Human Biology Lecture 2 2024
Instructor: Professor Rob Vandenberg
Institution: School of Medical Sciences, Faculty of Medicine and Health
Key Concept: The cell is a self-contained ecosystem.
Question Raised: How does “stuff” get in and out of the cell?
Structure: Phospholipid bilayer
Hydrophobic and Hydrophilic Regions
Impermeable to Most Essential Molecules and Ions:
Ions: K+, Na+, Ca2+, Cl-, HCO3-
Small water-soluble molecules: glucose
Large molecules: proteins and RNA
Permeable Substances:
Water molecules, small uncharged molecules like oxygen and carbon dioxide
Diffusion:
Molecules distribute evenly over time due to random motion (eliminates concentration gradients).
Example: Ink drop in water.
Definition: Diffusion of water through a semipermeable membrane.
Key Relationships:
Higher solute concentration = lower water concentration.
Water moves towards lower water concentration to reach equilibrium.
Characteristics of Plasma Membrane: Semi-permeable.
Examples of Solutions:
1 M glucose: 180 g/L
1 M lactose: 342 g/L
0.1 M glucose: 18 g/L
Tonicity Types:
Isotonic, Hypotonic, Hypertonic, based on solute concentration ratios.
1 M Sucrose vs. 0.3 M Sucrose:
Higher concentration of sucrose leads to a lower concentration of water.
Water moves to equalize concentration.
Non-rigid nature of cell membranes.
Osmosis Concept: "Salt sucks" due to osmotic pressure gradients.
Hypertonic, Isotonic, Hypotonic environments:
Effects on RBC appearance and functionality.
Methods of Ion Passage:
Gases can cross the lipid bilayer but ions cannot without assistance.
Functions:
Integral membrane proteins create pathways for substances to cross the membrane.
Types of proteins:
Channel proteins
Transporters (facilitated diffusion or active transport)
Function: Water channels that facilitate rapid water transport.
Importance in regulating water flow in organs like the kidney and gut.
Recognition: Peter Agre, Nobel Prize for Chemistry 2004.
Facilitated Diffusion: Movement of ions and nutrients through proteins without energy expenditure.
Active Transport: Requires energy (ATP), movement against the concentration gradient.
Active Transport:
Moves substances against the concentration gradient using energy (ATP).
Passive Transport:
Moves substances along the concentration gradient without energy.
Channels can become saturated, influencing the rate of substance movement.
Critical in cellular function: Ions conducting charge and establishing electrochemical potential differences.
Nobel Prize in Physiology or Medicine 1991:
Based on discoveries concerning single ion channels in cells.
Understanding concentrations in blood and their implications for cell function.
Mechanism:
Moves Na+ out and K+ into the cell.
Functions to maintain electrochemical gradients critical for cell life.
Electrochemical Balance:
Creates a negative membrane potential necessary for action potentials.
Action Potential in Nerves:
Phases: Depolarization, Repolarization, and Hyperpolarization.
Primary Roles of Glucose and Amino Acids:
Often use sodium gradient as a driving force.
Definitions:
Endocytosis: Molecule movement into cells.
Exocytosis: Release of molecules from cells.
Role:
Involves nutrient uptake, signal transduction, and recycling of synaptic vesicles.
Examples: Phagocytosis for engulfing particles.
Key Concepts to Understand:
Survival and function of a single cell in isolation.
Structures and functions of a cell and its organelles.
Regulation of substance flow across cell membranes.
Role of aquaporins and Na-K ATPase in maintaining gradients.
Mechanisms for transport of larger molecules.