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CELLULAR RESPIRATION Student Packet
SUMMARY ALL LIVING SYSTEMS REQUIRE CONSTANT INPUT OF FREE ENERGY • Cellular respiration is a catabolic pathway in which glucose and other organic fuels (such as starch, proteins and
fats) are oxidized to produce chemical energy in the form of ATP. • Hydrolysis of ATP releases a large amount of free energy and powers endergonic metabolic reactions required
to maintain organization, growth and reproduction. Excess of free energy results in storage and growth while insufficient acquired free energy results in loss of mass and ultimately death.
o ATP ⇌ ADP + Pi + energy ∆G for ATP hydrolysis = -7.3 kcal/mol
• Cellular respiration involves a series of redox reactions which transfer large amounts of energy. In oxidation, a molecule loses electrons by transferring them to another molecule, which gains electrons and thus undergoes reduction. Coenzymes NAD+ and FAD are the key electron acceptors/coenzymes in cellular respiration.
o NAD+ + H+ + 2e-⇌ NADH and FAD + 2e- + 2H+ ⇌ FADH2
• Two types of cellular respiration are aerobic and anaerobic. Aerobic respiration breaks down glucose in the presence of oxygen, releasing up to 32 molecules of ATP per 1 glucose molecule: C6H12O6 + O2 → CO2 + H2O + ATP
AEROBIC RESPIRATION occurs in three stages: 1. Glycolysis (in cytosol) harvests chemical energy by
oxidizing glucose to pyruvate. 2. Oxidation of pyruvate and Krebs cycle (a.k.a. citric
acid cycle) complete the breakdown of pyruvate in the matrix of mitochondria. Most of the released energy is used to form NADH and FADH2.
3. In oxidative phosphorylation, electrons delivered by coenzymes NADH and FADH2 are passed to a series of electron acceptors as they move toward the terminal electron acceptor, oxygen. The passage of electrons is accompanied by the formation of a proton gradient across the inner mitochondrial membrane. The flow of protons back to the mitochondrial matrix through ATP synthase generates large amounts of ATP. (In contrast, ATP molecules in steps 1 and 2 are produced through substrate level phosphorylation. In substrate level phosphorylation, a phosphate group is transferred from a substrate to ADP, forming ATP).
Aerobic vs Anaerobic Respiration
1. Glycolysis 2. Oxidation of Pyruvate and Krebs Cycle
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3. Oxidative Phosphorylation ANAEROBIC RESPIRATION (a.k.a. FERMENTATION) allows cells to break down glucose without oxygen as it produces 2 ATP molecules per one molecule of glucose in the cytosol. In anaerobic respiration, glycolysis is followed by alcohol or lactic acid fermentation. In the process, NAD+ is regenerated from NADH so that glycolysis can continue. • Glycolysis is the first step of both aerobic and anaerobic respiration. It occurs in nearly all organisms and is
thought to have evolved in ancient prokaryotes before there was O2 in the atmosphere.
ALCOHOL FERMENTATION:
LACTIC ACID FERMENTATION:
.
• Control of cellular respiration is based on regulating the activity of enzymes at strategic points in the catabolic pathways. Feedback inhibition is a common mechanism of regulation.
ATP Synthase
Feedback Inhibition
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MULTIPLE CHOICE QUESTIONS
1. Cellular respiration in eukaryotes involves a series of coordinated enzyme-catalyzed reactions that harvest free energy from simple carbohydrates. Which of the following events is the last step of aerobic cellular respiration? a. Pyruvate is transported from the cytoplasm to the mitochondrion where further oxidation occurs.
b. Electrons that are extracted in the series of Krebs cycle reactions are carried by NADH and FADH2 to the electron transport chain, followed by chemiosmosis.
c. Glycolysis rearranges the bonds in glucose molecules, releasing free energy to form ATP and resulting
in the production of pyruvate.
d. In the Krebs cycle, carbon dioxide is released from organic intermediates. ATP is synthesized from ADP
and inorganic phosphate via substrate level phosphorylation and electrons are captured by
coenzymes.
2. The electron transport chain captures free energy from electrons in a series of coupled reactions that
establish an electrochemical gradient across membranes. Which of the following is incorrect about the
electron transport chain in cellular respiration?
a. The electron transport chain occurs in the inner mitochondrial membrane in eukaryotes and in the
plasma membrane of prokaryotes.
b. Electrons delivered by NADH and FADH2 are passed to a series of electron acceptors as they move
toward the terminal electron acceptor, oxygen.
c. The passage of electrons is accompanied by the formation of a region of high proton concentration in
the mitochondrial matrix.
d. Decoupling oxidative phosphorylation from electron transport is involved in thermoregulation.
3. Organisms use free energy to maintain organization, grow and reproduce. The graph below shows the
relationship between the basal metabolic rate (BMR) per unit body mass and the size of the organism. Which
organism must eat a larger proportion of its weight in food each day?
a. Shrew
b. Elephant
c. Cat
d. Rat
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4. The chart below compares the annual energy expenditures for various functions of several animals. According to the data, a 4-kg male Adelie penguin has higher energy expenditure than a similarly-sized female eastern indigo snake.
The observed trend is primarily due to differences in a. relative size. b. mode of nutrition. c. mode of internal temperature regulation. d. mode of ATP production.
5. Phosphofructokinase (PFK) is an important regulatory enzyme that phosphorylates fructose-6-phosphate to produce fructose-1,6-bisphosphate during the 3rd step of glycolysis. Which of the following molecules might provide negative feedback inhibition on the phosphofructokinase enzyme? PFK Fructose-6-phosphate fructose-1,6-bisphosphate
a. ADP b. Fructose-6-phosphate c. Glucose d. ATP
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6. Glucose-fed yeast cells are moved from an aerobic environment to an anaerobic environment. What is the least
likely consequence of this move? a. Yeast cells will be able to produce ATP without oxygen. b. Yeast cells will generate ATP by alcohol fermentation. c. Yeast cells will consume glucose at a slower rate. d. Yeast cells will continue to undergo glycolysis.
7. The diagram below gives an example of how the exergonic reaction of ATP hydrolysis is used to drive the
endergonic synthesis of the amino acid glutamine.
How does ATP provide energy for this process? a. ATP fits into the active site of a reactant and catalyzes the endergonic reaction. b. A phosphate group from ATP is transferred to a reactant of the endergonic reaction, making it more
reactive. c. Free energy becomes available for the endergonic reaction by the conversion of ADP→ATP. d. ATP acts as a coenzyme that accepts electrons from the substrate.
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MATH GRID IN
1. ∆G for the following reaction is 3.6 kcal/mol:
glucose + Pi → glucose-6-phosphate + H2O. 1 ATP will be used to drive this reaction and ∆G for ATP hydrolysis is -7.3 kcal/mol. Calculate the ∆G for the overall reaction. Give your answer to the nearest tenth.
SHORT FREE RESPONSE QUESTIONS
1. Usually, vertebrates get their energy aerobically, with the circulatory system supplying oxygen. However, conditions can become anaerobic, such as in a heart muscle during a heart attack because of the inadequate supply of blood. Describe the mechanism of anaerobic cellular respiration in the heart muscle and predict the consequence of prolonged lack of blood supply to the heart muscle.
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2. Mitochondria are organelles where aerobic cellular respiration occurs and most ATP is generated. Discuss THREE structural features that allow mitochondria to capture and transform energy.
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LONG FREE RESPONSE QUESTION
An agricultural biologist was evaluating two newly developed varieties of wheat as potential crops. In an experiment, seedlings were germinated on moist paper towels at 20°C for 48 hours. Oxygen consumption of the two-day-old seedlings was measured at different temperatures. The data are shown in the graph below.
a. Calculate the rates of oxygen consumption in ml/min for each variety of wheat at 7°C and at 17°C. Show
your work (including your setup and calculation). b. Explain the relationship between metabolism and oxygen consumption. Discuss the effect of temperature
on metabolism for each variety of seedlings. c. In a second experiment, variety A seedlings at both temperatures were treated with a chemical that
prevents NADH from being oxidized to NAD+. Predict the most likely effect of the chemical on metabolism and oxygen consumption of the treated seedlings. Explain your prediction.
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