Download CH9 Sec 3: Cellular Respiration Glycolysis • Before you can use

CH9 Sec 3: Cellular Respiration
Glycolysis
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Before you can use energy from food, it must be released and transferred to ATP.
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The primary fuel for cellular respiration is glucose.
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Glycolysis occurs in the cytoplasm.
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In glycolysis, enzymes break down one six-carbon molecule of glucose into two three-carbon pyruvate
molecules.
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The breaking of a sugar molecule by glycolysis results in a net gain of two ATP molecules.
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This process of glycolysis is anaerobic, or takes place without oxygen.
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Glycolysis is the only source of energy for some prokaryotes.
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Other organisms use oxygen to release even more energy from a glucose molecule. Metabolic processes that
require oxygen are aerobic.
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In aerobic respiration, the pyruvate product of glycolysis undergoes another series of reactions to produce more
ATP molecules.
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Step 1, Breaking Down Glucose
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Two ATP molecules are used to break glucose into two smaller units. (2 – three Carbon sugars)
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Phosphate is attached to both of these three carbon sugars
Step 2, NADH Production
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Both three carbon sugars react with another phosphate (not ATP)
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Hydrogen atoms from these compounds transfer to two molecules of NAD+ resulting in 2 NADH
molecules
Step 3, Pyruvate Production
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Each of the 3 – carbon sugars are converted into pyruvate, resulting in 4 ATP molecules.
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2 ATP molecules were used in step one, 4 ATP molecules were created so net total for glycolysis is 2 ATP
molecules
Aerobic Respiration
Krebs Cycle
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Pyruvate (from glycolysis) is broken down and combined with other carbon compounds.
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Each time the carbon-carbon bonds are rearranged during the Krebs cycle, energy is released.
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Aerobic Respiration
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The 1st stage is the Krebs cycle
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Pyruvate is used
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CO2 released
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Produce electron carriers NADH and FADH2
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Electron carriers enter an electron transport chain powering ATP synthase
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Products 1 ATP, 3 NADH, 1 FADH2
Electron Transport Chain
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2nd stage takes place in the inner membranes of mitochondria
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Electron carriers NADH and FADH2
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from the Krebs cycle,
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transfer energy through the electron transport chain
Molecules can be produced 34 ATP
ATP Production
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Hydrogen ions diffuse through ATP synthase
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providing energy to produce several ATP molecules from ADP
Aerobic Respiration, continued
The Role of Oxygen
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End of the ETC, the electrons combine with an oxygen and hydrogen ions to form water molecules.
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If oxygen is not present, ETC stops and electron carriers are not recycled so Krebs Cycle also stops.
Fermentation
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To make ATP during glycolysis, NAD+ is converted to NADH.
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Organisms must recycle NAD+ to continue making ATP through glycolysis.
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The process in which carbohydrates are broken down in the absence of oxygen is called fermentation.
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Fermentation enables glycolysis to continue supplying a cell with ATP in anaerobic conditions.
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Two Types of Fermentation
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In lactic acid fermentation, pyruvate is converted to lactic acid.
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During alcoholic fermentation, one enzyme removes carbon dioxide from pyruvate.
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A second enzyme converts the remaining compound to ethanol, recycling NAD+ in the process.
Efficiency of Cellular Respiration
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In the first stage of cellular respiration, glucose is broken down to pyruvate during glycolysis, an anaerobic
process.
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Glycolysis results in a net gain of two ATP molecules for each glucose molecule that is broken down.
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In the second stage, pyruvate either passes through the Krebs cycle or undergoes fermentation. Fermentation
recycles NAD+ but does not produce ATP.
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Cells release energy most efficiently when oxygen is present because they make most of their ATP during
aerobic respiration.
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For each glucose molecule that is broken down, as many as two ATP molecules are made during the Krebs cycle.
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The Krebs cycle feeds NADH and FADH2 to the electron transport chain, which can produce up to 34 ATP
molecules.
Summary
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The breaking of a sugar molecule by glycolysis results in a net gain of two ATP molecules.
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The total yield of energy-storing products from one time through the Krebs cycle is one ATP, three NADH, and
one FADH2.
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Electron carriers transfer energy through the electron transport chain, which ultimately powers ATP synthase.
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Fermentation enables glycolysis to continue supplying a cell with ATP in anaerobic conditions.