Cellular Respiration Lecture 07 1 Objectives At the end of this - - PDF document

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Cellular Respiration

Lecture 07

 At the end of this series of lectures, you should be able to:

 Define terms.  Explain how breathing and cellular respiration are related.  Provide the overall chemical equation for cellular respiration.  Explain how the energy in a glucose molecule is released during cellular respiration.

Objectives

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 List the cellular regions where glycolysis, the citric acid cycle, and oxidative phosphorylation occur.  Compare the reactants, products, and energy yield of the three stages of cellular respiration.  Compare the reactants, products, and energy yield of alcohol and lactic acid fermentation.

Objectives

 Most energy for life is captured as solar energy by photosynthesis.  For most organisms that energy is converted to the usable form (ATP) by cellular respiration.

Energy for Life

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Mikael Häggström, CC BY‐SA 3.0, http://en.wikipedia.org/wiki/Cellular_respiration#mediaviewer/File:Auto‐and_heterotrophs.png

CHO 6O → 6CO 6HO 32 ATP Heat 6CO 12HO Light → CHO 6O 6HO

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Respiration

 Breathing

 inspiration (bringing air in)  expiration (moving air out)

 External respiration  Internal respiration  Cellular respiration

𝐷𝐼𝑃 6𝑃 → 6𝐷𝑃 6𝐼𝑃 32 𝐵𝑈𝑄 ℎ𝑓𝑏𝑢

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Overview Concepts

 Glucose can be burned and the energy released.

 Not biologically useful.

 Cellular respiration is the controlled release of energy from glucose.

 Some of the energy is captured in a biologically useful way.  Movement of electrons in oxidation‐reduction (redox) reactions.  Oxidation‐Reduction Reactions

 Oxidation – The loss of electrons from a substance  Reduction – The addition of electrons to a substance  These reactions occur in pairs

 One reaction donates the electrons and the other accepts the reactions.

 In biological reactions, you cannot see the electrons, but you can see hydrogen move which represents electron transfers.

Overview Concepts

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Cameron Garnham, CC BY‐SA 3.0, http://commons.wikimedia.org/wiki/File:Redox_Reminder.png

 NADH Coenzymes

 NAD+ accepts electrons and becomes reduced NADH

 Moves electrons in a controlled manner from one reaction to another.

Overview Concepts

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 Electron Transport Chains

 Electron transport chains are a series of carrier molecules that accept the electrons and move them down an energy gradient in a controlled fashion.  The movement of the electrons causes H+ to be pumped one side of the membrane to the other. This creates a gradient of H+. The movement of H+ back across the membrane is used to synthesize ATP.  O2 is the final electron acceptor – makes H2O

Overview Concepts

 Stages

 Glycolysis  Pyruvate Oxidation and Citric Acid Cycle (Krebs Cycle)  Oxidative phosphorylation (Electron Transport Chain)

Cellular Respiration

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OpenStax College, CC BY 3.0, http://cnx.org/contents/9d68abf9‐4c2e‐4ef7‐88d1‐c963c5c844b9@3

Cellular Respiration

 Glycolysis

 Occurs in the cytoplasm (cytosol)  Breaks (lyses) glucose into 2 3‐carbon compounds – pyruvate.  Requires an investment of ATP  Produces 2pyruvate, 2 ATP and 2 NADH 15 16

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Biology by OpenStax College is licensed under a Creative Commons Attribution 3.0

Glycolysis Glucose (C6) + 2 ADP + 2 Pi + 2 NAD+ → 2 ATP + 2 NADH + 2 Pyruvate (C3)

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Cellular Respiration

 Glycolysis

 Substrate level phosphorylation

 One method by which ATP is formed  Occurs in other reactions also  Passes a phosphate directly to ADP to form ATP  Requires appropriate enzyme

 Pyruvate Oxidation

 Occurs in the matrix of the mitochondria  Breaks the pyruvates into 2‐carbon compound (Acetyl CoA).  Requires coenzyme A (CoA)  Produces CO2 – waste product  Produces 2 Acetyl CoA and NADH

Cellular Respiration

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Biology by OpenStax College is licensed under a Creative Commons Attribution 3.0

2 Pyruvate (C3) + 2 O2 + 2 NAD+ + 2 CoA → 2 CO2 + 2 NADH + 2 Acetyl CoA (C2) Pyruvate Oxidation

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Cellular Respiration

 Citric Acid Cycle

 Also called the Krebs Cycle  Occurs in the matrix of the mitochondria  Completes the breakdown of glucose (Acetyl CoA) into CO2‐‐ waste product  Produces 2ATP, 6NADH, and 2FADH2 from each glucose (2 turns of the cycle)

Cellular Respiration

2 Acetyl CoA + 4 O2 + 6 NAD+ + 2 ADP + 2 Pi + 2 FAD+2 → 4 CO2 + 6 NADH + 2 ATP + 2 FADH2 Citric Acid Cycle

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 Oxidative Phosphorylation

 Occurs on the cristae of the mitochondria  Accepts electrons from NADH and FADH2

 Produced in glycolysis, pyruvate oxidation, and citric acid cycle.

 Uses electron transport chains to generate ATP  Produces ~28 ATP

Cellular Respiration

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 Oxidative Phosphorylation

 Chemiosmosis

 Uses energy stored in a hydrogen ion gradient to drive ATP synthesis.

 Occurs on the cristae of the mitochondria.

Cellular Respiration Cellular Respiration

7 O2 + 28 ADP + 28 Pi + 10 NADH + 2 FADH2 → 28 ATP + H2 O + 10 NAD+ + 2 FAD+2 Oxidative Phosphorylation

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Fvasconcellos, Public Domainhttp://en.wikipedia.org/wiki/Oxidative_phosphorylation#mediaviewer/File:Mitochondrial_electron_transport_chain%E2%80%94Etc4.svg

Cellular Respiration

 Each glucose molecule results in the production of about 32 ATP.

 Glycolysis: 2 ATP  Citric Acid Cycle: 2 ATP  Oxidative Phosphorylation: 28 ATP  About 34% of the glucose’s potential energy 29 30

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 Fermentation  Occurs in the absence of oxygen  Glycolysis does not require oxygen so it can still produce its 2 ATP per glucose.

 Need to regenerate NAD+ to continue accept electrons

 Other steps in cellular reaction require oxygen so they will not occur without oxygen.  Reduced efficiency

Anaerobic Respiration

 Lactic Acid Fermentation

 A process for regenerating NAD+  Occurs in muscle cells and certain bacteria  Pyruvate is converted to lactate (lactic acid)  Lactate is carried via the blood to the liver where, if there is enough oxygen, it is converted back to pyruvate.  Bacteria are use this technique to produce yogurt, cheese, soy sauce, and sauerkraut.

Anaerobic Respiration

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Darekk2, CC BY‐SA 3.0, http://en.wikipedia.org/wiki/Cellular_respiration#mediaviewer/File:Cellular_respiration.gif

 Alcohol Fermentation

 A process for regenerating NAD+  Occurs with some yeast (fungi)  Pyruvate is converted to CO2 and ethanol  Ethanol is toxic

Anaerobic Respiration

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Darekk2, CC BY‐SA 3.0, http://en.wikipedia.org/wiki/Cellular_respiration#mediaviewer/File:Cellular_respiration.gif

Other Metabolic Pathways

 Other organic molecules can be used as fuel for cellular respiration.

 Other macromolecules enter cellular respiration at different points.

 Fats generate more ATP than an equal mass of carbohydrates.  Proteins produce relatively little ATP

 Produces more waste (amine groups) – disposed of by urine

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