Energy II: Kreb's Cycle and Electron Transport Chain

Energy II: Kreb's Cycle and Electron Transport Chain

Tutorial 19 Learning Objectives

  • Illustrate the importance of redox (reduction-oxidation) reactions in cellular respiration.

  • Explain the role of electron carriers in biochemical processes.

  • List the main inputs and outputs of the Krebs Cycle (Citric Acid Cycle).

  • Diagram the structure of the mitochondrial membrane and illustrate the flow of electrons through the Electron Transport Chain (ETC).

  • Demonstrate how the hydrogen ion gradient across the inner mitochondrial membrane is produced.

  • Explain how ATP is produced through oxidative phosphorylation.

  • Describe how other molecules can enter the pathways of cellular respiration at various points.

Glycolysis Review Questions

Question #1

  • In which organisms does glycolysis occur?

    • Answer Options:

    • Neither aerobic nor anaerobic organisms.

    • Both aerobic and anaerobic organisms.

    • Aerobic organisms only.

    • Anaerobic organisms only.

Question #2

  • By the end of glycolysis, most of the energy contained in the original glucose molecule is now contained in:

    • Answer Options:

    • NADH

    • Pyruvate

    • ATP

    • Glucose

Cellular Respiration Review Question

  • Aerobic cellular respiration involves the flow of electrons from one chemical molecule to another: which of the following best describes this process?

    • Answer Options:

    • Electrons are transferred from glucose to carbon dioxide.

    • Electrons are transferred from oxygen to water.

    • Electrons are transferred from glucose to oxygen.

    • Electrons are transferred from oxygen to glucose.

Redox Reaction Practice Question

MCAT Question

  • In the redox reaction: pyruvate + NADH + H+ → lactate + NAD+, which reactant is oxidized and which is reduced?

    • Answer Options:

    • NADH is reduced and pyruvate is oxidized.

    • Lactate is reduced and NAD+ is oxidized.

    • Pyruvate is reduced and NADH is oxidized.

    • Lactate is reduced and pyruvate is oxidized.

Mitochondria

  • Pyruvate is converted to Acetyl CoA in the mitochondria if O2 is present.

Learning Guide #1: Kreb’s Cycle Location

  • The Krebs Cycle occurs in the mitochondrial matrix.

  • In mitochondria, Pyruvate is converted to Acetyl CoA, which also produces NADH and CO2.

  • Key Point: Glycolysis produces TWO molecules of pyruvate; thus, TWO molecules of Acetyl CoA enter the cycle for each ONE molecule of glucose.

The Krebs Cycle

  • The energy in Acetyl CoA is converted into the following:

    • Main Products:

    • 8 NADH

    • 2 FADH2

    • 2 ATP

    • 6 CO2, which accounts for all carbon contained in glucose released as CO2 during the Krebs Cycle.

Learning Guide #2: Total Products

  • Products produced per molecule of glucose, including conversion to Acetyl CoA and Kreb’s Cycle:

    1. 8 NADH

    2. 2 FADH2

    3. 2 ATP

    4. 6 CO2

Learning Guide #3: Electron Transfer

  • Electrons from the Krebs Cycle are transferred to the electron transport chain through:

    • Reduction of NAD+ and FAD.

Learning Guide #4: Electron Transport Chain (ETC)

  • The ETC converts energy in electron carriers into ATP:

    • NADH and FADH2 are oxidized back to NAD+ and FAD by proteins in the ETC.

    • The ETC is a series of redox reactions where electrons release energy as they move along the chain.

    • Final Electron Acceptor: Oxygen (O2), reduction of which produces H2O.

Electronegativity in the ETC

  • Electronegativity of molecules in the ETC is key as electrons are transferred.

ETC Practice Questions

Question #1

  • True or False: An electron just given up by NADH to the electron transport chain has more energy than one that is picked up by oxygen at the end of the ETC.

Question #2

  • Which of these molecules involved in cellular respiration is the most electronegative?

    • Answer Options:

    • Carbon Dioxide

    • Glucose

    • Oxygen

    • Water

Learning Guide #6: Mitochondrial Membrane

  • Mitochondria are enclosed by two membranes, each with a unique collection of embedded proteins.

    • The inner membrane is highly folded, containing embedded proteins that function in ATP synthesis.

    • The folds, known as cristae, increase the surface area, enhancing the mitochondrion's ability to produce ATP.

Learning Guide #8: Mitochondrial Structure and Function

  • The proteins of the ETC are located in the inner mitochondrial membrane, while the Krebs Cycle occurs in the mitochondrial matrix.

    • Concentration Gradient: Hydrogen ions (H+) are pumped across the inner membrane, generating a concentration gradient:

    • High [H+] in the intermembrane space, Low [H+] in the matrix.

    • This gradient creates a voltage difference due to the charge of H+ ions.

    • Greater concentration differences yield higher voltage.

Diffusion and ATP Production

  • The diffusion of H+ across the inner membrane into the matrix through ATP synthase releases free energy, which powers ATP formation.

    • Type of phosphorylation: Oxidative Phosphorylation through ATP Synthase.

ETC Practice Question #3

  • What powers the ATP synthase rotary motor?

    • Answer Options:

    • Pyruvate

    • The H+ gradient

    • ATP hydrolysis

    • Glucose

ETC Practice Question #4

  • The voltage between the inner mitochondrial membrane and matrix is variable. Which condition would lead to a decrease in voltage?

    • Answer Options:

    • An increase in NADH

    • A decrease in ATP synthesis

    • An increase in oxygen

    • A decrease in oxygen

Learning Guide #9: Conditions Favoring ETC Activity

  • Cellular conditions that favor increased activity of the electron transport chain and chemiosmosis include:

    • Low oxygen concentrations

    • Low NADH concentrations

    • High NAD+ concentrations

    • High ADP concentrations

Learning Guide #10: Effects of Cyanide on Cellular Respiration

  • Cyanide binds to an electron carrier within the ETC, blocking electron movement, leading to cessation of glycolysis and the Krebs Cycle as well.

    • The primary reasons for the halting of these stages include:

    • They run out of NAD+ and FAD.

Other Molecules in Cellular Respiration

  • Other molecules are processed using cellular respiration but enter at different points:

    • Pathways Include:

    • Proteins - Amino Acids

    • Polysaccharides - Glucose

    • Fats - Glycerol, Fatty Acids

Summary of Kreb’s Cycle

  • The Kreb’s Cycle occurs in the mitochondrial matrix.

  • Pyruvate is converted to Acetyl CoA before entering the cycle, producing 1 NADH and 1 CO2 per molecule of pyruvate.

    • Each glucose molecule results in TWO pyruvates.

  • CO2 exhaled is produced by the Kreb’s cycle, derived from glucose, and these atoms are released from our bodies.

  • Each molecule of Pyruvate converted to Acetyl CoA yields:

    • 4 NADH, 1 FADH2, 2 CO2, and 1 ATP.

Summary of Electron Transport Chain

  • Components of the ETC are embedded in the inner mitochondrial membrane.

  • Electron carriers NADH and FADH2 oxidize back to NAD+ and FAD, releasing electrons to components of the ETC.

    • Each component of the ETC is more electronegative to allow electrons to move between components spontaneously.

    • Larger electronegativity differences release more energy.

  • O2 acts as the terminal electron acceptor, which allows for maximal energy release.

Summary of Oxidative Phosphorylation

  • Movement of electrons from electron carriers (NADH, FADH2) to more electronegative components releases energy used for:

    • Active transport of H+ ions out of the mitochondrial matrix into the intermembrane space, creating a potential energy gradient.

  • H+ diffusion back into the matrix is facilitated by ATP synthase, converting potential energy into kinetic energy that powers ATP formation.

Respiration Practice Questions

Question #1

  • Regarding weight loss of 15 pounds: Where did those 15 pounds of atoms go?

    • Answer Options:

    • The atoms were released as CO2 and H2O.

    • The atoms were converted to heat and then released.

    • The atoms were converted to ATP, which weighs less than fat.

    • The atoms were broken down into fatty acids and glycerol, then eliminated from the body.

Question #2

  • During alcohol metabolism in humans, how many total molecules of NADH are produced in the catabolism of one molecule of ethanol (assumes Krebs cycle and ETC are functioning efficiently)?

    • Answer Options:

    • 3

    • 4

    • 5

    • 6

Respiration Practice Question Answer

  • In the catabolism of ethanol, reactions yield:

    • Ethanol → Acetylaldehyde (producing 1 NADH)

    • Acetylaldehyde → Acetate (producing 1 NADH)

    • Acetate → Acetyl CoA (producing 1 NADH)

    • Acetyl CoA → Krebs Cycle (producing 3 NADH + 1 FADH2).

  • Total NADH produced = 5 NADH.

Glycolysis Review Questions

  • Question #1: In which organisms does glycolysis occur?

    • Answer: Both aerobic and anaerobic organisms.

  • Question #2: By the end of glycolysis, most of the energy contained in the original glucose molecule is now contained in:

    • Answer: Pyruvate

Cellular Respiration Review Question

  • Aerobic cellular respiration involves the flow of electrons from one chemical molecule to another: which of the following best describes this process?

    • Answer: Electrons are transferred from glucose to oxygen.

Redox Reaction Practice Question (MCAT Question)

  • In the redox reaction: pyruvate + NADH + H+ → lactate + NAD+, which reactant is oxidized and which is reduced?

    • Answer: Pyruvate is reduced and NADH is oxidized.

ETC Practice Questions

  • Question #1: True or False: An electron just given up by NADH to the electron transport chain has more energy than one that is picked up by oxygen at the end of the ETC.

    • Answer: True

  • Question #2: Which of these molecules involved in cellular respiration is the most electronegative?

    • Answer: Oxygen

ETC Practice Question #3

  • What powers the ATP synthase rotary motor?

    • Answer: The H+ gradient

ETC Practice Question #4

  • The voltage between the inner mitochondrial membrane and matrix is variable. Which condition would lead to a decrease in voltage?

    • Answer: A decrease in oxygen

Respiration Practice Questions

  • Question #1: Regarding weight loss of 15 pounds: Where did those 15 pounds of atoms go?

    • Answer: The atoms were released as CO2 and H2O.

  • Question #2: During alcohol metabolism in humans, how many total molecules of NADH are produced in the catabolism of one molecule of ethanol (assumes Krebs cycle and ETC are functioning efficiently)?

    • Answer: 5

Glycolysis Review Questions

  • Question #1: In which organisms does glycolysis occur?

    • Answer: Both aerobic and anaerobic organisms.

  • Question #2: By the end of glycolysis, most of the energy contained in the original glucose molecule is now contained in:

    • Answer: Pyruvate

Cellular Respiration Review Question

  • Aerobic cellular respiration involves the flow of electrons from one chemical molecule to another: which of the following best describes this process?

    • Answer: Electrons are transferred from glucose to oxygen.

Redox Reaction Practice Question (MCAT Question)

  • In the redox reaction: pyruvate + NADH + H+

\rightarrow

lactate + NAD+, which reactant is oxidized and which is reduced?
* Answer: Pyruvate is reduced and NADH is oxidized.

ETC Practice Questions

  • Question #1: True or False: An electron just given up by NADH to the electron transport chain has more energy than one that is picked up by oxygen at the end of the ETC.

    • Answer: True

  • Question #2: Which of these molecules involved in cellular respiration is the most electronegative?

    • Answer: Oxygen

ETC Practice Question #3

  • What powers the ATP synthase rotary motor?

    • Answer: The H+ gradient

ETC Practice Question #4

  • The voltage between the inner mitochondrial membrane and matrix is variable. Which condition would lead to a decrease in voltage?

    • Answer: A decrease in oxygen

Respiration Practice Questions

  • Question #1: Regarding weight loss of 15 pounds: Where did those 15 pounds of atoms go?

    • Answer: The atoms were released as CO2 and H2O.

  • Question #2: During alcohol metabolism in humans, how many total molecules of NADH are produced in the catabolism of one molecule of ethanol (assumes Krebs cycle and ETC are functioning efficiently)?

    • Answer: 5