Problem 2 - Campbell Biology Concepts & Connections

Question

A biochemist wanted to study how various substances were used in cellular respiration. In one experiment, she allowed a mouse to breathe air containing \(\mathrm{O}_{2}\) "labeled" by a particular isotope. In the mouse, the labeled oxygen first showed up in a. ATP. b. NADH. c. \(\mathrm{CO}_{2}\). d. \(\mathrm{H}_{2} \mathrm{O}\).

Step-by-Step Solution

Answer

d. \(\text{H}_{2}\text{O}\)

Step 1: Understanding the Experiment

The biochemist used oxygen \(\text{O}_{2}\) labeled with a particular isotope to trace its path in the cellular respiration process in a mouse.

Step 2: Concept of Cellular Respiration

Cellular respiration is a series of metabolic processes that involve the use of oxygen in the production of energy (ATP), carbon dioxide \(\text{CO}_{2}\), water \(\text{H}_{2}O\), and other metabolites.

Step 3: Examine Each Option

a. ATP - ATP is the energy currency produced, but oxygen is not directly incorporated into ATP. b. NADH - NADH is an electron carrier, which transports electrons during respiration, not incorporating oxygen directly. c. \(\text{CO}_{2} \)- Carbon dioxide is produced in the process, but labeled oxygen shows up elsewhere first. d. \(\text{H}_{2}O}\) - Oxygen is used as the final electron acceptor in the electron transport chain and combines with protons to form water.

Step 4: Identify Labeled Oxygen First Appearance

Oxygen atoms from the labeled \(\text{O}_{2}\) first show up in water \(\text{H}_{2} \text{O}\) during cellular respiration as it acts as the final electron acceptor.

Key Concepts

Metabolic Processes

Metabolic processes are all the chemical reactions that occur within living organisms to maintain life. These processes allow cells to grow, reproduce, and respond to their environment. The main purpose of metabolic processes is to convert food into energy and building blocks for the cell. In cellular respiration, metabolic processes play a crucial role. They break down glucose and other molecules, ultimately generating energy in the form of ATP.

Cellular respiration involves multiple connected pathways:

• Glycolysis
• Krebs Cycle (Citric Acid Cycle)
• Electron Transport Chain (ETC)

Each of these pathways processes substrates differently, but they work together to ensure cells have the energy they need for various functions.

Electron Transport Chain

The Electron Transport Chain (ETC) is a series of protein complexes and other molecules found in the inner membrane of mitochondria. Its main function is to transfer electrons from electron donors (like NADH and FADH2) to electron acceptors (like oxygen) through redox reactions. This process establishes a proton gradient that drives the synthesis of ATP.

Here's how the ETC works:

• Electrons are donated by NADH and FADH2.
• These electrons are passed through a series of carrier proteins.
• As electrons move along these proteins, energy is released and used to pump protons (H⁺) into the intermembrane space of the mitochondria.
• This creates a high concentration of protons in the intermembrane space.

The final step involves the proton gradient driving ATP synthase, an enzyme that synthesizes ATP from ADP and inorganic phosphate by using the energy released as protons flow back into the mitochondrial matrix.

Final Electron Acceptor

The final electron acceptor in the electron transport chain is oxygen (O₂). This is a crucial step in cellular respiration because it allows the entire process to continue by accepting electrons and preventing a backlog that would halt energy production.

Some key points about the final electron acceptor:

• Oxygen combines with electrons and protons to form water (H₂O).
• This reduction of oxygen is essential for maintaining the flow of electrons through the ETC.
• Without oxygen to accept the electrons, the ETC would cease to function, and ATP production would stop.

In the case mentioned in the exercise, labeled oxygen first appears in water (H₂O) because it has combined with electrons at the end of the electron transport chain. This demonstrates the critical role oxygen plays in cellular respiration and ATP production.