Tag: biological oxidation

$C _4$ cycle or the Hatch-Slack pathway is a photosynthetic process in some plants. It is the first step in extracting carbon from carbon dioxide to be able to use it in sugar and other biomolecules. $C _4$ plants do not undergo phosphorylation due to their special mechanism to increase the $CO _2$ level for enzyme binding.

Co-enzymes are organic compounds, are bound to the the enzyme to make the enzyme catalytically active, but their association with the enzyme is only transient, usually occurring during the course of catalysis. Co-enzymes serve as co-factors in a number of different enzyme catalyzed reactions. The essential chemical components of many coenzymes are vitamins, e.g., coenzyme nicotinamide adenine dinucleotide (NAD) and NADP contain the vitamin niacin; flavin adenine dinucleotide (FAD) is derived from riboflavin vitamin.

Oxidative phosphorylation is an ATP generating process, which takes place in the inner membrane of mitochondria of aerobic organisms. In a generic sense, this process generates ATP via transferring electrons from $FADH _2$ or NADH via a series of complex carriers. Oxygen is a vital constituent of this process for its role as the final electron acceptor. Therefore, oxidative phosphorylation cannot take place in absence of oxygen. Hence, the correct answer is (D).

The metabolic process of releasing energy from food can be termed as oxidative phosphorylation. It occurs in the mitochondria of eukaryotic cell. In this process, the electrons are transported through different carriers ultimately to the oxygen molecule. these electrons reduce oxygen to form water and release energy which converts ADP to ATP. 

NAD$^+$ accepts electrons/H$^+$ released by water.

In chloroplast, the space enclosed by the inner membrane is called the stroma. It is colorless and homogeneous fluid. Phosphorylation is the process of addition of a phosphate group to ADP. The process of non-cyclic photophosphorylation takes place in the stroma lamellae with the help of enzymes present in it. Thus, the correct answer is option C. 

• Oxidative phosphorylation refers to the process by which ATP molecules (energy currency) are produced in the mitochondria.
  
• ATP is produced by the transfer of electrons from NADH or FADH2 to oxygen molecule with the help of electron carriers.
  
• Oxysomes or F0-F1 particles refers to small round structures present within the folds of the cristae of the inner mitochondrial membrane.
  
• F0 and F1 particles are found in the inner mitochondrial region and are attached to the cristae and help in ATP production and oxidation.
  

The respiratory breakdown of glucose in the presence of oxygen is an oxidative process. During this process, several intermediates such as pyruvic acid, isocitric acid, succinic acid and oxalic acid are oxidized. Each oxidation step involves the release of 2 H which goes to reduce various coenzymes i.e. NAD+ and FAD. Reduced NAD+ and FAD released in the glycolysis and Krebs cycle finally reduce oxygen to water. This transfer of H+ and e- from NADH + H+ or FADH2 to oxygen is not a simple process and the direct transfer of electrons from coenzymes to oxygen is thermodynamically not possible. To facilitate this transfer, many intermediate cytochromes and other carriers are arranged in a series which transport electrons from NADH or FADH2 to oxygen. This sequence of electron carriers constitutes electron transport system. The electron transport proceeds from carriers that have low redox potential to those having high redox potential. The electron transport down to the energy gradient through electron transport system leads to the formation of ATP from ADP and inorganic phosphate. This generation of ATP is called oxidative phosphorylation.