Question

Net gain of ATP molecules in complete aerobic breakdown of one molecule of glucose in most eukaryotes is _________.

• A. 38
• B. 40
• C. 34
• D. 36

Hint:

Prokaryotes lack mitochondria, so they do not need to transport glycolytic NADH across a membrane. This allows them to yield \( 38\text{ ATP} \) from one glucose molecule, compared to \( 36\text{ ATP} \) in most eukaryotes.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Aerobic cellular respiration is the metabolic process by which cells break down glucose in the presence of oxygen to produce energy in the form of ATP.
This process involves glycolysis, the transition reaction, the citric acid cycle (Krebs cycle), and the electron transport chain (ETC).
Detailed Explanation:
Let us break down the standard ATP yield from the complete oxidation of one molecule of glucose:
- Glycolysis: Produces \( 2\text{ net ATP} \) directly through substrate-level phosphorylation and \( 2\text{ NADH} \) molecules.
- Krebs Cycle: Generates \( 2\text{ ATP} \) (or GTP) directly, \( 6\text{ NADH} \), and \( 2\text{ FADH}_2 \).
- Transition Reaction: Generates \( 2\text{ NADH} \).
During oxidative phosphorylation in the ETC, each NADH typically yields \( 3\text{ ATP} \) (or \( 2.5\text{ ATP} \) in newer models) and each \(\text{FADH}_2\) yields \( 2\text{ ATP} \) (or \( 1.5\text{ ATP} \)).
In eukaryotes, the \( 2\text{ NADH} \) generated in the cytoplasm during glycolysis must be actively transported into the mitochondria.
In most tissues, this transport occurs via the glycerol-phosphate shuttle, which consumes \( 1\text{ ATP} \) per NADH transported.
This reduces the net ATP yield from those two glycolytic NADH molecules by \( 2\text{ ATP} \) (reducing their potential contribution from \( 6\text{ ATP} \) to \( 4\text{ ATP} \)).
Therefore, the theoretical maximum yield of \( 38\text{ ATP} \) (typical of prokaryotes) is reduced to a net gain of \( 36\text{ ATP} \) in most eukaryotic cells.

Step 2: Final Answer:
The net gain of ATP molecules in most eukaryotes is \( 36 \).