Sentence 1: In higher classes you will learn that this plasmid DNA is used to monitor bacterial transformation with foreign DNA. Nuclear membrane is found in eukaryotes. No organelles, like the ones in eukaryotes, are found in prokaryotic cells except for ribosomes. Prokaryotes have something unique in the form of infoldings of cell membrane called mesosomes.
This sentence provides a glimpse into advanced topics you’ll explore later. Plasmid DNA, found in some bacteria, is crucial for processes like bacterial transformation. Unlike eukaryotic cells, prokaryotes lack membrane-bound organelles and a defined nucleus. Instead, they have unique structures like mesosomes, which are infoldings of the cell membrane, and ribosomes, responsible for protein synthesis.
Sentence 2: A specialised differentiated form of cell membrane called mesosome is the characteristic of prokaryotes. They are essentially infoldings of cell membrane.
Mesosomes, unique to prokaryotes, are specialized structures formed by inward folding of the cell membrane. They play roles in various cellular processes, including cell wall formation, DNA replication, and respiration. This folding increases the surface area of the membrane, allowing for more efficient cellular functions.
Sentence 3: 8.4.1 Cell Envelope and its Modifications
This marks the beginning of a subsection focusing on the cell envelope, a crucial protective layer in prokaryotic cells, particularly bacteria. The cell envelope consists of the outermost glycocalyx, the cell wall, and the plasma membrane. Each layer performs distinct functions but acts together as a single protective unit.
Sentence 4: Most prokaryotic cells, particularly the bacterial cells, have a chemically complex cell envelope. The cell envelope consists of a tightly bound three layered structure i.e., the outermost glycocalyx followed by the cell wall and then the plasma membrane.
This introduces the cell envelope, a multilayered structure surrounding the bacterial cell. It acts as a barrier, protecting the cell from its environment. The glycocalyx, the outermost layer, can be a loose slime layer or a thick capsule. The slime layer aids in adhesion and protection, while the capsule provides additional protection and can enhance virulence.
Sentence 5: Bacteria can be classified into two groups on the basis of the differences in the cell envelopes and the manner in which they respond to the staining procedure developed by Gram viz., those that take up the gram stain are Gram positive and the others that do not are called Gram negative bacteria.
This explains how bacteria are classified based on their cell envelope structure using a staining technique called Gram staining. Gram-positive bacteria retain the purple stain and have a thick cell wall, while Gram-negative bacteria do not retain the stain and have a thinner cell wall with an outer membrane.
1. Bacteria smear preparation | v 2. Heat-fixing the smear | v 3. Crystal violet staining | v 4. Iodine treatment (mordant) | v 5. Decolorization with alcohol or acetone | v 6. Counterstaining with safranin | v 7. Examination under microscope | v 8. Gram-positive bacteria retain purple color | v 9. Gram-negative bacteria appear pink/red
Sentence 6: Glycocalyx differs in composition and thickness among different bacteria. It could be a loose sheath called the slime layer in some, while in others it may be thick and tough, called the capsule.
This delves deeper into the variations within the glycocalyx layer. The slime layer is a loose, sugary coating that can help bacteria adhere to surfaces and evade the immune system. The capsule is a thicker, more defined layer that provides protection from harsh environments and enhances virulence.
Sentence 7: The cell wall determines the shape of the cell and provides a strong structural support to prevent the bacterium from bursting or collapsing.
This emphasizes the crucial role of the cell wall in maintaining the shape and preventing the bacterial cell from bursting due to internal pressure. It also serves as a protective barrier against environmental stresses.
Sentence 8: The plasma membrane is selectively permeable in nature and interacts with the outside world. This membrane is similar structurally to that of the eukaryotes.
This explains the plasma membrane, the innermost layer of the cell envelope, which controls the passage of materials into and out of the cell, similar to a gatekeeper. Despite structural similarities to eukaryotic membranes, bacterial membranes may contain unique components.
Sentence 9: A special membranous structure is the mesosome which is formed by the extensions of plasma membrane into the cell. These extensions are in the form of vesicles, tubules and lamellae.
This revisits mesosomes, highlighting their potential functions. These infoldings of the plasma membrane may be involved in various cellular processes, including cell wall formation, DNA replication, and respiration. Additionally, they increase the surface area of the membrane and concentrate enzymes necessary for cellular functions.
Sentence 10: Bacterial cells may be motile or non-motile. If motile, they have thin filamentous extensions from their cell wall called flagella.
This introduces flagella, hair-like structures that some bacteria use for movement. The flagellum is composed of three parts: filament, hook, and basal body. Flagella play a crucial role in bacterial motility, allowing cells to move towards favorable environments or away from harmful conditions.
Sentence 11: Besides flagella, Pili and Fimbriae are also surface structures of the bacteria but do not play a role in motility.
This introduces pili and fimbriae, additional surface structures on some bacteria. Unlike flagella, they are not involved in movement. Pili, also known as conjugation pili, facilitate the transfer of genetic material between bacterial cells, while fimbriae help bacteria adhere to surfaces or host cells.
- Fimbriae, the tiny bristle-like fibers on some bacteria, play a crucial role in adhesion. They act like microscopic hooks or Velcro, allowing bacteria to attach to various surfaces:Rocks in streams: This attachment helps some bacteria establish themselves in flowing water environments.Host tissues: In pathogenic bacteria (those that cause disease), fimbriae can help them adhere to host cells, facilitating infection
Sentence 12: The pili are elongated tubular structures made of a special protein. The fimbriae are small bristle like fibres sprouting out of the cell.
This explains the structure and function of pili and fimbriae. Pili, also called sex pili, are involved in conjugation, allowing for the transfer of genetic material between bacterial cells. Fimbriae, on the other hand, aid in adherence to surfaces or host tissues, facilitating colonization and infection.
Sentence 13: 8.4.2 Ribosomes and Inclusion Bodies
This marks the beginning of a subsection focusing on ribosomes and inclusion bodies, essential components within the prokaryotic cell. Ribosomes are the sites of protein synthesis, while inclusion bodies store reserve materials in the cytoplasm.
Sentence 14: In prokaryotes, ribosomes are associated with the plasma membrane of the cell. They are about 15 nm by 20 nm in size and are made of two subunits – 50S and 30S units which when present together form 70S prokaryotic ribosomes.
This section highlights ribosomes, the protein-making factories of the cell, present in both prokaryotes and eukaryotes. Ribosomes consist of two subunits and are responsible for translating the genetic code into proteins. In prokaryotes, they are often found attached to the plasma membrane, where protein synthesis occurs.
Sentence 15: Several ribosomes may attach to a single mRNA and form a chain called polyribosomes or polysome.
This elaborates on the protein synthesis process. Polyribosomes, or polysomes, are clusters of ribosomes attached to a single mRNA molecule. This arrangement allows for efficient translation of the mRNA into proteins, speeding up the production process.
Sentence 16: Inclusion bodies: Reserve material in prokaryotic cells are stored in the cytoplasm in the form of inclusion bodies.
This introduces inclusion bodies, storage units within the cytoplasm of prokaryotic cells. They store reserve materials such as phosphate granules, glycogen granules, and gas vacuoles, aiding in cellular processes and providing a source of energy and nutrients when needed.