The previous tutorial concentrated on the first stages of cellular respiration (i.e., glycolysis). You should know that glycolysis produces pyruvate and some ATP. The pyruvate can be used in fermentation, but it can also be used in another manner. There are many high-energy electrons left in pyruvate. Next, you will learn how cells complete cellular respiration by oxidizing pyruvate to form carbon dioxide. You will also learn that these electrons are conveyed to an electron transport chain where they can participate in the synthesis of ATP. By the end of this tutorial you should have a basic understanding of:
This figure provides a good summary of the Krebs cycle, illustrating the main reactants (acetyl CoA, NAD+, FAD, ADP, and inorganic phosphate) and products (carbon dioxide, NADH, FADH2, and ATP) from what is actually a multistep process.
This figure emphasizes several important concepts about cellular respiration. First, note the locations of glycolysis, the Krebs cycle, and the electron transport chain and oxidative phosphorylation. Second, note how the electron carriers transport electrons to the transport chain, and the net amount of ATP generated at each step. In particular, compare the amount of ATP generated by oxidative phosphorylation to the amount generated by substrate-level phosphorylation. The maximum net yield of 38 ATPs per molecule of glucose is merely an estimate. Much of the energy bound in a molecule of glucose is actually lost as heat during metabolism. While this heat is actually a waste product, homeotherms ("warm-blooded" animals) capitalize on this waste and use it to maintain constant body temperatures.
This tutorial focused on the final steps of cellular respiration. Recall that at the end of glycolysis there is a net production of two molecules of ATP and two molecules of NADH. The ATP is produced via substrate-level phosphorylation; in this reaction, a phosphate group on an organic molecule is transferred directly (along with high-energy electrons) onto a molecule of ADP. Substrate-level phosphorylation also occurs once during the Krebs cycle.
In the next phase of cellular respiration, the high-energy electrons within NADH and FADH2 will be passed to a set of membrane-bound enzymes in the mitochondrion, collectively referred to as the electron transport chain. These electrons will provide energy to do work. Specifically, this work will involve the movement of positively charged hydrogen atoms (H+), also known as protons.
GLYCO (GLUCOSE) -- LYSIS (LYSE)
O2 NOT present
*Each FADH2=2ATP produced
Energy is also released in the form of NAD+..used to power glycolysis!
Cellular Respiration is the process
that releases energy from sugars in
the presence of oxygen.
C H O + 6O 6CO + 6H O + ATP
6 12 6 2 2 2
waste water energy
Each of the reactants are used at different stages of aerobic respiration
Each of the products is formed during different stages too!
The ENERGY that is released is primarily used to produce 34 to 36 ATP molecules per 1 glucose molecule.
results in the formation of fewer ATP molecules
in Muscled-Beings: Lactic Acid Fermentation
in Bacteria and yeast: Alcohol Fermentation
Lactic Acid Fermentation
occurs when O2 is not available
the pyruvic acid, formed during glycolysis, is broken down to lactic acid.
Respiration is a series of reactions in which 6-carbon glucose is oxidised to form . The energy released due to the oxidation of is used to synthesize ATP from adenosine diphosphate or ADP and inorganic phosphate or Pi.
The high-energy carriers NADH and FADH2 can themselves be oxidized by the electron transport chain. During oxidation, energy is lost by the oxidized molecule while energy is gained by the reduced molecule. The electron transport chain is composed of a series of molecules that alternatively become oxidized and reduced by one another. As these redox reactions occur, free energy is made available to do work, and that work is the movement of charged hydrogen atoms (protons) across a membrane. The electron transport chain is mostly contained within the membrane, and energetically, the electrons that pass from one molecule to the next have decreasing potential energies. The last molecule that is reduced is oxygen, which results in the generation of water. Some bacteria can use other molecules (e.g., nitrate, sulfate, or organic acids) as terminal electron acceptors, and hence can undergo cellular respiration under anaerobic conditions.