Introduction to Medical Biology and Genetics: Fundamental Cell Biology and Heredity

General Features of Cells

Overview of Cellular Life

Cells are the basic structural and functional units of all living organisms. Despite the diversity among the more than 10 million species on Earth, all species share fundamental cellular characteristics, especially in terms of heredity and reproduction.

• Heredity: All species reproduce, yielding copies of themselves. This process ensures the transmission of genetic information from one generation to the next.

• Genetic Information: Drives complex chemical systems essential for cell organization and survival.

• Cellularity: Organisms can be unicellular (single cell) or multicellular (many cells). Multicellular organisms arise from cell divisions starting from a single cell.

• Cells as Vehicles of Heredity: Each cell contains all hereditary information for its species.

Universal Features of Cells

Despite their diversity, all cells share several universal features related to their genetic material and biochemical processes.

• Hereditary Information: Stored in the same chemical form—nucleic acids (DNA or RNA).

• Nucleotide Universality: The four main nucleotides—Adenine (A), Cytosine (C), Guanine (G), Thymine (T) (or Uracil (U) in RNA)—are universal across species.

• Gene Expression Machinery: Proteins involved in reading and replicating hereditary information function similarly in different species.

• Energy Metabolism: Most cells use ATP (Adenosine Triphosphate) as their primary energy source.

• Enzymes: Proteins act as catalysts to increase the rate of chemical reactions.

• Cell Membrane: All cells are enclosed by a plasma membrane that regulates the passage of nutrients and waste.

• Ribosomes: Present in all cells for protein synthesis.

• Cytoplasm: The internal fluid environment where cellular processes occur.

Consequences of Cells: Taxonomy and Classification

Taxonomy and Diversity

The scientific study of living things involves their classification into hierarchical groups based on shared characteristics. This system is called taxonomy.

• Classification of Humans:

  • Domain: Eukaryota

  • Kingdom: Animalia

  • Phylum: Chordata

  • Class: Mammalia

  • Order: Primata

  • Family: Hominidae

  • Genus: Homo

  • Species: Homo sapiens

Additional info: Taxonomy helps organize biological diversity and understand evolutionary relationships.

Types of Cells: Prokaryotic vs. Eukaryotic

Cells are classified into two main types based on their structural and functional characteristics.

• Prokaryotic Cells: Include Bacteria and Archaea. They lack a true nucleus and membrane-bound organelles.

• Eukaryotic Cells: Include Protists, Fungi, Animals, and Plants. They possess a true nucleus and various organelles.

Additional info: Viruses and prions are not considered living cells but are important in genetics and disease.

Key Differences Between Prokaryotic and Eukaryotic Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	No true nucleus (nucleoid)	True nucleus with nuclear envelope
Organelles	Absent	Present (mitochondria, Golgi, etc.)
Cell Wall	Peptidoglycan (in bacteria)	Cellulose (plants), chitin (fungi), absent in animals
DNA Structure	Circular, no histones	Linear, with histones
Cell Division	Binary fission	Mitosis and meiosis

Additional info:

Prokaryotes transfer DNA fragments via processes like conjugation, while eukaryotes undergo sexual reproduction (meiosis).