Cell Structures: An Overview of Eukaryotic and Prokaryotic Cells

Chapter 6: Cell Structures

Overview of Cells

The study of cells is fundamental to understanding all living organisms. The cell theory forms the basis of modern biology and describes the properties shared by all cells.

• Cell Theory:

  • All organisms are composed of one or more cells.

  • Cells are the basic structural and functional unit of all living organisms.

  • Cells arise only from the division of preexisting cells.

• Examples of Cell Types: Bacteria, Archaea, Protists, Algae, Fungi, Animal cells, Plant cells.

Microscopy

Microscopy is essential for studying cells and their components, many of which are too small to be seen with the unaided eye. Different types of microscopes and techniques allow scientists to observe cellular structures in detail.

• Light Microscope (LM): Uses visible light passed through a specimen and glass lenses to magnify images of cells.

• Key Terms:

  • Refraction: The bending of light by lenses to magnify and focus the image.

  • Magnification: The ratio of an object's image size to its real size.

  • Resolution: The clarity of an image, defined as the minimum distance between two distinguishable points.

  • Contrast: The difference in brightness between parts of the sample, which helps distinguish structures.

Example: Using a light microscope, scientists can observe the general shape and arrangement of cells, but finer details require higher resolution techniques.

Types of Cells

Cells are classified into two major categories based on their structural characteristics: prokaryotic and eukaryotic.

• Prokaryotic Cells:

  • Domains: Bacteria and Archaea

  • All are single-celled organisms.

  • Organelles are not membrane-bound.

  • DNA is not enclosed in a nucleus; it is found in a circular chromosome.

  • Cell division occurs by binary fission.

• Eukaryotic Cells:

  • Kingdoms: Protists, Fungi, Animalia, and Plantae

  • Organelles are membrane-enclosed.

  • DNA is enclosed in a nucleus and organized in paired linear chromosomes.

  • Cell division occurs by mitosis and/or meiosis.

  • Generally much larger than prokaryotic cells.

Comparison of Prokaryotic and Eukaryotic Cells

All cells share certain features, but there are key differences between prokaryotic and eukaryotic cells.

• Common Features:

  • Plasma membrane

  • Cytoplasm (including cytosol)

  • Chromosomes (carry genes)

  • Ribosomes (synthesize proteins)

Feature	Prokaryotic Cells	Eukaryotic Cells
DNA Location	Not enclosed (nucleoid region)	Enclosed in nucleus
Organelles	Not membrane-bound	Membrane-bound
Cell Size	Generally smaller	Generally larger
Cell Division	Binary fission	Mitosis and/or meiosis

Additional info:

• Further study of cell structures includes organelles such as the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and cytoskeleton, which will be covered in detail in subsequent sections or chapters.

• Advanced microscopy techniques, such as electron microscopy, allow visualization of subcellular structures beyond the resolution of light microscopes.