Q.1. What is oxidation?
Ans. Oxidation is defined as the addition of O2 or removal of hydrogens or removal of electrons.
Q.2. What is meant by reduction?
Ans. Reduction is defined as the gain of electrons or addition of hydrogen atoms.
Q.3. What is the biomedical importance of Biologic oxidation?
Ans.
- To synthesize ATP molecules.
- As metabolic needs: If phenylalanine has to be metabolized in body, it has to be oxidized to Tyrosine which is needed for synthesis of thyroid hormones, catecholamines, melanin, etc.
- Molecular oxygen is incorporated into oxygenases.Many drugs, pollutants and chemical carcinogens are metabolized by enzymes of this class called as cytochrome P450 system.
Q.4. What are dehydrogenases?
Ans. Enzymes that remove hydrogens from a substrate are called dehydrogenases.
Q.5. What are the types of dehydrogenases?
Ans. Two types:
- Aerobic dehydrogenases
- Anaerobic dehydrogenases
Q.6. What are oxidases?
Ans. Oxidases are enzymes that catalyze removal of hydrogen and electrons from a substrate by directly using molecular O2 as acceptor.
Q.7. What are Hydroperoxidases? What is the clinical importance?
Ans. Hydroperoxidases are enzymes which decompose H2O2 to H2O and oxygen.
- Clinical importance:
Peroxides (H2O2) are harmful to body. Accumulation of peroxides lead to the generation of “free radicals” which can damage the biomembranes. Thus hydroperoxidases protect the body from harmful effects of H2O2.
Q.8. What are the types of hydroperoxidases?
Ans. They are mainly two:
- Catalase
- Peroxidases e.g. glutathione peroxidase.
Q.9. What are oxygenases?
Ans. Oxygenases are enzymes that catalyze the incorporation of O2 into a substrate molecule.
Q.10. What are the types of oxygenases?
Ans. They are mainly 2 types:
- Mono-oxygenases
- Di-oxygenases
Q.11. State the structure of ATP synthase.
Ans. The enzyme ATP synthase consists of:
- Headpiece with several polypeptides
- A Stalk which is attached to 8 peptides of headpiece.
- A Base piece made up of proteolipid.
Q.12. Explain the functions of different parts.
Ans.
- The stalk serves as the proton channel.
- The head piece protein assembly is called F1 unit which protrudes from the inner surface of the plasma membrane. F1 is considered to be α3 β3 γδ ε.
- The base piece consists of transmembrane integrae protein called F0 unit. It is thought to be α1 β2 l10 – 12.
- The F1 unit functions as an ATPase. F1 unit when bound to F0 serves as proton translocating ATP synthase and catalyses phosphorylation of ADP to ATP using the energy from the down gradient proton flow through the proton channel of F0.
Q.13. State the inhibitors of oxidative phosphorylation. How do they act?
Ans. Inhibitors of oxidative phosphorylation are:
- Oligomycin: Prevents stimulation of O2 uptake by ADP and phosphorylation of ADP → ATP
- Atractyloside: A toxic glycoside, it blocks the translocase that is responsible for the movement of ADP and ATP across the inner mitochondrial membrane.
- Bongregate: A toxin produced by pseudomonads. Acts similar to atractyloside.
Q.14. What are uncouplers?
Ans. Uncouplers are substances that uncouple oxidative phosphorylation in the respiratory chain (ETC). They prevent the formation of ATP but permits biologic oxidation to proceed resulting in generation of heat.
Q.15. State the uncouplers of oxidative phosphorylation.
Ans. The uncouplers of oxidative phosphorylation are:
- 2:4 Dinitrophenol (DNP)
- Dicoumarol (Vitamin K analogue)
- Calcium: Transport of calcium into mitochondria can cause uncoupling
- CCCP (Chloro carbonyl cyanide phenyl hydrazone): most active uncoupler
- Valinomycin: Produced by a type of streptomyces.
Transports K+ from the cytosol into matrix and H+ from matrix to cytosol thereby decreasing the proton gradient.
Q.16. What do you know of chemiosmotic hypothesis proposed by Mitchell?
Ans. Mitchell’s hypothesis proposes that biologic oxidation in the respiratory chain (ETC) generates protons (H+) which are ejected to the outside of inner mitochondrial membrane of the mitochondrion. The electrochemical potential difference resulting from the asymmetric distribution of the H+ is used to drive the mechanism for the formation of ATP.
Q.17. Name the antibiotic which completely blocks the biologic oxidation and phosphorylation in intact mitochondrion.
Ans. Oligomycin.
Q.18. Name the antibiotics responsible for K+ penetration through the mitochondrial membrane.
Ans.
- Valinomycin
- Nigericin
Q.19. What are the functions of complex I?
Ans.
- Acts as a proton pump
- Catalyzes transfer of two electrons from NADH + H+ to CoQ via FMN and FeS clusters.
- Permits one ATP formation (site I)
Q.20. What are the functions of complex II.
Ans.
- Flow of electrons from succinate to CoQ via FAD.H2.
- Cannot act as a proton pump.
- Cannot form ATP.
Q.21. What are the functions of complex III?
Ans.
- Acts as a proton pump.
- Catalyzes transfer of electrons only from CoQ .H2 to cytochrome C via cyt.b and cyt.c1.
- Can form one ATP (site II)
Q.22. What are the functions of complex IV?
Ans.
- Acts as a proton pump.
- Catalyzes transfer of electrons only from cyt.c to molecular O2 via cyt.a, Cu++ ions and a3 to form H2O. It is the terminal component of ETC.
- Flow of electrons is as follows:
Cyt.c → Cyt.a → Cu++ → Cyta3 → O2
- Can form one ATP (site III).
Q.23. What is the role of iron-sulphur protein (FeS; non-heme iron)?
Ans. FeS is associated with the flavo-proteins and with cytochrome b. The sulphur and Fe are thought to take part in the oxidation-reduction mechanism between flavin and CoQ.
Q.24. What is CoQ?
Ans.
- CoQ is also known as ubiquinone as it is ubiquitous in nature.
- It exists in mitochondria in the oxidized quinone form under aerobic conditions and in the reduced quinol form under anaerobic conditions.
- The structure of CoQ is very similar to vitamin K and vitamin E.
- It is a mobile lipid component of the ETC, it collects reducing equivalents from the more fixed flavoprotein complexes and passes the electrons only to the cytochromes.
Q.25. How the reducing equivalents are passed in ETC?
Ans. From NAD+ system to CoQ both hydrogen and electrons are passed. Beyond CoQ, it is electrons which are transferred through various cytochromes to molecular O2 and H+ goes to the media.