Cell Biology: Structure, Composition, and Organization
Cell: The Minimum Unit of Life
According to molecular biology, the cell is the minimum supramolecular organization that meets all the characteristics of living things. It is also defined as the smallest portion of material that fulfills vital functions, representing the unity of structure and function.
Cellular Composition and Specialization
Each cell possesses a chemical composition and similar structures. Some cells remain undifferentiated, while others specialize to fulfill specific functions. For example, neurons specialize in nerve impulse transmission. Moreover, the structure of cell organelles, the presence of certain organelles, and variations in chemical composition depend on structural and functional specialization.
The cell has a unit composition; that is, all cells are formed by the same chemical elements, molecules, macromolecules, and macromolecular aggregates.
Levels of Organization in Living Things
The levels of organization proceed as follows:
- Atom
- Simple molecule
- Compound molecule
- Macromolecule
- Supramolecular aggregate
- Cellular organelle
- Cell
The property of living matter is that it is not homogeneous, and the structures forming the molecular and cellular levels are diverse.
Essential Components of All Cells
All cells share the following components:
- Plasma or Cell Membrane: A composite double layer of phospholipids in which various proteins are embedded.
- Cytoplasmic Matrix or Cytoplasm: An almost liquid gel composed primarily of water, within which molecules and macromolecules such as carbohydrates, lipids, amino acids, and proteins are suspended.
- Genetic Material or Chromatin: This material allows for self-duplication and the transmission of species characteristics to offspring. It is formed by deoxyribonucleic acid (DNA) associated with proteins (histones).
Differences Between Eukaryotic and Prokaryotic Cells
Prokaryotes
In prokaryotes:
- The genetic material is free in the cytoplasm.
- The cell lacks a true nucleus.
- The boundary is only the plasma membrane (no true membrane-bound organelles, except for ribosomes, which have a different structure than those in eukaryotes).
- They are generally smaller than eukaryotes and lack specialized organelles.
- Prokaryotic organisms belong to the Archaea and Bacteria kingdoms (Monera).
Eukaryotes
In eukaryotes:
- The genetic material is contained within the nucleus. The nucleus is the fundamental feature of eukaryotic cells.
- They possess various molecular aggregates and specialized organelles in the cytoplasm, such as plastids and mitochondria, in addition to the plasma membrane.
- Eukaryotic organisms belong to the kingdoms Protoctista, Fungi, Plantae, and Animalia.