- C6H12O6 + 6O2 -> 6CO2 + 6H2O.
*This does not include the 34 ATP*
- Cellular respiration is a combustion reaction.
1. 2 ATPs are needed to get this process started (activation energy)
2. The break down of glucose occurs in the CYTOPLASM.
3. This creates two 3 carbon compounds. (anaerobic and called glycolysis because you are lying the glucose into pyruvate which releases 4 ATPs but only yields a net of 2).
4. The metabolic pathway of glycolysis is divergent and each pyruvic acid becomes an ACETYL CoA and enters a cyclic pathway known as the KREB'S CYCLE (must be aerobic).
- Many organisms perform cellular respiration, including animals, bacteria, fungi and protozoa.
Major Inputs & Outputs
- Glucose + 2NAD+ +2ATP + 4ADP + 2Pi
- 2 Pyruvate + 2 NADH + 2ADP + 4 ATP
Step 1. The first step is a condensation step, combining the two-carbon acetyl group (from acetyl CoA) with a four-carbon oxaloacetate molecule to form a six-carbon molecule of citrate. CoA is bound to a sulfhydryl group (-SH) and diffuses away to eventually combine with another acetyl group. This step is irreversible because it is highly exergonic. The rate of this reaction is controlled by negative feedback and the amount of ATP available. If ATP levels increase, the rate of this reaction decreases. If ATP is in short supply, the rate increases.
Step 2. Citrate loses one water molecule and gains another as citrate is converted into its isomer, isocitrate.
Steps 3 and 4. In step three, isocitrate is oxidized, producing a five-carbon molecule, α-ketoglutarate, together with a molecule of CO2 and two electrons, which reduce NAD+ to NADH. This step is also regulated by negative feedback from ATP and NADH and by a positive effect of ADP. Steps three and four are both oxidation and decarboxylation steps, which release electrons that reduce NAD+ to NADH and release carboxyl groups that form CO2 molecules. α-Ketoglutarate is the product of step three, and a succinyl group is the product of step four. CoA binds the succinyl group to form succinyl CoA. The enzyme that catalyzes step four is regulated by feedback inhibition of ATP, succinyl CoA, and NADH.
Step 5. A phosphate group is substituted for coenzyme A, and a high-energy bond is formed. This energy is used in substrate-level phosphorylation (during the conversion of the succinyl group to succinate) to form either guanine triphosphate (GTP) or ATP. There are two forms of the enzyme, called isoenzymes, for this step, depending upon the type of animal tissue in which they are found. One form is found in tissues that use large amounts of ATP, such as heart and skeletal muscle. This form produces ATP. The second form of the enzyme is found in tissues that have a high number of anabolic pathways, such as liver. This form produces GTP. GTP is energetically equivalent to ATP; however, its use is more restricted. In particular, protein synthesis primarily uses GTP.
Step 6. Step six is a dehydration process that converts succinate into fumarate. Two hydrogen atoms are transferred to FAD, producing FADH2. The energy contained in the electrons of these atoms is insufficient to reduce NAD+ but adequate to reduce FAD. Unlike NADH, this carrier remains attached to the enzyme and transfers the electrons to the electron transport chain directly. This process is made possible by the localization of the enzyme catalyzing this step inside the inner membrane of the mitochondrion.
Step 7. Water is added to fumarate during step seven, and malate is produced. The last step in the citric acid cycle regenerates oxaloacetate by oxidizing malate. Another molecule of NADH is produced.
- During the cycle, pyruvate is introduced into the mitochondrial matrix, and, through oxidation, is metabolized into adenosine triphosphate, a chemical form of energy.
Major Inputs & Outputs
- 2 aceytl CoA, 2 oxaloacetate, 2 ADP + P, 6 NAD+, 2 FAD
- 4 CO2, 2 ATP, 6 NADH + H+, 2 FADH2
Step 1 - Two electrons are passed from NADH into the NADH dehydrogenase complex. Coupled with this transfer is the pumping of one hydrogen ion for each electron.
Step 2 - The two electrons are transferred to ubiquinone. Ubiquinone is called a mobile transfer molecule because it moves the electrons to the cytochrome b-c1 complex.
Step 3 - Each electron is then passed from the cytchrome b-c1 complex to cytochrome c. Cytochrome c accepts each electron one at a time. One hydrogen ion is pumped through the complex as each electron is transferred.
Step 4 - The next major step occurs in the cytochrome oxidase complex. This step requires four electrons. These four electrons interact with a molecular oxygen molecule and eight hydrogen ions. The four electrons, four of the hydrogen ions, and the molecular oxygen, are used to form two water molecules. The other four hydrogen ions are pumped across the membrane.
Step 5 - The hydrogen pumping steps creates a gradient. The potential energy in this gradient is used by ATP synthase to form ATP from ADP and inorganic phosphate.
- The electron transport chain (ETC) is located in the inner membrane of the mitochondria.
Major Inputs & Outputs
- Many organisms perform cellular respiration, including animals, bacteria, fungi and protozoa
The Importance of Cellular Respiration
- Cellular respiration provides energy for living organisms. So, cellular respiration is important because it provides the energy for living organisms to perform all of the other necessary functions to maintain life. Most single-celled organisms, such as bacteria, do not require much energy and are able to survive on glycolysis and fermentation. Our ability to think, walk, and talk require enormous amounts of energy which can only be provided by aerobic respiration through the Krebs Cycle and the electron transport chain.
"Cellular Respiration." Biology Laboratory Manual | Cellular Respiration. N.p., n.d. Web. 09 Jan. 2017.
"Krebs Cycle." Krebs Cycle. N.p., n.d. Web. 09 Jan. 2017.
"Glycolysis." Khan Academy. N.p., n.d. Web. 09 Jan. 2017.