Cellular Components: Cytosol, Cytoskeleton, and Centrosome Dynamics

Hyaloplasm and Cytosol: Structure and Functions

The intracellular environment of the plasma membrane consists of a liquid solution called hyaloplasm or cytosol. The combination of the cytosol and all organelles forms the cytoplasm.

Structure of the Cytosol

The cytosol is an aqueous liquid that contains between 70% and 80% water. The remaining components are proteins, as well as small organic molecules, including amino acids, carbohydrates, and ATP.

The cytosol can exist in two physical states:

• Gel state: Has a viscous consistency.
• Sol state: Has a fluid consistency.

Functions of the Cytosol

The cytosol acts as a regulator of intracellular pH, functioning as a buffer that maintains a constant pH in the cytoplasm. Its functions include:

• Glycogenesis: Synthesis reactions of glycogen occur here.
• Glycogenolysis: Hydrolysis of glycogen to obtain glucose when the cell requires it.
• Biosynthesis: Synthesis of amino acids and fatty acids.

Many of the reactions involved require ATP and tRNA.

The Cytoskeleton: Filaments and Movement

The cytoskeleton is a network of protein filaments that facilitates cell movement and maintains cell shape. It comprises: actin microfilaments, intermediate filaments, and microtubules.

Actin Microfilaments

Its functions include muscle contraction, forming the mechanical skeleton of microvilli, mitosis, and amoeboid movement.

Intermediate Filaments

They are named intermediate because their size is between that of actin microfilaments and microtubules. They are structures formed by fibrous proteins, which are very sturdy and stable. They can be grouped into 3 classes:

• Keratin filaments: Provide shape.
• Neurofilaments: Maintain the shape of neurons.
• Vimentin filaments: Prevent the breaking of cell membranes.

Intermediate filaments primarily have structural functions and maintain cell shape.

Microtubules

These are hollow tubes formed by tubulin. Their functions are:

• Formation of the mitotic spindle.
• Intracellular transport (moving vesicles through the cytoplasm).
• Cell movement.

The Centrosome: Microtubule Organizing Center

The centrosome does not have a membrane. It has a central body composed of two centrioles surrounded by dense, amorphous pericentriolar material. The entire set of these components is called the Microtubule Organizing Center (MTOC).

Centriole Structure

Each centriole is a cylinder whose walls are formed by nine groups of three, or triplet, microtubules.