Chemiosmotic Hypothesis | Science for ACT PDF Download

OXIDATIVE PHOSPHORYLATION

Chemiosmotic theory / Coupling theory :

• During ETC of respiration CoQ & FMN can releases H+ ions in perimitochondrial space and leads to differenctial H⁺ ion concetration across inner mitochondrial membrane. This differential H+ ion concentration across inner mitochondrial membrane leads to creation of proton gradiant (PH gradient) and Electrical potential (diffrence of charge). Both are collectively known as Proton motive force (PMF).

• PMF do not allow stay of H⁺ ions in Peri mitochondrial space (PMS) so they return towards the matrix through F0 particles selectively.

• The passage of 3H⁺ ions activate ATP synthase and gives rise to 1ATP from ADP & Pi.

• Some physiologist believe that passage of 2H⁺ ions through F0 particle or coupling factor or proton channel leads to synthesis of 1 ATP.

Bioenergetics of respiration – (1 mol. of glucose)

EMP-Pathway

(i) ATP formed at substrate level phosphorylation ⇒ 4.ATP

(ii) ATP produced via ETS (2NADH₂) ⇒ 6 ATP

(iii) ATP consumed in glycolysis ⇒ 2 ATP

10 ATP – 2 ATP = 8 ATP

Gross – Expenditure = Net or Total gain

Direct Gain = 2 ATP

(2) Link reaction or Gateway reaction –

2NADH₂ = 6 ATP (via ETS)

Kreb's Cycle – (i) ATP produced at substrate level phosphorylation = 2 GTP/2ATP

• 1 Sucrose = 80 ATP

•  1 Fructose 1,6–Bisphosphate = 40 ATP

•  1 Pyurvic acid = 15 ATP

•  1 Acetyl Co-A or 1 TCA cycle = 12 ATP

• PPP is also called as Warburg - Dickens pathway/HMP shunt/Phosphogluconolactone pathway/ Carbohydrate degradation without mitochondria/Cytosolic oxidative decarboxylation/Horecker -Racker Pathway

• Glycolysis & TCA cycle is the main route of carbohydrate oxidation, but Warburg & Dickens (1935) discovered an alternative route of carbohydrate break down, existing in plants, some animal tissues (Mammary glands, adipose, liver & microbes).

• HMP/PPP occurs when

(i) NADPH₂ requirement of cell increases during biosynthetic processes.

(ii) When EMP pathway blocked by iodoacetate, fluorides, arsenates.

(iii) When mitochondria is busy in other pathways.

• Most of the intermediates are similar to Calvin cycle, but PPP is amphibolic and oxidative process.

• One ATP is utilised in phosphorylation of glucose, so net gain equals to 35 ATP. (12 NADPH2) Significance of HMP shunt :-

(1) An intermediate erythrose-P (4C) of this pathway is precursor of shikimic acid, which goes to synthesis of aromatic compounds and amino acids.

(2) This cycle provides pentose sugars Ribose-p for synthesis of nucleotides, nucleosides, ATP and GTP.

(3) A five carbon intermediate Ribulose-5-phosphate may used as CO₂ acceptor in green cells.

(4) This pathway produces reducing power NADPH2 for the various biosynthetic pathways, other than photosynthesis like fats synthesis, starch synthesis, hormone synthesis and chlorophyll synthesis.

(5) Intermediates like PGAL and fructose-6-phosphate of this pathway may link with glycolytic reactions. b-Oxidation of Fatty acids

• b-oxidation takes place mainly in perimitochondrial space but also in glyoxisome, peroxisome, cytosol.

• Liberation of 2C segments from the fatty acid mol. in the form of acetyl Co-A is known as b-oxidation. These acetyl-CoA provides ATP after oxidation in krebs cycle.

• Acetyl CoA is oxidised in TCA cycle to CO₂ & H₂O with the production of 12 ATP molecules.

Glyoxylate Cycle

• Discovered by Kornberg & Krebs,during germination of fatty seeds.

• This cycle converts fats into sugars so it is an example of gluconeogenesis in plants.

• Glyoxylate cycle occurs in glyoxysomes, cytosol, & mitochondria.