Introduction to Biological Transport and Macromolecules

The pH Scale and Basics of Transport

• The pH Scale:     * An acidic pH ranges from $0$ to $6.9$.     * A pH of $7$ is considered neutral.     * A pH of $7.1$ and beyond is classified as basic.

• Molecular Transport Concepts:     * Transport refers to why and how molecules move from one location to another.     * Passive Transport: Typically involves molecules moving from an area of high concentration to an area of low concentration.     * Osmosis: This process follows the solvent (water) rather than the actual water level relative to solute. In osmosis, water flows toward the higher solute concentration.

Questions & Discussion: Diffusion and Osmotic Movement

• Q: Can we go over this [chart] again?     * Response: The chart explores two concepts: Diffusion and Osmosis.     * Diffusion Explained: If there is a high concentration of something on one side, it naturally moves to an area of less concentration. Example: If everyone in the room moved outside where there is nobody.     * Solute Definition: A solute is anything being dissolved. Anything other than water is considered a solute.     * Directional Movement Example: If the outside has $30\%$ solutes and the inside has $10\%$, the solute will move from the outside to the inside (high to low).     * Water Movement (Osmosis): Water does not flow based on the high-to-low concentration of water itself, but rather based on the solute concentration. Water flows toward the higher solute concentration to dissolve it. Even if water is technically lower on the inside of a cell, if the outside solute is higher, water will leave the cell.

• Q: If it wasn't water, would the $30\%$ solute still go into the $10\%$?     * Response: Yes, if it is just solutes, the $30\%$ will always flow to the $10\%$.

• Metaphor for Water Flowing to Solute: Digestion is an example. If water did not flow out to break down a hamburger in your mouth, the burger would remain intact. Water is essential to dissolving and breaking down the solute (food).

• The Danger of Saltwater: Drinking saltwater can dehydrate or kill you because water flows toward the high salt concentration. Even though you have water in your body, the salt causes the water to leave your body at uncontrollable rates.

• Pure Water Availability: It is nearly impossible to find naturally occurring "just water." Saltwater has salt, freshwater has minerals, and spring water has electrolytes. Distilled water, created by removing all other elements with a machine, is the only condition where you have just water.

• Equilibrium and Molecular Motion:     * Molecules are consistently in motion and colliding (e.g., oxygen molecules in the air).     * Molecules only stop moving if they are frozen.     * In a situation with equal concentrations (e.g., $5$ molecules on each side), movement still occurs. For every molecule that moves one way, another moves back.     * Case Study (55/45 Comparison): In a hypothetical scenario involving $55\%$ and $45\%$ water, water will flow back and forth until it reaches $50\%$ on each side. If a student puts "equal movement" on a test for these scenarios, it is correct because there is always movement, even when balanced.

Macromolecules: Foundations of the Human Body

• Definitions:     * Macromolecule: A "big molecule."     * Polymers: Another name for macromolecules ("poly" means many).     * Monomers: The smaller pieces or building blocks that make up a polymer.     * Chemical Classification: Every macromolecule has a specific structure or symbol that identifies it (e.g., like a Toyota emblem vs. a Hyundai emblem on a car).

• The Four Major Macromolecules:     1. Carbohydrates     2. Lipids (Fats)     3. Proteins     4. Nucleic Acids

• Chemical Reactions (Lego Analogy):     * Synthesis (Dehydration): The process of creating a polymer from monomers. This involves losing a water molecule to form a chemical bond.     * Hydrolysis: The process of breaking down a polymer into monomers by introducing water into the reaction.

• The Biological Cycle (Hamburger Example):     * A hamburger is mostly protein (polymer).     * To build muscle, your body cannot just use the whole hamburger. It must break the protein down into monomers via hydrolysis.     * Once broken down, the body rebuilds the pieces into muscle via dehydration/synthesis.     * Body Survival: If you do not eat consistently, your body has no external pieces to build with. It will eventually break down its own pieces (muscles decay, liver/kidneys break down) until it can no longer function.

Carbohydrates: Energy and Structure

• Monomers (Monosaccharides):     * A monosaccharide is a single or simple sugar (saccharide = sugar).     * Key Examples: Glucose, fructose, galactose, mannose, ribose, and deoxyribose.

• Function and Efficiency:     * The primary role of carbohydrates is to provide energy in the form of $ATP$ via cellular respiration.     * Glucose is an easily accessible and versatile form of energy. Unlike fat (stored in adipose tissue), which is extremely difficult to break down, glucose is broken down quickly.     * Cravings: When blood sugar drops, the body craves sugar (like a Coke or candy bar) for a quick energy spike.

• The Brain's Reliance on Glucose:     * The brain primarily uses glucose for energy.     * The brain consumes over $50\%$ of the body's sugar. The body will prioritize supplying the brain with sugar even at the expense of other organs like the liver or heart.

• Disaccharides:     * Consist of two monosaccharides joined together.     * Sucrose: The common sugar found in candy bars and sugar packets. It must be broken down via hydrolysis to provide energy.

• Polysaccharides:     * Consist of thousands of monosaccharides joined together.     * Examples:         * Starch: How plants (which create glucose via photosynthesis) store sugar for later use.         * Glycogen: How humans store sugar. Glycogen is stored in the muscles and liver. If you haven't eaten, your liver goes through hydrolysis to turn glycogen back into glucose for your brain.         * Cellulose: Found in plants. It provides rigidity to plant stems (the "skeleton"). Humans cannot break down cellulose; it is known as fiber. Fiber aids digestion by pulling water into the colon.         * Chitin: A sugar that makes up the exoskeleton of arthropods like crabs and spiders.

• Glycogen Storage Disease: A rare condition where individuals can create glycogen but cannot break it down. This causes the liver to grow larger and larger as glycogen accumulates, which physicians can detect via palpation of the abdominal cavity.