Question

1. Glycolysis

2. Transition step

3. TCA cycle

4. Electron transport chain

For each of the above, answer the following questions:

Where in the cell does it take place? Prokaryote vs Eukaryote

Number of ATP molecules produced?

Number of NADH/FADH2 produced?

What goes in, and what leaves? (reactants vs end products)

Answer 1

Glycolysis is the first step of cellular respiration. It is the enzymatic break down of glucose to pyruvic acid or lactic acid. Glycolysis takes place in cell cytosol in both prokaryotes and eukaryotes. 2 molecules of ATP are produced in glycolysis. 2 molecules of NADH+H⁺ is produced in glycolysis but no FADH₂ is produced. Starting product of glycolysis is glucose and the end product is pyruvate (aerobic glycolysis) or lactate (anaerobic glycolysis).

The transition step or the intermediate step is the next of glycolysis. Here the pyruvate is converted into acetyl CoA. It also takes place in cytosol in prokaryotes and eukaryotes. No ATP is produced in this step. 2 molecules of NADH+H⁺ is produced in this step but no FADH₂ is produced. Starting product of this step is pyruvate and end product is acetyl CoA.

Next the acetyl CoA enters into the Krebs cycle or the citric acid cycle or the TCA (Tricarboxylic acid) cycle. TCA cycle occurs in mitochondrial matrix in eukaryotes but it occurs in cytosol in prokaryotes. 2 molecules of ATP (GTP equivalent) are produced in TCA cycle. 6 molecules of NADH+H⁺ is produced in TCA cycle and 2 molecules of FADH₂ is also produced. Starting products are acetyl CoA and oxaloacetate and end product is citrate.

Electron transport chain or ETC takes place in mitochondrial inner membrane in eukaryotes and in plasma membrane in case of prokaryoytes. NADH+H⁺ and FADH₂ undergoes complete oxidation to produce 34 molecules of ATP. NADH+H⁺ and FADH₂ are not produced in this step but rather is metabolized. NADH+H⁺ and FADH₂ are the starting product and end product is water (H₂O).