Cellular Respiration

Mader: Biology 8th Ed.

Cellular Respiration

Chapter 8


Figure 9.1 Energy flow and chemical recycling in ecosystems


Figure 9.5 An introduction to electron transport chains


Cellular Respiration

• A cellular process that requires oxygen and gives off carbon dioxide.– Most often involves complete breakdown

of glucose to carbon dioxide and water.Energy within a glucose molecule is

released slowly so that ATP can be produced gradually.

NAD+ and FAD are oxidation-reduction enzymes active during cellular respiration.


Mitochondrion Structure and Function


Figure 9.x1 ATP


Figure 9.2 A review of how ATP drives cellular work


Figure 9.4 NAD+ as an electron shuttle


Glucose Breakdown

• During glycolysis, glucose is broken down in cytoplasm to two molecules of pyruvate.

• During transition reaction, pyruvate is oxidized, NADH is formed, and waste carbon dioxide is removed.

• Citric acid cycle results in NADH and FADH2, release of carbon dioxide, and production of additional ATP.

• Electron transport chain produces 32 or 34 molecules of ATP.


Glucose Breakdown


Glycolysis

• Two ATP are used to activate glucose that splits into PGAL.

• Oxidation of PGAL and subsequent substrates results in four high-energy phosphate groups, which synthesize four ATP.

• Called Substrate-Level Phosphorylation


Figure 9.7 Substrate-level phosphorylation


Glycolysis


Figure 9.9 A closer look at glycolysis: energy investment phase (Layer 1)


Figure 9.9 A closer look at glycolysis: energy investment phase (Layer 2)


Figure 9.9 A closer look at glycolysis: energy payoff phase (Layer 3)


Figure 9.9 A closer look at glycolysis: energy payoff phase (Layer 4)


Figure 9.8 The energy input and output of glycolysis


Inside the Mitochondria

• End product of glycolysis, pyruvate, enters the mitochondria, where it is oxidized to carbon dioxide during the transition reaction and citric acid cycle.– CO2 and ATP are transported out of

mitochondria into the cytoplasm.


Figure 7.17 The mitochondrion, site of cellular respiration


Transition Reaction

• Connects glycolysis to the citric acid cycle.


Figure 9.10 Conversion of pyruvate to acetyl CoA, the junction between glycolysis and the Krebs cycle


Citric Acid Cycle

• Originally called Krebs cycle.


Figure 9.11 A closer look at the Krebs cycle (Layer 1)


Figure 9.12 A summary of the Krebs cycle


Electron Transport System

• As electrons pass down the electron transport system, energy is captured and ATP is produced.– Oxidative phosphorylation refers to the

production of ATP as a result of energy released by the electron transport system.

– The total of 32-34 ATP produced by ETS is calculated by allowing 3 ATP per NADH and 2 ATP per FADH2 that enter the ETS.


Figure 9.13 Free-energy change during electron transport


Figure 9.14 ATP synthase, a molecular mill


Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis


Figure 9.x2 Fermentation


Fermentation

• Glycolysis followed by reduction of pyruvate by NADH to either lactate or alcohol and carbon dioxide.– Anaerobic pathway.– Can provide rapid burst of ATP.

Lactic Acid Fermentation is common in muscle cells.


Fermentation


Fermentation

Alcohol--yeast produce wine and beer and cause bread to rise.

pyruvate + NADH + H+ C2H5OH (ethyl alcohol) + carbon dioxide + NAD+

Lactic Acid—bacteria produce yogurt, sauerkraut, cheese. Also in muscle cells when working anaerobically.

pyruvate + NADH + H+ lactic acid +NAD+


Figure 9.18 Pyruvate as a key juncture in catabolism


Comparison of the Efficiency of Cellular Respiration versus Fermentation

• One mole of glucose yields 686 kcal in a colorimeter.

• Cellular respiration has a yield of about 263 kcal.

• 1 ATP = 7.3 kcal; therefore7.3 kcal X 36 = 263 kcal

• 263/686 = 38% of available energy is used. What happened to the rest?

• Fermentation yields only 2 ATP or about 15/686 or 2% of available energy.


Metabolic Pool

• Carbohydrates, fats, and proteins can be used as energy sources.– Catabolism produces molecules that can

also be used for anabolism and other compounds.

All reactions in cellular respiration are part of a metabolic pool, and their substrates can be used for catabolism or anabolism.


Figure 9.19 The catabolism of various food molecules


Control of Cellular Respiration

• The important switch in the control of respiration is the enzyme phosphofructokinase.

• This enzyme catalyzes step 3 of glycolysis.• Phosphofructokinase is inhibited by ATP

and stimulated by ADP or AMP. • It is also inhibited by citric acid. This

synchronizes the rates of glycolysis and the Krebs Cycle.


Figure 9.20 The control of cellular respiration


Figure 9.6 An overview of cellular respiration (Layer 1)


Figure 9.16 Review: how each molecule of glucose yields many ATP molecules during cellular respiration

Cellular Respiration

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