Cellular Respiration can be seen more simply in the chemical equation:
(2)
The equation in words:
Glucose is needed to start glycolysis, and the oxygen is needed for the glycolysis to move through the Krebs cycle or go though fermentation. Through the use of enzymes carbon dioxide is produced and released from the six carbon compound in the Krebs cycle. Water is also produced in the electron transport chain when hydrogen ions and oxygen as well as electrons combine. Lastly ATP is created in the electron transport chain through a channel of protein.
In stage one of cellular respiration where glucose is broken down in the cytoplasm glycolysis occurs. During glycolysis one six carbon molecule of glucose is broken down into three pyruvates, this is helped by the use of enzymes. Pyruvate is an ion and a molecule that can either gain or loss one or more electrons. Pyruvate being an ion makes up a three carbon organic acid called pyruvic acid. Even after glycolysis, the pyruvate contains energy that had been once stored in the six carbon compound which is the glucose molecule.
Glycolysis diagram (4)
Providing that hydrogen atoms are transferred to NAD and electron acceptor NADH can be produced. NADH assists during glycolysis as the NADH gives electrons to other organic compounds. As a consequently to this NAD is produced that can then accept more electrons, apart from pyruvates being produced during glycolysis four ATP molecules are also produced. The glycolysis needs two ATP molecules for energy however it gains tow molecules making it four in total, so consequently having a total gain of two. Therefore glycolysis is the enzyme which helps the process that breaks down a glucose molecule into two three carbon pyruvates. The pyruvate is an ion produced during glycolysis. Two ATP help give energy to start glycolysis and the NADH helps glycolysis by giving electrons to other organic compounds and making NAD reproducible.
Throughout aerobic cellular respiration the pyruvate that is produced during glycolysis enters a mitochondrion where is it then converted into two carbon compounds, thus making a reaction. “A carbon dioxide molecule and a NADH molecule as well as a two carbon acetyl group are produced because of this reaction, the two carbon group gets attached to coenzyme a molecule which forms acetyl –CoA a compound”(2).
Krebs Cycle diagram (3)
At stage one previously to entering the Krebs cycle, pyruvate has to be converted into acetyl coenzyme A (CoA). This is done by taking away a carbon dioxide mole from the pyruvate, then removing an electron, to reduce an NAD+ into NADH. Then the enzyme called coenzyme A (CoA) is combined with the left over acetyl CoA and is then fed into the Kerbs cycle. Secondly citrate is formed when the acetyl group from acetyl CoA joins with oxaloacetate from the previous Krebs cycle. Then the citrate is converted into its isomer isocitrate, which is then oxidized to form the “5-carbon α-ketoglutarate. This step releases one molecule of CO2 and reduces NAD+ to NADH2+” (3) . Consequently the α-ketoglutarate is oxidized to succinyl CoA, yielding carbon dioxide and NADH2+. The succinyl CoA then releases coenzyme A and phosphorylates ADP into ATP. Succinate is then oxidized to fumarate, converting FAD to FADH2. The Fumarate is hydrolysed to form malate, which then is “oxidized to oxaloacetate, reducing NAD+ to NADH2+” (3). Therefore this cycle is back at the beginning of the Krebs Cycle as the glycolysis produces two pyruvate molecules from one glucose, and each glucose is processed through the Kreb cycle twice. For each molecule of glucose there are “six NADH2+, two FADH2, and two ATP”(3).
- ALLOT, Andrew 2003
Biology for the IB Diploma
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