Cellular Respiration
Respiration is a series of complex oxidation-reduction reactions in living things. In this process, cells get energy through the breakdown of various organic substances. There are two types of respiration aerobic and anaerobic.
Aerobic Respiration: (Gk. "Aeros" air)
Aerobic respiration takes place in the of molecular oxygen. Glucose is a high-energy molecule and its breakdown product is CO, and H2O, which are low-energy molecules thus the stored energy is released.
The electrons are removed from the substrate (e.g., glucose) and eventually received by an oxygen atom which combines with H' to form water. The overall equation of written as follows Enzymes
Respiratio0obic respiration for a breakdown of glucose can be C6H12O6+602
Anaerobic:
SADP+ 36Pi 6CO2+6H2O+36ATP
Anaerobic respiration takes place in the absence of molecular oxygen, it is also known as fermentation. It is an incomplete oxidation-reduction reaction. The energy released from the substrate (glucose) is a result of its molecular rearrangement and some of this energy is available to the cell.
The NADH is oxidized to NAD, it is called fermentation because glycolysis is followed by the reduction of pyruvate by NADH to either alcohol and CO2 or lactate.
Alcoholic Fermentation:
In primitive cells and cells of some eukaryotic organisms such as yeast and plants, pyruvate is further broken down by alcoholic fermentation into alcohol and CO2.
Lactic Acid Fermentation:
It takes place in many bacteria, animals, and muscles of humans. Each pyruvate molecule is converted into lactic acid in the absence of molecular oxygen.
Process of cellular respiration:
It takes place in four steps.
1. Glycolysis
3. Krebs cycle
2. Oxidation of pyruvic acid
4. Electron transport chain
4.2.2 Glycolysis of oxygen with pyruvate molecules.
It is found in all organisms and evolved before the Krebs cycle Glycolysis takes place in the cytoplasm and it is the breakdown of glucose into an ETC. This occurs in the cytosol of cytoplasm and does not require molecular c (thus probably first life was anaerobic bacteria). Each step is catalyzed by an enzyme. Glycolysis can be divided into two stages, the preparatory phase and the oxidative phase.
4.2.3 The Oxidation of Pyruvic Acid It takes place in two stages. Oxidation of pyruvic acid to form Acetyl C Oxidation of Acetyl Coenzyme A.
Oxidation of Pyruvic Acid:
It is a transition reaction during which CO, is released. The oxidation of pyruvic acid is called a transition reaction because it connects glycolysis and the Krebs cycle. In this reaction, pyruvate is converted to 2-carbon acetyl CoA by attaching coenzyme A.
It gives off carbon dioxide. This is an oxidation reaction in which electrons are removed from pyruvate by dehydrogenase that uses NAD as a coenzyme. This reaction occurs twice for each original glucose molecule.
Oxidation of Acetyl Coenzyme A:
It takes place through the Krebs cycle. As a first step 4-C compound oxaloacetate binds with 2-carbon acetyl CoA to become a 6-carbon compound. This 6-carbon 100
dioxide molecules are given off. Finally regenerating 4-carbon compound which is a free compound passes through a series of electron-yielding oxidation reactions. Two carbon
to bind another acetyl CoA. This cycle is called the citric acid
cycle or Krebs cycle.
4.2.4 Citric Acid Cycle or Krebs Cycle:
This is a cyclic metabolic pathway located in the matrix of mitochondria. The Krebs cycle was named after Sir Hans Krebs a British scientist who discovered it in 1930.
Steps of the Krebs cycle:
At the start of this cycle, the (2-C) acetyl group (produced by transition reaction) joins with a (4-C) oxaloacetate molecule, forming a 6-carbon citrate molecule. Citrate is converted to an isomer called isocitrate action rea ion)
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