Comparing Prokaryotic and Eukaryotic Cells

Cell Theory Overview

• Definition: Cell theory is a fundamental scientific theory that defines the properties of cells.

• Key Principles:

  • The cell is the fundamental unit of structure and function in living things.

  • All known living things are made up of cells.

  • All cells are basically the same in chemical composition.

  • Organisms can be unicellular (one cell) or multicellular (multiple cells).

Continued Principles of Cell Theory

• Origin of Cells:

  • All cells arise from pre-existing cells through the process of division.

• Hereditary Material:

  • Cells contain hereditary information (DNA) which is passed down during cell division.

• Metabolism:

  • Energy flow (metabolism and biochemistry) occurs within cells.

• Organism Activity:

  • An organism's activity relies on the collective activity of its cells.

Types of Cells

• General Categories:

  • There are two main types of cells: prokaryotic and eukaryotic.

  • Prokaryotic cells: Found in organisms of domains Bacteria and Archaea.

    • Etymology: From Greek πρό (pró) 'before' and κάρυον (káruon) 'nut, kernel'.

  • Eukaryotic cells: Found in protists, fungi, animals, and plants.

    • Etymology: From Greek eu, "well," and káruon "karyon".

Differences Between Prokaryotic and Eukaryotic Cells

• Size:

  • Eukaryotic cells are generally larger than prokaryotic cells.

  • Typical sizes:

    • Prokaryotic: 1–5 μm

    • Eukaryotic: 10–100 μm

• Nuclear Structure:

  • Eukaryotic cells have a nucleus enclosed by a double membrane.

  • Prokaryotic cells lack a nucleus; their DNA is in an unenclosed region called the nucleoid.

• Organelles:

  • Prokaryotic cells do not have membrane-bound organelles.

  • Eukaryotic cells contain membrane-bound organelles.

Structural Characteristics of Prokaryotic Cells

• Lack of Nucleus: Prokaryotic cells do not have a membrane-bound nucleus.

• Intracellular Structures: They lack many intracellular structures, making them simpler in organization.

• Key Features:

  • Plasma Membrane: Encloses the cytoplasm.

  • Ribosomes: Sites for protein synthesis.

  • Cell Wall: Rigid structure outside the plasma membrane.

  • Glycocalyx: Outer coating, which may be a capsule or slime layer.

  • Flagella: Locomotion organelles found in some prokaryotes.

  • Nucleoid: Site of DNA; not membrane-bound.

  • Plasmids: Small, circular DNA molecules, extra-chromosomal.

  • Fimbriae: Attachment structures on some prokaryotes.