Cell Biology Fundamentals: Structure, Function, Types

Posted on Apr 25, 2025 in Biology

Cell Theory Explained

Cell theory states:

  • The cell is the fundamental structural and anatomical unit of all living organisms. All organisms are formed by one or more cells.
  • The cell is the basic physiological or functional unit. Every cell is capable of maintaining life independently.
  • Cells are the unit of genetic origin. Every cell derives from a pre-existing cell.

Common Characteristics of All Cells

All cells share these common characteristics:

  • A cell membrane
  • A set of structures called organelles
  • Genetic material

Cell Types: Genetic Material Organization

Based on how their genetic material is organized, cells are classified as:

  • Prokaryotes
  • Eukaryotes

Differences: Prokaryotic vs. Eukaryotic Cells

Prokaryotic Cells

  • More primitive and simpler.
  • Their genetic material is free in the cytoplasm (lacking a nuclear membrane).
  • Have few cell organelles.
  • Do not typically form tissues or organs.

Eukaryotic Cells

  • More evolved and complex.
  • Genetic material is enclosed within a nuclear membrane.
  • Have numerous, specialized cellular organelles.
  • Often form tissues and organs (e.g., plant and animal cells).

Unique Structures in Plant and Animal Cells

  • Plant Cells: Possess a cell wall and chloroplasts.
  • Animal Cells: Possess lysosomes, centrioles, and often cilia or flagella.

Functions of Key Cell Organelles

  • Cell Wall: Provides protection, stiffness, and structural consistency to the cell (primarily in plants, fungi, bacteria).
  • Chloroplasts: Sites where photosynthesis occurs (in plant cells and some protists).
  • Lysosomes: Involved in cellular digestion and elimination of waste products and old organelles (primarily in animal cells).
  • Cilia and Flagella: Facilitate movement of the cell itself or the surrounding fluid.
  • Cytoplasm: The jelly-like substance where cellular organelles and the nucleus are suspended.
  • Ribosomes: Responsible for protein synthesis.
  • Mitochondria: Sites of cellular respiration, where energy is released from organic molecules.

Key Cellular Component Definitions

  • Cell Membrane: The outer boundary of the cell, selectively controlling the passage of substances.
  • Nucleus: Contains the cell’s genetic information (DNA); enclosed by a nuclear membrane and includes chromatin and the nucleolus.
  • Cytoplasm: The material within the cell membrane (excluding the nucleus) where organelles are suspended.
  • Ribosomes: Composed of RNA and protein; the site of protein synthesis; visible only with an electron microscope.
  • Endoplasmic Reticulum (ER): A network of membranes throughout the cytoplasm involved in transporting and storing substances, and protein/lipid synthesis.
  • Golgi Apparatus (Golgi Complex): Stacks of membranes involved in modifying, sorting, and packaging proteins and lipids for secretion or delivery.
  • Mitochondria: Organelles where cellular respiration occurs, releasing energy.
  • Vacuoles: Membrane-bound sacs for storing water, nutrients, and waste; often large in plant cells.

Control Molecule of the Cell

What molecule directs cell operation? Nucleic acids.

What are they called? DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid).

Where are they primarily located? Within the nucleus (in eukaryotes).

Cellular Nutrition Types

Cells obtain food through different nutritional modes:

  • Autotrophic Nutrition: Cells manufacture their own nutrients (e.g., via photosynthesis).
  • Heterotrophic Nutrition: Cells obtain nutrients by incorporating substances from external sources.

Bacteriophage (Bacterial Virus) Life Cycle Phases

The life cycle of a virus that infects bacteria (bacteriophage) typically involves:

  1. Attachment & Injection: The virus attaches to the host bacterium and injects its nucleic acid.
  2. Integration (Lysogenic Cycle – Optional): The viral nucleic acid may integrate into the host chromosome, remaining dormant (prophage) and replicating with the host.
  3. Activation & Replication (Lytic Cycle): Viral genes activate, using host machinery to synthesize new viral components (nucleic acids, proteins).
  4. Assembly: New virus particles are assembled.
  5. Lysis & Release: The host cell breaks open (lyses), releasing new viruses, often causing host cell death or disruption. These new viruses can infect other cells.