Photosynthesis and Cellular RespirationSection 3 CH7: Cellular Respiration

Photosynthesis and Cellular RespirationSection 3 Key Ideas How does glycolysis produce ATP? How is ATP produced in aerobic respiration? Why is fermentation important?

Photosynthesis and Cellular RespirationSection 3 Glycolysis Before you can use energy from food, it must be released and transferred to ATP. The primary fuel for cellular respiration is glucose. Glycolysis occurs in the cytoplasm.

Photosynthesis and Cellular RespirationSection 3 Glycolysis, continued In glycolysis, enzymes break down one six-carbon molecule of glucose into two three-carbon pyruvate molecules. The breaking of a sugar molecule by glycolysis results in a net gain of two ATP molecules. This process of glycolysis is anaerobic, or takes place without oxygen.

Photosynthesis and Cellular RespirationSection 3 Glycolysis, continued Glycolysis is the only source of energy for some prokaryotes. Other organisms use oxygen to release even more energy from a glucose molecule. Metabolic processes that require oxygen are aerobic. In aerobic respiration, the pyruvate product of glycolysis undergoes another series of reactions to produce more ATP molecules.

Photosynthesis and Cellular RespirationSection 3 Glycolysis, continued Step 1, Breaking Down Glucose –Two ATP molecules are used to break glucose into two smaller units. –Phosphate is attached to these 2 – three carbon sugars

Photosynthesis and Cellular RespirationSection 3 Step 2, NADH Production –Each of the three carbon sugars react with another phosphate (not ATP) –Hydrogen atoms from these compounds transfer to two molecules of NAD + resulting in 2 NADH molecules Glycolysis, continued

Photosynthesis and Cellular RespirationSection 3 Glycolysis, continued Step 3, Pyruvate Production –In a series of 4 reactions, each of the 3 – carbon sugars are converted into a 3 – carbon molecule of pyruvate, resulting in 4 ATP molecules. –2 ATP molecules were used in step one, 4 ATP molecules were created so net total for glycolysis is 2 ATP molecules

Photosynthesis and Cellular RespirationSection 3 Glycolysis

Photosynthesis and Cellular RespirationSection 3 Aerobic Respiration The first stage of aerobic respiration is the Krebs cycle, a series of reactions that produce electron carriers. The electron carriers enter an electron transport chain, which powers ATP synthase. Up to 34 ATP molecules can be produced from one glucose molecule in aerobic respiration.

Photosynthesis and Cellular RespirationSection 3 Aerobic Respiration, continued Krebs Cycle Pyruvate (from glycolysis) is broken down and combined with other carbon compounds. Each time the carbon-carbon bonds are rearranged during the Krebs cycle, energy is released. The total yield of energy-storing products from one time through the Krebs cycle is one ATP, three NADH, and one FADH 2.

Photosynthesis and Cellular RespirationSection 3 Aerobic Respiration, continued Electron Transport Chain The second stage of aerobic respiration takes place in the inner membranes of mitochondria, where ATP synthase enzymes are located. Electron carriers (NADH and FADH 2 ), produced during the Krebs cycle, transfer energy through the electron transport chain.

Photosynthesis and Cellular RespirationSection 3 Aerobic Respiration, continued ATP Production Hydrogen ions diffuse through ATP synthase, providing energy to produce several ATP molecules from ADP. ATP synthase is present on the inner membrane of the mitochondria. H + ions diffuse through a channel in this enzyme which provides energy to produce ATP from ADP.

Photosynthesis and Cellular RespirationSection 3 The Role of Oxygen At the end of the electron transport chain, the electrons combine with an oxygen atom and two hydrogen ions to form two water molecules. If oxygen is not present, the electron transport chain stops. The electron carriers are not recycled, so the Krebs cycle also stops. Aerobic Respiration, continued

Photosynthesis and Cellular RespirationSection 3 Fermentation To make ATP during glycolysis, NAD+ is converted to NADH. Organisms must recycle NAD+ to continue making ATP through glycolysis. The process in which carbohydrates are broken down in the absence of oxygen is called fermentation. Fermentation enables glycolysis to continue supplying a cell with ATP in anaerobic conditions.

Photosynthesis and Cellular RespirationSection 3 Fermentation, continued In lactic acid fermentation, pyruvate is converted to lactic acid. During alcoholic fermentation, one enzyme removes carbon dioxide from pyruvate. A second enzyme converts the remaining compound to ethanol, recycling NAD+ in the process.

Photosynthesis and Cellular RespirationSection 3 Two Types of Fermentation

Photosynthesis and Cellular RespirationSection 3 Fermentation, continued Efficiency of Cellular Respiration In the first stage of cellular respiration, glucose is broken down to pyruvate during glycolysis, an anaerobic process. Glycolysis results in a net gain of two ATP molecules for each glucose molecule that is broken down. In the second stage, pyruvate either passes through the Krebs cycle or undergoes fermentation. Fermentation recycles NAD+ but does not produce ATP.

Photosynthesis and Cellular RespirationSection 3 Fermentation, continued Efficiency of Cellular Respiration Cells release energy most efficiently when oxygen is present because they make most of their ATP during aerobic respiration. For each glucose molecule that is broken down, as many as two ATP molecules are made during the Krebs cycle. The Krebs cycle feeds NADH and FADH 2 to the electron transport chain, which can produce up to 34 ATP molecules.

Photosynthesis and Cellular RespirationSection 3 Visual Concept: Comparing Aerobic and Anaerobic Respiration

Photosynthesis and Cellular RespirationSection 3 Summary The breaking of a sugar molecule by glycolysis results in a net gain of two ATP molecules. The total yield of energy-storing products from one time through the Krebs cycle is one ATP, three NADH, and one FADH 2.

Photosynthesis and Cellular RespirationSection 3 Summary, continued Electron carriers transfer energy through the electron transport chain, which ultimately powers ATP synthase. Fermentation enables glycolysis to continue supplying a cell with ATP in anaerobic conditions.