So far, glycolysis and the Krebs cycle have produced a total of 4 molecules of ATP for each glucose molecule that was degraded. The rest of the ATP produced from the breakdown of glucose is produced in the next steps of cell respiration, through the electron transport chain and oxidative phosphorylation.
- The electron transport chain produces energy that drives the synthesis of ATP in oxidative phosphorylation. The electron transport chain consists of molecules (mostly proteins) that are embedded in the inner mitochondrial membrane. There are millions of such electron transport chains in the inner mitochondrial membrane.
- Sitting atop these proteins embedded in the membrane-associated molecules that are alternately reduced and oxidized as they accept and donate electrons.
- Each successive carrier in the electron transport chain has a higher electronegativity than the carrier before it, so the electrons are pulled downhill towards oxygen, the final electron acceptor the molecule with the highest electronegatvity.
- Cytochrome is a type of protein molecule that contains a heme prosthetic group and that functions as an electron carrier in the ETC of mitochondria and chloroplasts.
surrounding a single iron atom.
- The initial electron acceptor in the ETC is a flavoprotein called flavin mononucleitde or FMN, and it accepts an electron from NADH. The electron is passed down a series of molecules to oxygen, which is the final electron acceptor. Then it is combined with a couple of hydrogen atoms to form a molecule of water.
- FADH2 and NADH both donate electrons to the chain.
- *The ETC does not make ATP directly. It generates a proton gradient across the inner mitochondrial membrane, which stores potential energy that can be used to phosphorylate ADP.
- The electron transport chain doesn’t make any ATP itself. Instead these reactions are coupled to others to produce ATP in a process called Chemiosmois.
- The net result of ETC:
- a. To move free energy down a series of steps from FADH2 and NADH to oxygen
- b. To provide a source of energy for the creation of ATP through chemiosmosis.
~ Oxidative Phosphorylation and Chemiosmosis
- Also embedded in the mitochondrial inner membrane are protein complexes call ATP synthases.
- ATP synthetases phophorytetes ATP out of ADP plus inorganic phosphate.
- ATP synthetases use the energy from a proton gradient created by the ETC to power the synthesis of ATP.
~Related Metabolic Process
- In the absence of oxygen (remember that oxygen is the final electron acceptor in the electron transport chain, and without it this chain will not function), the cell goes through a process called fermentation.
- Fermentation takes place under anaerobic conditions—that is, when there is not oxygen present. Cell respiration takes place under aerobic conditioned (when oxygen is present). Fermentation consists of glycolysis and reactions that regenerate NAD+ (so that it can be reused during glycolysis).
- The two common types of fermentation are alcohol fermentation and lactic acid fermentation.
- In alcohol fermentation, pyruvate is converted to ethanol, releasing CO2 and oxidizing NADH in the process to create more NAD+
- In latic acid fermentation, pyruvate is reduced by NADH (and NAD+ is created in the process), and lactate is formed as a waste product.
- When oxygen is scarce, human muscle cells switch from aerobic respiration to lactic acid fermentaion. Lacatate accumulates, but is generally carried to the liver where it is converted back to pyruvate when oxygen becomes available.
A. Accepting electrons at the end of the electron transport chain.
B. The phosphorylation of ADP.
C. The citric acid cycle.
D. The oxidation of pyruvate to acetyl CoA.
2) Which process in eukaryotic cells will normally proceed whether O2 is present or absent?
A. The Krebs cycle
B. Oxidative phosphorylation
E. Electron transport
3) All of the following substances are produced in a muscle cell under anaerobic conditions except
E. Acetyl CoA.
4) All of the following are products or intermediaries in glycolysis except
5) A young relative of yours has never had much energy. He goes to a doctor for help and is sent to the hospital for some tests. There they discover his mitochondria can use only fatty acids and amino acids for respiration, and his cells produce more lactate than normal. Of the following, which is the best explanation of his condition?
A. His cells cannot move NADH from glycolysis into the mitochondria.
B. His cells contain something that inhibits oxygen use in his mitochondria.
C. His mitochondria lack the transport protein that moves pyruvate across the outer mitochondrial membrane.
D. His cells lack the enzyme in glycolysis that forms pyruvate.
E. His cells have a defective electron transport chain, so glucose goes to lactate instead of to acetyl CoA.
Answers: 1) A ; 2) C ; 3) E ; 4) A; 5) C