Chap 9 For Bio FInal

9.5 1. Consider the NADH formed during glycolysis. What is the final acceptor for its electrons during fermentation? What is the final acceptor for its electrons during aerobic respiration?

A derivative of pyruvate, such as acetaldehyde during alcohol fermentation, or pyruvate itself during lactic acid fermentation; oxygen

Electron Transport Chain

A number of molecules, mostly proteins, built into the inner membrane of the mitochondria of eukaryotic cells

9.6 3. What will happen in a muscle cell that has used up its supply of oxygen and ATP?

AMP will accumulate, stimulating phosphofruc- tokinase, and thus increasing the rate of glycolysis. Since oxygen is not present, the cell will convert pyruvate to lactate in lactic acid fermentation, providing a supply of ATP.

The rate of cellular respiration is regulated by its major product, ATP, via feedback inhibition. As the diagram shows, high levels of ATP inhibit phosphofructokinase (PFK), an early enzyme in glycolysis. As a result, the rate of cellular respiration, and thus ATP production, decreases. Feedback inhibition enables cells to adjust their rate of cellular respiration to match their demand for ATP. Suppose that a cell's demand for ATP suddenly exceeds its supply of ATP from cellular respiration. Which statement correctly describes how this increased demand would lead to an increased rate of ATP production? -

ATP levels would fall at first, decreasing the inhibition of PFK and increasing the rate of ATP production. (An increased demand for ATP by a cell will cause an initial decrease in the level of cellular ATP. Lower ATP decreases the inhibition of the PFK enzyme, thus increasing the rate of glycolysis, cellular respiration, and ATP production. It is the initial decrease in ATP levels that leads to an increase in ATP production.)

Oxidative Phosphorylation

ATP synthesis powered by the redox reactions of the electron transport chain

Reduction

Addition of electrons to another substance Becomes more negative

Did you know that.. -

Aerobic respiration yields up to 16 times as much ATP per glucose molecule as does fermentation - up to 32 molecules of ATP for respiration, compared with 2 molecules of ATP produced by substrate-level phosphorylation in fermentation.

Figure 9.20 - Tell me a bit about the pacemaker of cellular respiration, phosphofructokinase. -

Allosteric enzymes at certain points in the respiratory pathway respond to inhibitors and activators that help set the pace of glycolysis and the citric acid cycle. Phosphofructokinase, which catalyzes an early step in glycolysis is one such enzyme. It is stimulated by AMP (derived from ADP) but is inhibited by ATP and by citrate. This feedback regulation adjusts the rate of respiration as the cell's catabolic and anabolic demands change.

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.

Which process yields more ATP, fermentation or anaerobic respiration? Explain.

Anaerobic respiration yields more ATP. The 2 ATP produced by substrate-level phosphorylation in glycolysis represent the total en- ergy yield of fermentation. NADH passes its "high-energy" electrons to pyruvate or a derivative of pyruvate, recycling NAD+ and allowing glycolysis to continue. In anaerobic respiration, the NADH produced during glycolysis, as well as addi- tional molecules of NADH produced as pyruvate is oxidized, are used to generate ATP molecules. An electron transport chain captures the energy of the electrons in NADH via a series of redox reactions; ultimately, the electrons are transferred to an electronegative molecule other than oxygen.

Where does anaerobic respiration take place? -

Anaerobic respiration, takes place in certain prokaryotic organisms (yeast?) that live in environments without oxygen. These organisms have an electron transport chain but do not use oxygen as a final electron acceptor at the end of the chain. Oxygen performs this function very well because it is extremely electronegative, but other, less electronegative substances can also serve as final electron acceptors. Some "sulfate-reducing" marine bacteria for instance, use the sulfate ion at the end of their respiratory chain. Operation of the chain builds up a proton-motive force used to produce ATP, but hydrogen sulfide is produced as by product rather than water. The rotten-egg odor you may have smelled while walking through a salt marsh or a mudflat signals the presence of sulfate-reducing bacteria.

How is fermentation an extension of glycolysis? -

As an alternative to respiratory oxidation of organic nutrients, fermentation is an extension of glycolysis that allows continuous generation of ATP by the substrate-level phosphorylation of glycolysis. For this to occur, there must be a sufficient supply of NAD+ to accept electrons during the oxidation step of glycolysis. Without some mechanism to recycle NAD+ from NADH, glycolysis would soon deplete the cell's pool of NAD+ by reducing it all to NADH and would shut itself down for a lack of an oxidizing agent. Under aerobic conditions, NAD+ is recycled from NADH by the transfer of electrons to the electron transport chain. An anaerobic alternative is to transfer electrons from NADH to pyruvate, the end product of glycolysis.

In mitochondria, exergonic redox reactions a. are the source of energy driving prokaryotic ATP synthesis. b. provide the energy that establishes the proton gradient. c. reduce carbon atoms to carbon dioxide. d. are coupled via phosphorylated intermediates to endergonic processes.

B

How do fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen? -

Because most of the ATP generated by cellular respiration is due to the work of oxidative phosphorylation, our estimate of ATP yield from aerobic respiration is contingent on an adequate supply of oxygen to the cell. Without electronegative oxygen to pull electrons down the transport chain, oxidative phosphorylation eventually ceases. However, there are two general mechanisms by which certain cells can oxidize organic fuel and generate ATP without the use of oxygen: Anaerobic respiration and fermentation. The distinction between these two is that an electron transport chain is used in anaerobic respiration but not in fermentation. (The electron transport chain is also called the respiratory chain because of its role in both types of cellular respiration.)

How would anaerobic conditions (when no O2 is present) affect the rate of electron transport and ATP production during oxidative phosphorylation? (Note that you should not consider the effect on ATP synthesis in glycolysis or the citric acid cycle.) -

Both electron transport and ATP synthesis would stop. (Oxygen plays an essential role in cellular respiration because it is the final electron acceptor for the entire process. Without O2, mitochondria are unable to oxidize the NADH and FADH2 produced in the first three steps of cellular respiration, and thus cannot make any ATP via oxidative phosphorylation. In addition, without O2 the mitochondria cannot oxidize the NADH and FADH2 back to NAD+ and FAD, which are needed as inputs to the first three stages of cellular respiration.)

Compare and contrast aerobic and anaerobic respiration.

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.

Which metabolic pathway is common to both fermentation and cellular respiration of a glucose molecule? a. the citric acid cycle b. the electron transport chain c. glycolysis d. reduction of pyruvate to lactate

C

What processes in your cells produce the CO2 that you exhale?

CO2 is released from the pyruvate that is the end product of glycolysis, and CO2 is also released during the citric acid cycle.

The ATP that is generated in glycolysis is produced by substrate-level phosphorylation, a very different mechanism than the one used to produce ATP during oxidative phosphorylation. Phosphorylation reactions involve the addition of a phosphate group to another molecule. -

CORRECT STATEMENTS -A bond must be broken between an organic molecule and phosphate before ATP can form. -An enzyme is required in order for the reaction to occur -One of the substrates is a molecule derived from the breakdown of glucose INCORRECT STATEMENTS -The enzymes involved in ATP synthesis must be attached to a membrane to produce ATP -The phosphate group added to ADP to make ATP comes from free inorganic phosphate ions (In substrate-level phosphorylation, an enzyme transfers a phosphate group from one molecule (an intermediate in the breakdown of glucose to pyruvate) to ADP to form ATP. This is very different from the mechanism of ATP synthesis that takes place in oxidative phosphorylation.)

How are fats broken down in the body? -

Catabolism can also harvest energy stored in fats obtained either from food or from storage cells in the body. After fats are digested to glycerol and fatty acids, the glycerol is converted to glyceraldehyde 3-phosphate, an intermediate of glycolysis. Most of the energy of a fat is stored in the fatty acids.

What were the first organisms to produce O2? -

Cyanobacteria produced oxygen as a by-product of photosynthesis. Therefore, early prokaryotes may have generated ATP exclusively from glycolysis. The fact that glycolysis is today the most widespread metabolic pathway among Earth's organisms suggests that it evolved very early in the history of life. The cytosolic location of glycolysis also implies great antiquity; the pathway does not require any of the membrane bounded organelles of the eukaryotic cell, which evolved approximately 1 billion years after the prokaryotic cell (how the fk do we know this sht?!) Glycolysis is a metabolic heirloom from early cells that continues to function in fermentation and as the first stage in the breakdown of organic molecules by respiration.

What is the oxidizing agent in the following reaction? Pyruvate + NADH + H+ ---> Lactate + NAD+ a. oxygen b. NADH c. lactate d. pyruvate

D

9.4 2. In the absence of O2, what do you think would happen if you decreased the pH of the inter membrane space of the mitochondrium?

Decreasing the pH means addition of H+. This would establish a proton gradient even without the function of the electron transport chain, and we would expect ATP synthase to function and synthesize ATP. (In fact, it was experiments like this that provided support for chemiosmosis as an energy-coupling mechanism.)

What happens during lactic acid fermentation? -

During lactic acid fermentation, pyruvate is reduced directly to NADH to form lactate as an end product with no release of CO2. Lactate is an ionized form of lactic acid. Lactic acid fermentation by certain fungi and bacteria is used in the dairy industry to make cheese and yogurt.

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.

What are the three alternative cellular pathways for producing ATP by harvesting the chemical energy of food? -

Fermentation, anaerobic respiration, and aerobic respiration. All three use glycolysis to oxidize glucose and other organic fuels to pyruvate, with a net production of 2 ATP by substrate-level phosphorylation. And in all three pathways, NAD+ is the oxidizing agent that accepts electrons from food during glycolysis.

NADH and FADH2 are both electron carriers that donate their electrons to the electron transport chain. The electrons ultimately reduce O2 to water in the final step of electron transport. However, the amount of ATP made by electrons from an NADH molecule is greater than the amount made by electrons from an FADH2 molecule. -

Fewer protons are pumped across the inner mitochondrial membrane when FADH2 is the electron donor than when NADH is the electron donor. (Electrons derived from the oxidation of FADH2 enter the electron transport chain at Complex II, farther down the chain than electrons from NADH (which enter at Complex I). This results in fewer H+ ions being pumped across the membrane for FADH2 compared to NADH, as this diagram shows. Thus, more ATP can be produced per NADH than FADH2.)

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.

How does glycolysis and the citric acid cycle function as metabolic interchanges that enable our cells to convert some kinds of molecules to others as we need them? -

For example, an intermediate compound generated during glycolysis, dihydroxyacetone phosphate, can be converted to one of the major precursors of fats. If we eat more food than we need, we store fat even if our diet is fat free. Wow... Our metabolism is remarkably versatile and adaptable. ******** this means if you eat excess food it will be converted into fats. Would it be possible to eat low fat diets and at the same time eliminate the dihydroxyacetone phosphate, or disabling it using a drug in order to prevent our bodies natural instinct to turn the extra food into fats, this way we would not have to expend a lot of energy trying to lose it?

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.

How do we obtain most of our calories? -

Free glucose molecules are not common in the diets of humans and other animals. We obtain most of our calories in the form of fats, proteins, sucrose and other disaccharides, and starch, a polysaccharide. All these organic molecules in food can be used by cellular respiration to make ATP.

3. In glycolysis, the carbon-containing compound that functions as the electron donor is ____ -

Glucose

Under anaerobic conditions (a lack of oxygen), glycolysis continues in most cells despite the fact that oxidative phosphorylation stops, and its production of NAD+ (which is needed as an input to glycolysis) also stops. The diagram illustrates the process of fermentation, which is used by many cells in the absence of oxygen. In fermentation, the NADH produced by glycolysis is used to reduce the pyruvate produced by glycolysis to either lactate or ethanol. Fermentation results in a net production of 2 ATP per glucose molecule. During strenuous exercise, anaerobic conditions can result if the cardiovascular system cannot supply oxygen fast enough to meet the demands of muscle cells. Assume that a muscle cell's demand for ATP under anaerobic conditions remains the same as it was under aerobic conditions. What would happen to the cell's rate of glucose utilization? -

Glucose utilization would increase a lot. (ATP made during fermentation comes from glycolysis, which produces a net of only 2 ATP per glucose molecule. In contrast, aerobic cellular respiration produces about 30 ATP per glucose molecule. To meet the same ATP demand under anaerobic conditions as under aerobic conditions, a cell's rate of glycolysis and glucose utilization must increase about 15-fold.)

Return to figure 5.6b on page 72 and look at the arrangement of glycogen and mitochondria in the micrograph. What is the connection between glycogen and mitochondria? -

Glycogen is a storage polysaccharide in liver and muscle cells. When energy is needed, glucose units are hydrolyzed from glycogen. Glycolysis in the cytosol breaks down glucose to two pyruvate molecules, which are transported into the mitochondrion. Here they are further oxidized, ultimately producing the needed ATP.

What types of carbohydrates does glycolysis need for catabolism? -

Glycolysis can accept a wide range of carbohydrates for catabolism. In the digestive tract, starch is hydrolyzed to glucose, which can then be broken down in the cells by glycolysis and the citric acid cycle. Similarly, glycogen, the polysaccharide that humans and many other animals store in their liver and muscle cells, can be hydrolyzed to glucose between meals as fuel for respiration. The digestion of disaccharides, including sucrose, provides glucose and other monosaccharides as fuel for respiration.

How does pyruvate act as a key juncture in catabolism? [Figure 9.18] -

Glycolysis is common to fermentation and cellular respiration. The end product of glycolysis, pyruvate, represents a fork in the catabolic pathways of glucose oxidation. In a facultative anaerobe or a muscle cell, which are capable of both aerobic and cellular respiration and fermentation, pyruvate is committed to one of those two pathways, usually depending on whether or not oxygen is present.

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 occurs in alcohol fermentation? -

Here, pyruvate is converted to ethanol (ethyl alcohol) in two steps. The first step releases carbon dioxide from the pyruvate, which is converted to the two-carbon compound acetaldehyde. In the second step, acetaldehyde is reduced by NADH to ethanol. (Acetyl gained an electron). This regenerates the supply of NAD+ needed for the continuation of glycolysis. Many bacteria carry out alcohol fermentation under anaerobic conditions. Yeast (a fungus) also carries out alcohol fermentation. For thousands of years, humans have used yeast in brewing, winemaking, and baking. The CO2 bubbles generated by baker's yeast during alcohol fermentation allow bread to rise.

A glucose-fed yeast cell is moved from an aerobic environment to an anaerobic environment. How would its rate of glucose consumption change if ATP were generated at the same rate? -

I believe if the bacteria would have ATP generated 16 times slower if moved into an anaerobic environment. [9.5 - 2] The cell would need to consume glucose at a rate about 16 times the consumption rate in the aerobic environment (2 ATP are generated by fermentation versus up to 32 ATP by cellular respiration.) Nice was right.

Under anaerobic conditions (a lack of oxygen), the conversion of pyruvate to acetyl CoA stops. -

In the absence of oxygen, electron transport stops. NADH is no longer converted to NAD+, which is needed for the first three stages of cellular respiration. (NAD+ couples oxidative phosphorylation to acetyl CoA formation. The NAD+ needed to oxidize pyruvate to acetyl CoA is produced during electron transport. Without O2, electron transport stops, and the oxidation of pyruvate to acetyl CoA also stops because of the lack of NAD+.)

Figure 9.17 - Fermentation. Describe it. -

In the absence of oxygen, many cells use fermentation to produce ATP by substrate-level phosphorylation. Pyruvate, the end product of glycolysis, serves as an electron acceptor for oxidizing NADH back to NAD+, which can then be reused in glycolysis.

Explanation of 1-6 -

In the net reaction for glycolysis, glucose (the electron donor) is oxidized to pyruvate. The electrons removed from glucose are transferred to the electron acceptor, NAD+, creating NADH.

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 does fermentation consist of aside from glycolysis? -

It consists of glycolysis plus reactions that regenerate NAD+ by transferring electrons from NADH to pyruvate or derivatives of pyruvate. The NAD+ can then be reused to oxidize sugar by glycolysis, which nets two molecules of ATP by substrate-level phosphorylation.

What is fermentation? -

It is a way of harvesting chemical energy without using oxygen or any electron transport chain, in other words without cellular respiration.

What is phosphofructokinase? -

It is an allosteric enzyme with receptor sites for specific inhibitors and activators. It is inhibited by ATP and stimulated by AMP (adenosine monophosphate), which the cell derives from ADP. As ATP accumulates, inhibition of the enzyme slows down glycolysis. The enzyme becomes active again as cellular work converts ATP to ADP (and AMP) faster than ATP is being regenerated. Phosphofructokinase is also sensitive to citrate, the first product of the citric acid cycle.

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.

In the oxidation of pyruvate to acetyl CoA, one carbon atom is released as CO2. However, the oxidation of the remaining two carbon atoms—in acetate—to CO2 requires a complex, eight-step pathway—the citric acid cycle. Consider four possible explanations for why the last two carbons in acetate are converted to CO2 in a complex cyclic pathway rather than through a simple, linear reaction. -

It is easier to remove electrons and produce CO2 from compounds with three or more carbon atoms than from a two-carbon compound such as acetyl CoA. (Although it is possible to oxidize the two-carbon acetyl group of acetyl CoA to two molecules of CO2, it is much more difficult than adding the acetyl group to a four-carbon acid to form a six-carbon acid (citrate). Citrate can then be oxidized sequentially to release two molecules of CO2.)

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.

What is deamination? -

It is the removal of an amino group from an amino acid or other compound.

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.

Match each product of pyruvate metabolism with the condition under which it is produced. -

LACTATE fermentation in human muscle ETHANOL fermentation in yeast and bacteria ACETYL CoA aerobic oxidation (In the presence of oxygen, human cells carry out aerobic respiration, which yields acetyl CoA. In the absence of oxygen, human cells can carry out lactic acid fermentation, which yields lactate. Yeasts and many bacteria carry out alcohol fermentation, which takes place under anaerobic conditions, and produces ethanol.)

Oxidation

Loss of electrons from one substance Becomes more positive

PART C Now that you have determined which variable goes on each axis, the graph can be constructed. Assuming that the x-axis tick marks will be used to identify the thyroid hormone level of each type of rat, what bars should appear on the x-axis? -

Low, Normal, Elevated

Carbohydrates and Fats

Main energy yielding foods Reservoirs of electrons associated with hydrogen

Describe the difference between the two processes in cellular respiration that produce ATP: oxidative phosphorylation and substrate-level phosphorylation.

Most of the ATP produced in cellular respiration comes from oxidative phos- phorylation, in which the energy released from redox reactions in an electron transport chain is used to produce ATP. In substrate-level phosphorylation, an enzyme directly transfers a phosphate group to ADP from an intermediate sub- strate. All ATP production in glycolysis occurs by substrate-level phosphorylation; this form of ATP production also occurs at one step in the citric acid cycle.

5. ____ is the compound that functions as the electron acceptor in glycolysis -

NAD+

During the redox reaction in glycolysis, which molecule acts as the oxidizing agent? The reducing agent?

NAD+ acts as the oxidizing agent in step 6, accepting electrons from glyceraldehyde 3-phosphate, which thus acts as the reducing agent.

6. The reduced form of the electron acceptor in glycolysis is ____ -

NADH

Name the molecules that conserve most of the energy from the redox reactions of the citric acid cycle. How is this energy converted to a form that can be used to make ATP?

NADH and FADH2; they will donate electrons to the electron transport chain.

From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of glycolysis. -

NET INPUT -ADP -NAD⁺ -Glucose NET OUTPUT -ATP -NADH -Pyruvate, NOT INPUT OR OUTPUT -O₂ -CO₂ -coenzyme A -acetyl CoA (In glycolysis, the six-carbon sugar glucose is converted to two molecules of pyruvate (three carbons each), with the net production of 2 ATP and 2 NADH per glucose molecule. There is no O2 uptake or CO2 release in glycolysis.)

In the citric acid cycle (also known as the Krebs cycle), acetyl CoA is completely oxidized. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of the citric acid cycle. -

NET INPUT -Acetyl CoA -NAD⁺ -ADP NET OUTPUT -Coenzyme A -CO₂ -NADH -ATP NOT INPUT OR OUTPUT -Pyruvate -Glucose -O₂ (In the citric acid cycle, the two carbons from the acetyl group of acetyl CoA are oxidized to two molecules of CO2, while several molecules of NAD+ are reduced to NADH and one molecule of FAD is reduced to FADH2. In addition, one molecule of ATP is produced.)

NAD+

Nicotinamide Adenine Dinucleotide Coenzyme, electron carrier Cycles between the oxidized (NAD+) and reduced (NADH) states Functions as an oxidizing agent

Glycolysis

Occurs in cytosol Begins degradation process by breaking glucose into tow molecules of the pyruvate compound In Eukaryotes, pyruvate enters the mitochondrion and is oxidized to a compound called acetyl CoA

Citric Acid Cycle

Occurs in mitochondria (cytosol in prokaryotes) Breakdown of glucose to carbon dioxide is completed

What is fermentation? -

One catabolic process, fermentation, is a partial degradation of sugars or other organic fuel that occurs without the use of oxygen.

9.4 3. Membranes must be fluid to function properly. How does the operation of the electron transport chain support that assertion?

One of the components of the electron transport chain, ubiquinone (Q), must be able to diffuse within the membrane. It could not do so if the membrane were locked rigidly into place.

What type of cells can carry out aerobic oxidation of pyruvate (taking away electrons), but not fermentation? -

Only a few types such as cells of the vertebrate brain cannot carry out fermentation.

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.

1. When a compound donates (loses) electrons, that compound becomes ______. Such a compound is often referred to as an electron donor -

Oxidized

How are proteins utilized as fuels? -

Proteins can also be used for fuel, but first they must be digested to their constituent amino acids. Many of the amino acids are used by the organism to build new proteins. Amino acids present in excess are converted by enzymes to intermediates of glycolysis and the citric acid cycle. Before amino acids can feed into glycolysis or the citric acid cycle, their amino groups must be removed, a process called deamination. The nitrogenous refuse is excreted from the animal in the form of ammonia, urea, or other waste products.

4. Once the electron donor in glycolysis gives up its electrons, it is oxidized to a compound called _____ -

Pyruvate

Sort the following items according to whether they are reactants or products in the anaerobic reduction of pyruvate during lactic acid fermentation. -

REACTANTS -NADH -pyruvate PRODUCTS -NAD+ -lactate (When an animal engages in strenuous usage of its muscles, anaerobic conditions ensue, and pyruvate is reduced to lactate. In the process, NADH is oxidized to NAD+. This NAD+ can further oxidize glyceraldehyde-3-phosphate to produce more ATP.)

When the protein gramicidin is integrated into a membrane, an H+ channel forms and the membrane becomes very permeable to protons (H+ ions). If gramicidin is added to an actively respiring muscle cell, how would it affect the rates of electron transport, proton pumping, and ATP synthesis in oxidative phosphorylation? (Assume that gramicidin does not affect the production of NADH and FADH2 during the early stages of cellular respiration.) -

REMAINS THE SAME -pumping rate -electron transport rate -rate of oxygen uptake. DECREASES (OR GOES TO ZERO) -rate of ATP synthesis -size of protein gradient INCREASES -none (Gramicidin causes membranes to become very leaky to protons, so that a proton gradient cannot be maintained and ATP synthesis stops. However, the leakiness of the membrane has no effect on the ability of electron transport to pump protons. Thus, the rates of proton pumping, electron transport, and oxygen uptake remain unchanged.)

PART I Based on what you know about mitochondrial electron transport and heat production, predict which rats had the highest body temperature, and which had the lowest body temperature. -

Rats with elevated thyroid hormone had the highest body temperature; rats with low thyroid hormone had the lowest.

2. When a compound accepts (gains) electrons, that compound becomes ____. Such a compound is often referred to as an electron acceptor -

Reduced

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.

How can food be oxidized without cellular respiration? -

Remember, oxidation simply refers to the loss of electrons to an electron acceptor, so it does not need to involve oxygen. Glycolysis oxidizes glucose to two molecules of pyruvate. The oxidizing agent of glycolysis is NAD+, and neither oxygen nor any electron transfer chain is involved. Overall glycolysis is exergonic and some of the energy made available is used to produce 2 ATP (net) by substrate-level phosphorylation. If oxygen is present, then additional ATP is made by oxidative phosphorylation when NADH passes electrons removed from glucose to the electron transport chain. But glycolysis generates 2 ATP whether oxygen is present or not - that is, whether conditions are aerobic or anaerobic.

Each of the four stages of cellular respiration occurs in a specific location inside or outside the mitochondria. These locations permit precise regulation and partitioning of cellular resources to optimize the utilization of cellular energy. Stage of cellular respiration: glycolysis... acetyl CoA formation.... citric and cycle..... oxidative phosphorylation.. -

STAGE - LOCATION Glycolysis - Cytosol Acetyl CoA formation - Mitochondrial matrix Citric acid cycle - Mitochondrial matrix Oxidative phosphorylation - inner mitochondrial membrane (Cellular respiration begins with glycolysis in the cytosol. Pyruvate, the product of glycolysis, then enters the mitochondrial matrix, crossing both the outer and inner membranes. Both acetyl CoA formation and the citric acid cycle take place in the matrix. The NADH and FADH2 produced during the first three stages release their electrons to the electron transport chain of oxidative phosphorylation at the inner mitochondrial membrane. The inner membrane provides the barrier that creates an H+ gradient during electron transport, which is used for ATP synthesis.)

Considering the overall result of glycolysis, would you expect ATP to inhibit or stimulate activity of this enzyme? Explain.

Since the overall process of glycolysis results in net production of ATP, it would make sense for the process to slow down when ATP levels have increased sub- stantially. Thus, we would expect ATP to allosterically inhibit phosphofructoki- nase.

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.

Describe how the catabolic pathways of glycolysis and the citric acid cycle intersect with anabolic pathways in the metabolism of a cell.

The ATP produced by catabolic pathways is used to drive anabolic pathways. Also, many of the interme- diates of glycolysis and the citric acid cycle are used in the biosynthesis of a cell's molecules.

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 do the basic principles of supply and demand regulate the metabolic economy? -

The cell does not waste energy making more of a particular substance than it needs. If there is a glut of a certain amino acid, for example, the anabolic pathway that synthesizes that amino acid from an intermediate of the citric acid cycle is switched off. (wow..amazing) The most common mechanism for this control is feedback inhibition: The end product of the anabolic pathway inhibits the enzyme that catalyzes an early step of the pathway. This prevents the needless diversion of key metabolic intermediates from uses that are more urgent. Anabolic means to biosynthesize, therefore that means our bodies will synthesize a product that will go back and disable the pathway, which is similar to what would happen in a supply chain, where if there is no need for a certain product to go a certain way, because the destination (warehouse) already has too much of that product, I as the supply chain manager would tell the driver to bring the product back, or deliver it somewhere else, where it would be more productive (useful)

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.

9.5 2. A glucose fed yeast cell is moved from an aerobic environment to an anaerobic one. How would its rate of glucose consumption change if ATP were to be generated at the same rate?

The cell would need to consume glucose at a rate about 16 times the consumption rate in the aerobic environment (2 ATP are generated by fermentation versus up to 32 ATP by cellular respiration).

Compare the structure of a fat with that of a carbohydrate. What features of their structures make fat a much better fuel? -

The fat is much more reduced (it already has extra electrons); it has many -CH2- units, and in all these bonds the electrons are equally shared. The electrons present in a carbohydrate molecule are already somewhat oxidized (shared unequally in bonds), as quite a few of them are bound to oxygen. It seems as though the bottom line is that, the more electrons that a molecule has, the more energy (fuel) it can provide to the individual.

9.6 1. Compare the structure of a fat with that of a carbohydrate. What features of their structures make fat a much better fuel?

The fat is much more reduced; it has many ¬CH2¬ units, and in all these bonds the electrons are equally shared. The electrons present in a carbohydrate molecule are already somewhat oxidized (shared unequally in bonds), as quite a few of them are bound to oxygen. Electrons that are equally shared, as in fat, have a higher energy level than electrons that are unequally shared, as in carbohydrates. Thus, fat is a much better fuel than carbohydrate.

Briefly explain the mechanism by which ATP synthase produces ATP. List three locations in which ATP synthases are found.

The flow of H+ through the ATP synthase complex causes the rotor and attached rod to rotate, exposing catalytic sites in the knob portion that produce ATP from ADP and ~P . ATP synthases are found in the inner mi- i tochondrial membrane, the plasma membrane of prokaryotes, and membranes within chloroplasts.

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.

What will happen in a muscle cell that has used its supply of oxygen and ATP? -

The muscle cell will then begin the process of fermentation and produce lactic acid instead of ATP, I think. AMP will accumulate, stimulating phosphofructokinase, and thus increasing the rate of glycolysis. Since oxygen is not present, the cell will convert pyruvate to lactate in lactic acid fermentation, providing a supply of ATP. (very little I believe.)

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.

What is the evolutionary significance of Glycolysis? -

The role of glycolysis in both fermentation and respiration has an evolutionary basis. Ancient prokaryotes are thought to have used glycolysis to make ATP long before oxygen was present in Earth's atmosphere. The oldest known fossils of bacteria date back 3.5 billion years, but appreciable quantities of oxygen probably did not begin to accumulate in the atmosphere until 2.7 billion years ago (how the **** do we know this?).

How do human cells make ATP by lactic acid fermentation when oxygen is scarce? -

This occurs during the early stages of strenuous exercise, when sugar catabolism for ATP production outpaces the muscle's supply of oxygen from the blood. Under these conditions, the cells switch from aerobic respiration to fermentation. (Holy snipes no fking wonder this is what happens! I wonder how long it takes). The lactate that accumulates was previously thought to cause muscle fatigue and pain, but recent research suggests instead that increased levels of potassium ions may be to blame, while lactate appears to enhance muscle performance. In any case, the excess lactate is gradually carried away by the blood to the liver, where it is converted back to pyruvate by liver cells. Because oxygen is available, this pyruvate can then enter the mitochondria in liver cells and complete cellular respiration.

Redox Reactions

Transfer of electrons from one reactant to another

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.

DIAGRAM During acetyl CoA formation and the citric acid cycle, all of the carbon atoms that enter cellular respiration in the glucose molecule are released in the form of CO2. Use this diagram to track the carbon-containing compounds that play a role in these two stages. a. Acetyl CoA b.Citrate c. Isocitrate d. alpha-ketoglutarate e. Succinyl CoA f. Succinate g. Fumarate h. Malate i. Oxaloacetate -

a. 2C b. 6C c. 6C d. 5C e. 4C f. 4C g. 4C h. 4C i. 4C (This diagram of the citric acid cycle shows the carbon skeletons of each intermediate. The net result of this complex series of reactions is the complete oxidation of the two carbon atoms in the acetyl group of acetyl CoA to two molecules of CO2.)

DIAGRAM pyruvate is oxidized to __(a)__ NAD+ is reduced to __(b)__ and __(c)__ is reduced to __(d)__ -

a. CO2 b. NADH c. FAD d. FADH2 (As in glycolysis, the electrons removed from carbon-containing intermediates during acetyl CoA formation and the citric acid cycle are passed to the electron carrier NAD+, reducing it to NADH. The citric acid cycle also uses a second electron carrier, FAD (flavin adenine dinucleotide), the oxidized form, and FADH2, the reduced form.)

Glycolysis

begins degradation process by breaking glucose down into two molecules of a compounds called pyruvate.

cellular respiration

breaking down organic molecules and using an electron transport chain for production of ATP, aerobic/anaerobic process exergonic (-deltaG, spontaneous, stores less energy)

aerobic respiration

catabolic process in which oxygen is consumed as a reactant with the organic fuel

PART F Select Figure 2 (Figure 1)from the drop-down menu above the table to see a graphical version of the data. Which cell type(s) had the highest rate of oxygen consumption? -

cells from rats with elevated thyroid hormone

PART G Which cell type(s) had the lowest rate of oxygen consumption? -

cells from rats with low thyroid hormone

Fermentation

degradation of sugars or other organic fuel that occurs without the use of oxygen

Oxidizing Agen

electron acceptor

Oxidizing agent

electron acceptor

NAD+

electron carrier, coenzyme, nicotinamide adenine dinucleotide Cycles easily between oxidized and reduced state Enzymes remove a pair of H atoms from substrate, enzyme delivers both e- and one proton to NAD + while other proton is released

Reducing Agent

electron donor

Reducing agent

electron donor

Oxidation

loss of electrons

Catabolic pathways

metabolic pathways that release stored energy by breaking down complex molecules

anaerobic respiration

process used by some prokaryotes that uses substances other than oxygen as reactants

Among the products of glycolysis, which compounds contain energy that can be used by other biological reactions? -

pyruvate, ATP, and NADH (ATP is the main product of cellular respiration that contains energy that can be used by other cellular processes. Some ATP is made in glycolysis. In addition, the NADH and pyruvate produced in glycolysis are used in subsequent steps of cellular respiration to make even more ATP.)

PART A To see patterns in the data from an experiment like this, it is helpful to graph the data. A bar graph is used instead of a line graph because each type of liver cell was independent of the others. But first, you must determine which variable should go on each axis of the graph. What variable did the researchers intentionally vary in the experiment, and what are the units for this variable? -

thyroid hormone level of the rats chosen for the experiment, in relative units (Thyroid hormone level is the independent variable, which goes on the x-axis.)

In mitochondrial electron transport, what is the direct role of O2? -

to function as the final electron acceptor in the electron transport chain (The only place that O2 participates in cellular respiration is at the end of the electron transport chain, as the final electron acceptor. Oxygen's high affinity for electrons ensures its success in this role. Its contributions to driving electron transport, forming a proton gradient, and synthesizing ATP are all indirect effects of its role as the terminal electron acceptor.)

Redox Reactions

transfer of one or more electrons from one reactant to another

What are the types of fermentation, that differ in the end products formed from pyruvate? -

The two common types are alcohol fermentation and lactic acid fermentation.

What happens if citrate accumulates in mitochondria? -

Then some of it passes into the cytosol and inhibits phosphofructokinase. This mechanism helps synchronize the rates of glycolysis and the citric acid cycle. As citrate accumulates, glycolysis slows down, and the supply of acetyl groups to citric acid cycle decreases. If citrate consumption increases, either because of a demand for more ATP or because anabolic pathways are draining off intermediates of the citric acid cycle, glycolysis accelerates and meets the demand. Metabolic balance is augmented by the control of enzymes that catalyze other key steps of glycolysis and the citric acid cycle. Cells are thrifty, expedient, and responsive in their metabolisms. It is simply amazing that we have understood so much. There is so much more to learn.

PART H Do the results in the graph support the researchers' hypothesis? -

Yes; cells that were exposed to elevated thyroid hormone levels showed increased oxygen consumption, indicating that the efficiency of the electron transport chain was reduced.

What molecular products indicate the complete oxidation of glucose during cellular respiration?

The release of six molecules of CO2 represents the complete oxidation of glucose. During the processing of two pyruvates to acetyl CoA, the fully oxidized carboxyl groups (¬COO-) are given off as 2 CO2. The remaining four carbons are released as CO2 in the citric acid cycle as citrate is oxidized back to oxaloacetate.

Electron Transport Chain

breaks the fall of electrons to oxygen into several energy-releasing steps that is used to make ATP

PART F Which of the following graphs correctly represents the data from the experiment? -

LOW 4.2 NORMAL 4.7 ELEVATED 8.7

What is the downhill route for most electrons during cellular respiration? -

Glucose -> NADH -> electron transport chain -> oxygen.

PART D Assuming that the y-axis tick marks will be separated by 1.0 (0.0, 1.0, 2.0, and so on), what is the largest value that should appear on the y-axis? -

9.0

The final electron acceptor of the electron transport chain that functions in aerobic oxidative phosphorylation is a. oxygen. b. water. c. NAD+. d. pyruvate.

A

When electrons flow along the electron transport chains of mi- tochondria, which of the following changes occurs? a. The pH of the matrix increases. b. ATP synthase pumps protons by active transport. c. The electrons gain free energy. d. NAD+ is oxidized.

A

What is beta oxidation? -

A metabolic sequence called beta oxidation breaks the fatty acids down to two-carbon fragments, which enter the citric acid cycle as acetyl CoA. NADH and FADH2 are also generated during beta oxidation; they can enter the electron transport chain, leading to further ATP production.

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+.

Most CO2 from catabolism is released during a. glycolysis. b. the citric acid cycle. c. lactate fermentation. d. electron transport.

B

The immediate energy source that drives ATP synthesis by ATP synthase during oxidative phosphorylation is the a. oxidation of glucose and other organic compounds. b. flow of electrons down the electron transport chain. c. H+ concentration gradient across the membrane holding ATP synthase. d. transfer of phosphate to ADP.

C

If the following redox reaction occurred, which compound would be oxidized? Reduced? C4H6O5 + NAD+ → C4H4O5 + NADH + H+

C4H6O5 would be oxidized and NAD+ would be reduced.

Oxidation During Cellular Respiration

Fuel is oxidized Oxygen is reduced

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.

Consider the NADH formed during glycolysis. What is the final acceptor for its electrons during fermentation? What is the final acceptor for its electrons during aerobic respiration? -

I believe the final acceptor in fermentation is NAD+, or possibly the lactate/ethanol molecules themselves. For aerobic respiration I believe the final electron acceptor is oxygen. [9.5 - 1] The final acceptor for its electrons during fermentation is a derivative of pyruvate, such as acetaldehyde during alcohol fermentation, or pyruvate itself during lactic acid fermentation. The final acceptor for electrons during aerobic respiration is oxygen.

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.

During intense exercise, can a muscle cell use fat as a concentrated source of chemical energy. -

I would think so. When oxygen is present, the fatty acid chains containing most of the energy of a fat are oxidized and fed into the citric acid cycle and the electron transport chain. However, during intense exercise, oxygen is scarce in muscle cells, so ATP must be generated by glycolysis alone. (fermentation! this is why you begin to wear down over time. I wonder if athletes will be able to take shots of oxygen into their bodies in order to keep their bodies producing ATP). A very small part of the fat molecule, the glycerol backbone, can be oxidized via glycolysis, but the amount of energy released by this portion is insignificant compared to that released by the fatty acid chains. (This is why moderate exercise, staying below 70% maximum heart rate, is better for burning fat, because enough oxygen remains available to the muscles. (little confused.)

How does the cell go about controlling catabolism? -

If the cell is working hard and its ATP concentration begins to drop, respiration speeds up (in order to produce more ATP?). When there is plenty of ATP to meet demand, respiration slows down, sparing valuable organic molecules for other functions Again, control is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway. One important switch is the phosphofructokinase, the enzyme that catalyzes step 3 of glycolysis. That is the first step that commits the substrate irreversibly to the glycolytic pathway. By controlling the rate of this step, the cell can speed up or slow down the entire catabolic process. Phosphofructokinase can be thus considered the pacemaker of respiration.

What happens to all of the organic molecules of food that are not used to make ATP? -

In addition to calories, food must also provide the carbon skeletons that cells require to make their own molecules. Some organic monomers obtained from digestion can be used directly For example, amino acids from the hydrolysis of proteins in food can be incorporated into the organism's own proteins.Often, however, the body needs specific molecules that are not present as such in food.

In the last stage of cellular respiration, oxidative phosphorylation, all of the reduced electron carriers produced in the previous stages are oxidized by oxygen via the electron transport chain. The energy from this oxidation is stored in a form that is used by most other energy-requiring reactions in cells. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of oxidative phosphorylation. -

NET INPUT -NADH -ADP -O₂ NET OUTPUT -NAD⁺ -ATP -CO₂ -Water NOT INPUT OR OUTPUT -Pyruvate -Glucose -Acetyl CoA -Coenzyme A -CO₂. (In oxidative phosphorylation, the NADH and FADH2 produced by the first three stages of cellular respiration are oxidized in the electron transport chain, reducing O2 to water and recycling NAD+ and FAD back to the first three stages of cellular respiration. The electron transport reactions supply the energy to drive most of a cell's ATP production.)

In acetyl CoA formation, the carbon-containing compound from glycolysis is oxidized to produce acetyl CoA. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of acetyl CoA formation. -

NET INPUT -NAD⁺ -coenzyme A -pyruvate NET OUTPUT -NADH -acetyl CoA -CO₂ NOT INPUT OR OUTPUT -O₂ -ADP -glucose -ATP (In acetyl CoA formation, pyruvate (a product of glycolysis) is oxidized to acetyl CoA, with the reduction of NAD+ to NADH and the release of one molecule of CO2.)

What are obligate anaerobes? -

These are organisms that carry out only fermentation or anaerobic respiration. In fact, these organisms cannot survive in the presence of oxygen, some forms of which can actually be toxic (wow imagine that - life that doesn't need oxygen to exist) if protective systems are not present in the cell.

What are facultative anaerobes? -

These are organisms, including yeasts and many bacteria, that can make enough ATP to survive using either fermentation or respiration. On the cellular level, our muscle cells behave as facultative anaerobes. In such cells, pyruvate is a fork in the metabolic road that leads to alternative catabolic routes. Under aerobic conditions, pyruvate can be converted to acetyl CoA, and oxidation continues in the citric acid cycle via aerobic respiration. Under anaerobic conditions, lactic acid fermentation occurs: Pyruvate is diverted from the citric acid cycle, serving instead as an electron acceptor to recycle NAD+. To make the same amount of ATP, a facultative anaerobe has to consume sugar at a much faster rate when fermenting than when respiring.

What happens to compounds that are formed as intermediates of glycolysis and the citric acid cycle? -

These compounds can be diverted into anabolic pathways as precursors from which the cell can synthesize the molecule it requires. For example, humans can make about half of the 20 amino acids in proteins by modifying compounds siphoned away from the citric acid cycle; the rest are "essential amino acids" that must be obtained in the diet. Also, glucose can be made from pyruvate, and fatty acids can be synthesized from acetyl CoA. Of course these anabolic, or biosynthetic, pathways do not generate ATP, but instead consume it.

What makes fats such a great source of energy? -

This is due in large part due to their chemical structure and the high energy level of their electrons (equally shared between carbon and hydrogen) compared to those of carbohydrates. A gram of fat oxidized by respiration produces more than twice as much ATP as a gram of carbohydrate. Unfortunately, this also means that a person trying to lose weight must work hard to use up fat stored in the body because so many calories are stockpiled in each gram of fat. Its like a double edged sword. While fats are a great source of energy, they are also twice as hard to get rid of as regular carbohydrates.

9.6 4. During intense exercise, can a muscle cell use fat as a concentrated source of chemical energy? Explain.

When oxygen is present, the fatty acid chains containing most of the energy of a fat are oxidized and fed into the citric acid cycle and the electron trans- port chain. During intense exercise, however, oxygen is scarce in muscle cells, so ATP must be generated by glycolysis alone. A very small part of the fat molecule, the glycerol backbone, can be oxidized via glycolysis, but the amount of energy released by this portion is insignificant compared to that released by the fatty acid chains. (This is why moderate exercise, staying below 70% maximum heart rate, is better for burning fat—because enough oxygen remains available to the muscles.)

Under what circumstances might your synthesize fat molecules? -

When we consume more food than necessary for metabolic processes, our body synthesizes fat as a way of storing energy for later use.

9.6 2. Under what circumstances might your body synthesize fat molecules?

Whenweconsumemore food than necessary for metabolic processes, our body synthesizes fat as a way of storing energy for later use.

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.

Reduction

addition of electron

Which reactions in glycolysis are the source of energy for the formation of ATP and NADH?

he oxidation of the three-carbon sugar, glyceraldehyde 3-phosphate, yields energy. In this oxidation, electrons and H+ are transferred to NAD+, forming NADH, and a phosphate group is attached to the oxidized substrate. ATP is then formed by substrate-level phosphorylation when this phosphate group is trans- ferred to ADP.

PART B What variable responded to thyroid hormone level (the independent variable), and what are the units for this variable? -

oxygen consumption rate of liver cells, in nmol O2/min • mg cells (Oxygen consumption rate is the dependent variable, which goes on the y-axis.)

Respiration

the oxidation of glucose and other molecules in food