Cellular Classification: Prokaryotic vs Eukaryotic Cells

Cell Classification

• Cells on Earth are categorized into two groups: prokaryotic cells and eukaryotic cells.

Prokaryotic Cells

• Prokaryotes were the first cells to appear on the planet.
• All prokaryotes are single-celled.
• Examples of prokaryotes include bacteria and archaea.
• Prokaryotes are smaller cells that lack a nucleus and membrane-bound organelles.
• DNA in prokaryote cells is circular, looping around itself like a rubber band, and found in the nucleoid region.

Eukaryotic Cells

• Eukaryotic cells emerged 1.5 billion years after prokaryotes.
• The main difference between prokaryotes and eukaryotes is the presence of a central control structure, the nucleus, where DNA is housed.
• Examples of eukaryotes include plants, animals, and fungi.
• Eukaryotic cells can be part of multicellular organisms or single-celled organisms.
• DNA in eukaryotic cells is linear, with ends, like a piece of spaghetti.

Common Cell Structures

• All cells have a cell membrane, which surrounds and defines the inner environment of the cell.
• The cell membrane is composed of a phospholipid bilayer with proteins and additional components.
• All cells also have ribosomes and cytoplasm.

Additional Cell Structures

• Some prokaryotes and eukaryotes have a protective cell wall, a rigid structural support outside the cell membrane.
• Some cells have external appendages, such as cilia and flagella, which help with movement.
• Flagella are long extensions that move back and forth to facilitate cell movement, as seen in sperm cells.