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How Cells Harvest Chemical Energy

How Cells Harvest Chemical Energy. ATP Is Universal Energy Source. Photosynthesizers get energy from the sun Consumers get energy from plants or other organisms ENERGY is ALWAYS converted to the chemical bond energy of ATP Photosynthesis and Respiration are LINKED. Photosynthesis.

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How Cells Harvest Chemical Energy

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  1. How Cells Harvest Chemical Energy

  2. ATP Is Universal Energy Source • Photosynthesizers get energy from the sun • Consumers get energy from plants or other organisms • ENERGY is ALWAYS converted to the chemical bond energy of ATP • Photosynthesis and Respiration are LINKED

  3. Photosynthesis • Overall reaction: 6 CO2 + 12 H2O  C6 H12O6 + 6 O2 + 6 H2O Often shown as 6 CO2 + 6 H2O  C6 H12O6 + 6 O2

  4. Photosynthesis Overview Sunlight 12 H2O 6 CO2 ATP ADP + P Light Dependent Reactions Light-Independent Reactions NADPH NADP+ 6 O2 Glucose-P + 6 H2O Reactions occur in grana of the thylakoid membrane system Reactions occur in stroma

  5. Overview of Cellular Respiration • Glucose + 6 O2  6 CO2 + 6 H2O The overall reaction is exergonic. The energy given off is used to make ATP. 30 - 32 ATP

  6. Breathing O2 CO2 Lungs Bloodstream O2 CO2 Muscle cells carrying out Cellular Respiration Glucose  6 O2 6 CO2 6 H2O  30-32 ATP • Breathing and cellular respiration are closely related:

  7. Cellular Respiration and ATP • Cellular respiration releases the energy stored in glucose in a series of steps • The energy released is stored as ATP and released as heat • Aerobic respiration is ~34% efficient • Meaning… 34% of the energy stored in the glucose is captured and stored as ATP

  8. How Cells Make ATP • ATP is made in two ways during cellular respiration: • Substrate level phosphorylation • Glycolysis • Citric acid cycle (Krebs cycle) • Oxidative phosphorylation • Electrons transport system and chemiosmosis

  9. Substrate-level phosphorylation ENZYME ATP is made in an enzyme in a coupled reaction. Substrate gives energy and phosphate group (Pi) to ADP and makes ATP. Substrate Product Fig. 9.7

  10. Oxidative phosphorylation • Electron carriers (NADH and FADH2) deliver electrons to the Electron Transport Chain (ETC) on the inner membrane of the mitochondria • Electrons are passed from membrane protein to protein. • Each transfer releases energy and pumps H+ out of the matrix • Energy is used to create a chemical gradient • Gradient is used to drive ATP synthesis by the enzyme ATP synthase

  11. Overview of Cellular Respiration

  12. Carbohydrate Metabolism • The first pathway of carbohydrate metabolism is called glycolysis. • Glucose is the starting material for glycolysis. • Glycolysis reactions occur in the cytoplasm.

  13. Glycolysis • Step #1: Glucose is converted to glucose-6-phosphate in a phosphorylation reaction • Reaction is endergonic • Reaction requires an input of ATP • Step #2: A rearrangement reaction occurs to make fructose-6-phosphate

  14. Glycolysis • Step #3: Another phosphorylation reaction occurs to made fructose-1,6-diphosphate • Reaction is endergonic • Reaction requires an input of ATP • Step #4: Fructose-1,6-diphosphate is broken in to 2 three carbon compounds

  15. Glycolysis • 5 more steps occur and 2 pyruvate are made • These steps release energy and electrons. • Energy released is used to make ATP by substrate level phosphorylation • Electrons are attached to the electron carrier NAD+ to form 2 NADH • The NADH deliver electrons and H+ to the electron transport system

  16. More on NADH • Synthesis of NADH (simplified version): NAD+ + 2 e + H+ NADH • Is NAD+ oxidized or reduced in this reaction?

  17. Glycolysis Energy requiring steps: 2 ATP invested Energy releasing steps: 2 NADH formed 4 ATP formed Net yield is 2 ATP and 2 NADH Does NOT require O2 Occurs in the cytoplasm

  18. Glycolysis Summary • Where it occurs: • First substrate: (starting “material”) • End product: • Also made: • net gain of ____ ATP (why net?, how made?) • _____ NADH (made from?)

  19. Glycolysis Summary Where it occurs: Cytoplasm First Substrate:Glucose (6C) End product:2 Pyruvate (3C)

  20. Glycolysis Summary Also made • net gain of 2 ATP made by substrate-level phosphorylation • Pathway requires an input of 2 ATP to start and makes a total of 4 ATP • 2 NADH – each made from NAD+ ,2e and H+

  21. Energy Releasing Pathways • What happens to the products of glycolysis depends upon cell conditions.  Aerobic conditions • Preparatory step and Citric Acid/Krebs cycle • Electron transport chain Anaerobic conditions • Fermentation

  22. GLYCOLYSIS OR ANAEROBIC Conditions No oxygen present Net gain of 2 ATP AEROBIC RESPIRATION Oxygen present Net gain of 30-32 ATP

  23. GLYCOLYSIS OR • AEROBIC • RESPIRATION • Preparatory step • Krebs Cycle • Electron Transport Chain • Reactions occur in mitochondria • ANAEROBIC • Fermentation occurs • Type depends upon cell type • Reactions occur in cytoplasm

  24. Pathways ofAerobic Respiration • Glycolysis followed by Pyruvate oxidation • Citric Acid cycle • Also called Krebs Cycle • Electron Transport Chain (ETC) and Chemiosmosis

  25. Aerobic Conditions • The first reaction that occurs after glycolysis is pyruvate oxidation • Also called the Preparatory Step • This reaction occurs as the pyruvate enter the matrix of the mitochondria

  26. Pyruvate Oxidation • As the pyruvate enter the mitochondria each has a carbon removed and co-enzyme A added • Produced in the Prep. Step • 2 NADH (go to ETC) • 2 CO2 (diffuse out of mitochondria and cell)

  27. Cytoplasm Pyruvate Oxidation ------------------------------ ------------------------------ Matrix of the mitochondria

  28. Aerobic Respiration • For each glucose metabolized the Preparatory Step makes • 2 NADH - go to ETC • 2 CO2 - diffuse out of mitochondria and cell • 2 Acetyl Co-A - enter into Citric acid cycle *aka – Krebs cycle

  29. Pyruvate Oxidation Summary • Where and when it occurs: • Substrate: • End Product: • Also made: • ___________ • ___________

  30. Pyruvate Oxidation Summary Where and when it occurs: Occurs as pyruvate enter mitochondria, occurs under aerobic conditions Substrate: 2 Pyruvate (3C) End Product: 2 Acetyl-CoA (2C) Also made: • 2 CO2 • 2 NADH

  31. Citric Acid Cycle = Krebs Cycle • Step 1: Each Acetyl-CoA (2C) joins with an oxaloacetate (4C) to form a citrate (6C) • Rest of the citric acid cycle reactions occur • Last reaction produces another oxaloacetate (4C) which joins with the next available acetyl-co A……. • ATP, NADH, FADH2, and CO2 are made in these reactions….see board

  32. CoA Acetyl CoA CoA 2 carbons enter cycle Oxaloacetate Citrate +H+ NADH leaves cycle CO2 NAD+ CITRIC ACID CYCLE NAD+ Malate + H+ NADH + ADP P FADH2 ATP Alpha-ketoglutarate FAD leaves cycle CO2 Succinate NAD+ +H+ NADH

  33. In the Krebs cycle, the metabolism of 2 pyruvates made from a single glucose produces: • 2 ATP - by substrate-level phosphorylation • 6 NADH - go to ETC • 2 FADH2- go to ETC • 4 CO2- diffuse out of mitochondria and cell

  34. Citric Acid Cycle Summary • Where it occurs: • Starting substrates: • Last product of pathway: • Also made (in total for 2 acetyl-CoA entering) ____ CO2 ____ ATP (method made by?) ____ NADH ____ FADH2

  35. Citric Acid Cycle Summary • Where it occurs: matrix of mitochondria • Starting substrates: acetyl-CoA, oxaloacetate • Last product of pathway: oxaloacetate • Also made (in total for 2 acetyl-CoA) 4 CO2 2 ATP (by substrate level phophorylation) 6 NADH 2 FADH2

  36. Electron Transport Chain(ETC) • ETC occurs at electron carriers (proteins) located on the inner membrane of the mitochondria • Electrons from NADH and FADH2 are passed from one electron carrier to the next. • Transfers are called red-ox reactions • Each transfer releases energy

  37. ETC • Some of the electron carriers are also proton (H+) pumps • Use the energy released by the red-ox reactions (e transfer reactions) to pump H+ out of the matrix.

  38. H+ H+ H+ H+ H+ Protein complex H+ H+ Electron carrier ATP synthase H+ H+ Intermembrane space Inner mitochondrial membrane FADH2 FAD Electron flow 1 2 O2 + 2 NADH NAD+ H+ H+ Mitochondrial matrix H+ P ADP + ATP H+ H2O H+ Chemiosmosis Electron Transport Chain

  39. ETC • NADH and FADH2 each transfer2e and H+ to a specific ETS protein • Notice -- they do NOT start with the same ETC protein • In the process are the NADH and FADH2 oxidized or reduced?

  40. H+ H+ H+ H+ H+ Protein complex H+ H+ Electron carrier ATP synthase H+ H+ Intermembrane space Inner mitochondrial membrane FADH2 FAD Electron flow 1 2 O2 + 2 H+ NADH NAD+ H+ H+ P ADP + ATP H+ H2O Mitochondrial matrix H+ Chemiosmosis Electron Transport Chain

  41. ETC • H+ from the matrixfollow the electrons into proton pumps • At each proton pump the H+ are pumped out of the matrix into the intermembrane space • This creates an electrical & chemical gradient • Form of _________ energy

  42. ETC • Electron transfers stop when the last ETC protein transfers the 2e to oxygen which: • Joins with H+ to form water • The last electron acceptor is oxygen and water forms. (know this)

  43. Chemiosmosis and ATP Synthesis • ….back to the H+ ions pumped into the intermembrane space • The potential energy of H+ gradient is drive ATP synthesis at the enzyme ATP synthase

  44. ETC and ATP Synthesis • The enzyme ATP synthase is embedded in the inner membrane of the mitochondria • The flow of H+ through this enzyme releases energy and this energy is used to make ATP .

  45. Chemiosmosis and ATP Synthesis • This method of making ATP is called • Oxidative phosphorylation • Also referred to as chemiosmosis

  46. Chemiosmosis and ATP Synthesis • The more H+ pumped out of the matrix • The steeper the gradient • the more potential energy • the more ATP that can be made by ATP synthase

  47. ETC and ATP Synthesis • Each NADH made in the mitochondria results in enough H+ being pumped out of the matrix to make 2.5 ATP. • Each FADH2 results in enough H+ being pumped out of the matrix to make 1.5 ATP.

  48. NADH from Glycolysis • The NADH made in glycolysis must enter the matrix in order to deliver their electrons to the ETC • How they “enter” the mitochondria depends upon the cell type.

  49. NADH from Glycolysis • In most cells the 2 NADH made in glycolysis pass their electrons and H+ to FADin the matrix making: • 2 FADH2 -- take the electrons and H+ to the ETC where a total of ____ ATP are made

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