Cell Structure: The Fundamental Units of Life (General Biology 1, Module 4)

Cell Structure

Introduction to Cells

Cells are the basic building blocks of all living organisms. In single-celled organisms, the cell performs all necessary life functions, while multicellular organisms have specialized cells for different tasks.

• Definition: A cell is the smallest unit of life that can carry out all life processes.

• Example: Bacteria (single-celled), human muscle cell (multicellular organism).

Cell Theory

Cell theory is a foundational principle in biology, established by Theodor Schwann, Matthias Schleiden, and Rudolf Virchow.

• Cells are the basic units of life.

• All living organisms are made of cells.

• All cells come from preexisting cells.

Inside the Cell

Common Components of Cells

According to cell theory, all organisms consist of cells, which share several key components:

• Proteins: Perform most cellular functions, including catalyzing reactions and providing structural support.

• Nucleic acids: Store, transmit, and process genetic information (e.g., DNA and RNA).

• Carbohydrates: Provide chemical energy, structural support, and cellular identity.

• Plasma membrane: Serves as a selectively permeable barrier, controlling entry and exit of substances.

• Ribosomes: Sites of protein synthesis.

• Chromosome(s): Structures made of nucleic acids that transmit hereditary information.

• Cytoplasm: Internal cellular fluid (cytosol) where organelles are suspended.

Types of Cells

Prokaryotic vs. Eukaryotic Cells

Cells are classified into two fundamental types based on their morphology:

• Prokaryotes: Lack a membrane-bound nucleus. Examples include Bacteria and Archaea.

• Eukaryotes: Have a membrane-bound nucleus. Examples include plants, animals, fungi, and protists.

Organisms are further divided into three domains based on evolutionary history:

• Bacteria: Prokaryotic

• Archaea: Prokaryotic

• Eukarya: Eukaryotic

Microscopy

Types of Microscopes

Microscopes are essential tools for studying cells, as most cells are too small to be seen by the naked eye.

• Light Microscopes: Use visible light to illuminate specimens. Suitable for viewing live or fixed cells.

• Electron Microscopes: Use beams of electrons for much higher magnification and resolution. Only fixed specimens can be viewed.

Comparison Table: Light vs. Electron Microscopes

Feature	Light Microscope	Electron Microscope
Illuminating Source	Light	Electron beam
Specimen Preparation	Minutes to hours	Days
Specimen Type	Live or dead	Dead or dried
Resolving Power	~0.25 μm	~0.002 μm (2 nm)
Magnification	Up to 1,500x	Up to 100,000x or more
Image Color	Colored	Black and white

Key Terms:

• Magnification: Ratio of an object's image size to its actual size.

• Resolution: Minimum distance two points can be separated and still be distinguished as two points.

Formulas:

• $\text{Magnification} = \frac{\text{Image Size}}{\text{Actual Size}}$

Learning Objectives (Summary)

• Describe the role of cells in organisms.

• Compare and contrast light microscopy and electron microscopy.

• Summarize cell theory.

• Compare and contrast prokaryotic and eukaryotic cells.

• Describe the structure of prokaryotic and eukaryotic cells.

• Compare animal cells with plant cells.

• State the role of the plasma membrane and major organelles.

Summary Table: Key Cell Components and Functions

Component	Function
Proteins	Catalyze reactions, provide structure
Nucleic acids	Store and transmit genetic information
Carbohydrates	Energy, support, identity
Plasma membrane	Selective barrier
Ribosomes	Protein synthesis
Chromosomes	Hereditary information
Cytoplasm	Internal fluid, site for cellular processes

Additional info: These notes are based on introductory biology content, not general chemistry. However, the structure and function of cells is foundational for understanding biochemistry and molecular biology, which are relevant to advanced chemistry studies.