Respiratory Balance Sheet — Revision Notes

⚡ 30-Second Revision

Glycolysis (Cytoplasm): — Net 2 ATP (SLP), 2 NADH.
Pyruvate Oxidation (Matrix): — 2 NADH.
Krebs Cycle (Matrix): — 2 ATP (SLP, via GTP), 6 NADH, 2 FADH$_2$.
ETS/Oxidative Phosphorylation (Inner Membrane):

- 1 NADH $ightarrow$ 2.5 ATP - 1 FADH$_2$ $ightarrow$ 1.5 ATP

Shuttle Systems for Cytoplasmic NADH:

- Malate-Aspartate: 2 NADH $ightarrow$ $2 \times 2.5 = 5$ ATP - Glycerol-3-Phosphate: 2 NADH $ightarrow$ $2 \times 1.5 = 3$ ATP

Total ATP (Malate-Aspartate): — $2 + 5 + 5 + 20 = 32$ ATP
Total ATP (Glycerol-3-Phosphate): — $2 + 3 + 5 + 20 = 30$ ATP
CO$_2$ Release: — 2 (Pyruvate Oxidation) + 4 (Krebs Cycle) = 6 CO$_2$.

2-Minute Revision

The Respiratory Balance Sheet summarizes ATP production from one glucose molecule via aerobic respiration. It begins with Glycolysis in the cytoplasm, yielding a net of 2 ATP and 2 NADH. These 2 NADH then transfer their electrons to the mitochondria via shuttle systems; the Malate-Aspartate shuttle gives 5 ATP (2 x 2.

5), while the Glycerol-3-Phosphate shuttle gives 3 ATP (2 x 1.5). Next, two pyruvate molecules undergo oxidative decarboxylation, producing 2 NADH (5 ATP) and 2 CO$_2$. The two acetyl-CoA molecules then enter the Krebs Cycle, producing 2 ATP (via GTP), 6 NADH (15 ATP), 2 FADH$_2$ (3 ATP), and 4 CO$_2$.

All NADH and FADH$_2$ then feed into the Electron Transport System for oxidative phosphorylation. Summing these, the total theoretical ATP yield is 32 ATP (with Malate-Aspartate shuttle) or 30 ATP (with Glycerol-3-Phosphate shuttle).

Remember, oxygen is the final electron acceptor, crucial for this high ATP yield.

5-Minute Revision

Mastering the Respiratory Balance Sheet is about understanding the sequential energy capture across cellular respiration's four stages. Start by visualizing the process: Glucose enters Glycolysis in the cytoplasm, yielding a net of 2 ATP directly (substrate-level phosphorylation) and 2 NADH.

These cytoplasmic NADH molecules are key; their electrons must enter the mitochondria via one of two shuttle systems. If the Malate-Aspartate shuttle is active (common in liver, heart), each NADH yields 2.

5 ATP, totaling 5 ATP from glycolysis's NADH. If the Glycerol-3-Phosphate shuttle is used (muscle, brain), each NADH yields 1.5 ATP, totaling 3 ATP. This difference is crucial for the final ATP count.

Next, the two pyruvate molecules from glycolysis move into the mitochondrial matrix. Here, each undergoes oxidative decarboxylation (the Link Reaction), forming acetyl-CoA, releasing 1 CO$_2$ per pyruvate (total 2 CO$_2$), and producing 1 NADH per pyruvate (total 2 NADH). These 2 NADH contribute $2 \times 2.5 = 5$ ATP.

Then, the two acetyl-CoA molecules enter the Krebs Cycle (Citric Acid Cycle) in the mitochondrial matrix. For two turns of the cycle (one per acetyl-CoA), 2 ATP (via GTP, substrate-level), 6 NADH, and 2 FADH$_2$ are produced. These electron carriers contribute $6 \times 2.5 = 15$ ATP and $2 \times 1.5 = 3$ ATP, respectively, via oxidative phosphorylation. Additionally, 4 CO$_2$ molecules are released here.

Finally, all the NADH and FADH$_2$ (total 10 NADH and 2 FADH$_2$ if Malate-Aspartate shuttle is used) donate their electrons to the Electron Transport System (ETS) on the inner mitochondrial membrane. This drives oxidative phosphorylation, producing the bulk of ATP. Summing up:

Glycolysis: — 2 ATP (net SLP) + 5 ATP (from 2 NADH via Malate-Aspartate) = 7 ATP
Pyruvate Oxidation: — 5 ATP (from 2 NADH)
Krebs Cycle: — 2 ATP (SLP) + 15 ATP (from 6 NADH) + 3 ATP (from 2 FADH$_2$) = 20 ATP
Total: — $7 + 5 + 20 = 32$ ATP.

If the Glycerol-3-Phosphate shuttle is used, the total would be $2 + 3 + 5 + 20 = 30$ ATP. Remember the role of oxygen as the final electron acceptor in ETS, without which this entire high-yield process would halt. Also, be aware of the older convention (3 ATP/NADH, 2 ATP/FADH$_2$), which would yield 38 or 36 ATP.

Prelims Revision Notes

Respiratory Balance Sheet: NEET Quick Facts

I. Key Energy Carriers & Equivalents (Modern Convention):

ATP: — Adenosine Triphosphate, direct energy currency.
NADH: — Reduced Nicotinamide Adenine Dinucleotide. 1 NADH $ightarrow$ 2.5 ATP (via ETS).
FADH$_2$: — Reduced Flavin Adenine Dinucleotide. 1 FADH$_2$ $ightarrow$ 1.5 ATP (via ETS).

II. Stages of Aerobic Respiration & ATP/NADH/FADH$_2$ Yield per Glucose:

1
Glycolysis (Cytoplasm):

* Net ATP (Substrate-Level Phosphorylation): 2 ATP * NADH produced: 2 NADH

1
Pyruvate Oxidation (Link Reaction) (Mitochondrial Matrix):

* ATP: 0 * NADH produced: 2 NADH (from 2 pyruvate) * CO$_2$ released: 2 CO$_2$

1
Krebs Cycle (Citric Acid Cycle) (Mitochondrial Matrix) (2 turns per glucose):

* ATP (Substrate-Level Phosphorylation, via GTP): 2 ATP * NADH produced: 6 NADH * FADH$_2$ produced: 2 FADH$_2$ * CO$_2$ released: 4 CO$_2$

III. Shuttle Systems for Cytoplasmic NADH:

Cytoplasmic NADH cannot directly enter mitochondria.
Malate-Aspartate Shuttle (e.g., liver, heart, kidney): — Transfers electrons to mitochondrial NAD$^+$. Yields 2.5 ATP per cytoplasmic NADH. Total for 2 NADH = 5 ATP.
Glycerol-3-Phosphate Shuttle (e.g., muscle, brain): — Transfers electrons to mitochondrial FAD. Yields 1.5 ATP per cytoplasmic NADH. Total for 2 NADH = 3 ATP.

IV. Total Theoretical ATP Yield (per glucose):

Assuming Malate-Aspartate Shuttle:

* Glycolysis: 2 (SLP) + 5 (from 2 NADH) = 7 ATP * Pyruvate Oxidation: 5 ATP (from 2 NADH) * Krebs Cycle: 2 (SLP) + 15 (from 6 NADH) + 3 (from 2 FADH$_2$) = 20 ATP * Grand Total: 32 ATP

Assuming Glycerol-3-Phosphate Shuttle:

* Glycolysis: 2 (SLP) + 3 (from 2 NADH) = 5 ATP * Pyruvate Oxidation: 5 ATP (from 2 NADH) * Krebs Cycle: 20 ATP * Grand Total: 30 ATP

V. Older Convention (sometimes asked):

1 NADH $ightarrow$ 3 ATP; 1 FADH$_2$ $ightarrow$ 2 ATP
Total ATP (Malate-Aspartate): 38 ATP
Total ATP (Glycerol-3-Phosphate): 36 ATP

VI. Key Concepts:

Substrate-level Phosphorylation: — Direct ATP synthesis (Glycolysis, Krebs Cycle).
Oxidative Phosphorylation: — Indirect ATP synthesis via ETS and chemiosmosis (most ATP).
Oxygen: — Final electron acceptor in ETS; essential for high ATP yield.
Efficiency: — Aerobic respiration (30-32 ATP) is far more efficient than anaerobic (2 ATP).
CO$_2$ Release: — 6 CO$_2$ per glucose (2 from pyruvate oxidation, 4 from Krebs cycle).

Vyyuha Quick Recall

To remember the ATP yield from each stage (using modern 2.5/1.5 and Malate-Aspartate shuttle for 32 ATP):

Great Power Keeps Everyone Thriving!

Glycolysis: 7 ATP (2 direct + 5 from NADH)
Pyruvate Oxidation: 5 ATP (from NADH)
Krebs Cycle: 20 ATP (2 direct + 15 from NADH + 3 from FADH2)
ETS: Where the bulk of ATP is made from NADH/FADH2
Total: 32 ATP