2-1 Introduction

(12950 Reads)

Table of Contents| Chapter Article List| Printable Version | Printable Chapter

[Prev] | [Next]

Microorganisms typically face the world as single cells rather than as the multi-cellular assemblies of higher organisms. Each single cell must therefore contain all the structures necessary for managing its internal state and dealing with the outside environment. Not surprisingly, this evolutionary process results in the use of rather similar structures and processes to solve similar need in different microorganisms. However, prokaryotes have been on this Earth for a long period of time and this has allowed them to differentiate into a dizzying number of different species. Eukaryotic microbes are not quite so diverse, but they still display a remarkable range of properties. The diversity of the microbial organisms also means that this survey of structures is not exhaustive. No one cell contains all the structures that we describe here, but we will explore the more common structures that have been observed by scientists in the past 150 years as show in Figure 2-1. A distinction in this discussion must be made between the two types of prokaryotes: the Archaea and their cousins, the Bacteria. We will initially focus on the Bacteria, since that is what we know the most about. Many of the structures we will examine are found in both the Bacteria and the Archaea, but there are some significant differences and these will be covered at the end of the chapter. Finally, we will talk about the features that are distinctive among the microbial eukaryotes.

So how did scientists find out so much about such very small organisms? As you might guess, many techniques come into play when tackling a subject as complex as bacterial structure. Electron microscopes have been important, of course, but so have genetics, molecular biology and biochemistry. Microscopes help scientists to visualize where these structures are located and how they are arranged spatially in the microbe. Bacterial genetics and molecular biology identify and analyze the genes necessary for the synthesis and regulation of these structures. Biochemistry permits the detailed examination of each part separately, with implications for its role in the living bacterium. The powerful combination of these disciplines has provided a deep understanding of how a bacterium is put together, but there is still much to learn.

This chapter on microbial structure is separated into two sections. In the first section, we describe the chemical nature of the types of molecules and polymers that are important in carrying out the business of biology. In the second section, we examine the functional units in the cell, describing how the various chemical structures in the cell interact to carry out important cellular functions. In this discussion we assume that the student has had an introductory chemistry course (at least in high school) and is somewhat familiar with chemical notation.

First and foremost, it is important to point out that there are some universal structures that all living cells contain. They are the basic building blocks of life: DNA, RNA, protein and cellular membranes. Most, but not all, bacteria also possess cell walls. Beyond these essentials, the frequency of the rest of the structures we mention here ranges in the bacterial world from quite common to very rare.

[Prev] | [Next]

Table of Contents| Chapter Article List| Printable Version | Printable Chapter