The Cell: Structure and Function in Human Anatomy & Physiology

The Cell: Structure and Function

Basic Processes of Cells

Cells are the fundamental units of life, carrying out essential processes to maintain homeostasis and support the organism.

• Cell Metabolism: The sum of all chemical reactions within a cell, including Anabolic (building up), Catabolic (breaking down), and Oxidation-Reduction reactions. These processes provide energy and synthesize necessary molecules.

• Substance Transport: Movement of compounds into, out of, or within the cell. This includes nutrient uptake, waste removal, and intracellular trafficking.

• Communication: Cells interact with their environment and other cells through signaling molecules and membrane receptors, enabling coordination of activities.

• Reproduction: Most cells undergo Cell Division to produce new cells for growth, repair, and maintenance.

Overview of Cell Structure

Animal cells possess three major components, each with specialized functions:

• Plasma Membrane: The outer boundary of the cell, composed of a phospholipid bilayer with embedded proteins, carbohydrates, and cholesterol. It regulates the entry and exit of substances, provides structural support, and facilitates communication.

• Cytoplasm: The region between the plasma membrane and the nucleus, containing:

  • Cytosol: The intracellular fluid, a gel-like substance rich in proteins, ions, and RNA.

  • Organelles: Specialized structures that perform distinct cellular functions (e.g., mitochondria, ribosomes).

  • Cytoskeleton: A network of protein filaments that maintains cell shape, secures organelles, and enables movement.

• Nucleus: The control center of the cell, housing most of the cell's DNA and responsible for gene expression and regulation.

Functions of the Plasma Membrane

The plasma membrane is essential for maintaining cellular integrity and mediating interactions with the environment.

• Physical Isolation: Separates the cell from its surroundings, acting as a selective barrier.

• Structural Support: Provides shape and stability to the cell.

• Communication: Contains receptors and proteins for signaling and recognition.

• Transport Regulation: Controls the movement of substances into and out of the cell.

• Cell Identification: Glycoproteins and glycolipids on the membrane surface help identify the cell to other cells and the immune system.

The plasma membrane also defines and regulates fluid compartments:

• Intracellular Space: The area within the cell containing Intracellular Fluid (cytosol).

• Extracellular Space: The area outside the cell containing Extracellular Fluid (ECF).

Key Terms and Concepts

• Metabolism: All chemical reactions in a cell; includes anabolic (building) and catabolic (breaking down) processes.

• Cell Division: The process by which cells reproduce, essential for growth and repair.

• Phospholipid Bilayer: The fundamental structure of the plasma membrane, consisting of hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.

• Cytosol: The fluid portion of the cytoplasm where many metabolic reactions occur.

• Organelles: Membrane-bound structures with specialized functions (e.g., mitochondria for energy production, ribosomes for protein synthesis).

• Cytoskeleton: Protein filaments (actin, intermediate filaments, microtubules) that provide structural support and facilitate movement.

• Nucleus: Contains DNA and is the site of RNA synthesis; controls cellular activities by regulating gene expression.

Example: Cell Compartmentalization

Compartmentalization allows cells to carry out specialized functions efficiently. For example, the nucleus protects genetic material, while mitochondria generate ATP in a separate environment.

Additional info:

• Cellular processes such as metabolism and transport are tightly regulated to maintain homeostasis.

• Fluid compartments (intracellular and extracellular) are critical for nutrient exchange and waste removal.