What Are the Core Tenets of Cell Theory, and How Do Prokaryotic and Eukaryotic Cells Differ?

Prokaryotes vs. Eukaryotes: Two Domains of Life

We broadly categorize living organisms into two main types based on their cellular structure:

Prokaryotes: Before the Nucleus

The term "prokaryote" literally means "before nucleus." These cells have some defining characteristics:

• No membrane-bound nucleus: Their genetic material is located in a region called the nucleoid. Think of it as a nucleus-like area, but without a surrounding membrane.
• No mitochondria
• No other membrane-bound organelles
• Naked and circular DNA
• Generally unicellular
• Reproduce via binary fission
• Examples include bacteria.

Eukaryotes: True Nucleus

On the other hand, "eukaryote" means "true nucleus." These cells are more complex and feature:

• Membrane-bound nucleus: Their DNA is enclosed within a distinct nucleus.
• Mitochondria
• Other membrane-bound organelles
• Protein-bound and linear DNA
• Can be unicellular or multicellular
• Reproduce via mitosis or meiosis
• Examples include human beings.

The Four Fundamental Concepts of Cell Theory

The cell theory is a cornerstone of biology. It outlines the essential principles that govern all living organisms:

1. All living organisms are composed of cells. This might seem obvious now, but it was a groundbreaking realization!
2. The cell is the basic functional unit of life. Everything that defines life happens at the cellular level.
3. Cells arise only from pre-existing cells. This principle, known as omnis cellula e cellula, tells us that new cells are created by the division of existing ones.
4. Cells carry genetic information in the form of DNA (deoxyribonucleic acid). This DNA is passed from parent cells to daughter cells.

A Note on Viruses

It's important to mention viruses. They're a bit of a special case because they don't reproduce on their own; they require a host cell. Additionally, their genetic information is often RNA, not DNA. Because of these differences, the last two tenets of cell theory don't strictly apply to viruses, which is why they're often considered to be on the borderline of being classified as living organisms.

From Cells to Organisms

Cells are organized into increasingly complex structures:

• A group of similar cells forms a tissue.
• Different tissues working together form an organ.
• Multiple organs cooperating create an organ system (like the circulatory, respiratory, or digestive system).
• Organ systems work together to carry out the functions of a complete organism.