Learning Objectives

1. Explain why the human body needs to eat.
   On the most basic level, you need to eat to get the energy required to survive
   • Energy is required for building macromolecules (like proteins & nucleic acids)
   • Energy is required for life-sustaining processes like active transport

2. Define the term “metabolism”
   Metabolism is the sum of all the chemical reactions that occur in your cells to keep you alive

3. Describe the function of chemical bonds.
   Foods store energy in their chemical bonds
   • By breaking those chemical bonds, that energy is released into your cells
   • Your cells can use that energy immediately or store it by forming new chemical bonds

4. Explain how the structure of ATP makes it good for storing & releasing energy.
   ATP = adenosine triphosphate
   • ATP has 3 phosphate groups, so it has A LOT of energy
   • ATP is made when the cell has extra energy

5. Explain what happens in catabolic & anabolic reactions.
   Catabolic reactions break large polymers into smaller monomers
   • These reactions release energy

Anabolic reactions build large polymers from smaller monomers
• These reactions require energy

6. Explain what happens in endergonic & exergonic reactions.
   Exergonic reactions release energy
   • This is because the products of the reactions have LESS energy than the reactants

Endergonic reactions require energy
• This is because the products of the reactions have MORE energy than the reactants

7. Describe the relationship between catabolic, anabolic, endergonic, and exergonic reactions.
   Catabolic & anabolic reactions are paired
   • The monomers made in catabolic reactions are used to build polymers in anabolic reactions

Exergonic & endergonic reactions are paired
• The energy released in exergonic reactions is used to power endergonic reactions

8. Explain how ATP & ADP are related.
   ADP = adenosine diphosphate
   • ADP has 2 phosphate groups, so it has some energy
   • ADP is made when the cell uses the energy in ATP (by removing one of its phosphate groups)

9. Explain what happens during redox reactions.
   Redox is a type of chemical reaction in which the oxidation states of a reactant change.
   Oxidation is the loss of electrons or an increase in the oxidation state.
   Reduction is the gain of electrons or a decrease in the oxidation state.

10. Write the overall chemical equation for cellular respiration.
    C6H12O6 + 6O2 --> 6CO2 + 6H2O + 36 or 38 ATP

11. Identify the location where each step of cellular respiration occurs in the cell.

    Step 1: glycolysis - Splits the glucose into pyruvate molecules
    Glycolysis is the initial glucose-breaking process
    • Many chemical reactions break its chemical bonds, rearrange its elements, and harvest some of its energy

    Step 2: pyruvate oxidation - Moves the pyruvates into the mitochondria & processes them
    Each 3-carbon pyruvate still has A LOT of energy • The pyruvates are transported into the mitochondria so that energy can be harvested

    Step 3: the Citric Acid (Krebs) Cycle - Remove energy-rich electrons from the process pyruvates
    The Citric Acid Cycle harvests all the remaining energy in Acetyl Coenzyme A (Acetyl CoA)

    Step 4: oxidative phosphorylation - Use the energy from those high-energy electrons to build ATP
    Oxidative phosphorylation is the only cellular respiration process that requires oxygen (O2)
    O2 is the final electron acceptor at the end of the Electron Transport Chain (ETC)
    • Energy-poor electrons are donated to O2, making space for other electrons to continue to move through the ETC
    • If oxygen was not present, electrons would build up in the Electron Transport Chain & electron carriers would remain permanently reduced

12. Differentiate between substrate-level phosphorylation & chemiosmosis.
    In glycolysis & the Citric Acid Cycle, ATP synthesis occurs using substrate-level phosphorylation
    • A phosphate group is removed from one molecule (the substrate)
    • It is then directly attached to ADP Mechanism: In substrate-level phosphorylation, an enzyme directly transfers a phosphate group from a substrate molecule to ADP, forming ATP. This process does not involve the use of an electrochemical gradient.
    Location: It occurs in the cytoplasm during glycolysis and in the mitochondrial matrix during the Krebs cycle for cellular respiration. In photosynthesis, it can occur in the stroma of chloroplasts during the Calvin cycle.
    Energy Source: The energy for substrate-level phosphorylation comes directly from the chemical energy in substrate molecules, which are often intermediates in metabolic pathways like glycolysis or the Krebs cycle.
    Oxygen Requirement: It does not directly require oxygen, so it can occur under both aerobic and anaerobic conditions.

    Oxidative phosphorylation uses the Electron Transport Chain (ETC) & Chemiosmosis
    • First, the ETC creates a proton (H+) concentration gradient across the inner mitochondrial membrane
    • Then, ATP synthase uses the energy of that gradient to build ATP in a process called chemiosmosis ATP Synthase is the ATP-generating protein of oxidative phosphorylation The concentration of H+ (protons) is very high in the intermembrane space & much lower in the matrix • ATP synthase – which is embedded in the inner mitochondrial membrane – allows protons to move back into the matrix
    • The energy that is released when these protons move back in is called proton motive force ATP synthase uses the power of proton motive force to create new ATP
    • It takes the movement of 4 protons (H+) to make 1 molecule of ATP

13. List the number of carbons found in glucose & pyruvate.
    Glucose: Glucose is a six-carbon (C6) sugar molecule. It's the starting material for glycolysis, where it undergoes enzymatic breakdown.

    Pyruvate: Pyruvate, the end product of glycolysis, is a three-carbon (C3) molecule. Each glucose molecule is broken down into two molecules of pyruvate during glycolysis.

14. Identify the starting materials & products created by each of these processes: glycolysis, pyruvate oxidation, the Citric Acid Cycle (a.k.a. Krebs Cycle), and the Electron Transport Chain (and oxidative phosphorylation).

    Glucose:
    Starting materials: glucose (C6H12O6) + 2 ATP + 2 NAD+ Oxygen (O2) is NOT required for this process!
    Ending materials: 2 pyruvate (C3H4O3) + 2 (net) ATP + 2 NADH • Technically, 4 ATP are made, but 2 ATP are required, so the cell only gains 2 ATP • This ATP is made through substrate-level phosphorylation
    Location: the cytoplasm
    Stored Forms of Energy: The energy from glucose is stored in the 2 ATPs (net gain) and 2 NADH produced.

    Pyruvate oxidation:
    Starting materials: 2 pyruvate + 2 NAD+ + 2 Coenzyme A complexes
    Ending materials: 2 acetyl coenzyme A (acetyl CoA) + 2 CO2 + 2 NADH
    Location: the mitochondrial matrix (a.k.a. its center)
    Stored Forms of Energy: Energy is stored in the high-energy electrons of NADH.

    the Citric Acid Cycle (a.k.a. Krebs Cycle):
    • REMEMBER: one glucose molecule makes two acetyl CoA’s!
    Starting materials: 2 acetyl CoA + 6 NAD+ + 2 FAD (+ oxaloacetate )
    Ending materials: oxaloacetate + 4 CO2 + 2 ATP + 6 NADH + 2 FADH2
    Location: the mitochondrial matrix (a.k.a. its center)
    Stored Forms of Energy: Energy is stored in the high-energy electrons of NADH and FADH2, and in the ATP produced.

    the Electron Transport Chain (and oxidative phosphorylation):
    Starting Materials: Electrons carried by NADH and FADH2, and Oxygen as the final electron acceptor
    Ending Materials: Water (from the reduction of oxygen) and approximately 36 ATP molecules (?)
    Location: Inner mitochondrial membrane
    Stored Forms of Energy: The energy is stored in the ATP produced. This stage harnesses the energy from an electrochemical gradient (proton gradient) across the inner mitochondrial membrane through chemiosmosis.

15. Explain the function of electron carriers in cellular respiration.
    The Electron Transport Chain (ETC) uses energy from electron carriers to create the H+ concentration gradient
    Electron carriers “capture” the energy from one chemical reaction & transport it to a different part of the cell to be used • Electron carriers are like the Uber for electrons In cellular respiration, the primary electron carriers are NAD+ / NADH & FAD / FADH2

16. Explain how electrons are used to build a proton gradient across the inner mitochondrial membrane.
    Electrons (from NADH & FADH2) travel through each of the ETC protein complexes. Their energy is used by the proteins to pump H+ ions (a.k.a. protons) into the intermembrane space. By the end of the ETC, the electrons no longer store any energy & are combined with O2

17. Explain how the movement of protons is used to build ATP.
    ATP Synthase is the ATP-generating protein of oxidative phosphorylation
    The concentration of H+ (protons) is very high in the intermembrane space & much lower in the matrix
    • ATP synthase – which is embedded in the inner mitochondrial membrane – allows protons to move back into the matrix
    • The energy that is released when these protons move back in is called proton motive force
    ATP synthase uses the power of proton motive force to create new ATP
    • It takes the movement of 4 protons (H+) to make 1 molecule of ATP

18. Describe the role of oxygen in the process of cellular respiration.
    Oxidative phosphorylation is the only cellular respiration process that requires oxygen (O2)
    O2 is the final electron acceptor at the end of the Electron Transport Chain (ETC)
    • Energy-poor electrons are donated to O2, making space for other electrons to continue to move through the ETC
    • If oxygen was not present, electrons would build up in the Electron Transport Chain & electron carriers would remain permanently reduced

19. Describe the purpose of fermentation.
    Cells use fermentation when there is no oxygen present
    The goal of fermentation is to regenerate the oxidized electron carrier NAD+
    • Without this carrier, glycolysis cannot occur, and…
    • Without glycolysis, a cell has no ways to make ANY ATP

20. Explain how alcohol & lactic acid fermentation occur, including types of organisms using each pathway
    Alcohol fermentation is used by yeast to regenerate NAD+ • The pyruvate (made by glycolysis) is transformed into ethanol • This transformation requires electrons, which NADH provides, oxidizing it back into NAD+
    Alcohol fermentation is used in brewing & wine-making • This process generates a lot of CO2
    • Fermentation tanks have valves to help relieve the pressure this gas creates

    Lactic acid fermentation is used to regenerate NAD+ in bacteria, fungi, & mammals
    • The pyruvate (made by glycolysis) is transformed into lactic acid
    • This transformation requires electrons, which NADH provides, oxidizing it back into NAD+

    Lactic acid fermentation is used to make many different foods
    • Examples: yogurt, cheese, sourdough bread :3
    • Lactic acid leads to a tangy taste in these foods

21. Explain the role of feedback inhibition in regulating cellular respiration.

    The steps of cellular respiration are regulated using feedback inhibition
    • This means that the products of the chemical reactions can inhibit the continuation of the chemical reaction

    Many of the enzymes involved in respiration are sensitive to ATP
    • If A LOT of ATP is present, they are inactive
    • If A LITTLE ATP is present, they are active
    Other factors (like pH changes due to lactic acid buildup) can also influence enzyme activity