Respiration of Cell


Cellular respiration, also known as “oxidative metabolism” is one of the main ways to cells to get useful energy. This is the set of metabolic reactions and processes occurring in organisms’ cells to convert biochemical energy from nutrients into adenosine triphosphate (ATP) and then release waste products. Respiration reaction which is involved in catabolic reactions involves oxidation of one molecule and another reduction.

The releasedenergy in respiration is used to synthesize ATP to store this energy. Stored in ATPenergy is then used to drive processes requiring energy, including biosynthesis, movement or transport of molecules across cell membranes. In every living cell occursmetabolism process. One such process is catabolism. Catabolism is also known as dissimilation, because in this process stored energy be backgenerated or dismantled to carry out life processes.

Cellular respiration takes place inside the mitochondria through the process of glycolysis which is the process of changing the C3 to C6atom. It is followed by oxidative decarboxylation process that converts into C3 to C2 compoundsand C1 (CO2). Then the Krebs cycle changesC2 compounds into C1compounds (CO2ˉ). At every level produced energy in the form of ATP (Adenosine Tri Phosphate) and Hydrogen. Hydrogen that have energy join withacceptor hydrogen to take to transport electrons, hydrogen energy is released and accepted by O2 to H2O.

In respirationprocess isproducedCO2 compounds which are basic ingredients of anabolism process. In respiration processthe fuel cell is hexose sugar. The process is need free oxygen, so that the overall reaction can be written as follows:

C6H12O6 + 6CO2                       6CO2 + 6H2O + 675 cal

In aerobic respiration, hexose sugar is demolishedwitha very long process. The first time glucose as the base material having phosphorylation, that is the process of adding phosphate to glucose molecules to be fructose-1,6- diphosphate. On phosphorylation, ATP and ADP play an important role as phosphatefiller. The conversion of fructose-1, 6 – diphosphateinto CO2 and H2O can be divided into 4 stages;they are glycolysis, the distance reaction (oxidative decarboxylation), Krebs cycle and electron transfer.

1. Glycolysis

It is a series of glucoseconversionreaction into pyruvate acid molecules to produce NADH and ATP.

The properties of glycolysis are:

a. Can take place in aerobic and anaerobic

b. In glycolysis there are enzymatic activity and adenosine triphosphate (ATP) also adenosine diphosphate (ADP)

c. ADP and ATP participate in the transfer of phosphate from one molecule to another molecule

Glucose as substrate in aerobic respiration (and anaerobic) were obtained from photosynthesis. Beginning with the addition of one phosphate by ATP to glucose, forming glucose-6 phosphate and ATP shrinkto ADP. It is called phosphorylation of fructose-1, 6 – diphosphate and here glycolysis start.

Glycolysis starts from changes in fructose-1,6-diphosphate which has 6 pieces Catom is converted into 3-difosfogliseral-dehida (with 3 pieces of Catoms) and hydroxyl-acetone-phosphate. This demolition is assisted by the aldolaseenzyme. Then dihydroxyacetone phosphates become 3-fosfogliseraldehida also with the help of fosfitriosaisomeraseenzymes. Next fosfogliseraldehida compound with a phosphoric acid (H3PO4) and transformed into 1,3-difosfogliseraldehida. 1,3-difosfogliseralhida turn into1.3 diphosphoglyceric. With the help of dehydrogenase enzyme, the event occurred due to the addition of H2. With the help of transfosforilasefosfogliseratenzyme and Mg++ions,1,3-diphosphoglyceric acid loses one phosphate to turn into -3- fosfogliseratacid. Furthermore, acid-3-fosfogliserat becomes -2- fosfogliseratacidbecause of the influence of fosfogliseromutaseenzyme. With the help of enolaseenzymes and Mg++ions, the -2- fosfogliseratacidremoves H2O and becomes -2- phosphoenolpyruvateacid. The last change in glycolysis is the release of one phosphate from the -2- phosphoenolpyruvateacidinto pyruvate acid. Transphosphorylasephosphopyruvate enzyme and Mg++ionshelp this process while ADP increased to ATP.

2. Distance Reaction

After glycolysis occursdistance reaction (oxidative decarboxylation), that is the conversion of pyruvate acid into two acetyl CoA while producing CO2 and 2NHDH2 which the reaction is


2(C3H4O3) 2(C3H3O) – CoA + 2CO2

Pyruvate Acetyl CoA

Acetyl CoA is formed then enters the Krebs cycle.

3. Krebs Cycle (Citric Acid Cycle)

In this Krebs cycle (occurs atmitochondrial matrix) acetyl CoA is converted into CoA. Acetyl CoA joins with oxaloacetic acid to form citric acid. CoA is released making it possible to take another 2C fragment of pyruvate acid. Citric acid formation occurred early in the Krebs cycle, while the remaining two of the glucose carbon released as CO2. During the formation-formation, the required energy is released to combine phosphatewith ADP to form ATP molecules.

In the Krebs cycle, the demolition of carbon chains of glucose is complete. So as a result of glycolysis, the distance reaction, and the Krebs cycle was split one glucosemolecule 6 carbonbecomes 6 molecules 1 carbon, but it also produced two ATP molecules from glycolysis and two ATP again from the Krebs cycle.

4. Electron Transport System

In the electrontransportsystem took place packing energy from glucose to ATP. This reaction occurs within the membrane of the mitochondrion, hydrogen from the Krebs cycle is incorporated in the FADH2 and NADH converted to electrons and protons. In this electron transport system, oxygen is the final electron acceptor, after receiving an electron; O2 will react with H+to form H2O. In this system produced 34 ATP. So the total ATP produced by respiration, as follows:

Glycolysis                               2 NADH2   =   6 ATP            2 ATP

The distancereaction     2 NADH2   =   6 ATP

Krebs Cycle                             6 NADH2   = 18 ATP            2 ATP

                                                         2 FADH2    =   4 ATP

                                                                                      34 ATP            4 ATP

5. Aerob and Anaerobic Respiration

Aerobic respiration is a breathing process that requires oxygen from the air. There are some plants that the respiration activity decreased when the concentration of oxygen in the air below normal. For example:spinach, carrots and some other plants. Anaerobic respiration or fermentation can also be called intramolecular respiration. The purpose of fermentation with aerobic respiration is to get energy. It’s just that the energy produced is much less than aerobic respiration.

Aerobic respiration reaction:

C6H12O6                    6CO2 + 6H2O + 675 cal + 38 ATP

Anaerobic respiration reaction:

2C2H5OH                  C6H12O6 + 2CO2 + 21 cal + 2 ATP

Anaerobic respiration can take place in free air, but this process does not use O2 provided by air. Fermentation is sometimes referred as the brewing of alcohol or alcoholisation.

In aerobic and anaerobic respiration, pyruvate as the result of glycolysis acid is the substrate.

Perfect demolition occurred in the oxidation of pyruvic acid in aerobic respiration. From this process the resulting CO2 and H2O and  more energy 38 ATP.



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