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.

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