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Cellular Energy

Cellular Energy. In order to sustain life (steady state), cells constantly expend energy in the form of ATP hydrolysis the hydrolysis of ATP yields a molecule of A D P (adenosine di phosphate ) and a Phosphate group ATP → ADP + P

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Cellular Energy

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  1. Cellular Energy • In order to sustain life (steady state), cells constantly expend energy in the form of ATP hydrolysis • the hydrolysis of ATP yields a molecule of ADP (adenosine diphosphate) and a Phosphate group • ATP→ADP + P • Following ATP hydrolysis, the cell synthesizes new molecules of ATP using ADP and P • ADP + P → ATP • “recycling energy” • cells use the energy stored in the covalent bonds of monosaccharides, fatty acids and amino acids as an energy source (fuel) to resynthesize ATP

  2. Fuels for ATP Synthesis

  3. Cellular Respiration • Most cellsof the body use glucose (in the presence of O2that we inhale) as fuel source to synthesize molecules of ATP in a process called cellular respiration • The products include molecules of carbon dioxide that we exhale, and water • C6H12O6 + 6O2 + 38 ADP +38 P 6H2O + 6CO2 + 38 ATP • note that the number of atoms in the reactants equal the number of atoms in the products

  4. Cellular Respiration

  5. Cellular Respiration • The process of cellular respiration is divided into 3 sequential phases • Glycolysis • occurs in the cytoplasm of a cell • Krebs cycle (Citric acid cycle) • occurs in the mitochondrial matrix • The electron transport chain • occurs across the inner mitochondrial membrane • between the mitochondrial matrix and the intermembrane space

  6. Cellular Respiration Overview

  7. Cellular Respiration • During the phases of glycolysis and the Krebs cycle, a single molecule of glucose is gradually broken apart in 20 sequential biochemical reactions into different carbohydrate intermediates • only 4 molecules of ATP are synthesized during these phases by the energy released from the breaking of covalent bonds of the carbohydrate intermediates • As the glucose molecule is broken apart, the 12 hydrogen atoms are gradually removed and used to create a large H+ gradient between the intermembrane space and the matrix of the mitochondria • the H+ gradient is used as an energy source by the electron transport chain to synthesize the remaining 34 molecules of ATP

  8. Glycolysis Overview • Glycolysis = sugarbreaking • The first 7 biochemical reactions of cellular respiration are catalyzed by 7 different enzymes in the cytoplasm • Starts with 1 molecule of glucose (6 carbons) and ends with 2 molecules of pyruvic acid (3 carbons x 2 = 6 carbons)

  9. Glycolysis During glycolysis: Energy is invested as 2 ATPs are hydrolyzed during steps 1 and 3 One 6 carbon carbohydrate intermediate is split (lysis) into two 3 carbon carbohydrate intermediates during step 4 each of the 3 carbon carbohydrate intermediates molecules lose a H (becoming oxidized) which is accepted by a coenzyme called NAD+ (becoming reduced to NADH) during step 5 NADH carries H to the mitochondrial matrix to build the H+ gradient 4 molecules of ATP are synthesized 2 during step 6 2 during step 7

  10. Glycolysis

  11. Products of Glycolysis The products of glycolysis are: 2 molecules of ATP 4 are synthesized, but 2 are hydrolyzed at the beginning of glycolysis 2 molecules of pyruvic acid (3 carbon molecule) 2molecules of NADH Only 2 of 38 molecules of ATP are synthesized during glycolysis

  12. Pyruvic Acid The presence or absence of O2in the cell determines how the cell will use the 2 molecules of pyruvic acid at the end of glycolysis If O2 is present pyruvic acid will be used in the process of aerobic respiration 36 more molecules of ATP are synthesized as cellular respiration continues through the Krebs cycle and the electron transport chain If O2 is absent the pyruvic acid will be used in the process of anaerobic respiration (fermentation) produces no more ATP

  13. Anaerobic Fermentation In the absence of O2 (oxygen debt), the 2molecules of pyruvic acid from the end of glycolysis are converted into 2 molecules of lactic acid Anaerobic fermentation most commonly occurs in active skeletal muscle cells when they use O2 faster than it can be delivered by the respiratory and circulatory systems The accumulation of lactic acid causes: muscle proteins to partially denature leading to muscle weakening (fatigue) muscle soreness

  14. Aerobic Respiration In the presence of O2, the 2molecules of pyruvic acid from the end of glycolysis are transported into the mitochondrial matrix Each molecule of pyruvic acid is then converted into amolecule of Acetyl Coenzyme A (Acetyl CoA) required step between glycolysis and the Krebs cycle

  15. 2 Pyruvic Acid → 2 Acetyl CoA During the conversion of each of the 2 molecules of pyruvic acidto Acetyl CoA the following occurs: Decarboxylation (CO2 is removed) of pyruvic acid making acetic acid (2 carbons) One H is removed from acetic acid (oxidized) by NAD+ (reduced to NADH) and further contributes to the H+ gradient Coenzyme A in the mitochondrial matrix is added to the acetic acid to make acetyl CoA During this step the products are: 2 molecules of CO2 2 molecules of NADH 2molecules of Acetyl CoA used in the Krebs Cycle

  16. Krebs Cycle (Citric Acid Cycle) A series of 10 biochemical reactions which begins and ends (cyclic) with a molecule of citric acid Each acetic acid (2 carbons) is combined with a molecule of oxaloacetic acid in the mitochondrial matrix (4 carbons) to make citric acid (6 carbons) during step 1 Each citric acid is then decarboxylated twice (steps 4 and 6) and oxidized (H is removed during steps 3, 5, 8 and 10) as it is converted into different carbohydrate intermediates energy released from the hydrolysis of bonds is used to synthesize ATP during step 7 NAD+ (steps 3, 5 and 10) and FAD (step 8) are reduced to NADH and FADH2and further contributes to the H+ gradient in the mitochondria

  17. Krebs Cycle

  18. Products of Krebs Cycle • The reactions of the Krebs cycle produce: • 3 molecules of NADH • 1 molecule of FADH2 • 2 molecules of CO2 • 1 molecule of ATP • 1 molecule of oxaloacetic acid • Since each molecule of glucose yields two molecules of acetyl CoA, 2 Krebs cycles yield: • 6 NADH • 2 FADH2 • 4 CO2 • 2 ATP • 2 oxaloacetic acid • reenter the Krebs cycle of reactions after combined with another acetic acid

  19. Products of Glycolysis → Krebs Cycle • 4 ATP • 2 (net) from glycolysis • 2 from Krebs • 10 NADH (10 H from original glucose molecule) • 2 from glycolysis • 2 from (2) Pyruvic Acid → (2)Acetyl CoA • 6 from Krebs • 2 FADH2 (2 H from original glucose molecule) • 2 from Krebs • 6 CO2 (6 C from original glucose molecule) • 2 from (2) Pyruvic Acid → (2)Acetyl CoA • 4 from Krebs

  20. CO2 NADH NADH FADH2 NADH NADH ATP NADH ATP NAD NAD CO2 NAD NAD FAD NAD ADP 6C ADP 3C 2C 2C Citric Acid 4C Pyruvic Acid Acetyl CoA Acetate + OAA OAA ADP 4C CO2 ATP ADP ATP CoA 6C CO2 Glucose NADH NADH FADH2 NADH NADH ATP ADP ATP CO2 ATP NAD FAD NAD ADP ADP NAD 6C 3C 2C 2C Citric Acid 4C Pyruvic Acid Acetyl CoA Acetate + OAA OAA CO2 4C ADP CoA NAD NADH ATP GLYCOLYSIS KREBS (CITRIC ACID) CYCLE CYTOPLASM MITOCHONDIAL MATRIX

  21. Electron Transport Chain • A group of 3 integral proteins and 2 membrane coenzymes associated with the inner mitochondrial membrane called the electron transport chain (ETC) creates a H+ gradientbetween the intermembrane space and the matrix of the mitochondria using the H of from NADH and FADH2 that accumulate in the mitochondrial matrix as products of glycolysis and the Krebs cycle • 3 (integral) enzyme complexes of the ETC remove the H from NADH and FADH2 (oxidized back to NAD+ and FAD+) in the matrix

  22. ETC and Oxidative Phosphorylation FADH2 FAD+

  23. NADH and the Electron Transport Chain • NADH is oxidized by Enzyme complex 1 of the ETC • The H that is removed by Enzyme complex 1 is split into an electron (e-) and a proton (H+) • The e- is passed from the beginning to the end of the ETC and energizes the 1st, 2nd and 3rd Enzyme complexes along the way • Once energized, each enzyme complex pumps a free proton from the mitochondrial matrix into the intermembrane space (3 total)

  24. FADH2 and the Electron Transport Chain • FADH2 is oxidized by Enzyme complex 2 of the ETC • The H that is removed by Enzyme complex 2 is split into an electron (e-) and a proton (H+) • The e- is passed to the end of the ETC and energizes the 2nd and 3rd Enzyme complexes along the way • Once energized, each enzyme complex pumps a free proton from the mitochondrial matrix into the intermembrane space (2 total)

  25. Proton (H+) gradient • The movement of protons from the matrix into the intermembrane space creates a highH+ (pH = 7) concentration in the intermembrane space and a low H+ (pH = 8) concentration in the matrix • this proton gradient becomes the source of energy used by the mitochondria to synthesize ATP, which is released as H+ diffuse from the intermembrane space back into the matrix • The oxidation of NADH contributes more (pumps 3 H+) to the proton gradient than FADH2 (pumps 2 H+)

  26. ATP Synthase • ATP synthaseis an integral membrane protein in the inner mitochondrial membrane that has 2 functions: • it acts as a H+ channel • allows H+ to diffuse down its gradient from the intermembrane space into the matrix • it acts as an enzyme • uses the energy that is released by the diffusion of H+ to synthesize ATP from ADP and P • This type of ATP synthesis is called oxidativephosphorylation because, this process requires the oxidation of NADH and FADH2

  27. ATP Synthesis During Oxidative Phosphorylation • Because the oxidation of NADH contributes more to the proton gradient than the oxidation of FADH2, more ATP is synthesized from NADH than FADH2 • On average, for each NADH that is oxidized 3 molecules of ATP are synthesized • 10 NADH x 3 ATP = 30 ATP • On average, for each FADH2 that is oxidized 2 molecules of ATP are synthesized • 2 FADH2 x 2 ATP = 4 ATP • 34 of the 38 molecules of ATP are synthesized by oxidative phosphorylation

  28. Formation of Water • After the electrons arrive to the last enzyme complex of the ETC they are transferred to atoms of oxygen in the mitochondrial matrix • this makes oxygen especially negative • In the matrix, these oxygen atom are combined with the H+ that have diffused back into the matrix from the intermembrane space to form water (H2O) • the protons become “reunited” with their electron

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