Prokaryotic Cell Structure: Structures Within the Cytoplasm

II. THE PROKARYOTIC CELL: BACTERIA

B. PROKARYOTIC CELL STRUCTURE

3. Structures Located Within the Cytoplasm

a. Cytoplasm

The overall purpose of this Learning Object is to learn the chemical makeup and the functions of bacterial cytoplasm.

LEARNING OBJECTIVES FOR THIS SECTION

In this section on Prokaryotic Cell Structure we are looking at the various organelles or structures that make up a bacterium. As mentioned in the introduction to this section, a typical bacterium usually consists of:

a cytoplasmic membrane surrounded by a peptidoglycan cell wall and maybe an outer membrane;
a fluid cytoplasm containing a nuclear region (nucleoid) and numerous ribosomes; and
often various external structures such as a glycocalyx, flagella, and pili.

We will now look at the bacterial cytoplasm.

The Cytoplasm (def)

A. Structure and Composition

In bacteria, the cytoplasm refers to everything enclosed by the cytoplasmic membrane. About 80% of the cytoplasm of bacteria is composed of water. Within the cytoplasm can be found nucleic acids (DNA and RNA), enzymes and amino acids, carbohydrates, lipids, inorganic ions, and many low molecular weight compounds. The liquid component of the cytoplasm is called the cytosol. Some groups of bacteria produce cytoplasmic inclusion bodies that carry out specialized cellular functions.

B. Functions

While bacteria secrete exoenzymes (def) to hydrolize macromolecules into smaller molecules capable of being transported across the cytoplasmic membrane, the cytoplasm is the site of most bacterial metabolism (def). This includes catabolic reactions in which molecules are broken down in order to obtain building block molecules for more complex cellular molecules and macromolecules, and anabolic reactions used to synthesize cellular molecules and macromolecules. The chemical reactions occuring within the bacterium are under the control of endoenzymes (def).

Bacterial cytoplasm also contains helical actin-like proteins that contribute to cell shape.

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