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3. Protein Passageways Presentation

Protein Passageways

  • Importance of protein passageways in cell membranes.

Objectives

  • Course Objective #4: Distinguish between types of passive and active transport mechanisms through cell membranes.

  • Topics to Review:

    • Diffusion & Osmosis

    • Passive Transport

      • Powered by diffusion

      • Channels & carrier proteins

    • Active Transport

      • Powered by ATP hydrolysis

    • Additional Entry/Exit Methods

Review: How Salt Kills Slugs

  • Mechanisms of Salt Toxicity:

    • Salt ions invade cells and instigate lethal biochemical reactions.

    • Salt combines with water in cells, creating a viscous liquid that hinders movement; slugs get immobilized.

    • Water diffuses into slugs' cells due to salt causing cell explosion.

    • Water diffusion out of cells results in slugs succumbing to dehydration.

The Cell Membrane as a Barrier

  • Composed of a diverse mixture of macromolecules, ions, etc.

  • Separates the extracellular environment from the intracellular environment.

  • Regulates the entry and exit of substances.

Molecule Diffusion Across the Lipid Bilayer

  • Question: Which molecules diffuse most quickly?

    • Options: H2O, O2, H2PO4-, glucose, Na+

Introduction to Large / Charged Solutes

  • Examples include:

    • Water (exhibits a faster rate than osmosis)

    • Dietary sugars, amino acids, vitamins

    • Signaling and secreted molecules

    • Waste products

Passive Transport: Entering Cells by Diffusion

  • Passive Transport Characteristics:

    • No energy cost to the cell.

    • Movement across cell membranes driven by concentration gradients.

    • Facilitated diffusion uses proteins as passageways for large or charged solutes.

Membrane Protein Structure

  • Transmembrane/Integral Membrane Proteins:

    • Amphipathic nature with hydrophobic tails and hydrophilic heads.

    • Integral proteins exist within the phospholipid bilayer.

Channel Proteins

  • Recognize specific ions or molecules.

  • Provide open passageways for rapid transport.

  • Can be gated, allowing regulation of flow.

Question on Membrane Spanning Proteins

  • Question: Amino acids in the a-helices:

    • Face hydrophobic fatty acid chains: likely hydrophobic.

    • Face inner pore: likely hydrophilic.

Question on Osmosis

  • Question: Which statement about osmosis is correct?

    • Options covering isotonic, hypertonic solutions, aquaporins' role, etc.

Carrier Proteins

  • Mechanism: Specific solute binds, protein undergoes a conformational change and opens to the opposite side.

  • Speed compared to channels: may vary.

Active Transport

  • Key Characteristics:

    • Moves solutes against concentration gradients.

    • Energetically unfavorable and requires energy input, typically from ATP.

    • Example: Proton pump.

ATP as an Energy Intermediate

  • Structure and Function:

    • Adenosine Tri-Phosphate (ATP) consists of adenine, ribose, and inorganic phosphate.

    • Acts as the energy currency for cellular work and chemical synthesis.

Na/K ATPase: Transporting Against Gradients

  • High extracellular [Na], low intracellular [Na].

  • Mechanism includes:

    1. Na+ binding to pump and triggering phosphorylation by ATP.

    2. Conformational change expels Na+ outside the cell.

    3. K+ binding triggers release of phosphate, restoring original conformation.

Compare & Contrast: Facilitated Diffusion vs Active Transport

  • Key differences in mechanisms of transport and energy requirements.

Types of Biomolecules and Their Roles

  • Questions:

    • What kinds of biomolecules play crucial roles in barrier integrity, fluidity, and ion entry?

Additional Membrane Transport Mechanisms: Endocytosis and Exocytosis

  • Overview of processes and their significance for cellular function:

    • Endocytosis: Phagocytosis, pinocytosis, and receptor-mediated endocytosis.

    • Exocytosis: Mechanism for expelling materials from the cell.

Types of Endocytosis

  • Phagocytosis:

    • Ingestion of large particles (e.g., food).

  • Pinocytosis:

    • General intake of liquids.

  • Receptor-Mediated Endocytosis:

    • Specific solute intake via receptors.

Question on Immune Cells

  • Question: Invading bacteria uptake mechanism by immune cells:

    • Options: pinocytosis, exocytosis, osmosis, phagocytosis, facilitated diffusion.