MB 9.1
How is aerobic respiration similar to the combustion of gasoline in an automobile?
Although very different in mechanism, aerobic respiration is in principle similar to the combustion of gasoline in an automobile engine after oxygen is mixed with the fuel (hydrocarbons). Food provides the fuel for respiration, and the exhaust is carbon dioxide and water.
How is a ball losing PE when it rolls downhill similar to an electron loses PE?
An electron loses PE when it shifts from a less electronegative atom toward a more electronegative one, just as a ball loses PE when it rolls downhill. A redox reaction that moves electrons closer to oxygen, such as the burning (oxidation - loss of electrons) methane, therefore releases chemical energy that can be put to work.
What is an electron transport chain?
An electron transport chain consists of a number of molecules, mostly proteins, built into the inner membrane of the mitochondria of eukaryotic cells and the plasma membrane of aerobically respiring prokaryotes. Electrons removed from glucose are shuttled by NADH to the "top", higher-energy end of the chain. At the "bottom," lower-energy end, O2 captures these electrons along with hydrogen nuclei (H+), forming water.
How do electrons travel from glucose?
At key steps, electrons are stripped from the glucose. As is often the case in oxidation reactions, each electron travels with a proton - thus, as a hydrogen atom. The hydrogen atoms are not transferred directly to oxygen, but instead are usually passed to an electron carrier, a coenzyme called NAD+.
Is electrons transfer from NADH to oxygen endergonic or exergonic?
Electron transfer from NADH to oxygen is an exergonic reaction with a free-energy change of -53 kcal/mol (-222kJ/mol). Instead of this energy being released and wasted in a single explosive step, electrons cascade down the chain from one carrier molecule to the next in a series of redox reactions, losing a small amount of energy with each step until they finally reach oxygen, the terminal electron acceptor, which has a very great affinity for electrons. Each "downhill" carrier is more electronegative than, and thus capable of oxidizing, its "uphill" neighbor, with oxygen at the bottom of the chain. Therefore, the electrons removed from glucose by NAD+ fall down an energy gradient in the electron transport chain to a far more stable location in the electronegative oxygen atom. Put another way, oxygen pulls electrons down the chain in an energy-yielding tumble analogous to gravity pulling objects downhill.
How does NAD+ trap electrons from glucose and other organic molecules?
Enzymes called dehydrogenases remove a pair of hydrogen atoms (2 electrons and 2 protons) from the substrate (glucose), thereby oxidizing it. The enzyme delivers the 2 electrons along with 1 proton to its coenzyme, NAD+. The other proton is released as a hydrogen ion (H+) into the surrounding solution. By receiving 2 negatively charged electrons, but only 1 positively charged proton, NAD+ has its charged neutralized when it is reduced to NADH. The name NADH shows the hydrogen that has been received in the reaction. NAD+ is the most versatile electron accept in cellular respiration and functions in several of the redox steps during the breakdown of glucose.
How does cellular respiration bring oxygen and hydrogen together to form water?
First, in cellular respiration, the hydrogen that reacts with oxygen is derived from organic molecules rather than H2. Second, instead of occurring in one explosive reaction, respiration uses an electron transport chain to break the fall of electrons to oxygen into several-energy releasing steps.
If energy is released from a fuel all at once, why can it not be harnessed efficiently for constructive work?
For example, if a gasoline tank explodes, it cannot drive a car very far. Cellular respiration does not oxidize glucose in a single explosive step either. Rather, glucose and other organic fuels are broken down in a series of steps, each one catalyzed by an enzyme.
What is the downhill route for most electrons during cellular respiration?
Glucose -> NADH -> electron transport chain -> oxygen.
What is glycolysis?
Glycolysis, which occurs in the cytosol, begins the degradation process by breaking glucose into two molecules of a compound called pyruvate. In eukaryotes, pyruvate enters the mitochondrion and is oxidized to a compound called acetyl CoA, which enters the citric acid cycle.
What happens in the citric acid cycle?
Here, the breakdown of glucose to carbon dioxide is completed (In prokaryotes, these processes take place in the cytosol. Thus, the carbon dioxide produced by respiration represents fragments of oxidized organic molecules.
What does oxidation of organic fuel molecules during cellular respiration mean?
I believe this means that the organic fuels are having their electrons stripped off of them during cellular respiration in the mitochondria and this oxidation (stripping of electrons from them) results in energy being created. Now I wonder is the energy coming from the flow of the electrons, or from the electrons themselves? I see in the process of losing PE from a low EN substance, to a high EN substance, energy is released.
What happens in the third stage of respiration?
In the third stage of respiration, the electron transport chain accepts electrons from the breakdown products of the first two stages (most often via NADH) and passes these electrons from one molecule to another. At the end of the chain, the electrons are combined with molecular oxygen and hydrogen ions (H+), forming water.
What makes oxygen such a potent of all oxidizing agents (agents that gain electrons, in order to "reduce" the amount of positive charge on a substance - I wonder what else oxygen is used for).
It is because oxygen is so electronegative (meaning it has a very strong pull on electrons). The more electronegative the atom, the more energy is required to take an electron away from it.
Why are organic molecules that have an abundance of hydrogen excellent fuels?
It is because their bonds are a source of "hilltop" electrons, whose energy may be released as these electrons "fall" down an energy gradient when they are transferred to oxygen. In respiration, the oxidation of glucose transfers electrons to a lower energy state, liberating energy that becomes available for ATP synthesis.
What is NAD+?
It is nicotinamide adenine dinucleotide, a derivative of the vitamin niacin. NAD+ is well suited as an electron carrier because it can cycle easily between oxidized (NAD+, hence the + meaning loss of an electron) and reduced (NADH) states. As an electron accepter, NAD+ functions as an oxidizing agent (because it removes an electron from another substance, in order to add the electron to itself) during respiration.
How is the energy released at each step of the chain used?
It is stored in a form the mitochondrion (or prokaryotic cell) can use to make ATP from ADP. This mode of ATP synthesis is called oxidative phosphorylation because it is powered by the redox reactions of the electron transport chain.
What is reduction?
It is the addition of electrons to another substance.
What is oxidation?
It is the loss of electrons from one substance.
How do electrons that are extracted from glucose and stored as potential energy in NADH finally reach oxygen?
It will help to compare the redox chemistry of cellular respiration to a much simpler reaction: The reaction between hydrogen and oxygen to form water. Mix H2 and O2, provide a spark for activation energy, and the gases combine explosively. In fact, combustion of liquid H2 and O2 is harnessed to power the main engines of the space shuttle after it is launched, boosting it into orbit. The explosion represents a release of energy as the electrons of hydrogen "fall" closer to the electronegative atoms.
What is fermentation?
One catabolic process, fermentation, is a partial degradation of sugars or other organic fuel that occurs without the use of oxygen.
How do cells use organic compounds?
Organic compounds possess potential energy as a result of the arrangement of electrons in the bonds between their atoms. Compounds that can participate in exergonic reactions can act as fuels. With the help of enzymes, a cell systematically degrades complex organic molecules that are rich in potential energy to simpler waste products that have less energy. Some of the energy taken out of chemical storage can be used to do work; the rest is dissipated as heat.
What is substrate-level phosphorylation?
Oxidative phosphorylation accounts for almost 90% of the ATP generated by respiration. A smaller amount of ATP is formed directly in a few reactions of glycolysis and the citric acid cycle by a mechanism called substrate-level phosphorylation. This mode of ATP synthesis occurs when an enzyme transfers a phosphate group from a substrate molecule to ADP, rather than adding an inorganic phosphate to ADP as in oxidative phosphorylation. "substrate molecule" here refers to an organic molecule generated as an intermediate during the catabolism of glucose.
What is the addition of electrons to another substance called?
Reduction; negatively charged electrons added to an electron "reduce" the amount of positive charge of that atom.
What is the most prevalent and efficient catabolic pathway?
That is aerobic respiration, in which oxygen is consumed along with the organic fuel (aerobic is from the Greek "aer", air, and "bios", life). The cells of most eukaryotic and many prokaryotic organisms can carry out aerobic respiration. Some prokaryotes use substances other than oxygen as reactants in a similar process that harvests chemical energy without oxygen; this process is called anaerobic respiration.
If the following redox reaction occurred, which compound would be oxidized? Which reduced? C4H6O5 [+] NAD+ -> C4H4O5 [+] NADH [+] H+
The C4 would be oxidized and the NAD+ would be reduced.
How do the catabolic pathways that decompose glucose and other organic fuels yield energy?
The answer is based on the transfer of electrons during the chemical reactions. The relocation of electrons releases energy stored in organic molecules, and this energy ultimately is used to synthesize ATP.
What would holds back the flood of electrons to a lower energy state?
The barrier of activation energy. Without this barrier, a food substance like glucose would combine almost instantaneously with O2. If we supply the activation energy by igniting glucose, it burns in air, releasing 686 kcal (2,8780 kJ) of heat per mole of glucose (about 180 g). Body temperature is not high enough to initiate burning, of course, Instead if you swallow some glucose (food), enzymes in your cells will lower the barrier of activation energy, allowing the sugar to be oxidized in a series of steps.
How many moles of ATP are made for each molecule of glucose that is degraded to carbon dioxide and water via respiration?
The cell makes up to about 32 molecules of ATP, each with 7.3 kcal/mol of free energy. Respiration cashes in the large denomination of energy banked in a single molecule of glucose (686 kcal/mol) for the small change of many molecules of ATP, which is more practical for the cell to spend on its work.
What are the three stages of cellular respiration?
The harvesting of energy from glucose by cellular respiration is a cumulative function of three metabolic stages. 1. Glycolysis 2. Pyruvate oxidation and the citric acid cycle. 3. Oxidative phosphorylation: electron transport and chemiosmosis.
Why is methane combustion considered an energy-yielding redox reaction?
The reaction releases energy to the surroundings because the electrons lose potential energy when they end up being shared unequally, spending more time near electronegative atoms such as oxygen.
Compare and contrast aerobic and anaerobic respiration.
[9.1 -1] Both processes include glycolysis, the citric acid cycle, and oxidative phosphorylation. In aerobic respiration, the final electron acceptor is molecular oxygen O2; in anaerobic respiration, the final electron acceptor is a different substance.
Give me an overview of cellular respiration.
[Figure 9.6] During glycolysis, each glucose molecule is broken down into two molecules of the compound pyruvate. In eukaryotic cells, as shown, the pyruvate enters the mitochondrion. There it is oxidized to acetyl CoA, which is further oxidized to CO2 in the citric acid cycle. NADH and a similar electron carrier, a coenzyme called FADH2, transfer electrons derived from glucose to electron transport chains, which are built into the inner mitochondrial membrane. (In prokaryotes, the electron transport chains are located in the plasma membrane.) During oxidative phosphorylation, electron transport chains convert the chemical energy to a form used for ATP synthesis in a process called chemiosmosis.
