Unit 2 Lecture 5

Essential Amino Acids and Nutrients

• Essential Amino Acids: There are 9 out of 20 amino acids that organisms cannot produce internally and must obtain from their environment.

• Other organisms also have specific nutrients they must acquire externally.

Elemental and Organic Nutrients

• ** Elemental Nutrients (CHONPS - Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Sulfur, and Trace Elements):

  • Macronutrients: Required in large amounts, forming ordered groups for a reason.

    • Carbon (C): The background for organic compounds (e.g., sugar). It cannot be synthesized internally and must be provided as an organic nutrient, for example, in amino acids, nitrogenous bases, and vitamins.

    • Hydrogen (H): Essential, for example, in sugar.

    • Oxygen (O): Organisms are oxygen-dependent.

  • Intermediate Nutrients: Needed in significant quantities, but less than macronutrients.

    • Nitrogen (N): Crucial, even though most air is nitrogen, it must be assimilated. Essential for amino acids and nitrogenous bases.

    • Phosphorus (P)

    • Sulfur (S)

  • Micronutrients / Trace Elements: Required in small amounts (trace elements).

    • Examples include Nickel (Ni), Zinc (Zn), Copper (Cu), Iron (Fe).

    • These elements are absolutely necessary for correct cellular function, often as catalysts.

    • The amount needed is very small; for instance, consuming an iron nail or pennies for copper would be toxic due to excessive amounts.

    • Other possible trace elements mentioned include aluminum (Al).

• Organic Nutrients: Carbon-containing compounds that an organism cannot synthesize and must obtain from its environment (e.g., amino acids, nitrogenous bases, vitamins).

Organism Classifications by Nutrient Acquisition

• Chemotrophs: Organisms that gain energy entirely through chemical compounds.

• Photoautotrophs:

  • Primary producers. They perform photosynthesis.

  • Use inorganic compounds (e.g., water, carbon dioxide) as their carbon source.

  • Utilize sunlight as their energy source to produce organic compounds.

  • Examples include many microorganisms.

• Chemoheterotrophs:

  • Obtain both their carbon and energy from organic chemical compounds.

  • Examples include many free-living prokaryotes.

  • Saprobes: Free-living chemoheterotrophs that obtain nutrients and organic materials from dead organisms (e.g., dead plants, animals, bacteria).

  • Parasites: Chemoheterotrophs that obtain nutrients from live organisms (hosts).

    • To be successful, parasites generally do not kill their host, as the host's death would eliminate their nutrient source.

• Photoheterotrophs:

  • Gain energy from sunlight.

  • Obtain carbon from organic compounds (e.g., from the soil).

  • They perform photosynthesis but also require external organic carbon.

Cell Transport Mechanisms

• Permeability of the Phospholipid Bilayer:

  • Nonpolar molecules and lipids can easily pass through the lipid bilayer.

  • Polar molecules (e.g., carbohydrates, proteins, nucleic acids), ions (e.g., positively charged sodium, negatively charged chloride), and charged particles cannot easily pass and require assistance.

• Diffusion: The movement of molecules from an area of high concentration to an area of low concentration.

  • No energy (ATP) is required.

  • Simple Diffusion: Molecules pass directly through the cell membrane from high to low concentration.

  • Facilitated Diffusion: Molecules move from high to low concentration with the help of a membrane protein acting as a channel or a carrier.

    • Carrier proteins facilitate transport by changing shape to bind and release the molecule.

• Osmosis: A special type of diffusion referring specifically to the movement of water only.

  • Water moves across a selectively permeable membrane from a region of high water concentration to a region of low water concentration.

  • This movement helps maintain osmotic pressure, which is crucial for preventing cells from bursting or shrinking.

  • Tonicity (referring to the solute concentration of the extracellular fluid relative to the cell's cytoplasm):

    • Isotonic Solution: The extracellular fluid has the same amount of solute/water concentration as the inside of the cell.

      • Water moves into and out of the cell equally (e.g., via aquaporins), maintaining a balance. Cells function optimally.

      • Example: A 0.9\% saline solution is isotonic to human cells.

    • Hypotonic Solution: The extracellular fluid has a higher water concentration (lower solute concentration) than the inside of the cell.

      • Water moves into the cell, causing it to swell and potentially burst (visualized as a "big swollen meatball").

    • Hypertonic Solution: The extracellular fluid has a lower water concentration (higher solute concentration) than the inside of the cell.

      • Water moves out of the cell, causing it to shrink or crenate.

      • Example: Drinking excessive salt makes the extracellular fluid hypersaline, drawing water out of the body's cells.

• Active Transport:

  • Movement of molecules from an area of low concentration to an area of high concentration (against the concentration gradient).

  • Requires energy (ATP) because it's