Prokaryotic Cell Structure and Components

Overview and Definition of Prokaryotic Cells

  • Definition of a Prokaryotic Cell: A prokaryotic cell is defined as a primitive cell type.

  • Core Structural Characteristics:

    • It lacks a membrane-bound nucleus.

    • It lacks membrane-bound organelles (organells).

Structural Diagram of the Prokaryotic Cell

Labeled anatomical diagram of a prokaryotic cell illustrating the trilamellar cell envelope, surface appendages, and internal structures

The Prokaryotic Cell Envelope

  • Nature of the Envelope: The cell envelope is a trilamellar (trillamellar) boundary structure that surrounds the cell.

  • Layers of the Cell Envelope:

    • Glycocalyx:

    • Position: The outermost layer of the cell envelope.

    • Function: Serves in cellular protection.

    • Function: Prevents desiccation (dessication).

    • Middle Layer (Cell Wall):

    • Position: The intermediate or middle layer of the envelope.

    • Function: Imparts rigidity (riditity) and structural support to the cell.

    • Cell Membrane:

    • Position: The innermost layer of the cell envelope.

    • Function: Plays an essential role in absorption.

Surface Appendages and Internal Components

  • Surface Structures:

    • Pili: Outward-projecting, tubular surface structures extending from the envelope.

    • Flagella: Elongated, whip-like locomotory appendages anchored through the cell boundary.

  • Cytoplasmic and Genetic Components:

    • 70S70\text{S} Ribosomes: Ribosomal complexes distributed throughout the intracellular space for protein synthesis.

    • Nucleoid Region: The central, non-membrane-bound cytoplasmic region where the primary tangled genomic DNA is localized.

    • Plasmid: Small, independent circular DNA structures situated within the cytoplasm.