GLYCEROL-PHOSPHATE SHUTTLE SYSTEM - Respiration in plants, Biology, Class 11
GLYCEROL-PHOSPHATE SHUTTLE SYSTEM
In prokaryotes, shuttle mechanism is absent. They always get 38 ATP from aerobic respiration of 1 glucose mol.
Cyanide inhibits the activity of cytochrome oxidase & inhibits the oxidation of cyto-a3.
In mitochondria, of some plants alternative oxidase system is present, in which ETS continues even in presence of cyanides. This type of respiration is known as cyanide resistance respiration or Alternate electron pathway. Ex. Spinacea, Pisum.
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 donot allow stay of H+ ions in Perimitochondrial space (PMS) so they return towards the matrix through F0 particales selectively.
The passage of 3H+ ions activate ATP synthase and gives rise to 1ATP from ADP & Pi.
Some physiologist beleive 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)
(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)
(3) 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
Pentose phosphate pathway (PPP) / HMP (Hexose mono phosphate) Shunt / Warburg-Dickens pathways
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 kreb cycle.
Acetyl CoA is oxidised in TCA cycle to CO2 & H2O with the production of 12 ATPmolecules.
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 glyoxisome, cytosol, & mitochondria.
Cruick Shank & Pasteur (1898).
Fermentation is much similar to anaerobic respiration, but this is an extracellular process & substrate is present outside the cell. Energy released as heat, no ATP generated.
Buchner discovered the enzyme zymase complex, which is responsible for alcoholic fermentation.
Types of Fermentation :-
(i) When the one type of product formed in fermentation then it is called homofermentation.
(ii) When the products of fermentation process are more than one type, then process is heterofermentation.
(1) Alcoholic fermentation :-This is the oldest & the best known type of fermentation performed by yeast & some bacteria.
(2) Lactic acid fermentation :-It occurs during curd formation.
(3) Acetic acid fermentation This is aerobic fermentation
(4) Butyric acid fermentation :-In rancid butter, butyric acid fermentation takes place. Also in jute fiber.
Other eg. are curring of tea, tanning of leather, retting of fibers, processing of Tobacco
Respiratory quotient (R.Q.)
The ratio of the volume of CO2 released to the volume of O2 taken in respiration is called R.Q.
Value of R.Q. depends upon the type of respiratory substrate used & measured by Ganong's respirometer.
(1) Carbohydrates :- R.Q. = 1
Fatty seeds germination-castor, R.Q. < 1
At the time of formation of fatty seeds, (maturing fatty seed) R.Q. is more than 1 because more CO2 is released than O2 consumed.
(3) Organic acids :- (In succulent xerophytes at day time)
(4) Incomplete oxidation of carbohydrates :-In CAM plants during night :-R.Q. = 0
2C6H12O6+ 3O2 → 3C4H6O5 + 3H2O + Energy
(5) Protein :- R.Q. = 0.8 or 0.9 or < 1
(6) Anaerobic respiration :- RQ = ∝