Riveting Respiration

1. Riveting Respiration Chapter 9 notes So Why do we Breathe????

2. Background • Sun – Ultimate energy source for ecosystems • ATP – Usable cellular energy • Chemical Energy – Energy stored in chemical bonds • Fermentation – Partial breakdown of sugar WITHOUT using Oxygen

4. Cellular Respiration • Complete degrading (breakdown) of sugar using Oxygen (catabolic process) • Uses energy stored in food to make ATP • C6H12O6 + 6O2 6CO2 + 6H2O + Energy (ATP + heat) • ΔG = -686 kcal/mol – WOW!!! • ATP will be used to drive other processes that need energy through Phosphorylation

5. Redox Reactions • Oxidation-Reduction • Chemical reaction where one or more electrons are transferred from one reactant to another • Oxidation – loss of electron from substance • Reduction – Addition of electron to another substance

6. Redox Reactions • Complete transfer of electrons • Na + Cl Na+ + Cl – • Partial transfer of electrons • CH4 + 2O2 CO2 + Energy + 2H2O

8. Redox Reactions • When an electron is transferred from a less electronegative atom to a more electronegative atom, energy is released that can be used to do work

9. Redox Reactions • For respiration • C6H12O6 + 6O2 6CO2 + 6H2O • Glucose is oxidized and oxygen is reduced releasing lots of energy (remember oxygen is VERY electronegative)

10. Respiration • Performed mainly on carbohydrates and fats, but we will focus on GLUCOSE • Activation energy prevents these high energy goods from breaking down spontaneously – so we will need ENZYMES to make respiration happen • Glucose is broken down in a series of steps. Each step has its own enzyme

11. Respiration • Hydrogens are not transferred directly to Oxygen, but are first passed to a Coenzyme called NAD+ • NAD+ + electrons NADH • H+ (proton) is transferred to the solution • NADH will carry the electrons to an Electron transport chain and will be used to make ATP (more on this soon!!)

13. Electron Flow • Overall flow of electrons in respiration • FoodNADHelectron transport chainOxygen

15. 3 Main Steps to Cellular Respiration • 1. Glycolysis – happens in the cytosol. Breaks glucose into smaller compound (pyruvate) • 2. Citric Acid (Krebs) cycle – happens in the matrix of the mitochondria. Breaks down pyruvate to CO2 • 3. Electron transport chain – happens in the inner mitochondrial membrane. Generates ATP using electrons from steps 1 and 2

17. Glycolysis • Splits glucose (6 Carbons) into two molecules of pyruvate (3 C each) • No oxygen required (yet)

18. Glycolysis • Energy Investment Phase • 2 ATP are USED to phosphorylate glucose and convert it into two pyruvates • Energy Payoff Phase • After a series of enzyme catalyzed reactions: 4 ATP are produced by Substrate level phosphorylation (using a substrate to make ATP) • 2 NADH are produced by transferring electrons to NAD+

20. Glycolysis • Total Input • Glucose, 2ATP, 2NAD+ • Total Output • 2 Pyruvate, 4 ATP, 2NADH • Net ATP produced = 2

22. Got Oxygen??? • If oxygen is present – pyruvate moves into the mitochondria • Pyruvate is converted to Acetyl CoA in a series of 3 reactions (all with enzymes) • CO2is released • NAD+ gains an electron NADH • Acetyl CoA enters the Krebs cycle

24. Citric Acid (Kreb’s) Cycle • Occurs in mitochondria matrix • Cycle has 8 total steps (each catalyzed by different enzyme) • Step 1 – Acetyl CoA combines with Citrate (citric acid cycle) • Cycle happens 2 times (one for each Acetyl CoA)

25. Citric Acid Cycle • For Each Acetyl CoA • 3 NAD+ 3 NADH + 3H+ • 1 FAD  1 FADH2 • 1 ATP is produced (substrate level phosphorylation) • 2 CO2 are produced

26. Citric Acid Cycle • Total Inputs • 2 Acetyl CoA, 6 NAD+, 2 FAD, 2 ADP • Total Outputs • 6 NADH, 2 FADH2, 2 ATP, 4 CO2 (released when exhale)

28. Electron Transport Chain • Location- • Inner Mitochondrial Membrane • Series of molecules (mostly proteins) embedded in this membrane • Each part of the chain gets more and more electronegative until the end of the chain • OXYGEN is at the end of the • chain (most electronegative)

30. Electron Transport Chain • NADH and FADH2 from glycolysis and the Citric acid cycle carry their electrons to the electron transport chain • NADH releases electrons at the top of the chain. Electrons are pulled down the chain by the increasing electronegativity of each molecule • As the electrons fall, ATP is made through Chemiosmosis (more later)

31. Electron Transport Chain • FADH2 carries its electrons to the chain, but donates them a little further down the chain (not at the top) • These electrons are also pulled down the chain, producing ATP as they go FADH2 starts here

32. Chemiosmosis • Process that makes ATP • As electrons flow down the ETC, energy is released. • This energy is used to pump H+ (protons) across the membrane leaving a high concentration of H+ outside and a low concentration inside

34. Chemiosmosis • H+ wants to flow back in to the mitochondrial matrix to reach equilibrium • The only way for the H+ to get back in is through the enzyme ATP synthase • ATP synthase is an enzyme located in the inner mitochondrial membrane • As H+ moves through the membrane, it allows ADP to be phosphorylated making ATP (ADP + Pi ATP). • This is called Oxidative phosphorylation (using a redox rxn to make ATP)

37. Electron Transport Chain • Net outputs • For each NADH that enters the chain, 3 ATP are produced – Total = 30 ATP • For each FADH2 that enters the chain, 2 ATP are produced – Total = 4 ATP • Water is released by combination of O2 with H+ and electrons H2O

38. Respiration • Total ATP Production for Cellular Respiration • 2 ATP – Glycolysis • 2 ATP – Citric Acid Cycle • 34 ATP – Electron Transport • Total = 38 ATP

40. Fabulous Fermentation • Allows cells to generate ATP without Oxygen (anaerobic). ATP is made only by substrate level phosphorylation • Process involves Glycolysis + reactions to regenerate NAD+ (in respiration NAD+ is regenerated in the ETC)

41. Alcohol Fermentation • After glycolysis, pyruvate is converted to ethanol in order to regenerate NAD+. This allows glycolysis to continue again. • Occurs in Yeast and Bacteria • Used to make Alcohol

43. Lactic Acid Fermentation • After glycolysis, pyruvate is converted to lactate to regenerate ATP. • Used by Fungi and Bacteria • Important in dairy industry to make cheese and yogurt. • Also occurs in Human Muscle Cells during exercise. Muscles can’t get enough oxygen to keep up with respiration. Lactate builds up causing muscle cramps and fatigue.

45. Evolutionary Significance of Glycolysis • Glycolysis was probably used by the earliest prokaryotes to make ATP before oxygen was present in the atmosphere. • Evidence – Glycolysis occurs in the cytoplasm (not in mitochondria) and it is found in ALL living cells

46. What else can be used for Respiration?? • 1. Carbohydrates – Broken down into glucose then enter glycolysis • 2. Proteins – Broken down into amino acids which can enter the cycle later in glycolysis or in Citric Acid cycle (not normally used – need to use amino acids to make protein) • 3. Fats – Glycerol enters the cycle during glycolysis. Fatty acids are broken down into 2 Carbon fragments that enter at Kreb’s cycle

48. Control of Respiration • Cells do not make more ATP than they need • Cells can switch of respiration, usually by Feedback Inhibition of certain enzymes in the chain. • This prevents making unnecessary ATP and the molecules used in respiration can be used for other processes.