TCA Cycle and Oxidative Phosphorylation
Krebs cycle intermediates, electron transport chain and chemiosmosis. (Biology › Respiration in Plants, NEET UG syllabus.)
What is TCA Cycle and Oxidative Phosphorylation?
A central metabolic pathway in the mitochondrial matrix that completes the oxidation of acetyl CoA, generating CO2, NADH, FADH2, and ATP/GTP.
Key formula / rule: Overall Cellular Respiration
Key points
- Describe the steps and intermediates of the TCA cycle.
- Identify the products of the TCA cycle.
- Explain the components and function of the electron transport chain.
- Describe the process of chemiosmosis and ATP synthesis.
Common exam trap
Confusing the location of glycolysis (cytoplasm), TCA cycle (mitochondrial matrix), and ETC (inner mitochondrial membrane).
Definitions
- Term
TCA Cycle (Krebs Cycle)
- Meaning
A central metabolic pathway in the mitochondrial matrix that completes the oxidation of acetyl CoA, generating CO2, NADH, FADH2, and ATP/GTP.
- Term
Oxidative Phosphorylation
- Meaning
The metabolic pathway in which cells use enzymes to oxidize nutrients, releasing energy that is used to produce ATP from ADP and inorganic phosphate.
- Term
Electron Transport Chain (ETC)
- Meaning
A series of protein complexes and electron carriers embedded in the inner mitochondrial membrane that transfer electrons from NADH and FADH2 to oxygen, pumping protons across the membrane.
- Term
Chemiosmosis
- Meaning
The movement of ions (specifically H+ protons) across a selectively permeable membrane, down their electrochemical gradient, to generate ATP.
- Term
ATP Synthase
- Meaning
A large enzyme complex (Complex V) located in the inner mitochondrial membrane that uses the energy from the proton gradient to synthesize ATP from ADP and Π.
Learning objectives
Describe the steps and intermediates of the TCA cycle.
Identify the products of the TCA cycle.
Explain the components and function of the electron transport chain.
Describe the process of chemiosmosis and ATP synthesis.
Relate the TCA cycle and oxidative phosphorylation to overall ATP production in aerobic respiration.
Locate the cellular compartments where these processes occur.
Formulae
- Name
Overall Cellular Respiration
- Note
Summarizes the complete oxidation of glucose.
- Expression
C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (ATP)
- Name
TCA Cycle (per acetyl CoA)
- Note
Represents one turn of the cycle for one acetyl CoA molecule.
- Expression
Acetyl CoA + 3NAD+ + FAD + ADP + Π + 2H2O → 2CO2 + 3NADH + 3H+ + FADH2 + ATP + CoA
- Name
ATP Synthesis (Oxidative Phosphorylation)
- Note
The general reaction catalyzed by ATP synthase.
- Expression
ADP + Π + Energy (from proton gradient) → ATP + H2O
Prerequisites
Basic understanding of cellular respiration.
Knowledge of glycolysis and pyruvate oxidation.
Familiarity with mitochondrial structure.
Understanding of redox reactions and energy carriers (ATP, NADH, FADH2).
Common mistakes
Confusing the location of glycolysis (cytoplasm), TCA cycle (mitochondrial matrix), and ETC (inner mitochondrial membrane).
Incorrectly recalling the number of ATP/NADH/FADH2 produced at each stage.
Forgetting that oxygen is crucial as the final electron acceptor in aerobic respiration.
Mixing up the roles of NADH and FADH2 in the ETC (NADH enters at Complex I, FADH2 at Complex II).
Not understanding the concept of chemiosmosis as the driving force for ATP synthesis.
Keywords
TCA cycle
Krebs cycle
Citric acid cycle
Oxidative phosphorylation
Electron transport chain
ETC
Chemiosmosis
ATP synthase
Mitochondrial matrix
Inner mitochondrial membrane
NADH
FADH2
Proton gradient
Oxygen
ATP
Acetyl CoA
Oxaloacetate
Cytochromes
Practice preview
Where does the Krebs cycle (TCA cycle) primarily occur in eukaryotic cells?…
easy
Which of the following is the correct sequence of intermediates in the Krebs cycle after citrate formation?…
medium
The chemiosmotic hypothesis for ATP synthesis in mitochondria is based on the establishment of a proton gradient across which membrane?…
medium