Question 744 of 782

Which of the following organelles is primarily responsible for the synthesis of ATP through cellular respiration in eukaryotic cells?

  • Ribosome
  • Endoplasmic reticulum
  • Mitochondrion
  • Golgi apparatus

Correct Answer: C

Explanation
Correct Option: C. Mitochondrion Detailed Explanation:
  1. Understanding Cellular Respiration:
  2. Cellular respiration is the process by which cells convert nutrients (primarily glucose) into energy in the form of adenosine triphosphate (ATP). This process occurs in several stages: glycolysis, the citric acid cycle (Krebs cycle), and oxidative phosphorylation (electron transport chain and chemiosmosis).
  3. Role of the Mitochondrion:
  4. The mitochondrion is often referred to as the "powerhouse of the cell" because it is the primary site for ATP production through cellular respiration.
  5. In eukaryotic cells, the mitochondria are double-membraned organelles. The inner membrane is highly folded into structures called cristae, which increase the surface area for the reactions involved in ATP synthesis.
  6. ATP Synthesis Process:
  7. Glycolysis occurs in the cytoplasm and breaks down glucose into pyruvate, yielding a small amount of ATP and NADH.
  8. The pyruvate enters the mitochondrion, where it is converted into acetyl-CoA, which then enters the citric acid cycle. This cycle produces more NADH and FADH2, which are crucial for the next stage.
  9. The electron transport chain (ETC) occurs in the inner mitochondrial membrane. Here, electrons from NADH and FADH2 are transferred through a series of protein complexes, ultimately leading to the reduction of oxygen to water.
  10. As electrons move through the ETC, protons (H+) are pumped from the mitochondrial matrix into the intermembrane space, creating a proton gradient.
  11. This gradient drives ATP synthesis through chemiosmosis via ATP synthase, an enzyme that synthesizes ATP as protons flow back into the matrix.
  12. Why Other Options Are Incorrect:
  13. A. Ribosome: Ribosomes are the sites of protein synthesis, where amino acids are assembled into proteins based on mRNA templates. They do not play a role in ATP synthesis.
  14. B. Endoplasmic Reticulum (ER): The ER is involved in the synthesis of proteins (rough ER) and lipids (smooth ER), as well as the processing and transport of these molecules. It does not directly produce ATP.
  15. D. Golgi Apparatus: The Golgi apparatus is responsible for modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles. Like the ER and ribosomes, it does not synthesize ATP.
Summary of Key Points:
  • The mitochondrion is the primary organelle for ATP synthesis in eukaryotic cells through cellular respiration.
  • ATP production occurs mainly during the citric acid cycle and oxidative phosphorylation in the mitochondria.
  • Other organelles like ribosomes, the endoplasmic reticulum, and the Golgi apparatus have distinct functions unrelated to ATP synthesis.
Revision Summary:
  • Mitochondria are the "powerhouses" of the cell, responsible for ATP production.
  • Cellular respiration involves glycolysis, the citric acid cycle, and oxidative phosphorylation.
  • The electron transport chain and chemiosmosis are critical for ATP synthesis in mitochondria.
  • Other organelles (ribosomes, ER, Golgi apparatus) do not synthesize ATP.
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