General Biology: Fundamental Concepts and Molecular Basis of Life

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All living things share certain fundamental properties that distinguish them from non-living matter.

Cellular Organization: All living organisms are composed of one or more cells.
Metabolism: Living things carry out chemical reactions to obtain and use energy.
Homeostasis: The ability to maintain a stable internal environment.
Growth and Development: Organisms increase in size and complexity over time.
Reproduction: The ability to produce new individuals.
Response to Stimuli: Organisms can sense and respond to changes in their environment.
Evolutionary Adaptation: Populations change over generations through adaptations.

Atoms are the basic units of matter, and their interactions form the basis of all chemical substances.

Structure of an Atom: Consists of a nucleus (protons and neutrons) and electrons in orbitals.
Element: A substance made of only one type of atom.
Covalent Bonds: Atoms share electron pairs. Example: (water)
Ionic Bonds: Electrons are transferred from one atom to another, creating charged ions. Example: and in (table salt)
Polar Covalent Bonds: Electrons are shared unequally, resulting in partial charges. Example: The O-H bond in water.
Nonpolar Covalent Bonds: Electrons are shared equally. Example: molecule.

Water is essential for life due to its unique chemical and physical properties.

Molecular Structure: Water is a polar molecule with a bent shape, leading to hydrogen bonding.
Cohesion and Adhesion: Water molecules stick to each other (cohesion) and to other substances (adhesion).
High Specific Heat: Water can absorb a lot of heat before changing temperature.
Solvent Properties: Water dissolves many substances, making it a universal solvent.
Acids and Bases: Acids release ions in solution; bases accept or release ions.

Carbon's ability to form four covalent bonds makes it the backbone of organic molecules.

Macromolecules: Large molecules essential for life, including carbohydrates, proteins, lipids, and nucleic acids.
Polymerization: Monomers are joined to form polymers via dehydration synthesis; polymers are broken down by hydrolysis.

Carbohydrates are energy sources and structural components in cells.

Monosaccharides: Simple sugars (e.g., glucose, fructose).
Disaccharides: Two monosaccharides joined (e.g., sucrose).
Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose, glycogen).

Lipids are hydrophobic molecules important for energy storage, membrane structure, and signaling.

Fats and Oils: Composed of glycerol and fatty acids.
Saturated vs. Unsaturated Fatty Acids: Saturated have no double bonds; unsaturated have one or more double bonds.
Phospholipids: Major component of cell membranes, with hydrophilic heads and hydrophobic tails.
Steroids: Lipids with a four-ring structure (e.g., cholesterol).

Proteins are polymers of amino acids and perform a vast array of functions in cells.

Amino Acids: Building blocks of proteins, each with a central carbon, amino group, carboxyl group, and variable side chain (R group).
Peptide Bonds: Link amino acids together.
Protein Structure:
- Primary: Sequence of amino acids.
- Secondary: Local folding (alpha helices, beta sheets).
- Tertiary: Overall 3D shape.
- Quaternary: Association of multiple polypeptides.
Denaturation: Loss of protein structure and function due to environmental changes.

Cells are classified based on the presence or absence of a nucleus and membrane-bound organelles.

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent	Present
Membrane-bound Organelles	Absent	Present
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists

The cell membrane is a selectively permeable barrier composed mainly of a phospholipid bilayer with embedded proteins.

Fluid Mosaic Model: Describes the dynamic arrangement of phospholipids and proteins.
Phospholipid Bilayer: Hydrophilic heads face outward; hydrophobic tails face inward.
Membrane Proteins: Involved in transport, signaling, and structural support.

Cells regulate the movement of substances across membranes through various mechanisms.

Passive Transport: Movement down a concentration gradient without energy input.
- Diffusion: Movement of molecules from high to low concentration.
- Osmosis: Diffusion of water across a selectively permeable membrane.
- Facilitated Diffusion: Transport via membrane proteins.
Active Transport: Movement against a concentration gradient, requiring energy (usually ATP).
Bulk Transport: Endocytosis and exocytosis move large molecules or particles.

Eukaryotic cells contain specialized organelles that perform distinct functions.

Nucleus: Contains genetic material (DNA).
Mitochondria: Site of cellular respiration and energy (ATP) production.
Endoplasmic Reticulum (ER): Synthesizes proteins (rough ER) and lipids (smooth ER).
Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.
Lysosomes: Contain digestive enzymes for breakdown of macromolecules.
Chloroplasts: Site of photosynthesis in plant cells.

Eukaryotic organelles work together to maintain cellular function and homeostasis.

Proteins synthesized in the rough ER are modified in the Golgi apparatus and transported to their destinations.
Energy produced by mitochondria powers cellular processes.
Communication between organelles ensures efficient cellular operation.