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.