1. Cytoplasmic (Cell) Membrane
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- Located just inside the peptidoglycan layer.
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- Phospholipid bilayer similar to eukaryotic membranes, but does not contain sterols (except Mycoplasma species).
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- Functions:
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- transport of molecules into cell
- energy generation by oxidative metabolism
- synthesis of cell wall precursors
- secretion of enzymes, toxins, and other proteins
- signal transduction
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2. Mesosome
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- Involved in cell division
3. Cytoplasm
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- contains the nucleoid and ribosomes, nutrient granules, metabolites and plasmids.
- Ribosomes
- Differ in size and composition from eukaryotic ribosomes—selective target of several antibiotics that inhibit bacterial, but not eukaryotic protein synthesis.
- Ribosomes
- contains the nucleoid and ribosomes, nutrient granules, metabolites and plasmids.
2. Granules
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- Several different types; stain characteristically and can be used to help identify some bacteria.
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3. Nucleoid
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- Location of bacterial DNA chromosome (~2000 genes, no introns)
- No nuclear membrane, no nucleolus, no mitotic spindle, no histones.
- Location of bacterial DNA chromosome (~2000 genes, no introns)
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4. Plasmids
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- Extrachromosomal double-stranded, circular DNA molecules.
- Replicate independently of bacterial chromosome.
- Found in Gram-positive and Gram-negative bacteria.
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2. Transposons
Photo by Open.Michigan 
Frequently Asked Questions
What is the function of the cytoplasmic (cell) membrane in bacteria?
The cytoplasmic membrane in bacteria acts as a barrier just inside the peptidoglycan layer. It is crucial for transporting molecules into and out of the cell, generating energy through oxidative metabolism, and synthesizing cell wall precursors. Additionally, it plays a role in secreting enzymes, toxins, and proteins, and is involved in signal transduction, which helps the cell respond to its environment.
How does the bacterial cytoplasmic membrane differ from eukaryotic membranes?
The bacterial cytoplasmic membrane is a phospholipid bilayer similar to eukaryotic membranes but typically lacks sterols, which are present in eukaryotic membranes. An exception is the Mycoplasma species, which does contain sterols. This difference is significant because sterols contribute to membrane fluidity and stability in eukaryotic cells.
What role do mesosomes play in bacterial cells?
Mesosomes are infoldings of the bacterial cytoplasmic membrane that are thought to play a role in cell division. They may help with DNA replication and distribution during cell division by increasing the surface area of the membrane, facilitating various biochemical processes essential for cell division.
Why are bacterial ribosomes a target for certain antibiotics?
Bacterial ribosomes differ in size and composition from eukaryotic ribosomes. This makes them a selective target for antibiotics that inhibit protein synthesis in bacteria without affecting eukaryotic cells. Such antibiotics can bind to bacterial ribosomes and disrupt their function, effectively killing the bacteria or inhibiting their growth.
What is the function of plasmids in bacteria?
Plasmids are extrachromosomal, double-stranded, circular DNA molecules found in bacteria. They replicate independently of the bacterial chromosome and often carry genes that provide advantageous traits, such as antibiotic resistance. Plasmids can be transferred between bacteria, spreading these traits and contributing to genetic diversity and adaptability.
What is contained within the bacterial cytoplasm?
The bacterial cytoplasm contains several critical components, including the nucleoid, ribosomes, nutrient granules, metabolites, and plasmids. The nucleoid houses the bacterial DNA chromosome, while ribosomes are involved in protein synthesis. Nutrient granules store essential nutrients, and plasmids carry additional genetic information beneficial for the bacteria.
How do granules in bacterial cells help identify bacteria?
Granules in bacterial cells can vary in type and staining properties, which can be characteristic of specific bacteria. This staining ability allows for the identification of bacteria under a microscope, aiding in diagnosis and research. Granules store nutrients and other materials necessary for the bacterial cell's survival and function.
What is a nucleoid in bacterial cells?
The nucleoid is the region within a bacterial cell that contains its DNA. Unlike eukaryotic cells, bacterial DNA is not enclosed within a nuclear membrane and lacks structures like a nucleolus, mitotic spindle, or histones. The bacterial chromosome is typically a single, circular DNA molecule that contains about 2000 genes.