Chapter 8, Problem 38A

Summary Introduction

To discuss:

The roles of NADH and FADH₂ in cellular respiration

Introduction:

Organisms obtain energy through a process called cellular respiration. This process occurs in two stages; glycolysis and aerobic respiration. Glycolysis is an anaerobic process while aerobic respiration includes Krebs cycle and electron transport.

Answer to Problem 38A

NADH and FADH₂ are electron carriers. NADH and FADH₂ play a significant role in electron transport. They are used to move electrons into the electron transport chain. As they release electrons into the system, lots of energy is produced.

The high energy electrons and hydrogen ions from NADH and FADH₂ are used to convert ADP to ATP. More of NADH is used than FADH₂ in producing energy.

Explanation of Solution

Role of NADH and FADH₂- During glycolysis when glucose is broken down in the cytoplasm, two molecules of NADH are formed. NAD+ is an electron carrier similar to NADP used in photosynthesis. Just before Krebs cycle begins, pyruvate reacts with coenzyme A to form acetyl CoA. Carbon dioxide is released and NAD+ is converted to NADH. Later in Krebs cycle, citric acid is formed which is further broken down to form 2 molecules of carbon dioxide, one ATP, 3 NADH and 1 FADH₂. FAD is also an electron carrier similar to NAD⁺.

At the end of Krebs cycle 8 NADH and 2 FADH₂ molecules are formed. NADH and FADH₂ move to play a significant role in electron transport.

The final step in breakdown of glucose is electron transport during which high energy electrons and hydrogen ions from NADH and FADH₂ are used to convert ADP to ATP. As NADH and FADH₂ release electrons, the energy carriers are converted to NAD+ and FAD. Each NADH molecule produces 3 ATP and each group of FADH₂ produces 2 ATP.