Biology 107Biology 107

Cellular RespirationCellular Respiration

September 30, 2005September 30, 2005

Cellular Respiration IICellular Respiration IIStudent Objectives:Student Objectives: As a result of this lecture and the assigned reading, As a result of this lecture and the assigned reading,

you should understand the following:you should understand the following:

1.1. Respiration occurs in two (2) stages: 1) the Respiration occurs in two (2) stages: 1) the Krebs cycleKrebs cycle (citric acid (citric acid cycle) and 2) the terminal cycle) and 2) the terminal electron transport chainelectron transport chain. .

2.2. In eukaryotes these respiration reactions take place in mitochondria.In eukaryotes these respiration reactions take place in mitochondria.

3. Some enzymes of the Krebs cycle are in the matrix of mitochondria; Some enzymes of the Krebs cycle are in the matrix of mitochondria; other enzymes of the Krebs cycle and the enzymes of the electron other enzymes of the Krebs cycle and the enzymes of the electron transport system are in the membrane of the cristae of the inner transport system are in the membrane of the cristae of the inner membrane. The outer membrane is relatively permeable, while the membrane. The outer membrane is relatively permeable, while the inner membrane restricts passage of most molecules and ions, inner membrane restricts passage of most molecules and ions, including protons (Hincluding protons (H++ ions). ions).

Cellular Respiration IICellular Respiration II4.4. Compared to glycolysis, the Krebs cycle pays off big energy Compared to glycolysis, the Krebs cycle pays off big energy

dividends to the cell. dividends to the cell.

a.a. Each turn of the cycle makes 1 ATP molecule (by Each turn of the cycle makes 1 ATP molecule (by substrate substrate level phosphorylationlevel phosphorylation) and 4 other energy-rich ) and 4 other energy-rich molecules molecules (3NADH and 1 FADH(3NADH and 1 FADH22). ).

b.b. Since two molecules of acetyl CoA are processed for Since two molecules of acetyl CoA are processed for each each glucose precursor, the total yield is 2ATP, 6NADH, and 2 glucose precursor, the total yield is 2ATP, 6NADH, and 2

FADHFADH22 (compared to the total of 2ATP and 2NADH (compared to the total of 2ATP and 2NADH molecules molecules of glycolysis). of glycolysis).

5.5. No oxygen is required for the Krebs cycle.No oxygen is required for the Krebs cycle.

Cellular Respiration IICellular Respiration II6.6. After the Krebs cycle is completed, glucose is completely After the Krebs cycle is completed, glucose is completely

oxidized, but most of the energy is stored in electrons moved from oxidized, but most of the energy is stored in electrons moved from carbon atoms to the electron carriers NADcarbon atoms to the electron carriers NAD++ and FAD. and FAD.

7.7. In terminal electron transport, the high energy electrons stored in In terminal electron transport, the high energy electrons stored in the NADH and FADHthe NADH and FADH22 carriers are passed step-by-step to carriers are passed step-by-step to successively lower energy carriers embedded in the inner successively lower energy carriers embedded in the inner membrane of the mitochondrion until the electrons are finally membrane of the mitochondrion until the electrons are finally accepted by the low energy level oxygen atom.accepted by the low energy level oxygen atom.

8.8. As the electrons are passed down the electron transport chain, HAs the electrons are passed down the electron transport chain, H+ +

are transported from the matrix across the inner mitochondrial are transported from the matrix across the inner mitochondrial membrane to the intermembrane space and a concentration membrane to the intermembrane space and a concentration gradient of hydrogen ions is produced.gradient of hydrogen ions is produced.

Cellular Respiration IICellular Respiration II9.9. The theory of The theory of chemiosmotic couplingchemiosmotic coupling explains how the explains how the

concentration gradient of Hconcentration gradient of H++ is used to generate energy to make is used to generate energy to make ATP. ATP.

a.a. The enzyme complex The enzyme complex ATP synthaseATP synthase synthesizes ATP synthesizes ATP using the using the energy stored in the concentration gradient of Henergy stored in the concentration gradient of H++ ions (i.e., ions (i.e., protons) across the inner membrane, which is protons) across the inner membrane, which is relatively relatively impermeable to Himpermeable to H++. .

b.b. The HThe H++ ions tend to move down their concentration ions tend to move down their concentration gradient gradient toward the matrix of the mitochondrion. toward the matrix of the mitochondrion. Movement through the Movement through the ATP synthase is used to generate the ATP synthase is used to generate the ATP from ADP and ATP from ADP and inorganic phosphate.inorganic phosphate.

10.10. The process of generating ATP from the electron transport chain The process of generating ATP from the electron transport chain is called oxidative phosphorylation.is called oxidative phosphorylation.

Cellular Respiration ICellular Respiration I11.11. Fats, complex carbohydrates, and proteins may be funneled into Fats, complex carbohydrates, and proteins may be funneled into

glycolysis or the Krebs cycle. The most common convergent glycolysis or the Krebs cycle. The most common convergent point is acetyl CoA.point is acetyl CoA.

12.12. In prokaryotic cells (which lack mitochondria) the oxidative In prokaryotic cells (which lack mitochondria) the oxidative reactions are distributed between the cytoplasm and the plasma reactions are distributed between the cytoplasm and the plasma membrane.membrane.

Aerobic Respiration Occurs in the Eukaryotic Aerobic Respiration Occurs in the Eukaryotic Mitochondrion and Includes the Krebs Cycle Mitochondrion and Includes the Krebs Cycle and the Electron Transport Chain/Oxidative and the Electron Transport Chain/Oxidative

PhosphorylationPhosphorylation

Pyruvate is Converted into Acetyl Pyruvate is Converted into Acetyl CoA to Enter the Krebs CycleCoA to Enter the Krebs Cycle

Pyruvate is Transported into the Pyruvate is Transported into the Mitochondrion and Converted to Mitochondrion and Converted to

the 2-Carbon Acetyl CoAthe 2-Carbon Acetyl CoA

Steps of the Krebs CycleSteps of the Krebs Cycle

General Organization General Organization of the Electron of the Electron

Transport ChainTransport Chain

Electron Transport Chain Electron Transport Chain Establishes a HEstablishes a H+ + Gradient Across Gradient Across

the Inner Membranethe Inner Membrane

The The Movement of Movement of HH+ + Down Its Down Its

Concentration Concentration Gradient Gradient

Generates Generates ATPATP

Summary of Cellular RespirationSummary of Cellular Respiration

Catabolic PathwaysCatabolic Pathways

Catabolic Catabolic PathwaysPathways

Example of Example of Regulation Regulation

Mechanisms Mechanisms for Catabolic for Catabolic

PathwaysPathways