Meeting in General-20250802_171617-Meeting Recording

Cell Theory & Core Definition

• Cell = basic structural, functional, and reproductive unit of all living organisms.
• Modern Cell Theory (3 postulates)
  • The cell is the smallest living unit in all organisms.
  • All living things are composed of cells.
  • All cells arise from pre-existing cells.
• Levels of biological organization build upward from cells to tissues, organs, systems, and the organism.

Major Categories of Cells

• Prokaryotic Cells
  • No membrane-bound nucleus; DNA free-floating in cytoplasm.
  • Lack membrane-bound organelles (no mitochondria, ER, etc.).
  • Generally smaller than eukaryotes; examples: bacteria, archaea.
• Eukaryotic Cells
  • Possess true membrane-bound nucleus containing DNA.
  • Contain membrane-bound organelles (mitochondria, Golgi, ER…).
  • Usually larger; examples: plants, animals, fungi, protists.
• Shared basic parts (both cell types)
  • Plasma membrane
  • Cytoplasm
  • Ribosomes (non-membranous in prokaryotes; free or ER-bound in eukaryotes)

Universal Structural Components

• Cytoplasm
  • Gel-like cytosol + organelles; site of most metabolic reactions.
  • Functions as cellular “room space” holding organelles and providing medium for chemical reactions.
• Plasma (Cell) Membrane
  • Thin, flexible lipid bilayer acting as security gate—regulates entry/exit of water, ions, nutrients, wastes.
  • Facilitates cell-to-cell communication and provides limited protection.

Organelle Overview (Eukaryotic Focus)

• Nucleus – Control center; stores DNA, coordinates replication, gene expression, repair.
• Mitochondria – Powerhouse; produce ATP via Krebs cycle & electron transport.
• Endoplasmic Reticulum (ER)
  • Rough ER: studded with ribosomes; synthesizes/initially modifies proteins.
  • Smooth ER: lipid synthesis, detoxification, carbohydrate metabolism.
• Golgi Apparatus – Stack of cisternae; modifies, sorts, packages, and ships proteins/lipids ("Shopee sorting center").
• Lysosomes – Enzyme-filled sacs; intracellular digestion of waste & old organelles ("garbage disposal").
• Vacuoles – Storage sacs for water, food, ions, wastes (large central vacuole in plant cells).
• Peroxisomes – Oxidative vesicles; break down fatty acids/amino acids, detoxify $H<em>2O</em>2$ via catalase.
• Proteasomes – Large protein complexes (non-membranous); degrade misfolded or unneeded proteins (ubiquitin-tag system).

Plant-Specific Structures

• Chloroplasts – Contain chlorophyll; conduct photosynthesis (autotrophic food production; solar panels of the cell).
• Cell Wall – Rigid external layer (cellulose) providing support & protection.
• Large Central Vacuole – Maintains turgor pressure, storage, waste sequestration.

Cellular Metabolism & Core Functions

• Metabolism = sum of all chemical reactions inside a cell.
  • Catabolism: break down nutrients → release energy (some lost as heat, helping keep body at $36.7${–}$37.7\,^{\circ}\text{C}$).
  • Anabolism: synthesis of macromolecules (proteins, lipids, nucleic acids).
• Synthesis of Molecules – Cells manufacture proteins, lipids, enzymes; dictates cell’s structural & functional identity (e.g., keratin in skin, contractile proteins in muscle).
• Communication – Chemical (hormones, neurotransmitters) & electrical (neurons, muscles) signaling maintains homeostasis.
• Reproduction & Inheritance
  • Mitosis: produces two genetically identical daughter cells for growth/repair.
  • Meiosis: specialized division generating gametes.
  • All somatic cells ("most cells") contain complete genome copy.

Microscopy Toolbox

• Light Microscope – Uses light; views general features (cell membrane, nucleus) of cells, tissues, bacteria.
• Electron Microscopes (use beams of electrons)
  • Scanning EM (SEM): 3-D surface images.
  • Transmission EM (TEM): high-resolution internal ultrastructure (mitochondria, ER arrangement).

External Cell Surface Specializations

• Cilia – Short, hair-like; powered by microtubules + dynein; move substances across cell surface (e.g., respiratory epithelium).
• Flagella – Longer; provide locomotion (e.g., sperm tail).
• Microvilli – Minute, non-motile membrane folds; greatly increase surface area for absorption (intestine, kidney). Analogy: toothbrush bristles.

Cytoplasm, Cytoskeleton & Internal Architecture

• Cytoskeleton Components
  • Microtubules (tubulin; hollow tracks): maintain shape, form spindle, compose cilia/flagella.
  • Actin Filaments (microfilaments; thin ropes): shape changes, movement, support microvilli.
  • Intermediate Filaments (rope-like): tensile strength, resist stress.
• Centrosome & Centrioles – Microtubule-organizing center near nucleus; duplicate & form