TCA Cycle and Electron Transport System

TCA Cycle includes redox, dehydration, hydration, and decarboxylation reactions. The waste product, carbon dioxide, as well as other sets of reactants necessary to restart the original reaction, are also produced. Energy from the chemical bonds of glucose is stored in a variety of energy carrier molecules at the end of the TCA Cycle: four ATPs, two FADH 2 molecules, and ten NADH molecules. The electron transport chain is responsible for transferring energy from electron carriers to more ATP molecules, which serve as “batteries” for the cell’s function.

Steps of TCA Cycle

The TCA cycle is an eight-step closed-loop sequence of reactions

• The two-carbon acetyl CoA is joined with a four-carbon oxaloacetic acid and hydrolysed to form citric acid or citrate, a six-carbon molecule

• Citrate is then restructured into isocitrate, a six-carbon isomer of citrate, by dehydrating and then hydrating it

• When isocitrate is oxidised, it undergoes decarboxylation, which releases a carbon dioxide molecule. The coenzyme NAD+ is reduced to NADH, a different dinucleotide. The five-carbon molecule -ketoglutarate is formed when the carbon molecule is removed

• Another carbon molecule is released when the -ketoglutarate molecule is oxidised and NAD+ is reduced to generate NADH. The unstable succinyl CoA chemical is formed when the four-carbon molecule generated interacts with Coenzyme A

• The Coenzyme A in succinyl CoA is replaced by a phosphate group, which is subsequently transferred to ADP (adenosine diphosphate) to produce ATP. In some organisms, the phosphate groups are transferred from GDP (guanosine diphosphate) to GTP (guanosine triphosphate). Succinate is the four-carbon molecule that remains

The TCA cycle’s final steps regenerate oxaloacetic acid from succinate

• Succinate is oxidised to produce fumarate, a four-carbon compound. By transferring two hydrogen atoms, the electron carrier FAD (flavin adenine dinucleotide) is reduced to FADH2.

• With the addition of a water molecule, fumarate is transformed to malate, a four-carbon molecule

• The initial reactant, oxaloacetic acid, is regenerated when malate is oxidised. By transferring one hydrogen atom, the coenzyme NAD (nicotinamide adenine dinucleotide) is reduced to NADH

The TCA Cycle’s Products and Functions

• In TCA cycle two molecules of carbon are created per cycle, along with three molecules of NADH, one molecule of FADH2, and one molecule of ATP or GTP. Each glucose molecule generates two acetyl CoA molecules, enough for two cycles. The per-glucose yield can be calculated by multiplying these products by two. Though only one ATP (or GTP) is directly created per cycle, the products NADH and FADH2 can make ATP (or GTP) in a subsequent cellular respiration process termed oxidative phosphorylation

• The Krebs cycle’s primary job is to produce energy, which is then stored and delivered as ATP or GTP. Other biosynthetic reactions rely on the cycle to produce intermediates that are needed to make other compounds including amino acids, nucleotide bases, and cholesterol. All cells that utilise oxygen have the Krebs cycle. The Krebs cycle, when combined with the process of oxidative phosphorylation, produces the majority of the energy utilised by aerobic cells, with a percentage of energy provided for humans exceeding 95%

ATP for Life in the Fast Lane: The Electron Transport Chain

• In stage 3 of aerobic respiration, the pathways for producing ATP are quite similar to the electron transport networks employed in photosynthesis. In both electron transport chains, energy carrier molecules are positioned in succession within a membrane so that energy-carrying electrons cascade from one to the other, losing a little energy in the process

• The energy lost during photosynthesis and aerobic respiration is used to push hydrogen ions into a compartment, resulting in an electrochemical or chemiosmotic gradient across the surrounding membrane. The energy stored in the chemiosmotic gradient is utilised by ATP synthase to produce ATP in both processes

• The electron transport chain, also known as the “respiratory chain,” is embedded in the inner membrane of the mitochondria for aerobic respiration. The high-energy electrons are donated to energy carrier molecules within the membrane by the FADH 2 and NADH molecules created during glycolysis and the Krebs Cycle. The energy they lose as they move from one carrier to another is used to drive hydrogen ions into the mitochondrial intermembrane gap, resulting in an electrochemical gradient

• The ion channel/enzyme ATP synthase transforms hydrogen ions’ energy to ATP as they flow “down” the gradient, from the outer to the inner compartment. It’s worth noting that creating and maintaining a concentration gradient of hydrogen ions, which is later utilised by ATP synthase to create stored energy, needs energy (ATP)

• To put it another way, it requires energy to create energy. Chemiosmosis, first established by Nobel laureate Peter D. Mitchell, connects the electron transport chain to ATP production via a hydrogen ion gradient. Oxidative phosphorylation refers to the process of using energy to phosphorylate ADP to create ATP

• Low-energy electrons and low-energy hydrogen ions combine with oxygen to produce water after travelling through the electron transport chain. By accepting “spent” hydrogens, oxygen drives the whole set of ATP-producing processes within the mitochondrion. Because oxygen is the final electron acceptor, no portion of the process can take place without it, from the Krebs Cycle to the electron transport chain

• One glucose molecule’s worth of FADH2 and NADH + H+ can be converted into as much as 34 ATP through the electron transport chain. The sum of 38 ATP fits the overall equation for aerobic cellular respiration when the four ATP produced in glycolysis and the Krebs Cycle are combined together:

6O2 + C6H12O6 (stored chemical energy) + 38ADP + 39 Pi -> 38ATP (stored chemical energy) + 6CO2 + 6H2O

Conclusion

Cellular respiration transfers energy from one molecule of glucose to 38 molecules of ATP when oxygen is present, releasing carbon dioxide and water as waste. Food energy that is “deliverable” has evolved into energy that may be used for work within the cell, such as intracellular transport, ion and molecule pumping across membranes, and the construction of big organic molecules.