Cellular Respiration - AP Biology

Cellular respiration begins with the process of breathing in oxygen and consuming glucose. Through a series of reactions they eventually produce energy in the form of and heat, as well as byproducts such as , which is exhaled, and water molecules.

The electron transport chain (ETC) is responsible for oxidative phosphorylation, resulting in the production of ATP. The ATP is produced by a proton gradient made as electrons are transported throughout the chain. Inhibition of this process by "Substance Y" will block the formation of a proton gradient. Blocking the proton gradient will not allow for oxidative phosphorylation to occur, thus greatly decreasing the amount of ATP produced.

FADH2 is directly attached onto the second protein of the electron transport chain and therefore the electrons of FADH2 (electron carrier) are dropped off at the second protein not the first. As a result, the electrons from FADH2 do not pump as much electrons across the membrane as NADH. This results in a lower proton gradient created from FADH2 then NADH and therefore less ATP production from FADH2.

Remember that NADH and FADH2 are electron carriers and do not directly create any energy. The movement of the electrons through the electron transport chain also does not create energy directly, but does create a proton gradient that is later used to create energy. The movement of protons down its proton gradient through ATP synthase does, however, generate energy. It actually generates around 30 ATP molecules per one glucose.

In both cellular respiration and photosynthesis, chemiosmosis occurs. Chemiosmosis is the process in which the creation of a proton gradient leads to the transport of proton down its concentration gradient to produce ATP. This occurs in the electron transport chain in both mitochondrias and chloroplast. In the photosynthesis it occurs when the electron is transported from photosystem II to photosystem I.

A reducing agent works as an electron donor, so it is ultimately giving away electrons to another molecule and ultimately making that other molecule more negative in charge, or reduced in charge. Note that a reducing agent is itself oxidized. Also recall the mnemonic OIL RIG (Oxidation Is Loss of electrons, Reduction Is Gain of electrons).

Oxygen is the final electron acceptor in aerobic respiration. It becomes water upon being reduced by the accepted electrons, which explains why water is one of the products of respiration. Without the presence of oxygen, electrons would remain trapped and bound in the final step of the electron transport chain, preventing further reaction.

NADH and FADH2 are necessary to donate electrons to the electron transport chain.

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).

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.