1. Compare and contrast prokaryotic and eukaryotic cells
2. Compare and contrast the major classes of microorganisms

Microbiology (Kaiser) Unit 1, Chapter 1: Fundamentals of Microbiology

The term “microorganism” or “microbe” refers to a vast and diverse group of organisms which are too small to be seen with the naked eye. For example, viruses are often measured in nanometers (nm), and bacteria are usually between 0.2 and 5 micrometers (μm), but the largest bacteria can grow up to 2cm long.

Though often associated with disease, it is important to remember that, like other organisms, microbes can be benign, or even helpful to humans. Often, microbes can only cause disease or benefit in certain host species. Medical microbiology tends to focus on the microorganisms that cause harm to humans.

Microorganisms, and all other organisms can be classified as either prokaryotes or eukaryotes. Prokaryotes are found in the domains Bacteria and Archaea while eukaryotes are found in the domain Eukarya.

One of the main differences between prokaryotes and eukaryotes is the presence or absence of internal membranes. In the eukaryotic cell, membrane-bound compartments called organelles perform specific metabolic functions within the cell. For example, the mitochondria is a membrane-bound structure which generates ATP in a process called cellular respiration. In a prokaryotic cell, however, organelles are absent and metabolic functions are not compartmentalised. Instead, the plasma membrane that surrounds the prokaryotic cell is often the site of these functions.

This lack of compartmentalisation applies to genetic material as well. Eukaryotes have a nucleus in which the majority of the cell’s DNA is found in the form of linear chromosomes. In a prokaryote, DNA is found in the nucleoid, generally in the form of a tightly wound circular chromosome.

Ribosomes are used to translate RNA in both prokaryotes and eukaryotes. However, prokaryotes have a 70S ribosome composed of a 30S and a 50S subunit while eukaryotes have an 80S ribosome composed of a 40S and a 60S subunit. This affects the molecules which bind to them, and some antibiotics are able to bind to (and inactivate) prokaryotic ribosomes without binding to eukaryotic ribosomes.

1. Campbell Biology: Australian & New Zealand Edition (11th ed.). Australia: Pearson. 19 Oct 2016. ISBN 9781488613715.