Answer the following questions

Plant Physiology (Functional Organisation)

Respiration

6. What are enzymes involved in phosphorylation and dephosphorylation reactions in EMP pathway?

i) Enzymes involved in phosphorylation are

a) Hexokinase and phosphofructio kinase.

(ii) Enzymes involved in dephosphorylation are

a) Phosphoglycerate Kinase

b) Pyruvate Kinase

7. Respiratory quotient is zero in succulent plants. Why?

Respiratory quotient is zero in succulent plants like opuntia, Bryophyllum carbohydrate are partially oxidised to organic to acid, particularyl malic acid without corresponding release of CO₂ but O₂ is consumed hence the RQ value will be zero

2C₆H₁₂O₆ [Glucose] + 3O₂ → 3C₄H₆O₅ [Malic acid] + 3H₂O + Energy

R.Q. of glucose in succulents = [ Zero molecule of CO₂ ] / [ 3 molecules of O₂ ]

= O (zero) 

8. Explain the reactions taking place in mitochondrial inner membrane.

Electron and hydrogen (proton) transport takes place across four multiprotein complexes (I-IV). They are.

1. Complex-I (NADH dehydrogenase).

It contains a flavoprotein (FMN) and associated with non-heme iron Sulphur protein (Fe-S). This complex is responsible for passing electrons and protons from mitochondrial NADH (Internal) to Ubiquinone (UQ).

NADH + H⁺ + UQ ↔  NAD⁺ + UQH₂

2. In plants, an additional NADH dehydrogenase (External) complex is present on the outer surface of inner membrane of mitochondria which can oxidise cytosolic NADH + H^+.

Ubiquinone (UQ) or Coenzyme Quinone (Co Q) is a small, lipid soluble electron, proton carrier located within the inner membrane of mitochondria).

3. Complex-II (succinic dehydrogenase) It contains FAD flavoprotein is associated with non-heme iron Sulphur (Fe-S) protein. This complex receives electrons and protons from succinate in Kerbs cycle and is converted into fumarate and passes to ubiquinone.

Succinate + UQ → Fumarate + UQH₂

4. Complex-III (Cytochrome bc₁ complex) This complex oxidises reduced ubiquinone (ubiquinol) and transfers the electrons through Cytochrome bc₁ Complex (Iron Sulphur center bc1 complex) to cytochrome c.

UQH₂ + 2Cyt c _oxidized

                 _↑↓

UQ + 2Cyt c_reduced + 2H⁺

5. Complex IV (Cytochrome c oxidase) Complex IV is the terminal oxidase and brings about the reduction of 1/2 O₂ to H₂O. Two protons are needed to form a molecule of H₂O (terminal oxidation).

2Cyt c_oxidized + 2H⁺ + 1/2 O₂

                       _↑↓

2Cyt c_reduced + H₂O

9. What is the name of alternate way of glucose breakdown? Explain the process involved in it?

• Pentose phosphate pathway is the alternate pathway for breakdown of glucose.

• Pentose phosphate pathway was described by warburg, Dickens and Lipmann (1938).

• It is also known as Hexose mono phosphate shunt (HMP shunt) or Direct oxidative phase and non - oxidative phase.

• The oxidative phase convert six molecules of six carbon Glucose 6 phosphate to 6 molecules of five carbon sugar Ribulose - 5 Phosphate with loss of 6CO₂ and generation of 12 NADPH + H⁺

• Non oxidative pathway convert Ribulose - 5 - phosphate molecules to various intermediates such as

Ribose - 5 - phosphate (5C)

Xylulose - 5 - phosphate (5C)

Glyceraldehyde - 3 - phosphate (3C)

Sedoheptulose - 7 - phosphate (7C) and

Erythrose – 4 – phosphate (4C)

• Finally five molecules of glucose 6 -phosphate is regenerated

6 x Glucose - 6 - phosphate + 12NADP⁺ + 6H₂O

                               ↓

5 x glucose - 6 - phosphate + 6CO₂ + Pi + 12 NADPH + 2H⁺

The net result of complete oxidation of one glucose - 6 - phosphate yield 6CO₂ and 12 NADPH + H⁺. The oxidative pentose phosphate pathway is controlled by glucose - 6 - phosphate dehydrogenase enzyme which is inhibited by high ratio of NADPH to NADP+.

10. How will you calculate net products of one sucrose molecule upon complete oxidation during aerobic respiration as per recent view?

Sucrose is dissacharide it will convert into glucose and fructose. In glycolysis both will give glyceraldehyde - 3 phosphate that undergo further process of respiration to yield 36 ATPS. So Net products of one sucrose molecule during aerobic respiration will yield 72 ATP.