Cellular Respiration - AP Biology

Aerobic cellular respiration is the process of breaking down glucose to form intermittent electron electron carriers, which eventually donate their electrons to the final electron acceptor, oxygen, at the end of the electron transport chain. This process produces usable energy in the form of ATP, as well as waste produced of carbon dioxide and water.

One way to divide prokaryotes is into aerobes and anaerobes. Aerobes are organisms that can survive and grow in the presence of oxygen while anaerobes did not require oxygen for survival and growth. All aerobes can produce ATP with or without oxygen (though they may need oxygen for survival. However some anaerobes are harmed by the presence of oxygen (obligate anaerobes). These anaerobes can produce ATP through glycolysis or anaerobic respiration, where another molecule besides oxygen is used as the final electron acceptor for the electron transport chain.

If no oxygen is available, anaerobic respiration will occur. This can either be lactic acid fermentation, or alcoholic fermentation. In alcoholic or lactic acid fermentation, the pyruvate are decarboxylated and ultimately used to produce either ethanol or lactic acid, and regenerate NAD+ which will be reused for another cycle of glycolysis (2 ATP are produced for each round of glycolysis).

The two main products that result from the breakdown of glucose are carbon dioxide and water. Carbon dioxide is produced during pyruvate dehydrogenase and the Krebs cycle. Water is formed at the end of the electron transport chain where two electrons (hydrogens) are added to oxygen (the final electron acceptor).

If no oxygen is available, anaerobic respiration will occur. This can either be lactic acid fermentation, or alcoholic fermentation. In alcoholic or lactic acid fermentation, the pyruvate are decarboxylated and ultimately used to produce either ethanol or lactic acid, and regenerate NAD+ which will be reused for another cycle of glycolysis (2 ATP are produced for each round of glycolysis).

In the absence of oxygen, pyruvate produced during glycolysis will be used for either lactic acid or alcoholic fermentation, producing lactic acid or ethanol (as waste products) and regenerating NAD+ to be used for another cycle of glycolysis. This fermentation occurs in the cytosol of the cell.

Pyruvate decarboxylation is an oxidative decarboxylation reaction, or an oxidation reaction where a carboxylate group is removed. This reaction converts pyruvate which was produced through glycolysis to acetyl CoA to be used in the Citric Acid Cycle.

The pyruvate dehydrogenase complex is an enzyme complex that consists of 3 enzymes, which work together to catalyze the pyruvate decarboxylation reaction, where pyruvate is converted to acetyl CoA.

Pyruvate decarboxylation occurs in the mitochondrial matrix. The acetyl CoA produced from the pyruvate decarboxylation reaction will undergo the Citric Acid cycle also in the mitochondrial matrix.

During glycolysis, for each molecule of glucose, two molecules of pyruvate are produced ( glucose+ NAD+ + 2 ADP + 2Pi-> 2 pyruvate+ 2 ATP + 2NADH+. These 2 molecules of pyruvate then undergo the pyruvate decarboxylation reaction: 2(pyruvate+ CoA-SH+ NAD+ -> NADH+ CO2+ acetyl CoA).

The pyruvate decarboxylation reaction is pyruvate+ CoA-SH+ NAD+ -> NADH+ CO2+ acetyl CoA.

During the pyruvate decarboxylation reaction , a thioester bond links the acetyl group of pyruvate with coenzyme A to produce acetyl CoA.

Glycolysis happens in the cytosol (the fluid containing the organelles) of the cell. The next step in cellular respiration, the citric acid cycle, occurs in the mitochondria.

NAD+ is required as an oxidizing agent (accepting electrons from other molecules) during glycolysis. As it accepts electrons, it becomes NADH, a byproduct of glycolysis. NADH can be reverted back to NAD+ to continue glycolysis through the process of fermentation, but is usually used to donate the added electron to the electron transport chain later in the cell metabolism process. The electron is used to power the protein pumps that create the proton gradient that powers ATP synthase.

Glycolysis is the first step of cellular respiration and, in the process of splitting glucose into two pyruvate molecules, does not require oxygen.

Pyruvate decarboxylation, the citric acid cycle, and oxidative phosphorylation are all steps in aerobic respiration, and thus require the presence of oxygen.

Fermentation oxidizes molecules of NADH to NAD+ so the cell can have oxidizing agents for any subsequent glycolysis reactions. It does not, however, produce any usable energy in the process.

Fermentation leads to the production of ethanol in yeast cells and lactic acid in muscle cells.

Glycolysis occurs in the cytosol of cells. Once finished, the two pyruvate products are transported into the mitochondria to go through the citric acid cycle, at a cost of 1 ATP per pyruvate. Neither the nucleus, nor the endoplasmic reticulum have any function in glycolysis or the citric acid cycle.

The conversion of glucose to two pyruvate molecules in glycolysis produces a net total of two direct ATP. When fructose-1,6-bisphosphate enters glycolysis, it bypasses the two steps involved that normally cost one ATP each, therefore, there is no required input and the net total is four produced ATP.

We have to remember that each step beyond the conversion of fructose-1,6-bisphosphate to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate happens twice, or we would come up with two ATP created.

Glycolysis is the first step in cellular respiration, and is seen in both aerobic and anaerobic respiration. The products of glycolysis are pyruvate, NADH, ATP, and water. Oxygen is only a product of the light reactions of photosynthesis; it is consumed as a reactant in the electron transport chain.