Energy and Life

1. Introduction to Energy and Metabolism

• Metabolism: The chemical processes that occur within a living organism to maintain life.

• Chemical Waste: Byproducts of metabolism that need to be removed.

• Chemical Energy: Energy stored in the bonds of chemical compounds, primarily in the form of ATP.

  • Components:

    • Carbon Dioxide

    • Carbohydrates

    • Water

    • Fats

    • Proteins

    • Others

2. Learning Outcomes

• Identify external energy sources supporting life:

  • Inorganic Chemicals (e.g., Fe, H2, H2S, NH3)

  • Sunlight (Photosynthetically Active Radiation, PAR)

• Autotrophs: Organisms that synthesize carbohydrates directly from CO2 (e.g., via photosynthesis or chemosynthesis).

  • Convert CO2 to carbohydrate molecules enabling life.

• Heterotrophs: Organisms that cannot synthesize carbohydrates from CO2 and must consume organic material.

  • Obtain food by eating autotrophs or other heterotrophs.

• Metabolic Definitions:

  • Metabolism: Overall biochemical processes within an organism.

  • Anabolism: Metabolic processes that build molecules.

  • Catabolism: Metabolic processes that break down molecules.

  • Endergonic Reactions: Reactions that require energy input.

  • Exergonic Reactions: Reactions that release energy.

• ATP and GTP: Energy-rich molecules supporting endergonic reactions in cells.

3. Energy Requirement in Organisms

• All Prokaryotes and Eukaryotes require energy for:

  • Development

  • Growth

  • Maintenance

  • Repair

  • Reproduction

  • Response to environmental stimuli.

• Viruses require energy from host cells to replicate.

4. External Energy Sources

• Cells require external energy to produce energy-rich molecules (ATP, GTP), which fuel life processes.

  • Sources: Food molecules, sunlight, H2S.

5. Autotrophs

• Autotrophs create their own food by synthesizing carbohydrates from CO2.

  • Photosynthetic Autotrophs:

    • Capture sunlight to generate energy-rich ATP and NADPH.

    • Use Photosynthetically Active Radiation (PAR) to enhance photosynthesis.

6. Chemosynthesis

• Some autotrophs utilize chemosynthesis:

  • Prokaryotes living in extreme conditions (e.g., tubeworms) convert CO2 to carbohydrates using inorganic chemicals (e.g., H2S).

  • Inorganic Chemicals: Lacking carbon-hydrogen bonds, they can serve as energy sources for ATP and NADH production.

7. Heterotrophs

• Heterotrophs cannot perform photosynthesis or chemosynthesis; they need to consume organic materials (autotrophs or heterotrophs) for energy.

  • Must obtain food (carbohydrates, lipids, nucleic acids, proteins) externally.

8. ATP in Cellular Processes

• All cells utilize ATP to fuel energy-requiring (endergonic) reactions.

  • The bond between phosphate groups in ATP (PO4 to PO4) stores crucial energy.

  • Food supplies the necessary energy to synthesize ATP.

  • ATP is a fundamental component of RNA.

9. GTP in Cellular Reactions

• All cells utilize GTP for particular endergonic reactions.

  • Structure includes three PO4 groups, ribose, and guanine.

  • GTP also has energy-storing phosphate bonds and derives energy from food molecules.

10. ATPase Enzymes

• ATPase enzymes facilitate energy release from ATP.

  • Involves hydrolysis (addition of H2O) at specific phosphate bonds to release energy for cellular processes.

• Connects ATP hydrolysis to endergonic reactions requiring energy.

11. Magnesium Ion Requirement

• ATPase enzymes require Mg++ as a cofactor to function effectively.

  • Inactive without Mg++, active with it.

  • Mg++ ions are essential for ~300 cellular reactions.

12. Continuous ATP Supply

• Cells need a constant supply of ATP to meet energy demands.

  • Each cell can consume over a billion ATP molecules per second.

  • Individual ATP molecules are resynthesized ~10,000 times daily.

13. Daily ATP Production

• The human body's daily ATP synthesis is equivalent to its mass (roughly 50-100 kg).

  • Average ATP molecules in the human body range between 50-250 grams at any given time.

14. Circulatory System's Role

• The circulatory system provides oxygen (O2) and glucose, essential for ATP production in cells.

  • Continuous ATP synthesis is necessary to meet energy needs.

15. ATP Synthesis Locations

• Eukaryotic cells synthesize ATP in:

  • Cytosol (via glycolysis)

  • Mitochondria (requires oxygen)

  • Nucleus (via NUDIX5 enzyme converting ADP-ribose into ATP).

16. Coupling Reactions

• Cells couple endergonic reactions to exergonic reactions:

  • Example: ATP hydrolysis coupled with glutamine synthesis.

  • ATP hydrolysis releases excess energy aiding in maintaining core body temperature (~37°C).

17. Importance of Efficient ATP Synthesis

• Inefficient ATP synthesis can disrupt numerous cellular processes, leading to medical issues.

  • Niacin (B3): Essential for NAD+ synthesis.

  • Pellagra: Nutritional disorder from insufficient niacin, leading to symptoms of dementia, dermatitis, and diarrhea (3 Ds).

18. Study Guide Questions

• Define:

  • Metabolism, Anabolism, Catabolism, Endergonic Reaction, Exergonic Reaction.

  • Autotroph & Heterotroph.

• How do autotrophs and heterotrophs obtain energy-rich carbohydrates?

• Identify energy sources driving:

  • Chemosynthesis

  • Photosynthesis.

• Describe processes utilizing energy from:

  • Sunlight (PAR) to create carbohydrates.

  • Inorganic chemicals to create carbohydrates.

• Outline cellular functions of ATP, GTP, and ATPase enzymes.

• Discuss the necessity for constant ATP production and the consequences of ATP malfunctions.