Cell Biology Notes

Overview

• Cells are the smallest living units of an organism.
• All cells share three common features:
  • Cell Membrane: Separates the inside of the cell from its environment.
  • Cytoplasm: Jelly-like fluid inside the cell.
  • DNA: Genetic material of the cell.

Types of Cells

Eukaryotic Cells

• Have organelles, including a nucleus and specialized parts.
• More complex, found in plants and animals.

Prokaryotic Cells

• Lack a nucleus and membrane-enclosed organelles.
• Genetic material not contained within a nucleus.
• Always unicellular, e.g., bacteria.

Organelles

• Definition: "Little organs"; specialized parts of a cell with unique functions.

Nucleus

• Control center of the cell, contains DNA.
• Chromatin: Tangled form of DNA found inside the nuclear membrane.
• During cell division, DNA condenses into chromosomes.
• Nucleolus: Structure within the nucleus where ribosomes are made.

Ribosomes

• Synthesize (make) proteins.
• Can be free-floating or attached to the Endoplasmic Reticulum (ER).

Endoplasmic Reticulum (ER)

• A membrane-enclosed passageway for transporting materials.
• Rough ER: Ribosomes attached to it.
• Smooth ER: No ribosomes attached.

Golgi Apparatus (Golgi Body)

• Receives proteins and customizes them for cell use.
• Modifications include folding proteins into usable shapes and adding lipids or carbohydrates.

Vacuoles

• Sac-like structures for storing materials.
• Central Vacuole in plant cells: Stores water.

Lysosomes

• Garbage collectors that dispose of damaged or worn-out cell parts.
• Filled with enzymes to break down cellular debris.

Mitochondria

• The powerhouse of the cell.
• Produce ATP through cellular respiration.
• More mitochondria are found in energy-demanding cells.

Cytoskeleton

• Maintains cell shape.
• Composed of:
  • Microfilaments: Thread-like, made of protein.
  • Microtubules: Thin hollow tubes.

Chloroplasts (in Plant Cells)

• Site of photosynthesis; captures sunlight for energy.
• Contains chlorophyll, giving plants their green color.

Cell Wall (in Plant Cells)

• Provides shape, support, and protection.
• Animal cells do not have a cell wall.

Unique Cell Structures

• Cilia: Microscopic hair-like projections in some human cells (e.g., respiratory tract) that help trap inhaled particles.
• Flagella: Tail-like structures; facilitates movement in some bacteria and sperm cells.

Summary

• Eukaryotic Cells: Have a nucleus and membrane-enclosed organelles (plant and animal cells).
• Prokaryotic Cells: Unicellular organisms without a nucleus (e.g., bacteria).
• All cells have a cell membrane, cytoplasm, and genetic material.
• Both plant and animal cells have mitochondria; only plant cells have chloroplasts.