Biology 12 - Inside the Mitochondria - Section 6-4

UNIT A: Cell Biology

Chapter 2: The Molecules of Cells

Chapter 3: Cell Structure and Function

Chapter 4: DNA Structure and Gene Expression

Chapter 5: Metabolism: Energy and Enzymes

Chapter 6: Cellular Respiration:

Section 6.4

Chapter 7: Photosynthesis

In this chapter you will learn about the many chemical reactions, known as cellular respiration, that break down molecules such as glucose to produce the ATP that fuels physical activities.

UNIT A Chapter 6: Cellular Respiration

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Chapter 6: Cellular Respiration

Why are there differences between the aerobic and anaerobic pathways? How is the energy of a glucose molecule harvested by a cell? How are other organic nutrients, such as proteins and fats, used as energy?

6.4 Inside the Mitochondria

When oxygen is present, the final reactions of cellular respiration occur: preparatory reaction, citric acid cycle, and electron transport chain reactions.•Preparatory (prep) reaction occurs in the mitochondrial matrix and is the oxidation of pyruvate to acetyl CoA, which enters the citric acid cycle

For each glucose, two pyruvates are oxidized to two acetyl CoA.

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The citric acid cycle occurs in the matrix and is a cyclical pathway that converts the acetyl groups to CO2.

•ATP, NADH, and FADH2 are produced

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Citric Acid Cycle

From Figure 6.8 Citric Acid Cycle.

Citric Acid Cycle

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From Figure 6.8 Citric Acid Cycle.

• To start, acetyl-CoA joins with a C4 to form a C6

• During the cycle, each acetyl from the prep reaction is released as two CO2, oxidations produce NADH + H+ and FADH2, and substrate-level ATP synthesis occurs

By the end of the citric acid cycle, the six carbons originally in glucose have become part of six CO2 molecules.

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Inputs and Outputs of the Citric Acid Cycle

Electron Transport/ATP Synthesis

The electron transport chain is in the cristae of mitochondria.•Electrons are passed along a series of carriers•High energy e− enter the system and low-energy e −exit

•NADH + H + becomes NAD+ and FADH2 becomes FAD +

•Energy is captured in the form ofa hydrogen ion gradient

•O2 receives e −that exit and react with H+ to form H2O

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From Figure 6.9 The electron transport chain.

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From Figure 6.9 The electron transport chain.

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The components of the electron transport chain have a specific arrangement in the cristae of the mitochondria.•H+ ions are pumped from the matrix to the intermembrane space. This produces an unequal distribution of H+ ions, called an electrochemical gradient•The H+ move back from the intermembrane space to the matrix by passing through the ATP synthase complex. This causes the enzyme complex to produce ATP from ADP and phosphate.•ATP synthesis is said to occur by chemiosmosis

Organization of Cristae

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Organization of Cristae

Figure 6.10 Organization and function of the electron transport chain.

Energy Yield from Cellular Respiration

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The maximum ATP yield from the complete oxidation of glucose can be calculated.•Glycolysis (cytoplasm): 2 ATP

•Citric acid cycle (matrix): 2 ATP

•Electron transport chain and chemiosmosis: 26 to 28 ATP

Experimental observations show: •2-3 ATP per NADH in electron transport chain

•1-2 ATP per FADH2 in electron transport chain

In many cells, NADH produced in the cytoplasm by glycolysis requires ATP for transport into the mitochondria.

Energy Yield from Cellular Respiration

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Figure 6.11 Accountingof the maximumenergy yield perglucose moleculebreakdown.

Efficiency of Cellular Respiration

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To determine how much of the energy in glucose becomes available to the cell:

•Difference in energy between reactants (glucose and O2) and products (CO2 and H2O) = 686 kcal

•Breaking of 30 phosphate bonds in the conversion of 30 ATP to 30 ADP + 30 phosphates = 219 kcal

Therefore, 219/686, or 32%, of available energy is transferred from glucose to ATP. The remaining energy dissipates as heat.

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Check Your Progress

1. Explain the relationship between the metabolic pathways within the mitochondria with glycolysis.

2. Calculate the number of NADH, FADH2, and ATP molecules produced by each stage of cellular respiration per glucose molecule.

3. Discuss why there is variation in the number of ATP molecules produced per glucose.

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Science

Biology 12 - Inside the Mitochondria - Section 6-4