Eukaryotic Cells: The Building Blocks of Life

🌟 Key NEET Concepts:

  • 🔄 Fluid Mosaic Model of the cell membrane
  • 🌱 Plant vs. Animal Cells (cell wall, plastids, vacuoles)
  • 🔋 Mitochondria & Chloroplasts as energy powerhouses
  • 📦 Endomembrane System (ER, Golgi, lysosomes)
  • 🧬 Nucleus & Chromosomes (chromatin, centromere types)

🧩 Cell Basics

Eukaryotic cells (in plants, animals, fungi & protists) have:

  • 🔬 A true nucleus with a nuclear envelope
  • 🧪 Membrane-bound organelles that divide the cell into compartments
  • 🌐 Cytoskeleton for shape and movement

Plant vs. Animal Cells:
🌿 Plant cells: Cell wall, plastids (like chloroplasts), big central vacuole
🐾 Animal cells: Centrioles (absent in most plants), no cell wall

🧠 Nucleus (Cell’s Control Center)

  • Discovered by Robert Brown (1831)
  • Surrounded by double-membrane nuclear envelope with pores
  • Contains:
    • 🧵 Chromatin (DNA + proteins)
    • ⚫ Nucleolus: Makes ribosomal RNA (rRNA)
  • ❓ Fun fact: Mature red blood cells lack a nucleus!

📦 Endomembrane System (Team Players!)

These organelles work together:

  • Endoplasmic Reticulum (ER):
    • 🌐 Network of tubules in cytoplasm
    • ⛓️ Rough ER (with ribosomes): Makes proteins
    • 🛢️ Smooth ER (no ribosomes): Makes lipids
  • Golgi Apparatus:
    • 📦 Stacks of flattened sacs (cisternae)
    • ✉️ Packages materials into vesicles for transport/secretion
    • 🔀 Modifies proteins from ER & makes glycoproteins
  • Lysosomes:
    • 🧼 Membrane bags filled with digestive enzymes
    • ♻️ Break down carbs, proteins, lipids & nucleic acids
  • Vacuoles:
    • 💧 Membrane-bound storage space (water, sap, waste)
    • 🌱 In plants: Huge vacuole with tonoplast membrane
    • 🆙 Moves stuff against concentration gradient

Note: Mitochondria & chloroplasts are NOT part of this system!

🔋 Energy Organelles

  • Mitochondria (Powerhouse! ⚡):
    • 🥪 Double membrane with inner folds (cristae)
    • 📈 Increases surface area for energy production
    • 🧬 Makes ATP via aerobic respiration
    • Has its own DNA & ribosomes (70S)
  • Plastids (Only in plants & algae):
    • 🟢 Chloroplasts: Have chlorophyll for photosynthesis
    • 🟠 Chromoplasts: Store colorful pigments (carotenoids)
    • ⚪ Leucoplasts: Store nutrients (starch, oils, proteins)
    • Structure:
      • 🥬 Double membrane with inner space (stroma)
      • 🥞 Membrane discs = thylakoids (in stacks = grana)
      • 💡 Light reactions in grana, dark reactions in stroma

🔧 Other Key Parts

  • Ribosomes:
    • 🔧 Made of RNA + proteins (no membrane)
    • 🧱 Build proteins (“protein synthesis”)
    • 🧬 Eukaryotic: 80S (60S + 40S), Prokaryotic: 70S (50S + 30S)
  • Cytoskeleton:
    • 🕸️ Protein network (microtubules, microfilaments)
    • 🏗️ Gives cell shape & helps movement
  • Cilia & Flagella:
    • 👢 Hair-like structures for cell movement
    • 🔬 Core = axoneme with “9+2” microtubule pattern
    • 🧲 Emerge from basal bodies (like centrioles)
  • Centrosome & Centrioles:
    • 🎯 Cylindrical centrioles in perpendicular pairs
    • 🕸️ Made of 9 tubulin triplet fibrils
    • 🧬 Form spindle fibers during cell division (animals)

🧬 Chromosome Structure

  • 🪢 Centromere: Constriction holding 2 chromatids
  • 📍 Kinetochore: Disc structure on centromere sides
  • 🔣 Types by centromere position:
    • ⏺️ Metacentric: Middle centromere (equal arms)
    • ↕️ Sub-metacentric: Off-center (unequal arms)
    • ↘️ Acrocentric: Near end (one very short arm)
    • 🔚 Telocentric: Terminal centromere
  • 🛰️ Satellite: Tiny fragment from secondary constriction

💎 Summary

Every eukaryotic cell has:
Cell membrane + Nucleus + Cytoplasm
➕ Plants: Cell wall, plastids, large vacuole
➕ Animals: Centrioles
Organelles work together to keep cells alive! 🎉