The cell wall cannot be observed through light microscopy or simple stains. It may be demonstrated by microdissection, reaction with specific antibodies, mechanical rupture of the cell, differential staining procedures or by electron microscopy.

Viewing the Cell Wall

The cell wall is composed of peptidoglycan, a mucopeptide (formed by N acetyl glucosamine & N acetyl muramic acid) linked to peptide chains. Teichoic acids are embedded into the cell wall and may be linked to lipids (Lipoteichoic acid). These Lipotechoic acids connect peptidoglycan to the cytoplasmic membrane and gives the cell wall its rigidity. 

Composition of the Cell Wall

Gram Positive vs. Gram Negative Bacteria

The outer membrane is only found in gram-negative bacteria and serves as the first barrier to the external surroundings. It is composed of lipopolysaccharides and phospholipids. 

Outer Membrane

Peptidoglycan makes up the cell walls of bacteria. It is composed of alterating long chain molecules called N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). NAM and NAG are connected to each other with peptide bridges. Peptidoglycan is only in bacteria which makes it a key target for antibiotics.

Peptidoglycan

The cell wall in bacterial cells is very rigid and provides a stable shape to the cell. It is essential for bacterial growth and division. It is important in preventing the cell from bursting from osmotic pressure changes.

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- Cell Wall
- Plasma Membrane
- Cytoplasm
- Ribosomes
- Mesosomes
- Cytoplasmic Inclusions
- Nucleoid
- Capsule
- Flagella
- Pilus
- Fimbriae
- Plasmid DNA
- Endospore
- Inclusion Bodies

Bacterial Structures

Al-mohanna, Moshtaq & H., quine. (2016). MORPHOLOGY AND CLASSIFICATION OF BACTERIA. 

Morphology and Classification of Bacteria

https://openstax.org/details/books/microbiology/

Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

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Cell Wall

The cytoplasm consists of organic and inorganic solutes and free floating ribosomes. Chromosomal DNA and plasmids are located in this region.

Cytoplasm

Mesosomes store respiratory enzymes and aid in cellular reproduction. These vesicles are formed by the invagination of the plasma membrane into the cytoplasm. 

Mesosomes

Inclusions can store nutrients or gas needed for the cells metabolism or buoyancy. Inclusions are important in reducing build up of osmotic pressure as the cell accumulates compounds.

Cytoplasmic Inclusions

The capsule is the extracellular layer of the bacterial cell. Generally, they are composed of polysaccharides and proteins. The capsule may allow a bacteria to be more infectious by making it more difficult to be engulfed by white blood cells. 

Capsule

Flagella are hair like filaments that extend from the cytoplasmic membrane to the external part of the cell. The flagella functions in cell motility. 

Flagella

This structure is found in both gram positive and gram negative bacteria. It is located under the cell wall and acts as a semipermeable barrier, controlling the flow of metabolites, between the cell wall and the cytoplasm. 

Plasma Membrane

Fimbriae are short bristle-like strands that extend from the bacteria by the hundreds. They are important in cell adhesion, infection, and colonization.

Fimbriae

The pilus is a appendage that extends to reach surfaces or other bacteria. The sex pilus is a specific pilus important in transferring DNA between bacterial cells.

Pilus

Prokaryotes do not have a nucleus. DNA and DNA-associated proteins are in the nucleoid region. It is a condensed area of DNA in the cell.

Nucleoid

Plasmids are circular, extrachromosomal DNA. Cells can have hundreds of plasmids. They can carry important genes for antibiotic resistance or conjugation.

Plasmid DNA 

Ribosomes are made up of RNA and proteins. They are responsible for translating mRNA into proteins. Ribosomes are present in the cytoplasm.

Ribosomes

Some bacteria are capable of forming endospores through the process of sporulation. The endospore contains that bacterial genome and keeps the bacterium in a dormant state. It is formed when the vegetative cell forms a septum and divides asymmetrically. This action separates the DNA forespore from the cell to eventually form the endospore. The bacterial forms the endospore when in environment is not suitable for growth. It also allows the bacterium to be dormant when exposed to harsh chemicals, radiation or low nutrients.

Endospores

Some bacteria are capable of forming inclusion bodies which are used for holding excess materials like nutrients or proteins. These cell structures decrease osmotic pressure in the cell by containing these compounds in inclusion bodies. 

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