General Biology: Structure and Function of Biomolecules

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This section introduces the fundamental properties of life and the scientific methods used in biological research.

Properties of Life: Life is characterized by organization, metabolism, responsiveness, growth, development, reproduction, and adaptation.
Scientific Investigations: Biologists use observation, hypothesis formation, experimentation, and analysis to understand living systems. The scientific method involves ongoing cycles of these steps, with conclusions based on evidence.
Example: Testing the effect of light on plant growth by forming a hypothesis, conducting experiments, and analyzing results.

This section covers the structure of atoms, the nature of chemical elements, and the types of bonds that form biological molecules.

Structure of an Atom: Atoms consist of a nucleus (protons and neutrons) and electrons in orbitals.
Elements: Pure substances consisting of only one type of atom; essential elements for life include carbon, hydrogen, oxygen, and nitrogen.
Types of Chemical Bonds:
- Ionic Bonds: Transfer of electrons between atoms (e.g., NaCl).
- Covalent Bonds: Sharing of electron pairs between atoms (e.g., H2O).
- Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., between water molecules).
Importance of Bonds: The type of bond affects the properties and functions of molecules in biological systems.
Macromolecules: Large molecules (proteins, nucleic acids, carbohydrates, lipids) built from smaller subunits (monomers).
Example: Water's unique properties (cohesion, adhesion, high specific heat) arise from hydrogen bonding.

This section explores the structure of proteins, the properties of amino acids, and the relationship between protein structure and function.

Water Solubility and Amino Acids: The solubility of amino acids and proteins depends on the polarity and charge of their side chains.
Protein Structure Levels:
- Primary Structure: Sequence of amino acids in a polypeptide chain.
- Secondary Structure: Local folding into alpha-helices and beta-sheets, stabilized by hydrogen bonds.
- Tertiary Structure: Overall 3D shape of a single polypeptide, determined by interactions among side chains.
- Quaternary Structure: Association of multiple polypeptide chains.
Protein Folding and Denaturation: Proper folding is essential for function; denaturation (by heat, pH, chemicals) disrupts structure and function.
Protein Function: Proteins serve as enzymes, structural components, transporters, and more in living organisms.
Example: Hemoglobin's quaternary structure enables oxygen transport in blood.

This section describes the structure and function of carbohydrates, including simple sugars and complex polysaccharides.

Monosaccharide Variations: Monosaccharides (e.g., glucose, fructose) differ in carbon number and arrangement.
Polysaccharide Structure and Storage: Polysaccharides like starch and glycogen store energy; cellulose provides structural support in plants.
Carbohydrate Structure-Function Relationship: The branching and linkage types in polysaccharides affect their digestibility and function.
Example: Glycogen is highly branched, allowing rapid release of glucose in animals.

This section covers the major classes of lipids, their roles in biological membranes, and mechanisms of membrane transport.

Major Types of Lipids:
- Fats (Triglycerides): Energy storage molecules composed of glycerol and fatty acids.
- Steroids: Lipids with a characteristic four-ring structure (e.g., cholesterol).
- Phospholipids: Major components of cell membranes, with hydrophilic heads and hydrophobic tails.
Phospholipid Bilayer Formation: Spontaneous assembly in water due to hydrophobic and hydrophilic interactions.
Membrane Permeability:
- Small nonpolar molecules (O2, CO2) cross easily.
- Polar molecules and ions (H2O, Na+, glucose) require transport proteins.
Fatty Acid Types:
- Saturated: No double bonds; solid at room temperature.
- Unsaturated: One or more double bonds; liquid at room temperature.
- Trans Fats: Unsaturated fats with trans double bonds; associated with health risks.
Osmosis: Diffusion of water across a selectively permeable membrane.
Membrane Transport:
- Passive Transport: Movement down a concentration gradient (includes simple and facilitated diffusion).
- Active Transport: Movement against a gradient, requiring energy (e.g., sodium-potassium pump).
Example: The sodium-potassium pump uses ATP to maintain ion gradients across the plasma membrane.

Transport Type	Energy Required?	Direction	Example
Simple Diffusion	No	Down gradient	O2 crossing membrane
Facilitated Diffusion	No	Down gradient	Glucose via carrier protein
Active Transport	Yes (ATP)	Against gradient	Sodium-potassium pump

The sodium-potassium pump hydrolyzes ATP to move 3 Na+ ions out and 2 K+ ions into the cell: