Inside the Cell: Structure and Function of Prokaryotic and Eukaryotic Cells

Chapter 7: Inside the Cell

Introduction

This chapter explores the internal structures of cells and how their collaboration gives rise to the properties of life. The study of cell structure and function is fundamental to understanding all biological processes.

Prokaryotic and Eukaryotic Cell Types

Cell Theory and Classification

• Cell Theory: All living organisms are composed of cells, which are the fundamental units of life.

• Cells are divided into two fundamental types:

  • Eukaryotes: Have a membrane-bound nucleus.

  • Prokaryotes: Lack a membrane-bound nucleus.

Bacterial and Archaeal Cell Structures and Their Functions

Genetic Material

• Prokaryotes contain a single, circular chromosome.

• The chromosome is located in a region called the nucleoid.

• They may also have small, circular DNA molecules called plasmids, which often carry genes beneficial for survival.

Ribosomes

• Ribosomes are complexes of RNA and protein.

• They are the sites of protein synthesis.

Cell Envelope and Surface Structures

• Prokaryotic cells are surrounded by a plasma membrane and usually a cell wall.

• Some prokaryotes have an additional capsule (composed of polysaccharides) outside the cell wall, which offers protection and helps in attachment.

• The internal compartment, excluding the nucleus in eukaryotes, is called the cytoplasm.

• Flagella: Long, whip-like filaments that rotate to propel the cell.

• Fimbriae: Needle-like projections that promote attachment to other cells or surfaces.

Diagram: Prokaryotic Cell Structure

Key labeled structures: Ribosomes, Plasmid, Cytoplasm, Chromosome, Plasma membrane, Cell wall.

Summary Table: Prokaryotic Cell Components and Functions

Component	Function
Chromosome (nucleoid)	Stores genetic information
Plasmid	Extra genetic elements; often carry advantageous genes
Ribosome	Protein synthesis
Plasma membrane	Selective barrier; regulates entry/exit of substances
Cell wall	Structural support and protection
Capsule	Protection; helps in attachment (not always present)
Flagellum	Cell movement
Fimbriae	Attachment to surfaces

Key Terms

• Chromosome: A DNA molecule containing genetic information.

• Nucleoid: The region in a prokaryotic cell where the chromosome is located.

• Plasmid: Small, circular DNA molecule independent of the main chromosome.

• Ribosome: Molecular machine for protein synthesis.

• Flagellum: Structure for locomotion.

• Fimbriae: Structures for attachment.

Example: Escherichia coli (E. coli)

E. coli is a common prokaryotic organism found in the intestines of animals. It has a single circular chromosome, plasmids, a cell wall, and often flagella for movement.

Additional info: Prokaryotic cells are generally smaller than eukaryotic cells and lack membrane-bound organelles. Their simple structure allows for rapid growth and adaptation to changing environments.