Sabtu, 12 Maret 2011

How does the Energy Is Produced

Have you ever fell tired? What did you think on that condition? It is caused by our energy decreased. Do you know how the energy produced does? The energy is the result of decomposition of food, such as carbohydrate, protein, and fat. Food will be processed on 3 kinds of process called glycolisis, Krebs’s cycle, and electron transfer. (Before we explain about it, we would like to take carbohydrate for sample)

First, carbohydrate is damaged by our teeth and our enzyme. The enzyme not only destroys the form of carbohydrate, but also changes the chemical compound of carbohydrate to be simple such as glucose. After that, the carbohydrate is absorb into the intestine, and circularized by our blood.

Secondly, after the glucose entered to the cell, the glycolysis process is start. Glycolysis is the metabolic pathway that converts glucose, C6H12O6, into pyruvate, C3H6O3-. The free energy released in this process is used to form the high energy compounds, ATP (adenosine triphosphate) and NADH (reduced nicotinamide adenine dinucleotide). The sequence of glycolysis divided into 2 phase. They are preparatory phase and pay – off phase.

In preparatory phase there are 5 steps and in the pay off phase there 5 steps too.

Preparatory phase

1. The first step in glycolysis is phosphorylation of glucose by a family of enzymes called hexokinases to form glucose 6-phosphate (G6P). This reaction consumes ATP, but it acts to keep the glucose concentration low, promoting continuous transport of glucose into the cell through the plasma membrane transporters

2. G6P is then rearranged into fructose 6-phosphate (F6P) by glucose phosphate isomerase. Fructose can also enter the glycolytic pathway by phosphorylation at this point.The change in structure is an isomerization, in which the G6P has been converted to F6P. The reaction requires an enzyme, phosphohexose isomerase, to proceed. This reaction is freely reversible under normal cell conditions

3. The energy expenditure of another ATP in this step is justified in 2 ways: The glycolytic process (up to this step) is now irreversible, and the energy supplied destabilizes the molecule. Because the reaction catalyzed by Phosphofructokinase 1 (PFK-1) is energetically very favorable, it is essentially irreversible, and a different pathway must be used to do the reverse conversion during gluconeogenesis

4. Destabilizing the molecule in the previous reaction allows the hexose ring to be split by aldolase into two triose sugars, dihydroxyacetone phosphate, a ketone, and glyceraldehyde 3-phosphate, an aldehyde.

5. Triosephosphate isomerase rapidly interconverts dihydroxyacetone phosphate with glyceraldehyde 3-phosphate (GADP) that proceeds further into glycolysis. This is advantageous, as it directs dihydroxyacetone phosphate down the same pathway as glyceraldehyde 3-phosphate, simplifying regulation.

Pay – off Phase

1. The triose sugars are dehydrogenated and inorganic phosphate is added to them, forming 1,3-bisphosphoglycerate.The hydrogen is used to reduce two molecules of NAD+, a hydrogen carrier, to give NADH + H+ for each triose. Hydrogen atom balance and charge balance are both maintained because the phosphate (Pi) group actually exists in the form of a hydrogen phosphate anion (HPO42-)which issociates to contribute the extra H+ ion and gives a net charge of -3 on both sides.

2. This step is the enzymatic transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP by phosphoglycerate kinase, forming ATP and 3-phosphoglycerate. At this step, glycolysis has reached the break-even point: 2 molecules of ATP were consumed, and 2 new molecules have now been synthesized. This step, one of the two substrate-level phosphorylation steps, requires ADP; thus, when the cell has plenty of ATP (and little ADP), this reaction does not occur. Because ATP decays relatively quickly when it is not metabolized, this is an important regulatory point in the glycolytic pathway.

3. Phosphoglycerate mutase now forms 2-phosphoglycerate. Notice that this enzyme is a mutase and not an isomerase. Whereas an isomerase changes the oxidation state of the carbons of the compound, a mutase does not.

4. Enolase next forms phosphoenolpyruvate from 2-phosphoglycerate.

5. A final substrate-level phosphorylation now forms a molecule of pyruvate and a molecule of ATP by means of the enzyme pyruvate kinase. This serves as an additional regulatory step, similar to the phosphoglycerate kinase step.

So, from this process our body gets 2 molecule of ATP and 2 molecule of NADH.

Thirdly, the pyruvate acid (the simple form of glucose) entered into Krebs’s cycle.

Krebs’s cycle is a series of enzyme-catalysed chemical reactions of central importance in all living cells that use oxygen as part of cellular respiration.

  • The citric acid cycle begins with acetyl-CoA transferring its two-carbon acetyl group to the four-carbon acceptor compound (oxaloacetate) to form a six-carbon compound (citrate).
  • The citrate then goes through a series of chemical transformations, losing two carboxyl groups as CO2. The carbons lost as CO2 originate from what was oxaloacetate, not directly from acetyl-CoA. The carbons donated by acetyl-CoA become part of the oxaloacetate carbon backbone after the first turn of the citric acid cycle. Loss of the acetyl-CoA-donated carbons as CO2 requires several turns of the citric acid cycle. However, because of the role of the citric acid cycle in anabolism, they may not be lost since many TCA cycle intermediates are also used as precursors for the biosynthesis of other molecules.
  • Most of the energy made available by the oxidative steps of the cycle is transferred as energy-rich electrons to NAD+, forming NADH. For each acetyl group that enters the citric acid cycle, three molecules of NADH are produced.
  • Electrons are also transferred to the electron acceptor Q, forming QH2.
  • At the end of each cycle, the four-carbon oxaloacetate has been regenerated, and the cycle continues.

From this process we get 2 molecule of ATP, 8 molecule of NADH and 2 molecule of FADH.

Fourthly the NADH and FADH entered into electron transfer process. From this process we get 34 molecule of ATP.

ATP is a chemical compound which as saver of high point of energy. So the form of our energy is ATP.

Those all about the process of forming of energy, so keep our pattern eat.

Thanks for your attention.

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