Glycolysis

Step 1:A phosphate group is added to glucose in the cytoplasm of a cell by the enzyme hexokinase. During the process, glucose is given a phosphate group from ATP, resulting in glucose 6-phosphate, or G6P. This stage involves using up one ATP molecule.

Step 2: G6P is isomerized into fructose 6-phosphate (F6P) by the enzyme phosphoglucomutase. Isomers share the same molecular formula but have unique atomic configurations.

Two pyruvate molecules remain at the end of glycolysis and are still very rich in energy that can be extracted. Although no ATP is directly produced during pyruvate oxidation, it is the next step in the process that releases the residual energy in the form of ATP

Step 1. Pyruvate loses a carboxyl group, which is then released as a carbon dioxide molecule, leaving a two-carbon molecule in its place.
Step 2. The two-carbon molecule from step one is oxidized, and the electrons lost during the oxidation are
picked up by NAD+ to form NADH The two-carbon oxidised molecule, an acetyl group (is joined to Coenzyme A (CoA), an organic molecule derived from vitamin B5, to form acetyl (CoA). Acetyl is sometimes referred to as a carrier molecule, and its function in this instance is to transport the acetyl group to the citric acid cycle.

Citric Acid cycle

Step 2. As citrate is transformed into its isomer, isocitrate, one water molecule is lost and another is gained.

Step 3. Isocitrate is oxidised in step three, resulting in the formation of the five-carbon molecule -ketoglutarate, a CO2 molecule, and two electrons that reduce NAD+ to NADH. ADP has a positive impact on this step while ATP and NADH have a negative feedback loop that controls it.

The processes of steps three and four are oxidation and decarboxylation, which liberate electrons that convert NAD+ to NADH and carboxyl groups that produce CO2 molecules. Step three results in -ketoglutarate, and step four results in a succinyl group. CoA binds to the succinyl group, resulting in succinyl equivalent to ATP.

Step 5. A high-energy bond is created in step five by replacing coenzyme A with a phosphate group. This energy is utilised in substrate-level phosphorylation to produce either guanine triphosphate (GTP) or ATP during the succinyl group's conversion to succinate. Depending on the kind of animal tissue they are found in, the enzyme, also known as an isoenzyme, comes in two different forms for this step. One type is present in organs like the heart and skeletal muscle that use a lot of ATP. This type generates ATP. The liver is one of the tissues that contains a lot of anabolic pathways and therefore contains the second form of the enzyme. GTP is produced by this form. Energy-wise, ATP and GTP are equivalent.

Electron Transport chain

Oxidative phosphorylation includes the electron transport chain (ETC) and chemiosmosis. The outer mitochondrial membrane-bound proteins and organic molecules that make up the ETC are its constituent parts. Then, in a series of redox reactions, electrons move through these molecules and release energy. The energy released causes the proton gradient to form. The protein ATP-synthase uses this to produce significant amounts of ATP during chemiosmosis.

The Electron transport chain reactions: NADH +1/202+ADP+Pi ----- NAD++ ATP + H2O

As the initial electron donor, NADH is converted by enzyme complex I into NAD+ together with the release of a proton from the matrix The electron is therefore transferred to complex II, where it converts succinate to fumarate. In complex IV, molecular oxygen (O2) serves as an electron acceptor and transforms into a water molecule (H2O). Each enzyme complex transports electrons while releasing protons in the intermembranous space.

In the end, the electron transport chain converts one molecule of glucose into 32 molecules of ATP through hydrogen oxidation, and it also produces NAD and FAD that can be recycled during glycolysis.

Step 6: The dehydration process turns succinate into fumarate. Transferring two hydrogen atoms to FAD results in FADH2. Although these atoms' electrons have enough energy to reduce FAD, they lack the necessary energy to reduce NAD+. In contrast to NADH, this carrier stays affixed to the enzyme and delivers the electrons straight to the electron transport chain. The enzyme that acts as a catalyst this step is situated inside the inner membrane of the mitochondrion, which enables this process.

Step 7. Malate is created with the addition of water to fumarate . By oxidising malate, the citric acid cycle's final step regenerates oxaloacetate. During the process, an additional NADH molecule is created.

In the citric acid cycle, a six-carbon citrate molecule is created when an acetyl group from acetyl CoA is joined to a four-carbon oxaloacetate molecule. For every acetyl group added to the cycle, citrate undergoes a series of steps that result in the release of two carbon dioxide molecules. Three NAD+ molecules are converted to NADH, one FAD molecule to FADH2, and either ATP or GTP, depending on the type of cell, are produced during the process (by substrate-level phosphorylation). When there are enough reactants present, the citric acid cycle proceeds continuously because the first reactant and final product are one and the same.

One molccules of pyruvate prodcues 15 ATPs

Step 3:To create fructose 1,6-bisphosphate, or FBP, the enzyme phosphofructokinase transfers a phosphate group to fructose 6 phosphate (F6P) using an additional ATP molecule. So far, two ATP molecules have been used.

Step 4: Fructose 1,6-bisphosphate is broken down by the enzyme aldolase into two molecules: an aldehyde and a ketone. These two sugars, glyceraldehyde 3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP), are isomers of one another.
DHAP is quickly transformed into GAP in step 5 by the enzyme triose-phosphate isomerase (these isomers can inter-convert). The glycolysis process requires GAP as a substrate.

Step 6: In this reaction, the enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH) performs two jobs. By transferring one of the hydrogen (H+) molecules from GAP to the oxidising compound nicotinamide adenine dinucleotide (NAD+), it first dehydrogenates GAP, resulting in NADH + H+.

The oxidised GAP is then combined by GAPDH with a phosphate from the cytosol to create 1,3-bisphosphoglycerate (BPG). This process of dehydrogenation and phosphorylation takes place on both of the GAP molecules created in the preceding phase.