🏭 Cell Organelles

Nucleus

Structure:

• Nuclear envelope (double membrane with pores)
• Nucleolus (ribosome assembly)
• Chromatin (DNA + proteins)

Function:

• Stores genetic information (DNA)
• Controls cell activities
• Site of transcription

Endomembrane System

Endoplasmic Reticulum (ER)

Rough ER:

• Studded with ribosomes
• Protein synthesis and modification
• Makes membrane proteins and secreted proteins

Smooth ER:

• No ribosomes
• Lipid synthesis
• Detoxification (liver)
• Calcium storage (muscle)

Golgi Apparatus

• Stack of membrane sacs (cisternae)
• Modifies, sorts, packages proteins
• Adds tags (glycosylation)
• Ships proteins to destinations

Lysosomes (Animals)

• Contain digestive enzymes
• Break down macromolecules
• Autophagy (digest old organelles)
• Apoptosis (programmed cell death)

Vacuoles

Plant central vacuole:

• Storage (water, ions, pigments)
• Maintains turgor pressure
• Waste disposal

Animal vacuoles:

• Smaller, temporary
• Food vacuoles (phagocytosis)
• Contractile vacuoles (osmoregulation)

Energy Organelles

Mitochondria

Structure:

• Double membrane
• Outer membrane (smooth)
• Inner membrane (cristae - folded)
• Matrix (inner space)

Function:

• Cellular respiration
• ATP production
• Own DNA (maternal inheritance)
• Divide independently

Chloroplasts (Plants)

Structure:

• Double membrane
• Thylakoids (stacked in grana)
• Stroma (fluid)

Function:

• Photosynthesis
• Convert light → chemical energy
• Own DNA
• Divide independently

Cytoskeleton

Three types of fibers:

1. Microfilaments (actin):

   • Thinnest (7 nm)
   • Cell shape, movement
   • Muscle contraction
   • Cytoplasmic streaming

2. Intermediate filaments:

   • Medium (8-12 nm)
   • Structural support
   • Nuclear lamina
   • Keratin in hair/nails

3. Microtubules:

   • Thickest (25 nm)
   • Cell shape, organelle movement
   • Chromosome separation (spindle fibers)
   • Cilia and flagella structure

Other Organelles

Ribosomes

• Protein synthesis
• Free ribosomes → cytoplasmic proteins
• Bound ribosomes → secreted/membrane proteins
• NOT membrane-bound

Peroxisomes

• Contain enzymes
• Break down fatty acids
• Detoxify harmful substances
• Produce hydrogen peroxide → water

Centrioles (Animals)

• Pair of cylindrical structures
• Organize microtubules
• Form spindle apparatus in cell division

Key Concepts

1. Nucleus stores DNA and controls cell
2. Endomembrane system makes, modifies, transports proteins
3. Mitochondria produce ATP (cellular respiration)
4. Chloroplasts capture light energy (photosynthesis)
5. Cytoskeleton provides structure and movement
6. Organelles compartmentalize cellular functions