Study Notes: Chemistry, Cells, and Tissues (Chapters 2–4, ANP College Course)

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Tailored notes based on your materials, expanded with key definitions, examples, and context.

Chapter 2: Chemistry Comes Alive

Phospholipids: Structure and Arrangement

Phospholipids are essential components of cell membranes, forming a bilayer that separates the cell from its environment.

Hydrophilic Heads: The heads are polar and attracted to water (hydrophilic), facing outward toward aqueous environments.
Hydrophobic Tails: The tails are nonpolar and repel water (hydrophobic), facing inward, away from water.
Arrangement: In membranes, phospholipids form a bilayer with hydrophilic heads facing the exterior and interior of the cell, and hydrophobic tails sandwiched in between.
Example: The plasma membrane of animal cells.

Organic vs. Inorganic Molecules; Acids vs. Bases

Molecules in biology are classified as organic or inorganic, and acids and bases play key roles in chemical reactions.

Organic Molecules: Contain carbon and are typically found in living organisms (e.g., proteins, lipids, carbohydrates).
Inorganic Molecules: Do not contain carbon-hydrogen bonds (e.g., water, salts, acids, bases).
Acids: Proton donors; release hydrogen ions (H+) in solution.
Bases: Proton acceptors; pick up H+ ions or release hydroxyl ions (OH-).
pH Scale: Acids have pH 1–5; bases have pH 8–14.
Example: Hydrochloric acid (HCl) is an acid; sodium hydroxide (NaOH) is a base.

Atomic Number and Neutrons

Atoms are defined by their atomic number and mass number.

Atomic Number: Number of protons in the nucleus; written as a subscript to the left of the atomic symbol.
Finding Neutrons:
Example: Carbon-12 has 6 protons (atomic number 6) and 6 neutrons (mass number 12).

Chemical Bonds and Reactions

Chemical bonds are formed or broken during chemical reactions, which are represented by equations.

Reactants: Substances entering into a reaction.
Products: Resulting chemical end products.
Balanced Equations: Show amounts of reactants and products.
Example:

Valence Electrons and Stability

Valence electrons determine an atom's chemical reactivity and stability.

Octet Rule: Atoms gain, lose, or share electrons to achieve 8 electrons in their valence shell.
Example: Sodium (Na) loses one electron to achieve stability; chlorine (Cl) gains one.

Chapter 3: Cells: The Living Units

Basic Parts of the Cell and Their Functions

All cells share three basic structural components.

Plasma Membrane: Flexible outer boundary; regulates entry and exit of substances.
Cytoplasm: Intracellular fluid containing organelles.
Nucleus: DNA-containing control center; directs cellular activities.

Structure of the Cell Membrane

The cell membrane is a phospholipid bilayer with embedded proteins.

Phospholipid Bilayer: Provides structural integrity and selective permeability.
Membrane Proteins: Allow cell communication, transport, and structural support.
Specialized Functions: Some proteins float freely; others are anchored.

Cell Junction Types and Their Functions

Cell junctions connect cells and regulate movement of substances.

Tight Junctions: Integral proteins fuse to form an impermeable seal; prevent passage between cells. Useful in intestinal lining.
Desmosomes: Linker proteins interlock, allowing flexibility and resistance to tearing. Found in skin and heart tissue.
Gap Junctions: Connexons form channels for small molecules and electrical signals. Important in cardiac and smooth muscle.

Active vs. Passive Transport

Transport across membranes can be active or passive.

Passive Transport: No energy required; substances move down concentration gradients.
Active Transport: Requires energy (usually ATP); substances move against gradients.

Types of Diffusion

Diffusion is the movement of molecules from high to low concentration.

Simple Diffusion: Nonpolar, lipid-soluble substances pass directly through the bilayer.
Facilitated Diffusion: Hydrophilic molecules use protein carriers or channels.
Osmosis: Movement of water across a selectively permeable membrane.

Osmotic Solutions: Isotonic, Hypertonic, Hypotonic

Cells respond differently to various osmotic environments.

Isotonic: Same osmolarity as cell; cell volume unchanged.
Hypertonic: Higher osmolarity; water leaves cell, causing shrinkage (crenation).
Hypotonic: Lower osmolarity; water enters cell, causing swelling or bursting.

Vesicular Transport and Functions

Vesicular transport moves large particles and fluids via vesicles.

Requires ATP: Energy-dependent process.
Examples: Endocytosis (import), exocytosis (export).

Cell Adhesion Molecules (CAMs)

CAMs are proteins that mediate cell interactions and movement.

Anchor cells: To extracellular matrix or each other.
Assist movement: Help cells migrate.
Attract WBCs: To injury or infection sites.
Transmit signals: Direct cell migration, proliferation, and specialization.

Plasma Membrane Receptors

Membrane receptors bind chemical signals and mediate cellular responses.

Contact Signaling: Cells recognize each other via unique surface receptors.
Chemical Signaling: Receptor-ligand interactions alter cell activity.

Cytoplasm Composition

The cytoplasm contains cytosol, inclusions, and organelles.

Cytosol: Gel-like solution with water, proteins, salts, sugars.
Inclusions: Insoluble molecules (e.g., glycogen, pigments).
Organelles: Specialized structures for metabolic functions.

Organelles and Their Functions

Organelles perform distinct cellular functions.

Mitochondria: Powerhouse; ATP production; contains own DNA/RNA.
Ribosomes: Protein synthesis; free or membrane-bound.
Endoplasmic Reticulum (ER): Rough ER synthesizes proteins; smooth ER synthesizes lipids.
Golgi Apparatus: Modifies, packages proteins and lipids.
Peroxisomes: Detoxify substances; neutralize toxins.
Lysosomes: Digestive enzymes; breakdown bacteria, viruses, toxins.
Endomembrane System: Includes ER, Golgi, vesicles, lysosomes, nuclear and plasma membranes.
Cytoskeleton: Network of rods; supports cell shape and movement.
Centrioles: Basis for cilia and flagella; microtubular structures.

Cytoskeleton and Its Components

The cytoskeleton provides structural support and facilitates movement.

Microfilaments: Thinnest; made of actin; involved in cell shape and movement.
Intermediate Filaments: Medium size; tough, ropelike; resist pulling forces; special names (neurofilaments, keratin).
Microtubules: Largest; hollow tubes; maintain cell shape, transport organelles.

Cellular Extensions

Some cells have extensions for movement or increased surface area.

Cilia: Move materials across cell surface.
Flagella: Propel cells (e.g., sperm).
Microvilli: Increase surface area for absorption.

Chromatin and Chromosome Structure

Chromatin is the complex of DNA and proteins; chromosomes are condensed chromatin.

Composition: 30% DNA, 60% histone proteins, 10% RNA.
Nucleosome: DNA wrapped around histones.
Chromosomes: Condensed chromatin; protect DNA during cell division.

Cell Cycle

The cell cycle describes the life stages of a cell.

Interphase: Cell grows and performs normal functions.
Mitotic Phase: Cell divides into two daughter cells.

Types of RNA and Their Roles

RNA types are essential for protein synthesis.

Messenger RNA (mRNA): Carries genetic code from DNA; produced by transcription.
Ribosomal RNA (rRNA): Structural component of ribosomes; site of protein synthesis.
Transfer RNA (tRNA): Carries amino acids; anticodon pairs with mRNA codon during translation.

Transcription and Translation

Gene expression involves transcription and translation.

Transcription: DNA code is copied to mRNA.
Translation: mRNA is decoded to assemble polypeptides.

Apoptosis and Cell Aging

Apoptosis is programmed cell death, important for development and health.

Process: Mitochondria release chemicals activating caspases, which degrade DNA and cytoskeleton.
Outcome: Cell shrinks and is phagocytized by macrophages.

Chapter 4: Tissue: The Living Fabric

Definition of Tissue and Histology

Tissues are groups of similar cells performing a common function; histology is the study of tissues.

Tissue: Groups of cells with similar structure and function.
Histology: Study of tissue structure and function.

Microscopy of Human Tissue: Steps

Microscopy involves preparing tissues for observation.

Fixed: Tissue preserved with solvent.
Sectioned: Cut into thin slices for light/electron transmission.
Stained: Enhances contrast; light microscopy uses dyes, electron microscopy uses metal coatings.

Epithelial Tissue: Forms and Functions

Epithelial tissue covers surfaces and lines cavities; functions include protection, absorption, filtration, excretion, secretion, and sensory reception.

Covering and Lining Epithelia: External and internal surfaces (e.g., skin).
Glandular Epithelia: Secretory tissue in glands (e.g., salivary glands).

Special Characteristics of Epithelial Tissue

Epithelial tissue has unique structural features.

Polarity: Apical (top) and basal (bottom) surfaces; apical may have microvilli.
Specialized Contacts: Tight junctions and desmosomes bind cells together.
Supported by Connective Tissue: Reticular lamina and basement membrane reinforce tissue.
Avascular but Innervated: No blood vessels; nourished by diffusion; supplied by nerves.
Regeneration: High capacity for renewal; stimulated by damage.

Classification of Epithelia

Epithelia are classified by layers and cell shape.

Layers: Simple (one layer) or stratified (multiple layers).
Shapes: Squamous (flat), cuboidal (cube), columnar (tall).
Apical Layer: Stratified epithelia are named by the shape of the apical layer.

Structure, Function, and Location Example

Simple squamous epithelium is a key example.

Structure: Single layer of flattened cells with disc-shaped nuclei.
Function: Diffusion and filtration; secretes lubricating substances.
Location: Kidney glomeruli, air sacs of lungs, lining of heart, blood vessels, lymphatic vessels, serosae.

Endocrine vs. Exocrine Glands

Glands are classified by how they release their products.

Exocrine Glands: Release secretions onto surfaces or into cavities via ducts; examples include sweat, oil, and salivary glands.
Endocrine Glands: Ductless; release hormones into interstitial fluid, which is picked up by blood or lymph.

Structural Elements of Connective Tissues

Connective tissue is the most abundant tissue, with diverse functions.

Functions: Binding, support, protection, insulation, storage, transport.

Types of Connective Tissues

Connective tissues are classified into four main types.

Connective Tissue Proper: Loose (areolar, adipose, reticular) and dense (regular, irregular, elastic).
Cartilage: Matrix from chondroblasts/chondrocytes; tough, flexible, avascular.
Bone: Osseous tissue; supports, protects, stores fat, synthesizes blood cells; rich in collagen and calcium salts.
Blood: Fluid tissue; cells in plasma; transports nutrients, wastes, gases.

Structures, Functions, and Locations of Connective Tissues

Type	Structure	Function	Location
Areolar (Loose)	Gel-like matrix with all fiber types	Wraps and cushions organs	Under epithelia
Adipose (Loose)	Closely packed fat cells	Stores energy, insulates, protects	Under skin, around kidneys
Dense Regular	Parallel collagen fibers	Attaches muscles to bones	Tendons, ligaments
Cartilage	Chondrocytes in lacunae, matrix 80% water	Support, flexibility	Joints, ear, nose
Bone	Osteocytes in lacunae, hard matrix	Support, protection, blood cell formation	Skeletal bones
Blood	Cells in plasma	Transport nutrients, gases, wastes	Blood vessels

Additional info: Some explanations and examples were expanded for clarity and completeness, including the table summarizing connective tissue types.