Citric Acid Cycle and Respiration Flashcards
Give an overview of cellular respiration
Stage 1: Glycolysis – generation of pyruvate to form acetyl CoA (fatty acids & some amino acids also generate acetyl CoA)
Stage 2: Citric acid cycle – redox reactions to harness energy via electron carriers (NAD+ & FAD), producing CO2
Stage 3: Oxidative phosphorylation – oxidation of coenzymes: electron transfer & reduction of O2 & synthesis of ATP (ADP phosphorylation)
- Aerobic phases (2 & 3) – cellular respiration – consumption of O2 / production of CO2
Explain where in the cell the citric acid cycle and oxidative phosphorylation take place
The Mitochondrion
- Site of eukaryotic oxidative metabolism
- Number of cristae vary depending on cells metabolic requirements
- After glycolysis and generation of pyruvate, metabolism takes place within the mitochondria
- The selective permeability of the inner membrane to most ions & metabolites, enables generation of ionic gradients – key to ATP synthesis
Describe the synthesis of Acetyl CoA
In the mitochondrial matrix:
- Pyruvate (& fatty acids/amino acids) are degraded into acetyl
- Acetyl group are added to Coenzyme A (CoA)»_space; Acetyl CoA
- Acetyl - CoA is a high energy compound - hydrolysis of the thioester bond = ΔG -33 kJ/mol (more than ATP hydrolysis -30.5 kJ/mol)
What are the products of Citric acid cylce
- 2 x CO2
- 1 x GTP
- 3 x NADH + H+
- 1 x FADH2
What is the first step of the citric acid cycle?
- First step: condensation of the acetyl group (2-carbon) of acetyl CoA with keto acid oxaloacetate (4-carbon) by citrate synthase
- Highly exergonic reaction due to the thiodiester bond large - ΔG, essential to drive the cycle forward - [oxaloacetate]mito is normally very low
- Liberated CoA participates in oxidative decarboxylation of another pyruvate
What is Flavin Adenine Dinucleotide (FAD)
- Coenzyme formed from the vitamin riboflavin (vitamin B2)
- FAD bound to the enzyme succinate dehydrogenase (only citric acid cycle enzyme bound to the inner mitochondrial membrane)
- FAD reduced to FADH2
- Will be oxidized via the electron transport chain
How are enzymes inhibited in the citric acid cycle
- Inhibition of enzymes involved in these stages by levels of:
- ATP
- Acetyl-CoA
- NADH
- CO2
What are the first three steps of the electron transport chain
- Reduced coenzymes (NADH and FADH₂) deliver electrons to Complex I (NADH) and Complex II (FADH₂).
- Electrons are transferred through a series of redox reactions, where each complex is reduced as it accepts electrons and oxidized as it passes them on.
- As electrons move through Complexes I, III, and IV, energy is released and used to pump H⁺ ions into the intermembrane space, creating a proton gradient.
What are steps 4 to 6 of the electron transport chain
- Coenzyme Q (ubiquinone) transfers electrons from Complex I and II to Complex III, while cytochrome c transfers electrons from Complex III to Complex IV. (You mentioned “Cytochrome X,” but it should be cytochrome c).
- At Complex IV, electrons combine with oxygen (O₂) and protons (H⁺) to form water (H₂O):
2H++½O2+2e−→H2O2H++½O2+2e−→H2O2H⁺ + ½O₂ + 2e⁻ → H₂O - The proton gradient drives ATP synthesis as H⁺ ions flow back into the matrix through ATP synthase, generating ATP from ADP + Pᵢ.
Name complex I
NADH-Q reductase
What happens at complex I
Oxides NADH + H+, reduces coenzyme Q
Name complex II
Succinate-Q-reductase
What happens at complex II?
Oxidises FADH2, reduces coenzyme Q
Name complex III
Q-cytochrome C oxidoreductase
What happens at complex III
Oxidises coenzyme Q, reduces cytochrome c
Name Complex IV
Cytochrome C oxidase
What happens at complex IV
Oxidises cytochrome c, reduces O2 to H2O
What are the electron transport chain inhibitors
Both poisons bind to cytochrome C oxidase (complex IV)
- Cyanide
- Carbon monoxide
What does the proton gradient create?
- The proton gradient creates:
- pH gradient - H+ concentration in matrix lower than in the intermembranous space
- A voltage across the membrane
What is a freely permeable region?
Complex V - ATP synthase
