Introduction to Biological Macromolecules and Cellular Homeostasis

Acids release hydrogen ions when dissolved in water, whereas basic solutions cause a high release of hydroxide ions ( $OH^-$ ).
The pH scale classifies the strength of acids and bases from $0$ to $14$ , where $0$ is most acidic, $14$ is most basic, and $7$ is neutral (representing balanced hydrogen and hydroxide ions).
Human blood maintains a pH range between $7.35$ and $7.45$ (also noted within ranges up to $7.50$ ).
Buffers are substances that minimize pH changes to help maintain stable internal conditions.
Homeostasis is the process of maintaining stable internal conditions within an organism.

Question / Prompt: What molecules are found in pizza dough and cheese besides carbohydrates and fats?
Response / Discussion: Gluten was suggested; however, gluten is made of amino acids. Amino acids build proteins. Pizza contains three major nutrient molecules: carbohydrates, lipids (fats), and proteins.

The four major biological macromolecules (also called biomolecules or molecules of life) are:
- Carbohydrates: Provide quick, immediate energy; burned first by the body before lipids.
- Lipids: Function in long-term energy storage, thermal insulation, protective organ coatings, cellular membrane structure, and hormone synthesis.
- Proteins: Serve diverse roles including enzymatic catalysis, movement, cellular defense, structural support, and hormone signaling.
- Nucleic Acids: Store cellular genetic information (such as DNA and RNA).

Macromolecules are large polymers assembled from simple subunits called monomers.
Dehydration Reaction: Synthesizes polymers by removing a water molecule to bind monomers together.
Hydrolysis: Breaks down polymers into individual monomer subunits by adding a water molecule.

Monosaccharides: Simple carbohydrates consisting of a single sugar subunit (e.g., glucose).
Disaccharides: Carbohydrates composed of two linked sugar subunits (e.g., lactose in milk, sucrose).
Polysaccharides: Complex carbohydrates consisting of many sugar subunits:
- Storage Polysaccharides: Starch in plants; glycogen in animals and humans.
- Structural Polysaccharides: Cellulose forms plant cell walls. Humans lack the enzyme required to digest cellulose, so it acts as dietary fiber to clean the colon. Herbivores (such as cows) can break down and absorb cellulose.

Lipids do not mix with water, but play critical non-energy roles in organisms.
Phospholipids: Construct cell membranes via a phospholipid bilayer. The negatively charged phosphate head interacts with water inside and outside the cell, while nonpolar lipid tails face inward toward each other.
Cholesterol: Used by the body to produce bile acids (which emulsify fats) and steroid hormones. Excess dietary cholesterol can accumulate and line arteries, contributing to cardiovascular issues.
Steroid Hormones: Includes sex hormones such as estrogen and testosterone.

Amino acids are the monomer subunits of proteins.
A protein's specific three-dimensional shape determines its biological function.
Key examples of protein functions:
- Movement: Actin and myosin proteins drive muscle contraction.
- Defense: Immunoglobulins and antibodies target infectious agents like viruses and bacteria.
- Structure: Keratin in skin and hair.
- Egg Proteins: Albumin.
Denaturation: Occurs when environmental factors (such as heat) alter a protein's shape, causing it to lose function (e.g., clear egg white albumin turning permanently into an opaque white solid). Some proteins can regain functionality once normal conditions are restored.