Cell Biology Fundamentals: Structure, Discovery, and Organelles

The Cell: Discovery and Fundamental Theory

Key Discoveries in Cell Biology

The journey into understanding cells began with groundbreaking observations:

• Robert Hooke, using a simple microscope he built, observed and described "cells" in cork in 1665.
• In 1674, Anton van Leeuwenhoek was the first to observe and describe living cells and microorganisms in water, which he called "animalcules."
• The botanist Robert Brown discovered a corpuscle inside plant cells in 1831, which he named the nucleus.
• The medical term "protoplasm" was introduced by Johannes Purkinje in 1839 to designate the liquid substance that fills the cell, essential for its health and integrity.

The Cell Theory

In 1838-1839, the botanist Matthias Schleiden and zoologist Theodor Schwann affirmed that all living things, both plants and animals, are composed of cells. This fundamental principle became known as the Cell Theory, stating that the cell is the basic unit of life.

Eukaryotic Cells: Structure and Function

Types of Eukaryotic Cells

Eukaryotic cells are characterized by possessing a true nucleus and various membrane-bound organelles. While sharing many common features, there are distinct differences between animal and plant cells:

• Animal Cells

  Animal cells typically feature a centrosome with cylindrical structures called centrioles, which are involved in cell division.

• Plant Cells

  Plant cells have a rigid cell wall that provides protection and structural support. They also possess channels called plasmodesmata, which connect one cell to another, facilitating communication and transport. Plant cells typically contain large vacuoles for storage and maintaining turgor pressure, and chloroplasts for photosynthesis.

Eukaryotic Cell Structure

The fundamental components of a eukaryotic cell include:

• Plasma Membrane

  It is a protective layer that surrounds the cell, isolating its internal environment and regulating the exchange of substances with the exterior.

• Nucleus

  The nucleus contains the cell's genetic material (DNA) and is separated from the rest of the cell by a porous double membrane known as the nuclear envelope.

• Cytoplasm

  An aqueous medium that fills the cell, containing a complex network of protein fibers called the cytoskeleton. The cytoskeleton is involved in cell movement, shape maintenance, and division. The cytoplasm also houses various cellular organelles.

• Centrosome

  Primarily found in animal cells, the centrosome controls the movement of cytoskeleton fibers and plays a crucial role in cell division.

Cellular Organelles and Their Functions

These specialized cellular elements are responsible for different vital functions:

• Endoplasmic Reticulum (ER)

  A network formed by flattened sacs and tubules. If its conduits have ribosomes attached, it is called Rough ER (involved in protein synthesis and modification). If it lacks ribosomes, it is Smooth ER (involved in lipid synthesis, detoxification, and calcium storage).

• Golgi Apparatus

  Composed of stacks of flattened membrane-bound sacs called cisternae. Substances from the endoplasmic reticulum accumulate here, are processed, sorted, and packaged into small vesicles for transport within or outside the cell.

• Ribosomes

  Small particles formed by ribosomal RNA (rRNA) and proteins. They are the sites of protein synthesis (translation).

• Mitochondria

  Spherical or elongated organelles often referred to as the "powerhouses" of the cell. They are the primary sites where cellular respiration occurs, generating ATP (energy) for the cell.

• Lysosomes

  Membranous vesicles originating from the Golgi apparatus. They contain hydrolytic enzymes that break down complex molecules into simpler ones, acting as the cell's "recycling centers."

• Vacuoles

  Membranous vesicles whose internal contents accumulate different products, including water, nutrients, and waste. They play diverse roles in storage, waste removal, and maintaining turgor pressure (especially large in plant cells).