Cellular Respiration C 6 H 12 O 6 + 6O 2 -----> 6CO 2 + 6H 2 0 + energy (heat and ATP) 1. Energy Capacity to move or change matter Forms of energy are important to life include Chemical, radiant (heat & light), mechanical, and electrical Energy can be transformed from one form to another Chemical energy is the energy contained in the chemical bonds of molecules Radiant energy travels in waves and is sometimes called electromagnetic energy. An example is visible light Photosynthesis converts light energy to chemical energy Energy that is stored is called potential energy According to the Law of Thermodynamics, energy cannot be created or destroyed, just change forms. Also, some usable energy will be lost, usually as heat, so the total amount of usable energy decreases. 2. Adenosine triphosphate (ATP) Energy carrying molecule used by cells to fuel their cellular processes ATP is composed of an adenine base, ribose sugar, & 3 phosphate (PO 4 ) groups
The PO 4 bonds are high-energy bonds that require energy to be made & release energy when broken ATP is made & used continuously by cells Every minute all of an organism's ATP is recycled Phosphorylation refers to the chemical reactions that make ATP by adding P i to ADP ADP + P i + energy «ATP + H 2 O Enzymes (ATP synthetase& ATPase) help break & reform these high energy PO 4 bonds in a process called substrate-level phosphorylation When the high-energy phosphate bond is broken, it releases energy, a free phosphate group, & adenosine diphosphate (ADP)
3. Enzymes in Metabolic Pathways: Biological catalysts Speeds up chemical reactions Lowers the amount of activation energy needed by weakening existing bonds in substrates Highly specific protein molecules Have an area called the active site where substrates temporarily join Form an enzyme-substrate complex to stress bonds Enzyme usable enzyme substrate complex
4. Energy Carriers During Respiration: NADH: A second energy carrying molecule in the mitochondria; produces 3 ATP FADH 2 : A third energy carrying molecule in the mitochondria; produces 2 ATP 5. Mitochondria: Has outer smooth, outer membrane & folded inner membrane Folds are called cristae Space inside cristae is called the matrix & contains DNA & ribosomes Site of aerobic respiration Krebs cycle takes place in matrix Electron Transport Chain takes place in cristae
6. Cellular Respiration Overview: C 6 H 12 O 6 + 6O 2 -----> 6CO 2 + 6H 2 0 + energy (heat and ATP) Controlled release of energy from organic molecules (most often glucose) Glucose is oxidized (loses e-) & oxygen is reduced (gains e-) The carbon atoms of glucose (C 6 H 12 O 6 ) are released as CO 2 Generates ATP (adenosine triphosphate) The energy in one glucose molecule may be used to produce 36 ATP Involves a series of 3 reactions --- Glycolysis, Kreb's Cycle, & Electron Transport Chain 7. Glycolysis: Occurs in the cytoplasm Summary of the steps of Glycolysis: a. 2 ATP added to glucose (6C) to energize it. b. Glucose split to 2 PGAL (3C). (PGAL = phosphoglyceraldehyde) c. H+ and e- (e- = electron) taken from each PGAL & given to make 2 NADH. d. NADH is energy and e- carrier. e. Each PGAL rearranged into pyruvate (3C), with energy transferred to make 4 ATP (substrate phosphorylation). f. Although glycolysis makes 4 ATP, the net ATP production by this step is 2 ATP (because 2 ATP were used to start glycolysis). The 2 net ATP are available for cell use. g. If oxygen is available to the cell, the pyruvate will move into the mitochondria & aerobic respiration will begin.
Net Yield from Glycolysis 4 NADH 2 2 CO 2 4 ATP ( 2 used to start reaction) h. If no oxygen is available to the cell (anaerobic), the pyruvate will be fermented by addition of 2 H from the NADH (to alcohol + CO2 in yeast or lactic acid in muscle cells). This changes NADH back to NAD+ so it is available for step c above. This keeps glycolysis going!
Alcoholic Fermentation 8. Aerobic Respiration: Lactic Acid Fermentation Occurs in the mitochondria Includes the Krebs Cycle & the Electron Transport Chain Pyruvic acid from glycolysis diffuses into matrix of mitochondria & reacts with coenzyme A to for acetyl-coa (2-carbon compound) CO 2 and NADH are also produced 9. Kreb's Cycle: Named for biochemist Hans Krebs Metabolic pathway that indirectly requires O 2 Kreb's Cycle is also known as the Citric acid Cycle
Requires 2 cycles to metabolize glucose Acetyl Co-A (2C) enters the Kreb's Cycle & joins with Oxaloacetic Acid (4C) to make Citric Acid (6C) Citric acid is oxidized releasing CO 2, free H +, & e - and forming ketoglutaric acid (5C) Free e - reduce the energy carriers NAD + to NADH 2 and FAD + to FADH 2 Ketoglutaric acid is also oxidized releasing more CO 2, free H +, & e - The cycle continues oxidizing the carbon compounds formed (succinic acid, fumaric acid, malic acid, etc.) producing more CO 2, NADH 2, FADH 2, & ATP H 2 O is added to supply more H + CO 2 is a waste product that diffuses out of cells Oxaloacetic acid is regenerated to start the cycle again NADH 2 and FADH 2 produced migrate to the Electron Transport Chain (ETC) 10. Electron Transport Chain: Net Yield from Kreb's Cycle (2 turns) 6 NADH 2 2 FADH 2 4 CO 2 2 ATP Found in the inner mitochondrial membrane or cristae Contains 4 protein-based complexes that work in sequence moving H+ from the matrix across the inner membrane (proton pumps) A concentration gradient of H + between the inner & outer mitochondrial membrane occurs H + concentration gradient causes the synthesis of ATP by chemiosmosis Energized e - & H+ from the 10 NADH 2 and 2 FADH 2 (produced during glycolysis & Krebs cycle) are transferred to O 2 to produce H 2 O (redox reaction)
O 2 + 4e - + 4H + 2H 2 O Energy Yield from Aerobic Respiration Glycolysis Kreb's Cycle Total 4 NADH 2 6 NADH 2 10 NADH 2 x 3 = 30 ATP 0 FADH 2 2 FADH 2 2 FADH 2 x 2 = 4 ATP 2 ATP 2 ATP 4 ATP 38 ATP Most cells produce 36-38 molecules of ATP per glucose (66% efficient) Actual number of ATP's produced by aerobic respiration varies among cells