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Biochemistry

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Carbohydrates

Question
19 out of 40
 

ADP to ATP transfer in mitrochondria is affected by (AIIMS Nov 2010)



A Atracyclocide
B Oligomycine

C Antimycine
D Rotenone

Ans. A Atractyloside (Ref: Harper, 28th edition, Chapter 13, Respiratory chain…. )

Many Poisons Inhibit the Respiratory Chain

a. Much information about the respiratory chain has been obtained by the use of inhibitors, and, conversely, this has provided knowledge about the mechanism of action of several poisons. They may be classified as inhibitors of the respiratory chain, inhibitors of oxidative phosphorylation, and uncouplers of oxidative phosphorylation.

b. Barbituratessuch as amobarbital inhibit electron transport via Complex I by blocking the transfer from Fe-S to Q. At sufficient dosage, they are fatal in vivo. Antimycin A and dimercaprolinhibit the respiratory chain at Complex III.

c. The classic poisons H2S, carbon monoxide, and cyanide inhibit Complex IV and can therefore totally arrest respiration. Malonate is a competitive inhibitor of Complex II.

d. Atractylosideinhibits oxidative phosphorylation by inhibiting the transporter of ADP into and ATP out of the mitochondrion. By inhebetiny ADP ATP Translocase.

e. Uncouplers dissociate oxidation in the respiratory chain from phosphorylation. These compounds are toxic in vivo, causing respiration to become uncontrolled, since the rate is no longer limited by the concentration of ADP or Pi.

f. The uncoupler that has been used most frequently is 2,4-dinitrophenol, but other compounds act in a similar manner.

g. Thermogenin (or the uncoupling protein) is a physiological uncoupler found in brown adipose tissue that functions to generate body heat, particularly for the newborn and during hibernation in animals.

h. The antibiotic oligomycin completely blocks oxidation and phosphorylation by blocking the flow of protons through ATP synthase.

  1. Non-shivering thermogenesis: The mitochondria found in brown adipose tissue contain a unique uncoupling protein called thermogenin, which allows the controlled entry of protons without ATP sythesis in order to generate heat.
  2. The protein is a 33kd dimer, structurally related to the adenine nucleotide porter. It is inhibited by GTP, and activation is controlled by the sympathetic nervous system.
  3. This process is particularly important in new-born babies, which can lose heat very rapidly to their surroundings, but also occurs in adults and in hibernating animals.
  4. In contrast to the more familiar white adipose tissue, brown fat has an excellent capillary blood supply and can achieve very high metabolic rates.
  5. The major depot in humans is behind the shoulder blades, with other patches along the spine. The brown colour arises from the respiratory enzymes. Thermahene is manual uncoupler.
  6. Is MakReference: University of Leeds, Faculty of Biological Sciences, UK

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