Introduction to metabolism.
Specific and general pathways
of carbohydrates, lipids and
protein metabolism
METABOLISM
The series of changes that a substance
undergoes after absorption from the
gastrointestinal tract where by it ...
CATABOLISM AND ANABOLISM

The process by which it is used in the
synthesis of tissue components are
referred to as “anabo...
METABOLIC PATHWAYS
This is process of substance convertion in
some part of metabolism.
They can be :
1.Aliphatic
(glyc...
TYPES OF REACTION
EXERGONIC REACTION
(ENERGY LIBERATING)
ATP + H2O → ADP + PHOSPHATE + 34
KJ/MOLE

ENDERGONIC REACTION
(...
The modern views on the biological oxidation
All the enzymes involved in this process of biological
oxidation belong
to th...
3. Anaerobic Dehydrogenases
AH2 (reduced) + B (oxidised) → A (oxidised) + BH2 (reduced)
- NAD+ linked dehydrogenases AH2 +...
Citric acid
cycle supplies
NADH and
FADH2 to the
electron
transport
chain
Electrons of NADH or FADH2 are used to reduce molecular oxygen to
water.
A large amount of free energy is liberated.

The ...
The flow of electrons through carriers leads to the pumping of protons out
of the mitochondrial matrix.
The resulting
dist...
THE ELECTRON TRANSPORT CHAIN
Series of enzyme complexes (electron carriers)
embedded in the inner mitochondrial membrane,
...
High-Energy Electrons: Redox Potentials and Free-Energy
Changes

In oxidative phosphorylation, the electron transfer
poten...
E'o (reduction potential) is a measure of how easily a
compound can be reduced (how easily it can accept
electron).
All co...
Important characteristic of ETC is the amount of energy
released upon electron transfer from one carrier to
another.
This ...
• Mobile coenzymes: ubiquinone
(Q) and cytochrome c serve as
links between ETC complexes
• Complex IV reduces O2 to water
THE RESPIRATORY CHAIN CONSISTS OF FOUR
COMPLEXES
I
II

Components of electrontransport chain are
arranged in the inner
mem...
Complex I (NADH-ubiquinone oxidoreductase)
Transfers electrons from NADH to Co Q (ubiquinone)
Consist of:
- enzyme NADH de...
Complex II (succinate-ubiquinon oxidoreductase)

Transfers electrons from succinate to Co Q.
Form 1 consist of:
- enzyme s...
Complex III (ubiquinol-cytochrome c oxidoreductase)
Transfers electrons from ubiquinol to cytochrome c.
Consist of: cytoch...
Complex IV (cytochrome c oxidase)
Transfers electrons from cytochrome c to O2.
Composed of: cytochromes a and a3.
Catalyze...
The Chemiosmotic Theory
• Proposed by Peter Mitchell in the
1960’s (Nobel Prize, 1978)
• Chemiosmotic theory: electron
tra...
Active Transport of ATP, ADP and Pi Across the
Inner Mitochondrial Membrane
• ATP must be transported to the cytosol, and ...
Respiratory control
The most important factor in determining the rate of
oxidative phosphorylation is the level of ADP.
Th...
REGULATION OF OXIDATIVE
PHOSPHORYLATION
Coupling of Electron Transport with ATP Synthesis
Electron transport is tightly co...
Specific and general pathway etc(new)2013
Specific and general pathway etc(new)2013
Specific and general pathway etc(new)2013
Specific and general pathway etc(new)2013
Specific and general pathway etc(new)2013
Specific and general pathway etc(new)2013
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Respiratory chain mechanism

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Specific and general pathway etc(new)2013

  1. 1. Introduction to metabolism. Specific and general pathways of carbohydrates, lipids and protein metabolism
  2. 2. METABOLISM The series of changes that a substance undergoes after absorption from the gastrointestinal tract where by it is used for synthesis of some of the tissue components or is broken down or otherwise altered and eliminated from the body through urine, feces, sweat or respiration.
  3. 3. CATABOLISM AND ANABOLISM The process by which it is used in the synthesis of tissue components are referred to as “anabolism” And the process by which it is broken down into simpler products are referred to as “catabolism”
  4. 4. METABOLIC PATHWAYS This is process of substance convertion in some part of metabolism. They can be : 1.Aliphatic (glycolysis, β-oxidation of fatty acids) 2.Cyclic (Kreb’s cycle, urea synthesis cycle) 3.Unbranched  (Pentose pathway of glucose oxidation).
  5. 5. TYPES OF REACTION EXERGONIC REACTION (ENERGY LIBERATING) ATP + H2O → ADP + PHOSPHATE + 34 KJ/MOLE ENDERGONIC REACTION (ENERGY REQUIRING) ADP + PHOSPHATE -+34 → ATP + H20 KJ/MOL
  6. 6. The modern views on the biological oxidation All the enzymes involved in this process of biological oxidation belong to the major class of oxidoreductases 1. Oxidases AH2 + O2 —————— ——> A + H2O Cytochrome oxidase, which is the terminal component of ETC, belongs to this category. It contains heme and is described under the components of ETC. 2. Aerobic Dehydrogenases AH2 + O2 ----—> A + H2O2. These enzymes are flavoproteins and the product is usually hydrogen peroxide.
  7. 7. 3. Anaerobic Dehydrogenases AH2 (reduced) + B (oxidised) → A (oxidised) + BH2 (reduced) - NAD+ linked dehydrogenases AH2 + NAD+ → A + NADH + H+ - FAD-linked Dehydrogenases - Cytochromes 4. Hydroperoxidases (All these enzymes use H2O2 as a reactant ) a)Peroxidase: H2O2 + AH2 —(peroxidase)——> 2H2O + A b) Catalase 2H2O2 -—----(catalase)— —> 2H2O + O2 5. Oxygenases These are enzymes which catalyse reactions where oxygen is transferred and incorporated into a substrate a) Mono-oxygenases A-H + O2 + BH2 —(hydroxylase)—» A-OH + H2O + B b) Di-oxygenases A + O2 → AO2
  8. 8. Citric acid cycle supplies NADH and FADH2 to the electron transport chain
  9. 9. Electrons of NADH or FADH2 are used to reduce molecular oxygen to water. A large amount of free energy is liberated. The electrons from NADH and FADH2 are not transported directly to O2 but are transferred through series of electron carriers that undergo reversible reduction and oxidation.
  10. 10. The flow of electrons through carriers leads to the pumping of protons out of the mitochondrial matrix. The resulting distribution of protons generates a pH gradient and a transmembrane electrical potential that creates a protonmotive force. ATP is synthesized when protons flow back to the mitochondrial matrix through an enzyme complex ATP synthase. The oxidation of fuels and the phosphorylation of ADP are coupled by a proton gradient across the inner mitochondrial membrane.
  11. 11. THE ELECTRON TRANSPORT CHAIN Series of enzyme complexes (electron carriers) embedded in the inner mitochondrial membrane, which oxidize NADH2 and FADH2 and transport electrons to oxygen is called respiratory electron-transport chain (ETC). The sequence of electron carriers in ETC NADH FMN Fe-S succinate FAD Fe-S Co-Q Fe-S cyt c1 cyt b cyt c cyt a cyt a3 O2
  12. 12. High-Energy Electrons: Redox Potentials and Free-Energy Changes In oxidative phosphorylation, the electron transfer potential of NADH or FADH2 is converted into the phosphoryl transfer potential of ATP. Phosphoryl transfer potential is ∆G°' (energy released during the hydrolysis of activated phos-phate compound). ∆G°' for ATP = -7.3 kcal mol-1 Electron transfer potential is expressed as E'o, (also called redox potential, reduction potential, or oxidation-reduction potential) require 0.34 EV for 1 macroergic bond.
  13. 13. E'o (reduction potential) is a measure of how easily a compound can be reduced (how easily it can accept electron). All compounds are compared to reduction potential of hydrogen wich is 0.0 V. The larger the value of E'o of a carrier in ETC the better it functions as an electron acceptor (oxidizing factor). Electrons flow through the ETC components spontaneously in the direction of increasing reduction potentials. E'o of NADH = -0.32 Evolts (strong reducing agent) E'o of O2 = +0.82 Evolts (strong oxidizing agent)
  14. 14. Important characteristic of ETC is the amount of energy released upon electron transfer from one carrier to another. This energy can be calculated using the formula: ∆Go’=-nF∆E’o n – number of electrons transferred from one carrier to another; F – the Faraday constant (23.06 kcal/volt mol); ∆E’o – the difference in reduction potential between two carriers. When two electrons pass from NADH to O2 : ∆Go’=-2*96,5*(+0,82-(-0,32)) = -52.6 kcal/mol And 43.4 kcal/mol (FADH2).
  15. 15. • Mobile coenzymes: ubiquinone (Q) and cytochrome c serve as links between ETC complexes • Complex IV reduces O2 to water
  16. 16. THE RESPIRATORY CHAIN CONSISTS OF FOUR COMPLEXES I II Components of electrontransport chain are arranged in the inner membrane of mitochondria in packages called respiratory assemblies (complexes). succinate FMN IV III I NADH III Fe-S Co-Q II FAD Fe-S Fe-S cyt b IV cyt c 1 cyt c cyt a cyt a3 O2
  17. 17. Complex I (NADH-ubiquinone oxidoreductase) Transfers electrons from NADH to Co Q (ubiquinone) Consist of: - enzyme NADH dehydrogenase (FMN - prosthetic group) - iron-sulfur clusters. NADH reduces FMN to FMNH2. Electrons from FMNH2 pass to a Fe-S clusters. Fe-S proteins convey electrons to ubiquinone. QH2 is formed. The flow of two electrons from NADH to coenzym Q leads to the pumping of four hydrogen ions out of the matrix.
  18. 18. Complex II (succinate-ubiquinon oxidoreductase) Transfers electrons from succinate to Co Q. Form 1 consist of: - enzyme succinate dehydrogenase (FAD – prosthetic group) - iron-sulfur clusters. Succinate reduces FAD to FADH2. Then electrons pass to Fe-S proteins which reduce Q to QH2 Form 2 and 3 contains enzymes acyl-CoA dehydrogenase (oxidation of fatty acids) and glycerol phosphate dehydrogenase (oxidation of glycerol) which direct the transfer of electrons from acyl CoA to Fe-S proteins. Complex II does not contribute to proton gradient.
  19. 19. Complex III (ubiquinol-cytochrome c oxidoreductase) Transfers electrons from ubiquinol to cytochrome c. Consist of: cytochrome b, Fe-S clusters and cytochrome c1. Cytochromes – electron transferring proteins containing a heme prosthetic group (Fe2+ ⇔ Fe3+). Oxidation of one QH2 is accompanied by the translocation of 4 H+ across the inner mitochondrial membrane. Two H+ are from the matrix, two from QH2
  20. 20. Complex IV (cytochrome c oxidase) Transfers electrons from cytochrome c to O2. Composed of: cytochromes a and a3. Catalyzes a four-electron reduction of molecular oxygen (O2) to water (H2O): O2 + 4e- + 4H+ → 2H2O Translocates 2H+ into the intermembrane space
  21. 21. The Chemiosmotic Theory • Proposed by Peter Mitchell in the 1960’s (Nobel Prize, 1978) • Chemiosmotic theory: electron transport and ATP synthesis are coupled by a proton gradient across the inner mitochondrial membrane Mitchell’s postulates for chemiosmotic theory 1. Intact inner mitochondrial membrane is required 2. Electron transport through the ETC generates a proton gradient 3. ATP synthase catalyzes the phosphorylation of ADP in a reaction driven by movement of H+ across the inner membrane into the matrix
  22. 22. Active Transport of ATP, ADP and Pi Across the Inner Mitochondrial Membrane • ATP must be transported to the cytosol, and ADP and Pi must enter the matrix • ADP/ATP carrier, adenine nucleotide translocase, exchanges mitochondrial ATP4- for cytosolic ADP3• The exchange causes a net loss of -1 in the matrix (draws some energy from the H+ gradient) • Phosphate (H2PO4-) is transported into matrix in symport with H+. Phosphate carrier draws on ∆pH. • Both transporters consume proton-motive force
  23. 23. Respiratory control The most important factor in determining the rate of oxidative phosphorylation is the level of ADP. The regulation of the rate of oxidative phosphorylation by the ADP level is called respiratory control
  24. 24. REGULATION OF OXIDATIVE PHOSPHORYLATION Coupling of Electron Transport with ATP Synthesis Electron transport is tightly coupled to phosphorylation. ATP can not be synthesized by oxidative phosphorylation unless there is energy from electron transport. Electrons do not flow through the electron-transport chain to O2 unless ADP is phosphorylated to ATP. Important substrates: NADH, O2, ADP Intramitochondrial ratio ATP/ADP is a control mechanism High ratio inhibits oxidative phosphorylation as ATP allosterically binds to a subunit of Complex IV

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