Cell Structures and Functions: Microtubules, Organelles, and Cell Communication

Centrioles

Duplicated during interphase before cell division; Found in animal cells; Spindle fibers attach here (nucleating site for microtubules)

Centrosome

Houses 2 centrioles

Cilia & Flagella

Used for movement; Made of microtubules; Anchored by basal bodies (kinetosomes, structurally identical to centrioles)

Rough ER (Protein Factory)

Covered with ribosomes; Produces proteins including: Enzymes, Receptor proteins, Membrane proteins (permeable), Insulin (communication), Antibodies (immunity), Collagen, Connective tissue proteins, Cartilage proteins, Keratin, Hormones (hydrophilic), Blood proteins, Muscle tissue proteins; Vesicles ship protein products; Surrounds the nucleus

Ribosomes

Created by nucleolus inside the nucleus; Made of ~60% RNA molecules and ~40% protein; Composed of 2 subunits (quaternary structure); Function as ribozymes; Build proteins from mRNA instructions; Nucleolus houses ribosome parts

Smooth ER (Lipid Factory)

Produces lipids including: Glycerol, Fatty acids, Phospholipids, Steroids, Estrogen & testosterone, Cholesterol; Hormones (hydrophobic); Detoxifies drugs and poisons; Stores calcium and involved in calcium metabolism (muscle contractions); Surrounds the nucleus with rough ER

Golgi Apparatus ("Post Office")

Modifies proteins and lipids; Ships products in vesicles

Lysosome

Function: digestion; Surrounded by a phospholipid bilayer; Contains enzymes inside vesicle

Microtubules

Transport pathways; Structural support (cytoskeleton); Movement (spindle fibers, cilia, sperm flagella); Hollow structure

Microfilaments

Cytoskeleton fibers made of actin; Actin + myosin → muscle contractions; Stabilized by Van der Waals forces

Mitochondria

Site of cellular respiration; Break down sugar, fat, and protein into ATP; Aerobic (with oxygen) and anaerobic (without oxygen)

Nucleus

Coordinates growth, metabolism, protein synthesis, and reproduction; Houses DNA as chromatin (loosely bound); Contains nucleolus (makes ribosomes)

Peroxisomes

Phospholipid bilayer vesicle with crystalline core; Contain oxidase enzymes → reduce oxygen to water (H₂O) or hydrogen peroxide (H₂O₂) safely; Eliminate free radicals (O₁, extremely reactive); Compartment for oxidation reactions (loss of electrons or increase in oxidation state); Involved in synthesis of bile acids (extracellular digestion)

Plasma Membrane (Cell Membrane)

Phospholipid bilayer; Found in all cells; Components: Phospholipids, Proteins (channels and receptors), Carbohydrates (markers/antigens), Cholesterol (fluidity or rigidity)

Vacuole

Storage for water, food, nutrients, toxins, poisons; Large in plant cells, small in animal cells; Contractile vacuoles release water and control tonic state

Gap Junctions

Found in animal cells; Membranes are joined for exchange

Plasmodesmata

Found in plant cells; Openings in cell walls for connection to neighboring cells; Water transport via xylem; nutrient/sugar transport via phloem

Chloroplast

Site of photosynthesis; Converts sunlight into glucose; Produces organic products: glucose, fatty acids, starch

Cell Wall

Provides structure, waterproofing, flexibility, and rigidity; Plants: cellulose; Fungi: chitin (contains nitrogen); Bacteria: peptidoglycan (murein); Antibiotic penicillin prevents amino acid crosslinks → causes lysis; Insects also use chitin for exoskeletons

Cytosol / Cytoplasm

Fluid layer between membrane and nucleus; Includes cytoskeleton and cytoplasm; "Intra-" = within; intracellular = inside the cell