2-17-25 ch 7A intro to cellular respiration & photosynthesis

Cellular Respiration Overview

• Definition: Cellular respiration is a metabolic process through which cells convert glucose from food into energy in the form of ATP.

• Occurrence: Almost all living organisms perform some form of cellular respiration, including plants.

Role of Glucose

• Source of Energy: Glucose is derived from the food consumed and serves as a primary energy source for cells.

• Utilization in Respiration: During cellular respiration, glucose is broken down to release energy.

• High Energy Molecule: Glucose, being a monosaccharide, is a high energy molecule; however, it is not used directly due to its excessive energy content.

Photosynthesis and Cellular Respiration in Plants

• Plants conduct photosynthesis in the presence of sunlight, converting solar energy into chemical energy stored in glucose.

• At night or in the absence of sunlight, plants still require energy, leading them to perform cellular respiration using the stored glucose to produce ATP.

Importance of ATP

• Energy Currency: ATP (adenosine triphosphate) is the primary energy currency of the cell, utilized in nearly all energy-requiring processes inside cells.

• Energy Release: Cells typically need at least one ATP, often more, to facilitate biochemical reactions.

• Analogy: Using glucose directly for energy is like having a $100 bill to make small change; it has excess energy, making it impractical for immediate small-scale use.

Glycolysis: The First Step in Cellular Respiration

• Definition: Glycolysis is the initial stage of cellular respiration, where glucose is broken down into smaller molecules.

• Process: It involves splitting the six-carbon glucose molecule into two three-carbon molecules, which is much more manageable for the cell.

  Pre-Krebs Phase in Cellular Respiration

  Definition: The Pre-Krebs phase is the stage that occurs after glycolysis and prior to the Krebs cycle (Citric Acid Cycle).

  Process Overview:

  • After glycolysis, pyruvate (the product of glucose breakdown) is transported into the mitochondria.

  • Each pyruvate undergoes decarboxylation, where one carbon atom is removed, resulting in a two-carbon molecule called acetyl-CoA.

  Key Functions:

  • Formation of Acetyl-CoA: Acetyl-CoA serves as the substrate for the Krebs cycle.

  • Production of NADH: The conversion process reduces NAD+ to NADH, which carries high-energy electrons for the electron transport chain.

  • Release of CO2: Carbon dioxide is produced as a byproduct and is exhaled by organisms.

  Importance: This phase connects glycolysis and the Krebs cycle, facilitating energy extraction from glucose for cellular respiration.

Krebs Cycle (Citric Acid Cycle)

• Definition: Following glycolysis, the Krebs cycle completes the breakdown of glucose derivatives, extracting more energy.

• Role of Electron Carriers: The Krebs cycle produces NADH and FADH2, which are key electron carrier molecules that store energy extracted from glucose.

Electron Transport Chain and Chemiosmosis (E.T.C)

• Final Stage: The process culminates in the electron transport chain, where the energy from NADH and FADH2 is used to produce a significant amount of ATP.

• Hydrogen Electrons: The electrons released during the breakdown of glucose are stored in the hydrogen components of NADH and FADH2, playing a critical role in ATP production.

Summary

• Cellular respiration effectively transforms the energy stored in glucose into usable ATP through a series of well-defined stages: glycolysis, the Krebs cycle, and the electron transport chain. This process is vital for the energy needs of both animals and plants.

Key Parts of Cellular Respiration Overview:

1. Definition: Cellular respiration is the process of converting glucose from food into energy (ATP).

2. Occurrence: Conducted by almost all living organisms, including plants.

3. Role of Glucose: Glucose is the primary energy source; it is broken down during respiration to release energy.

4. Photosynthesis and Respiration: Plants convert solar energy to glucose via photosynthesis and later use that glucose for energy at night through respiration.

5. Importance of ATP: ATP is the main energy currency of the cell, crucial for energy-requiring processes.

6. Glycolysis: The initial breakdown of glucose into smaller molecules.

7. Krebs Cycle: Further breakdown of glucose derivatives producing NADH and FADH2 for energy extraction.

8. Electron Transport Chain: Final stage where significant ATP is produced using energy from NADH and FADH2

Fate of 6 Molecules through Glycolysis, Pre-Krebs, and Krebs Cycle

1. Glycolysis:

   • Starting Material: One 6-carbon glucose molecule.

   • Process: The glucose molecule is split into two 3-carbon molecules known as pyruvates.

   • Energy Produced: A net gain of 2 ATP and 2 NADH molecules is generated.

2. Pre-Krebs Phase:

   • Starting Material: The two pyruvate molecules produced from glycolysis.

   • Process: Each pyruvate (3-carbons) undergoes decarboxylation, losing one carbon as CO2, and is then converted into acetyl-CoA (2-carbons).

   • Byproduct: 2 CO2 molecules are released (one from each pyruvate).

   • Energy Produced: 2 NADH molecules are made from the conversion of the pyruvates to acetyl-CoA.

3. Krebs Cycle:

   • Starting Material: Two acetyl-CoA molecules from the Pre-Krebs phase.

   • Process: Each acetyl-CoA enters the cycle, combining with a 4-carbon molecule to form citric acid (6-carbons). This results in several transformations, where two carbon atoms are released as CO2 in each cycle iteration.

   • Energy Produced: For each acetyl-CoA, the cycle produces 3 NADH, 1 FADH2, and 1 ATP, resulting in a total of 6 NADH, 2 FADH2, and 2 ATP from 2 acetyl-CoA molecules.

   • Byproduct: 4 CO2 molecules are released (2 for each original glucose).

Summary:

The transformation of one glucose molecule through glycolysis yields two pyruvates, leading to the formation of two acetyl-CoA molecules in the Pre-Krebs phase, ultimately resulting in the complete oxidation and energy extraction in the Krebs cycle.