4) Summarize the inputs and outputs of the citric acid cycle (Krebs cycle): 3. What goes in? b. What comes out? gain of ATP per glucose? Has any ATP been produced? If so, what is the net C. citric acid cycle take place in eukaryotes? d Where does the
The Correct Answer and Explanation is:
Summary of the Citric Acid Cycle (Krebs Cycle):
a. What goes in?
The citric acid cycle begins when acetyl-CoA enters the cycle. This molecule is derived from the breakdown of carbohydrates, fats, and proteins. Each glucose molecule produces two molecules of acetyl-CoA. The cycle also requires NAD⁺, FAD, and ADP as inputs, which are used as electron carriers and energy currency precursors.
b. What comes out?
For each acetyl-CoA molecule that enters the cycle, the outputs are:
- 3 NADH molecules
- 1 FADH₂ molecule
- 1 ATP (or GTP, which is functionally equivalent)
- 2 CO₂ molecules
Since one glucose molecule generates two acetyl-CoA molecules, the cycle turns twice per glucose. Therefore, the total outputs per glucose are:
- 6 NADH
- 2 FADH₂
- 2 ATP
- 4 CO₂
c. Gain of ATP per glucose? Has any ATP been produced?
Yes, ATP is produced. The citric acid cycle directly produces 2 ATP molecules per glucose (1 per cycle turn). However, the main energy gain comes from the high-energy electron carriers. These NADH and FADH₂ molecules proceed to the electron transport chain, where much more ATP is generated. In total, the NADH and FADH₂ produced by the citric acid cycle contribute to the production of approximately 22 ATP through oxidative phosphorylation.
d. Where does the citric acid cycle take place in eukaryotes?
In eukaryotic cells, the citric acid cycle occurs in the mitochondrial matrix, which is the innermost compartment of the mitochondria. This organelle is often called the powerhouse of the cell because of its role in energy production.
In summary, the citric acid cycle is central to cellular respiration. It oxidizes acetyl-CoA to CO₂, reduces NAD⁺ and FAD to NADH and FADH₂, and generates ATP, all within the mitochondria of eukaryotic cells
