Biology Chapter: Movement of Molecules

Movement of Molecules

• Passive transport: Movement of molecules across a membrane without energy input. This includes diffusion and osmosis.
  • Diffusion: Molecules move from an area of high concentration to an area of low concentration. The rate of diffusion is affected by factors like temperature, concentration gradient, and the size of the molecules.
  • Osmosis: The diffusion of water across a selectively permeable membrane. Water moves from a region of high water potential to a region of low water potential. Important in maintaining cellular homeostasis.
• Active transport: Movement of molecules across a membrane requiring energy input (usually ATP). Moves substances against their concentration gradient.
  • Examples: Sodium-potassium pump, endocytosis, exocytosis.
  • Importance: Essential for transporting substances needed by the cell against concentration gradients, like nutrient absorption and removal of waste products.
• Facilitated diffusion: Molecules move down their concentration gradient with the help of transport proteins embedded in the cell membrane. This is a type of passive transport, needing no energy.
  • Carrier proteins: Bind to molecules and change shape to move them across the membrane.
  • Channel proteins: Create a hydrophilic pore for molecules to pass through. Typically specific for the type of molecule they transport.
• Bulk Transport: Large particles and macromolecules are transported across the membrane.
  • Endocytosis: Plasma membrane surrounds the substance and forms a vesicle/vacuole to bring it into the cell. Includes phagocytosis (cell eating) and pinocytosis (cell drinking).
  • Exocytosis: Substances are discharged from the cell by fusing vesicles with the plasma membrane. Excretion of waste or release of hormones.

Enzymes

• Biological Catalysts: Speed up chemical reactions in living organisms without being consumed in the process.
• Specificity: Each enzyme is highly specific for a particular substrate. Active site that is shaped to fit with the substrate and catalyzes the reaction.
• Factors Affecting Enzyme Activity:
  • Temperature: Optimal temperature exists for each enzyme, where activity is highest. Too high can denature enzymes.
  • pH: Each enzyme has an optimal pH range. Changes greatly affect enzyme shape and activity.
  • Substrate Concentration: Increasing substrate concentration increases enzyme activity until the enzyme becomes saturated.
• Enzyme Inhibitors: Substances that reduce enzyme activity.
  • Competitive inhibitors: Resemble the substrate and compete for the active site.
  • Non-competitive inhibitors: Do not resemble the substrate, bind to a different site (allosteric site), causing the enzyme to change shape, and affecting function.
• Enzyme Regulation: Controlling the rate at which enzymes work.
  • Allosteric regulation: Molecules bind to regions other than the active site, affecting enzyme shape and activity.
  • Feedback inhibition: The end product of a metabolic pathway inhibits the enzyme earlier in the pathway, preventing overproduction.
• Enzyme Structure:
  • Active site: Region on the enzyme that binds to the substrate.
  • Substrate: The molecule that the enzyme acts upon.
  • Product: The resulting molecules formed during the reaction.
• Induced Fit: Enzyme changes shape slightly when substrate binds, forming a tighter interaction for maximum efficiency.
• Naming Conventions:
  • Often end with "-ase" like amylase, lipase, catalase.
• Activation energy: Enzymes catalyze reactions by lowering activation energy - the energy needed for the reaction to begin.

This quiz focuses on the movement of molecules across membranes, exploring passive transport methods such as diffusion and osmosis, as well as active transport processes that require energy. Test your knowledge on how these mechanisms contribute to cellular homeostasis and nutrient absorption.