Lecture Notes: Cells and Their Structures

Basic Characteristics of All Cells

• Smallest living units of an organism
• Common features:
  • Cell membrane: Separates the cell's interior from the external environment
  • Cytoplasm: Jelly-like fluid inside the cell
  • DNA: Genetic material of the cell

Types of Cells

Eukaryotic Cells

• Have organelles, including a nucleus
• More advanced and complex
• Found in plants and animals

Prokaryotic Cells

• Do not have a nucleus or membrane-enclosed organelles
• Contain genetic material not within a nucleus
• Always unicellular (e.g., bacteria)

Organelles and Their Functions

Nucleus

• Control center of the cell
• Contains DNA, which dictates cell functions
• Chromatin: Tangled form of DNA inside the nuclear membrane
• Chromosomes: Condensed DNA when the cell is ready to divide
• Nucleolus: Structure inside the nucleus where ribosomes are made

Ribosomes

• Synthesize proteins
• Can be free-floating in the cytoplasm or attached to the endoplasmic reticulum (ER)

Endoplasmic Reticulum (ER)

• Membrane-enclosed passageway for transporting materials
• Rough ER: Has ribosomes attached
• Smooth ER: Does not have ribosomes attached

Golgi Apparatus (Golgi Body)

• Modifies and customizes proteins into usable forms
• Proteins emerge from the ER in vesicles and are received by the Golgi apparatus, which folds them or adds materials like lipids or carbohydrates

Vacuoles

• Sac-like structures for storage
• Central vacuole: Stores water in plant cells

Lysosomes

• Garbage collectors that take in damaged or worn out cell parts
• Contain enzymes to break down cellular debris

Mitochondria

• Powerhouse of the cell
• Creates ATP molecules during cellular respiration to provide energy
• Cells needing more energy have more mitochondria

Cytoskeleton

• Maintains the cell's shape
• Includes microfilaments (protein threads) and microtubules (hollow tubes)

Chloroplasts (in plant cells)

• Site of photosynthesis
• Contains green pigment called chlorophyll

Cell Wall (in plant cells)

• Provides shape, support, and protection
• Not present in animal cells

Unique Cell Structures

Cilia

• Microscopic hair-like projections
• Found in respiratory tract cells, help trap and expel inhaled particles

Flagella

• Tail-like structures aiding in cell movement
• Present in some bacteria and sperm cells in humans

Summary

• Eukaryotic cells: Plant and animal cells with nucleus and organelles
• Prokaryotic cells: Unicellular organisms without nucleus or organelles
• All cells have a cell membrane, cytoplasm, and genetic material
• Both plant and animal cells have mitochondria, but only plant cells have chloroplasts