CellMetabolism

Cellular Metabolism Learning Goals

• Understanding Cellular Energy: Learn how cells create and use energy.

• Biochemical Pathways: Explore the biochemical pathways of cellular respiration.

• Energy Management: Understand how energy is trapped, converted, and stored within cells.

Bioenergetics

• Basic Principles of Energy:

  • Energy: Defined as the capacity to do work.

    • Kinetic Energy: Energy of motion.

    • Potential Energy: Stored energy, objects not in motion.

  • Energy can take forms such as:

    • Mechanical energy

    • Heat

    • Sound

    • Electricity

    • Light

Potential and Kinetic Energy

• Potential Energy: Stored energy that an object has due to its position.

• Kinetic Energy: The energy that an object possesses due to its motion.

Units of Energy in Bioenergetics

• Common Measurement: Understanding energy in terms of heat - thermodynamics.

• Units Used:

  • Kilocalorie (kcal): 1 kcal = 1000 calories (amount of heat needed to raise 1g of water 1°C).

  • Joule: 1 joule = 1.239 calories.

Energy Flow in Ecosystems

• Energy enters ecosystems primarily from the sun (> 13 x 10^23 cal/year).

• Energy Storage: Stored as potential in chemical bonds.

• Reactions of Energy Transfer:

  • Oxidation: Loss of electrons.

  • Reduction: Gain of electrons.

Redox Reactions

• Coupled Reactions: Oxidation and reduction occur together, collectively termed redox reactions.

• Energy Transfer: Reduced molecules store more energy due to the addition of electrons.

Laws of Thermodynamics in Energetics

1. Conservation of Energy: Energy cannot be created or destroyed, only transformed.

2. Entropy: Disorder (entropy) is continuously increasing in the universe. Natural processes tend toward disorder.

Endergonic and Exergonic Reactions

• Endergonic Reactions: Energy is supplied (non-spontaneous reactions).

• Exergonic Reactions: Energy is released (spontaneous reactions).

Activation Energy

• Definition: The energy required to break chemical bonds and initiate reactions.

• Role of Catalysts: Lower activation energy, enabling reactions to occur more easily.

Adenosine Triphosphate (ATP)

• ATP as Energy Currency: ATP is the primary energy carrier in cells, facilitating nearly all energy-driven processes.

• Structure of ATP:

  • Comprised of ribose (sugar), adenine (organic base), and a triphosphate group.

• Energy Storage: Energy stored in the triphosphate group through high-energy bonds, unstable due to negative charge repulsion.

Biochemical Pathways in Metabolism

• Metabolism: The total of all chemical reactions within an organism.

  • Anabolic Reactions: Energy-consuming reactions that synthesize complex molecules.

  • Catabolic Reactions: Energy-releasing reactions that break down complex molecules into simpler ones.

• Biochemical Pathways: Products of one reaction typically serve as substrates for the next.

Feedback Inhibition in Biochemical Pathways

• Definition: The end products of metabolic pathways inhibit earlier steps to regulate their own production.

Evolution of Metabolism

• Key Processes:

  • Degradation

  • Glycolysis

  • Anaerobic photosynthesis

  • Nitrogen fixation

  • Oxygen-forming photosynthesis

  • Aerobic respiration

Glycolysis:**

• Process: Breakdown of glucose into pyruvate, yielding ATP.

  • Net Result: 4 ATP produced, 2 used; net gain of 2 ATP and 2 NADH.

  • Energy Extraction: From glucose in a series of enzyme-mediated reactions.

Stages of Glycolysis

1. Priming Reactions: ATP usage to phosphorylate glucose.

2. Cleavage: Splitting of 6-carbon compound into two 3-carbon molecules.

3. Energy-Harvesting: Conversion of molecules into pyruvate; ATP generation occurs.

Pyruvate Oxidation**

• Process: Converts pyruvate into CO2 and acetyl-CoA, producing NADH.

• Significance: Prepares molecules for entry into the Krebs cycle.

The Krebs Cycle**

1. Entry of Acetyl-CoA: Acetyl-CoA combines with oxaloacetate.

2. Reactions: Nine total reactions; generates ATP and reduces NAD+ to NADH.

3. Outputs: Produces CO2 and high-energy electron carriers (NADH and FADH2).

Electron Transport Chain (ETC)**

• Function: Primary site for ATP production during aerobic respiration.

• Mechanism: Electrons transferred through proteins, generating an electrochemical gradient for ATP synthesis.

Chemiosmosis**

• Proton pumps create a gradient, driving protons back into the matrix through ATP synthase, producing ATP.

Yield of ATP**

• Theoretical net yield from aerobic respiration is approximately 36 ATP per glucose molecule; actual yield can vary due to inefficiencies.

Other Catabolic Pathways**

• Fats and proteins can also act as alternative energy sources, undergoing similar metabolic processes.

Anaerobic Respiration**

• Alternative Pathway: Some organisms utilize inorganic molecules in the absence of oxygen for ATP production.