Cell Structure: Prokaryotes & Eukaryotes
Understanding the fundamental building blocks of all life
🔬 1. All Living Things Are Made of Cells
All living organisms — from the tiniest bacterium to the largest whale — are composed of cells. The cell is the basic structural and functional unit of life. Cells fall into two broad categories based on their internal organization:
🦠 Prokaryotic Cells
Pro- = "before" | -karyon = "nucleus"
Found in organisms of domains Bacteria and Archaea. These cells lack a membrane-bound nucleus.
🧫 Eukaryotic Cells
Eu- = "true" | -karyon = "nucleus"
Found in animals, plants, fungi, and protists (Domain Eukarya). These cells have a membrane-bound nucleus.
🧬 2. Four Features ALL Cells Share
Despite their differences, every cell on Earth shares four common components:
Plasma Membrane
A phospholipid bilayer that separates the cell's interior from its external environment and controls what enters/exits.
Cytoplasm
A jelly-like substance filling the cell interior where chemical reactions occur and organelles are suspended.
DNA
The genetic material that carries instructions for building proteins and controlling cell activities.
Ribosomes
Molecular machines that read mRNA and synthesize (build) proteins essential for cell function.