Chee Cheong Fun: What happen inside my tummy after I......

In the previous post, it is mentioned that a plain flavor Chee Cheong Fun without any filling and sauces provides higher amount of carbohydrates compared to other nutrients. So how does carbohydrate metabolism happens in the human body? That, amigo, is our discussion today.

In carbohydrate metabolism, the essential processes include Glycolysis, Tricarboxylic Acid Cycle (TCA) and Electron Transport Chain (ETC). These three are core processes that assist to generate energy (eg. ATP) in homo-sapient a.k.a human body.

Glycolysis

[Adapted from Kirchner 2001]

Glycolysis, also known as Emden-Meyerhof pathway, catalyzes the oxidation of glucose or glycogen to pyruvate and lactate thus, produced energy. This process occurs in cell named cytosol. It provides intermediates for other metabolic pathway in the human body to generate energy. Two crucial types of product can be formed from this process. The first being acetyl CoA (converted from pyruvate) through the aerobic glycolysis that is the major substrate for TCA cycle. The other type of product is lactate that formed by anaerobic glycolysis. Glycolysis can be regulated in many ways such as availability of substrate, concentration of enzymes (hexokinase, phosphofructokinase, pyruvate kinase) that is responsible for rate limiting steps, allosteric regulation of enzymes, covalent modification of enzymes and hormonal regulation. At the end of glycolysis, a major 8 ATP will be produced from aerobic glycolysis and 2 ATP from anaerobic glycolysis.

TCA/ Kreb’s Cycle

[Adapted from Ritter and Genzel 2002]

The TCA Cycle or citric acid cycle occurs entirely in the cell mitochondria. It is considered as a traffic cycle, not a closed cycle as this process involve leaving and entering of compounds. Unlike glycolysis, this cycle provides the building blocks for the synthesis of amino acids and heme. Besides, this cycle happens twice for each glucose molecule transferred from glycolysis. There are two pyruvate molecules generated for each glycolysis that occurred. These pyruvates must be transferred into the matrix of mitochondria through specific pyruvate transporter before entering the cycle as Acetyl-CoA. In the end, a total of 12 ATP will be generated from this cycle. On the other hand, the regulation of this process can be done by activate and inhibit the enzyme activities (pyruvate dehydrogenase complex, citrate synthase, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase complex) as well as making the availability of ADP to generate more energy.

ETC

[Adapted from Lloyd 2004]

In the ETC process, the NADH and FADH2 formed during the glycolysis and TCA cycle will be used to generate energy. ETC takes place in the inner membrane of the cell mitochondria in which each energy-rich reduced coenzymes (NADH and FADH2) donates a pair of electron to a specialized set of electron carriers. As the electrons passed down the ETC, they lose their free energy and parts of the energy will be captured and stored to form ATP.

That's all for today, folks. Did I just bored you?