Characteristics of Protozoa

III. PROTOZOA

A. CHARACTERISTICS OF PROTOZOA

The overall purpose of this Learning Object is to learn some of the characteristics of protozoa and introduce how they replicate.

LEARNING OBJECTIVES FOR THIS SECTION

Protozoa

A. Characteristics of Protozoa

Protozoa are unicellular eukaryotic microorganisms lacking a cell wall and belonging to the Kingdom Protista. Although there are nearly 20,000 species of protozoa, relatively few cause disease. Most inhabit soil and water.

For More Information: A Comparison of Prokaryotic and Eukaryotic Cells from Unit 1

Protozoa reproduce asexually by the following means:

1. fission: One cell splits into two. (def)

2. schizogony: Multiple fission. The nucleus divides many times before the cell divides. The single cell then separates into numerous daughter cells. (def)

3. budding: Buds form and pinch off of the parent cell. (def)

Some protozoa also reproduce sexually by fusion of gametes (def) (see the life cycle of Plasmodium).
The vegetative, reproducing, feeding form of a protozoan is called a trophozoite (def). Under certain conditions, some protozoa produce a protective form called a cyst (def) that enable them to survive harsh environments. Cysts allow some pathogens to survive outside their host.

TPS Question

B. The Role of Protozoan Cytoplasmic Membrane Components in Initiating Body Defense
In order to protect against infection, one of the things the body must initially do is detect the presence of microorganisms. The body does this by recognizing molecules unique to microorganisms that are not associated with human cells. These unique molecules are called pathogen-associated molecular patterns or PAMPs (def). (Because all microbes, not just pathogenic microbes, possess PAMPs, pathogen-associated molecular patterns are sometimes referred to as microbe-associated molecular patterns or MAMPs.)
Components of protozoa that function as PAMPs include GPI-anchored proteins (GPI = Glycosylphosphatidylinositol) and mannose-rich glycans (short carbohydrate chains with the sugar mannose or fructose as the terminal sugar) that function as PAMPs. These mannose-rich glycans are common in microbial glycoproteins and glycolipids but rare in those of humans. These PAMPs bind to pattern-recognition receptors or PRRs (def) on a variety of defense cells of the body and triggers innate immune defenses such as inflammation (def), fever, and phagocytosis.

For More Information: Pathogen-Associated Molecular Patterns (PAMPs) from Unit 4

For More Information: Pattern-Recognition Receptors from Unit 4

For More Information: Inflammation from Unit 4

Flash Animation showing the release of GPI-anchored proteins in parasites and their subsequent binding to pattern-recognition receptors on a macrophage.

html5 version of animation for iPad showing the release of GPI-anchored proteins in parasites and their subsequent binding to pattern-recognition receptors on a macrophage.

We will now briefly look at some medically important protozoa classified into phyla based on their motility. Illustrations can be found in your Lab Manual in Lab 22.

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