24 The reduction part of the equation nThese are passed onto O2 via the electron transport chain nC6H12O6 + 6O2 6CO2 + 6H2O Oxygen reduced to water 21 Electron transport chain and oxidative phosphorylation 22 11  3/25/24 Electron transport chain 4 large protein complexes in inner mitochondrial membrane – Complexes 1, 2, 3 and 4 2 electron carriers – Q and cytochrome c 23 Q Also known as ubiquinol/ubiquinone or coenzyme Q Shuttles electrons between Complex 1 and Complex 3 (if electrons originate from NADH) Shuttles electrons between Complex 2 and Complex 3 (if electrons originate from FADH2) Included in face creams (antioxidant) 24 12  3/25/24 Cytochrome c Small protein - fairly well conserved through evolution Cytochrome c: 100 – 104 amino acids long Cytochromes are redox-active proteins containing a heme, with a central Fe atom at its core, as a cofactor. They are involved in electron transport chain and redox catalysis. Used in evolutionary studies 25 Cytochrome c Chapter 3 – Biology2e 26 13  3/25/24 Cytochrome c Me and the Chimp – identical Rhesus monkey – differs by one amino acid The chimp is more closely related to me than the rhesus monkey Used to construct clades 27 Other components of the electron transport chain can also be used in evolutionary studies In this study cytochrome b (see next slide) was used to investigate phylogenetic relationships in owls Ruru/Morepork https://www.youtube.com/watch?v= gAc8-YDzWZw 28 14  3/25/24 Electrons lose energy as they move toward the electronegative O2 Move through various cofactors and coenzymes (e.g. Fe-S, various cytochromes) Potential energy is transformed into kinetic energy - shape changes in the proteins 29 Complex 3 This bit swivels 30 15  3/25/24 Shape changes enable Complexes 1, 3 and 4 to act as proton pumps Move protons from the matrix into the intermembrane space Per pair of electrons: Complex 1 moves 4 protons Complex 3 moves 4 protons Complex 4 moves 2 protons Complex 2 moves 0 protons Per NADH 10 protons moved Per FADH2 6 protons moved 31 Proton gradient – form of potential energy (lecture 2) Free energy is essentially a measure of something's stability. Higher G = greater instability = greater order 32 16  3/25/24 ATP synthase forms a pathway for protons to move down their electrochemical gradient 33 ATP synthase forms a pathway for protons to move down their electrochemical gradient 34 17  3/25/24 Uncouplers In some cells mitochondria contain uncouplers Uncoupling proteins move protons back across membrane – not through ATP synthase ATP isn’t produced Potential energy is converted to kinetic energy (heat) Keeps the bear warm when hibernating and enables the skunk cabbage to attract insects for pollination 35 ATP yield per glucose 36 18  3/25/24 In the absence of O2 – fermentation (anaerobic respiration) 37 Other Catabolic pathways 38 19  3/25/24 Getting energy from fats A major function of fats is energy storage Humans and other mammals store their fat in adipose cells 39 Getting energy from fats b oxidation occurs in the mitochondrial matrix Each acyl unit coming off 3 NADH, 1FADH2, 1ATP Electron transport chain oxidative phosphorylation Acyl units 40 20  3/25/24 Getting energy from fats Glucose – ~32 ATPs – Total storage carbohydrate in body could produce approx 110,000 mmol ATP – 16.7 mmol s-1 Triacylglycerol - > 300 ATPs – Total storage fat in body could produce 4,000,000 mmol ATP – Slowly – 6.7 mmol ATP sec-1 41 Prokaryotes No organelles – no mitochondria Glycolysis and citric acid cycle occur in cytosol Electron transport proteins and ATP synthase in the plasma membrane Protons pumped out of the cell and re- enter via ATP synthase producing ATP Higher yields of ATP per glucose – Why?? Energetic cost of moving ATP out of the mitochondria – prokaryotes don’t have this problem 42 21