Chapter 9
In general terms, distinguish between fermentation and cellular respiration.
Cellular respiration requires oxygen, fermentation can be undergone without oxygen
Explain why ATP is required for the preparatory steps of glycolysis.
Two molecules of ATP are consumed as glucose is split into two three-carbon sugars (glyceraldehyde 3-phosphate).The conversion of these molecules to pyruvate produces two NADH and four ATP by substrate-level phosphorylation.
Describe the ATP cycle
It begins with carbohydrate metabolism which starts with glucose (simple sugar). As it goes through glycolysis (an anaerobic - without oxygen- process) it produces a net of 2 ATP and reduces (adds hydrogen ions) to the enzyme NAD to form NADH + H+. The end result is two 3-carbon molecules of pyruvic acid. At that point if there is no oxygen the process turns the pyruvic acid into lactic acid and it is stored in the muscles. If there is oxygen, you move to the next process called the Kreb's cycle. The pyruvic acid loses one carbon to carbon dioxide and reduces one NAD to NADH + H+ and also takes in a substance called Acetyl CoA. which has two carbons (remember one of the 3 from pyruvic acid went to CO2). Acetyl CoA picks up the result of the previous turn of the Kreb's cycle which is a 4 carbon molecule of oxaloacetic acid. The two combine to form a 6 carbon molecule of citric acid (hence the other name - the Citric Acid Cycle) which is the beginning of the cycle. As the cycle goes around 3 NAD's pick up hydrogen and become NADH + H+, an enzyme of FAD picks up a hydrogen and becomes FADH2, 2 CO2 molecules are released and one ADP is phosphorlyzed (gains phosphate) and becomes 1 ATP. These are the results of ONE turn of the Kreb's cycle. Remember there were two molecules of pyruvic acid, so it takes TWO revolutions of the Kreb's cycle to metabolize 1 molecule of glucose and the results are, therefore, 6 NADH + H+, 2 FADH2, 4 CO2's and 2 ATP's. The last part is the Electron Transport Chain (ETC). In the ETC, an NADH + H+ and and FADH2 are oxidized (lose their hydrogens) and the hydrogens split apart. The positively charged protons go through the membrane via cytochromes which take from them inside to outside the membrane. (This occurs in the inner membrane of the mitochondria so the protons to to the intermembrane space between the inner membrane and outer membrane of the mitochondria.) Due to the protons, the charge outside the membrane is positive. Electrons stay inside and the charge is negative. The electrons move from one cytochrome to the next and the next, down the line, becoming more negatively charged each time. The negative charge, pulls the positively charged proteins along with the electrons down the membrane. When they reach the ATP Synthase complex, the negative charge pulls the protons inside. As they pass through ATP Synthase, they make it spin. The spinning pulls ADP's and phosphates into it and it creates 32-38 ATP's. The hydrogens inside bind with oxygen that is also inside the membrane and form water. This is the main process. Keep in mind that proteins break down into amino acids and lipids break down into glycerol and fatty acids, all of which can enter at either the glycolysis stage or where Acetyl CoA joins up and go through the Kreb's cycle and ETC to be turned into energy (ATP).
Describe the evidence that suggests that glycolysis is an ancient metabolic pathway.
It occurs, with variations, in nearly all organisms, both aerobic and anaerobic. The wide occurrence of glycolysis indicates that it is one of the most ancient known metabolic pathways.[3] It occurs in the cytosol of the cell.
Describe the structure and function of the ATP synthase
o Each are made up of multiple polypeptides. The 4 are: Stator: H+ ions flowing down their gradient enter a half channel in a stator which is anchored in the membrane Rotor: H+ ions enter binding sites within a rotor, changing the shape of each subunit so that the rotor spins within the membrane Internal rod: spinning of the rotor causes an internal rod to spin as well. This rod extends like a stalk into the knob below it, which is held stationary by part of the stator Catalytic knob: turning of the rod activates catalytic sites in the knob that produce ATP from ADP and phosphate
Compare the processes of fermentation and cellular respiration. What is the mechanism of ATP synthesis in fermentation?
o Fermentation is the process of deriving energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. o This is in contrast to cellular respiration, where electrons are donated to an exogenous electron acceptor, such as oxygen, via an electron transport chain
Explain why it is not possible to state an exact number of ATP molecules generated by the oxidation of glucose.
o Phosphorylation and the redox reactions are not directly coupled to each other, so the ratio of number of NADH to number of ATP is not a whole number. o The ATP yield varies slightly depending on the type of shuttle used to transport electrons from the cytosol into the mitochondrion o The proton-motive force generated by the redox reactions of respiration may drive other kinds of work, such as mitochondrial uptake of pyruvate from the cytosol
Explain in general terms how redox reactions are involved in energy exchanges.
Electrons are transferred from one atom to another, or move to a lower energy orbital on the covalent bond of an atom
List the products of the citric acid cycle. Explain why it is a cycle
6NADH + 4CO2 + 2ATP + 2FADH2 . It is a cycle because the pyruvic acids go through twice
Write the summary equation for cellular respiration. Write the specific chemical equation for the degradation of glucose.
C6H12O6 (glucose) + 6O2 (oxygen) ---------> 6CO2 (carbon dioxide) + 6H2O (water) + energy; same just minus energy
Explain the role of catabolic and anabolic pathways in cellular metabolism.
Catabolic pathways release energy by breaking down complex molecules to simpler compounds. Anabolic pathways consume energy to build complicated molecules from simpler ones
Describe the point at which the carbons of glucose is completely oxidized during cellular respiration.
Glucose is completely oxidized after chemiosmosis
Name the three stages of cellular respiration and state the location in the eukaryotic cell where each stage occurs
Glycolysis, citric acid cycle, oxidative phosphorylation Glycolysis is located in the cytosol, citric acid cycle and oxidative phosphorylation is located in the mitochondrial matrix.
Summarize the net ATP yield from the oxidation of a glucose molecule by constructing an ATP ledger.
Glycolysis--2 net ATP from substrate-level phosphorylation 2 NADH yields 6 ATP (assuming 3 ATP per NADH) by oxidative phosphorylation;Transition Reaction--2 NADH yields 6 ATP (assuming 3 ATP per NADH) by oxidative phosphorylation;Citric Acid Cycle--2 ATP from substrate-level phosphorylation 6 NADH yields 18 ATP (assuming 3 ATP per NADH) by oxidative phosphorylation 2 FADH2 yields 4 ATP (assuming 2 ATP per FADH2) by oxidative phosphorylation Total Theoretical Maximum Number of ATP Generated per Glucose in Prokaryotes--38 ATP: 4 from substrate-level phosphorylation; 34 from oxidative phosphorylation; In eukaryotic cells, the theoretical maximum yield of ATP generated per glucose is 36 to 38, depending on how the 2 NADH generated in the cytoplasm during glycolysis enter the mitochondria and whether the resulting yield is 2 or 3 ATP per NAD
Describe how the carbon skeleton of glucose changes as it proceeds through glycolysis.
In glycolysis, the skeleton will change in two ways. The ring must be opened, and then the glucose will be cleaved into 2 3-carbon molecules known as glyceraldehyde. These are straight chained.
In general terms, explain how the exergonic "slide" of electrons down the electron transport chain is coupled to the endergonic production of ATP by chemiosmosis
In mitochondria, exergonic redox reactions produce the H+ gradient that drives the production of ATP
Compare the fate of pyruvate in alcohol fermentation and lactic acid fermentation
Pyruvate is changed into lactic acid in animal fermentation. In plant fermentation it is changed into alcohol and carbon dioxide
Describe where pyruvate is oxidized to acetyl CoA, what molecules are produced, and how this process links glycolysis to the citric acid cycle
Pyruvate is decarboxylated. The oxidized carboxyl group is converted to CO2 which is released. 2 remaining carbon molecules are oxidized into acetate. The e-s are stored temporarily in coenzyme NAD+ (NADH after reduction). Coenzyme A attaches to the acetate, forming Acetyl-CoA. Acetyl-CoA is the first substrate in the citric acid cycle
Explain where and how the respiratory electron transport chain creates a proton gradient
The proton gradient is produced by the movement of electrons along the electron transport chain. The chain is an energy converter that uses the exergonic flow of electrons to pump H+ from the matrix into the intermembrane space. The protons pass back to the matrix through a channel in ATP synthase, using the exergonic flow of H+ to drive the phosphorylation of ADP. Thus, the energy stored in a H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis.
State the basic function of fermentation
To oxidize organic fuel and to generate ATP without the use of oxygen
Describe how food molecules other than glucose can be oxidized to make ATP. Why does fat have more calories per gram than carbohydrate?
Each NADH and FADH2 molecule formed represents stored energy... contain high energy electrons from food molecules which are carried to an electron transport chain; Plants manufacture their own food by photosynthesis using energy from sunlight. Cells harvest the chemical energy stored in organic molecules and use it to regenerate ATP, the molecule that drives most cellular work. ADP + P + energy ATP
Explain how glycolysis and the citric acid cycle can contribute to anabolic pathways.
Glycolysis and the citric acid cycle contribute by making ATP, they also generate electrons for the Electron Transport Chain (ETC). The ETC then uses those electrons to make a proton gradient in the mitochondria which in turn powers the enzyme ATP-synthase to make a whole bunch of ATP.
Describe the role of NAD+ in cellular respiration
NAD acts as an electron and hydrogen carriers in some oxidation-reduction reactions.
In general terms, explain the role of the electron transport chain in cellular respiration
NADPH passes electrons to the electron transport chain, from which they eventually combine with hydrogen ions and oxygen to form water.
Define oxidation and reduction
Oxidation is the loss of an electron Reduction is gain of an electron
Explain how ATP production is controlled by the cell, and describe the role that the allosteric enzyme phosphofructokinase plays in the process.
Phosphofructokinase (PFK) is a glycolytic enzyme that catalyzes the irreversible transfer of a phosphate from ATP to fructose-6-phosphate: fructose-6-phosphate + ATP fructose-1,6-bisphosphate + ADP In part because of the irreversible nature of this step in glycolysis, PFK is the key regulatory enzyme for glycolysis. When ATP levels are high in the cell, the cell no longer needs metabolic energy production to occur. In this case, PFK's activity is inhibited by allosteric regulation by ATP itself, closing the valve on the flow of carbohydrates through glycolysis.
Distinguish between substrate-level phosphorylation and oxidative phosphorylation.
Substrate-level: production of ATP molecules via transfer of a phosphate group from an intermediate high-energy substrate directly to ADP. Oxidative: production of ATP molecules from the redox reactions of an electron transport chain. Gylcolysis and Krebs cycle use substrate-level phosphorylation. Electron transport chain uses oxidative phosphorylation.