Summary Easy to understand notes on respiratory chain and oxidative phosphorylation
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Cours
Biochemistry (BIOCHEMI)
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Cebu Doctor\'s University
Book
Harpers Illustrated Biochemistry 30th Edition
These are notes on Harper's Biochemistry Chapter 13 - The Respiratory Chain and Oxidative Phosphorylation. This is a summarized version of the chapter which you can read for a quick understanding of the chapter.
Harper's illustrated biochemistry (BMI2601) -EXAMINATION AND ASSIGNMENTS QUESTION + ANSWERS
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Respiratory chain and oxidative phosphorylation - Binding change mechanism
Mitochondria Respiratory chain provides most of the energy captured during
catabolism through oxidative phosphorylation (90%)
- Powerhouse of the cell
- Where capture of free energy happens Respiration control ensures a constant supply of ATP
- Respiration will generate ATP thru oxidative
phosphorylation - Oxidation and phosphorylation are tightly coupled.
- Has a double membrane Oxidation cannot proceed via the respiratory chain
o Outer is permeable to most metabolites without concomitant phosphorylation of ADP
Acyl-CoA synthetase - States of respiratory control
Glycerol phosphate acyltransferase 1. Availability of ADP and substrate
o Inner is selectively permeable 2. Availability of substrate only
Necessitates exchange transporters 3. Capacity of the respiratory chain itself, when
Cardiolipin all the substrates and components are present
Enzymes of respiratory chain in saturating amounts
ATP synthase 4. Availability of ADP only (most cells in the
Membrane transporters resting state)
5. Availability of oxygen only
Respiratory chain
Many poisons inhibit the respiratory chain
- Oxidizes reducing equivalents
- Acts as proton pump 1. Barbiturates – complex I
- Collects and transports reducing equivalents, directing 2. Antimycin A and dimercaprol – complex III
them to their final reaction with oxygen to form water 3. H2S, carbon monoxide, cyanide – complex IV
- Oxidative phosphorylation 4. Malonate – complex I
o Liberated free energy is trapped as high- 5. Atractyloside – transporter of ADP to ATP out of the
energy phosphate mitochondrion
6. Oligomycin – blocks flow of protons through ATP
Components of the respiratory chain are contained in 4 large synthase
protein complexes embedded in the inner mitochondrial 7. Uncouplers – dissociate oxidation in the respiratory
membrane chain from phosphorylation
a. 2,4-dinitrophenol – most used uncoupler
4 large protein complexes b. Thermogenin – in brown fat
- NADH-Q oxidoreductase or Complex I Exchange diffusion systems involving transporter proteins that
- NADH to coenzyme Q or ubiquinone span the membrane are present in the membrane for exchange
- Q-cytochrome c oxidoreductase or Complex III of anions against OH- ions and cations against H+ ions.
- Passes electrons to cytochrome c
- Cytochrome c oxidase or Complex IV Ionophores
- Passes electrons to oxygen then forming
water - Lipophilic molecules that complex specific cations
- Succinate-Q reductase or Complex III - Facilitate transport of specific cations through biologic
- For substrates with more positive redox membranes
potentials than NAD+/NADH - Valinomycin
- Instead of Complex I - Dinitrophenol
Flavoproteins & Iron-Sulfur Proteins (Fe-S > single electron Energy-linked transhydrogenase
transfer reactions) are components of the respiratory chain
- Protein in the inner mitochondrial membrane
complexes I, II, and III
- Couples the passage of protons down the
Q accepts electrons via complexes I and II electrochemical gradient
The Q cycle couples electron transfer to proton transport in Oxidation of extramitochondrial NADH is mediated by substrate
complex III shuttles
- Electrons are passed from QH2 to cytochrome c via - Substrate pairs – transfer of reducing equivalents
complex III through mitochondrial membrane
- Glycerolphosphate shuttle
Molecular oxygen is reduced to water via complex IV - Malate shuttle – more universal
Chemiosmotic theory Ion transport in mitochondria is energy linked
- Electron transport via the respiratory chain creates a The creatine phosphate shuttle facilitates transport of high-
proton gradient which drives the synthesis of ATP energy phosphate from mitochondria
- Proton motive force is the driver
- Complex I, II, and III acts as proton pumps Fatal infantile mitochondrial myopathy and renal dysfunction –
- Can account for respiratory control and the action of severe diminution or absence of most oxidoreductases of the
uncouplers respiratory chain
ATP Synthase MELAS
- Membrane-located - inherited condition due to Complex I or IV deficiency
- Forms ATP in the presence of Pi + ADP - may be involved in Alzheimer disease and diabetes
- Several subunits of the protein form a ball-like shape mellitus
arranged around an axis known as F1
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