Cellular Respiration

Key Definitions

• Catabolism: The breakdown of complex molecules into simpler ones, releasing energy.

• Anabolism: The synthesis of complex molecules from simpler ones, requiring energy input.

• Oxidation: The loss of electrons from a molecule, often associated with the gain of oxygen or loss of hydrogen.

• Reduction: The gain of electrons by a molecule, often associated with the loss of oxygen or gain of hydrogen.

• Beta Oxidation: The metabolic process by which fatty acids are broken down in the mitochondria to generate acetyl-CoA, NADH, and FADH2.

NAD+ in Cellular Respiration

NAD+ acts as an electron carrier. During glycolysis and the TCA cycle, it is reduced to NADH as it accepts electrons. NADH then transports these electrons to the electron transport chain.

• Example: In glycolysis, NAD+ is reduced to NADH when glyceraldehyde-3-phosphate is oxidized.

ATP Production in Glycolysis

ATP is produced in glycolysis via substrate-level phosphorylation, where a phosphate group is directly transferred from a substrate to ADP.

• Formula:

• Example: Phosphoenolpyruvate (PEP) transfers its phosphate to ADP, forming ATP.

Role of O2 in Cellular Respiration

Oxygen serves as the final electron acceptor in the electron transport chain, allowing for the complete oxidation of glucose and production of water.

• Without O2: Cells undergo fermentation instead of oxidative phosphorylation.

Metabolic Reactions in Complete Oxidation of Glucose

• Glycolysis: Glucose is split into two pyruvate molecules.

• Pyruvate Oxidation: Pyruvate is converted to acetyl-CoA.

• TCA Cycle (Krebs Cycle): Acetyl-CoA is oxidized, producing NADH, FADH2, and CO2.

• Oxidative Phosphorylation: NADH and FADH2 donate electrons to the electron transport chain, generating ATP.

Metabolic Processes Requiring O2

• Require O2: Oxidative phosphorylation, TCA cycle (indirectly, as it depends on NAD+ regeneration).

• Do not require O2: Glycolysis, fermentation.

Products of Glycolysis and TCA Cycle

• Glycolysis: 2 ATP, 2 NADH, 2 pyruvate.

• TCA Cycle: Per glucose: 2 ATP (GTP), 6 NADH, 2 FADH2, 4 CO2.

Phosphorylation Impact

Phosphorylation is the addition of a phosphate group to a molecule, often regulating enzyme activity or energy transfer.

• Example: ATP formation from ADP.

Carbon Molecules Entering TCA Cycle

• Each pyruvate (3C) is converted to acetyl-CoA (2C), which enters the TCA cycle.

Metabolic Process Producing Most ATP

• Oxidative phosphorylation produces the most ATP per glucose molecule.

Location of Metabolic Processes

• Glycolysis: Cytoplasm

• TCA Cycle: Mitochondrial matrix

• Oxidative Phosphorylation: Inner mitochondrial membrane

ATP Production in Oxidative Phosphorylation

• ATP is produced by chemiosmosis, not substrate-level phosphorylation.

Metabolic Process Requiring Proton Gradient

• Oxidative phosphorylation requires a proton gradient across the inner mitochondrial membrane.

Fate of Lactate

• Lactate is produced during anaerobic glycolysis and can be converted back to pyruvate in the liver (Cori cycle).

Photosynthesis

Relationship Between Light Reactions and Calvin Cycle

The light reactions generate ATP and NADPH, which are used by the Calvin cycle to fix carbon dioxide into sugars.

• Example: ATP and NADPH produced in the thylakoid membrane are consumed in the stroma during the Calvin cycle.

Highest Initial Energy Molecule in Electron Transport Chain

• NADH (cellular respiration) and NADPH (photosynthesis) have the highest initial energy when entering their respective electron transport chains.

Events of the Electron Transport Chain

• Electrons are transferred through a series of protein complexes, releasing energy to pump protons and create a gradient.

• Final electron acceptor is O2 (cellular respiration) or NADP+ (photosynthesis).

Immediate Source of Energy for ATP Synthase

• The proton gradient across the membrane provides the immediate energy for ATP synthase.

• Formula:

Organisms Capable of Photosynthesis

• Plants, algae, and cyanobacteria are capable of photosynthesis.

Location of Light Reactions and Calvin Cycle

• Light reactions: Thylakoid membrane

• Calvin cycle: Stroma of the chloroplast

Pigment Types Absorbed by Orange Plants

• If a plant appears orange, it absorbs blue and green wavelengths; pigments like carotenoids are present.

Products of Light Reactions Used by Calvin Cycle

• ATP and NADPH are produced in the light reactions and used in the Calvin cycle.

Role of Pigment in Light-Harvesting Complex

• Pigments absorb light energy and transfer it to the reaction center, initiating electron flow.

Relationship Between Wavelength and Energy of a Photon

• Energy is inversely proportional to wavelength:

• Shorter wavelengths have higher energy.

Location of Electron Transport Chain in Plants

• Located in the thylakoid membrane of chloroplasts.

Photorespiration

• Photorespiration occurs when Rubisco combines O2 with RuBP instead of CO2, leading to a wasteful pathway.

Electron Flow During Photosynthesis

• Electrons flow from water to NADP+ via photosystem II and I, producing NADPH.

Process in Photosynthesis Driven by Light Energy

• The light reactions, specifically the excitation of electrons in photosystems, are directly driven by light energy.