Cellular Respiration

Energy Processing

Photosynthesis and cellular respiration are two fundamental biological processes that enable organisms to capture, store, and utilize energy. These processes are closely linked in the flow of energy and cycling of matter within ecosystems.

• Photosynthesis allows plants and other autotrophs to capture energy from sunlight and convert it into chemical energy stored in sugar molecules.

• Energy from the sun is transformed into potential energy in the bonds of glucose during photosynthesis.

• The general equation for photosynthesis is:

• Plants can store the produced sugars or use them immediately in cellular respiration.

Cellular Respiration

Cellular respiration is the process by which cells break down glucose and other organic molecules to release energy for cellular activities. This process is nearly the reverse of photosynthesis and is essential for the production of ATP.

• ATP (Adenosine Triphosphate) is the primary energy currency of the cell, coupling endergonic (energy-requiring) and exergonic (energy-releasing) reactions.

• ATP is constantly used and regenerated; each ATP molecule is cycled more than once per minute in active cells.

• ATP is a very unstable molecule, which makes it efficient for energy transfer but unsuitable for long-term energy storage.

• The general equation for cellular respiration is:

• Cellular respiration yields approximately 29 ATP molecules per glucose molecule.

• Because water is a smaller molecule than carbon dioxide, cells lose more weight in carbon dioxide during respiration.

Energy vs Atoms

Both photosynthesis and cellular respiration involve the conversion of energy and the rearrangement of atoms, particularly carbon, within molecules.

• Energy conversion is closely tied to the breaking and forming of chemical bonds between carbon atoms.

• It is important to track both the flow of energy and the movement of atoms (e.g., carbon) during these processes.

• Example: In glucose, carbon atoms are combined and later released as carbon dioxide during respiration.

Different Ways of Making ATP

Cells can produce ATP through several metabolic pathways, depending on the availability of oxygen and other factors.

• Aerobic respiration: Occurs in the presence of oxygen and is the most efficient pathway for ATP production.

• Alternate electron acceptors: Used by some organisms when oxygen is not available (anaerobic conditions).

• Fermentation: An anaerobic process that is less efficient and occurs in the absence of oxygen in some organisms.

• Why ~29 ATP (vs 38)? The theoretical maximum yield is 38 ATP, but in practice, cells typically produce about 29 ATP per glucose due to losses in efficiency and transport.

Energetic Coupling

Energetic coupling refers to the linking of exergonic and endergonic reactions, allowing cells to efficiently harness and utilize energy.

• Glucose can be burned in a single step, but cells release energy gradually through a series of redox reactions.

• The overall equation for glucose oxidation is:

• Energy released from glucose oxidation is coupled to the synthesis of ATP and other energy carriers.

• Cellular respiration consists of four interconnected processes/stages:

  • Glycolysis

  • Pyruvate processing

  • Citric acid cycle

  • Electron transport chain + oxidative phosphorylation

• When simplified: ;

First 3 Stages of Cellular Respiration

The initial stages of cellular respiration involve the controlled release of energy from glucose and the transfer of electrons to carrier molecules.

• Energy is released from glucose via electrons carried by NADH and FADH2.

• These stages also produce carbon dioxide and a few ATP molecules.

• Substrate-level phosphorylation: ATP is produced by the direct transfer of a phosphate group from a phosphorylated substrate to ADP.

• This process is exergonic, except for the reverse reaction.

Last Stage of Cellular Respiration

The final stage involves the electron transport chain, where energy in NADH and FADH2 is used to drive the production of ATP.

• Electrons from NADH and FADH2 are transferred to the electron transport chain, coupling multiple redox reactions to the transport of H+ ions across a membrane.

• This creates a proton gradient that powers ATP synthesis via oxidative phosphorylation.

Summary Table: Key Processes in Cellular Respiration

Additional info: The notes have been expanded to include definitions, equations, and a summary table for clarity and completeness. The original content was fragmented; topics have been logically grouped and explained in academic context.