Cellular Respiration Flashcards

Cellular Respiration

Aerobic Cellular Respiration

• Requires oxygen (O_2).

• Produces more energy than anaerobic respiration.

• Occurs with glucose (C6H{12}O_6).

• Process in the mitochondria that uses oxygen to break down glucose.

• Some of the potential energy stored in glucose is captured by NAD^+ and transformed into NADH.

• Exergonic and catabolic process.

• Produces CO2, H2O, and a significant amount of energy in the form of ATP.

• Balanced chemical equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP)

Steps in Aerobic Cellular Respiration

Step 1: Glycolysis (Sugar Cutting)

• Location: Cytosol of all cells.

• One molecule of glucose splits into two molecules of pyruvate.

• Inputs: Glucose, NAD^+, ADP.

• Outputs: 2 pyruvate, ATP, NADH.

• No O_2 involvement.

• Produces some ATP.

Step 2: Pyruvate Oxidation (Transition Step) / Acetyl CoA Formation

• Location: Mitochondria matrix.

• Anaerobic.

• Inputs: 2 pyruvate.

• Outputs: Acetyl CoA, CO_2 (carbons removed from pyruvate).

• Oxygen is not directly involved, but it is the terminal electron acceptor at the end of the electron transport chain.

• Acetyl CoA: Removing CO_2 from pyruvate and combine with remaining carbon (acetyl) with Coenzyme A to form Acetyl CoA.

Step 3: Krebs Cycle (Citric Acid Cycle)

• Acetyl CoA is broken in half, hydrogens removed and attached to NAD^+ to make NADH.

• Inputs: Acetyl CoA, NAD^+, ADP.

• Outputs: CO_2, NADH, ATP.

• Location: Matrix.

• Intermediate electron carriers: FAD to FADH_2.

• No O_2 involved.

Step 4: Electron Transport Chain (ETC)

• A chain of enzymes that transport electrons.

• Location: Inner membrane.

• Inputs: NADH, FADH2, O2.

• Outputs: NAD^+, FAD, H_2O.

• Intermediate electron carriers: NADH, FADH_2.

• O2 is involved as the final electron acceptor, becoming water (H2O) through reduction.

• A proton gradient is formed, which sets the stage for ATP production.

Step 5: Chemiosmotic Phosphorylation

• Diffusion of protons (H^+).

• Input: H^+, ADP.

• Outputs: 34 ATP.

• A lot of ATP is produced in this step.

• Location: Inner membrane.

ATP Production Overview

• Only ETC involves oxygen directly.

• Glycolysis produces some ATP.

• Pyruvate oxidation: No ATP made.

• Krebs cycle: A few ATP are made.

• ETC: No ATP made directly.

• Chemiosmotic phosphorylation: A lot of ATP is made (34 ATP).

Additional Information

• Glycolysis is the same for every living thing on Earth.

• Two intermediate electron carriers: NAD^+ and FAD.

  • NAD^+ receives protons and electrons to become NADH.

  • FAD receives protons and electrons to become FADH_2.

• Substrate-level phosphorylation: ATP generated through enzymes with substrate and active site, occurs in glycolysis and Krebs cycle.

• Chemiosmotic phosphorylation: ATP generated using ATP synthase where the physical flow of protons through the enzyme provides energy to combine ADP and phosphate.

• Protons are pumped from the matrix to the intermembrane compartment (active transport).

• Prior to being pumped, the protons were part of NADH and FADH_2.

• The protons were first attached to glucose; glucose is oxidized and transferred to electron carriers like NAD^+ and FAD.

• Electrons are the source of energy for pumps.

Anaerobic Respiration

• Occurs without O_2.

• If O_2 isn't present, electrons will not be removed, and the whole process will shut down.

Electron Transport Chain and Energy Levels

• After the ETC, electrons are in a low (ground) energy state because they have passed through the ETC and powered proton pumps, gradually losing energy along the way.

• During chemiosmotic phosphorylation, ATP synthase allows the protons to flow down from the intermembrane compartment to the matrix; an example of passive transport.

ATP Production in Bacteria

• Bacteria make ATP without mitochondria, but they still make NADH and FADH_2 and use the outer membrane like the inner membrane of mitochondria.

• The ETC in bacterium is found in the outer membrane of the cell.

Alternative Substrates for ATP Production

• Complex carbohydrates are broken down to pyruvate to make ATP.

• Lipids are modified to make ATP via beta-oxidation, which breaks down fatty acids into smaller molecules (acetyl CoA) to generate energy.

• Proteins are modified to make ATP by deamination, which removes an amino group (NH_2) from a molecule (commonly an amino acid).

Preferential Substrate Utilization

• Cells preferentially utilize glucose for ATP production because of its efficient breakdown and ready availability for transport.

• Lipids are ideal for energy storage because bonds release a lot of energy when broken down, don't require water for storage, and are slow burning.