BIO123.ch5.OER.Liz.notes.blanks

Chapter 5 - Structure and Function of the Cell Membrane and an Introduction to Energy

Chapter Objectives

• Understand the fluid mosaic model of cell membranes.

• Describe the functions of key components (phospholipids, proteins, carbohydrates).

• Differentiate between molecules that can pass through the membrane directly vs. those needing transport proteins.

• Explain passive transport and the processes of simple diffusion and facilitated diffusion.

• Understand osmosis and how cells respond in different tonic environments (hypertonic, hypotonic, isotonic).

• Define tonicity and its relevance to passive transport.

• Explain active transport, including endocytosis (phagocytosis, pinocytosis, receptor-mediated) and exocytosis.

• Discuss energy flow through living systems and metabolic pathways.

• Understand the difference between anabolic and catabolic reactions; provide examples.

• Describe thermodynamics, laws, and concepts of energy (

entropy, kinetic vs. potential, endergonic vs. exergonic).

• Explain enzyme function and the role of activation energy.

5.1 The Cell Membrane

• Plasma Membrane Functions:

  • Defines the outer boundary of cells/organelles.

  • Manages transport in/out of cells.

  • Receives external signals for cellular response.

  • Adheres to neighboring cells.

• Fluid Mosaic Model:

  • Contains diverse components (phospholipids, cholesterol, proteins, carbohydrates).

  • Flexible, stable structure that is constantly reformed.

  • Materials are mobile and adaptable.

• Phospholipid Bilayer:

  • Phospholipids have a polar (hydrophilic) phosphate head facing extracellular and intracellular fluid and nonpolar (hydrophobic) fatty acid tails facing inward.

  • Forms the boundary of cells and membrane-bound organelles.

• Membrane Proteins:

  • Two types: Integral (embedded) and Peripheral (attached to inner/outer side).

  • Functions:

    • Transport pathways for specific molecules.

    • Cell identification.

    • Signaling molecule binding.

    • Attachment to the cytoskeleton.

    • Facilitate surface reactions.

• Carbohydrates:

  • Interact with the extracellular side; include glycoproteins and glycolipids.

  • Ahce for cell recognition and form a protective coating (glycocalyx).

• Cholesterol:

  • Maintains membrane fluidity and stabilizes phospholipids against temperature changes.

5.2 Passive Transport

• Definition: Some substances pass through membranes easily (e.g., small, nonpolar molecules like oxygen).

• Process:

  • Movement occurs without cellular energy, using a concentration gradient (difference in concentration).

• Types:

  • Diffusion: Movement down concentration gradient until equilibrium.

  • Facilitated Diffusion: Requires specific transport proteins for larger, polar or charged particles (e.g., water via aquaporins).

• Factors Affecting Diffusion Rate:

  • Greater concentration difference leads to faster diffusion.

  • Smaller molecules diffuse quicker.

  • Higher temperatures increase movement speed.

  • Thick cytoplasm slows movement.

  • Nonpolar materials diffuse faster.

  • Surface area and distance affect rates.

• Osmosis:

  • Diffusion of water through membranes, influenced by solute concentration.

  • Tonicity:

    • Refers to the concentration of solutes in a solution affecting cell volume.

    • Hypotonic: Lower solute concentration outside (cells swell).

    • Isotonic: Equal solute concentration (normal cell volume).

    • Hypertonic: Higher solute concentration outside (cells shrink).

5.3 Active Transport

• Definition: Movement of materials against a concentration gradient requiring energy.

• Examples:

  • Sodium-potassium pump (maintaining gradients in human cells).

  • Electron transport chains in mitochondria/chloroplasts.

• Endocytosis:

  • Movement of large molecules into cells by vesicle formation (e.g., phagocytosis, pinocytosis).

• Exocytosis:

  • Movement of materials out of the cell using vesicles.

5.4 Energy and Metabolism

• Energy: Essential for all living things; the sun is the primary energy source.

• Metabolic Pathways: Series of linked chemical reactions (e.g., cellular respiration, photosynthesis).

• Metabolism: The sum of anabolic (building) and catabolic (breaking down) reactions, both facilitated by enzymes.

5.5 Laws of Thermodynamics

• Thermodynamics: Study of energy and work.

• Laws:

  • Energy cannot be created or destroyed (First Law); it transforms.

  • Energy transfer is not 100% efficient; some energy is lost as heat (increased entropy).

• Entropy: Disorder in a system; higher entropy means more disorder.

5.6 Types of Energy

• Kinetic Energy: Energy in motion.

• Potential Energy: Stored energy (e.g., chemical energy).

• Free Energy: Usable energy for reactions (breaking bonds releases free energy).

• ATP: Adenosine triphosphate; crucial for energy transfer in living systems, produced through anabolic reactions and utilized in catabolic reactions.

5.7 Enzymes

• Enzymes: Protein catalysts accelerating reactions by lowering activation energy; highly specific for substrates.

• Function: Facilitate bond-breaking/formation, allowing repeated use without change.

• Enzyme Regulation: Controlled by environmental conditions (temperature) or inhibitors (competitive/non-competitive).

• Cofactors and Coenzymes: Molecules assisting enzymes, which can be inorganic ions or organic compounds (vitamins).

Chapter Conclusion

• Membrane structure is maintained through the fluid mosaic model, with components that regulate transport and response.

• Passive (diffusion, osmosis) and active transport play critical roles in cellular function.

• Energy dynamics (thermodynamics and ATP) are vital for metabolism and enzymatic function.