Table of Contents
Important Topic Of Biology: Cell Envelope
What is a Cell Envelope?
A cell envelope is a combination of cell membranes, cell walls, and outer membranes if any. Usually, this envelope features prokaryotes like viruses. It includes the inner cell wall and the bacterial cell wall.
The cell envelope provides structural integrity to the cell. In prokaryotes, it protects the cell from internal turgor-induced stress caused by high concentrations of macromolecules within the cell.
There are two types of bacterial cell envelopes:
- Gram-positive cell wall
- Gram-negative cell wall
| S.NO | CONTENT |
| 1. | INTRODUCTION TO CELL WALL |
| 2. | TYPES OF BACTERIAL CELL |
| 3. | CELL ENVELOPE CONSTRUCTION |
| 4. | PARTS OF CELL ENVELOPE |
| 5. | CELL ENVELOPE FUNCTIONS |
| 6. | PARTS OF CELL ENVELOPES |
| 7. | FAQ’S |
Types of Bacterial Cell Envelopes
- Gram-positive Cell Envelope: The gram-positive bacterial cell envelope forms a thick layer of the peptidoglycan cell wall. This helps to retain violet crystal dyes during gram contamination. The cell wall is composed of teichoic acid and lipoteichoic acid.
- Gram-negative Cell Envelope: A gram-negative cell envelope contains a thin layer of the peptidoglycan cell wall as a result of which the cell wall can retain its greenish-white color in color removal during gram contamination. The outer layer is made up of lipopolysaccharides and phospholipids.
- Mycobacteria: The mycobacterial cell envelope differs from that of gram-positive and gram-negative bacteria. It does not have an outer cell membrane but has a cell wall made up of peptidoglycan, arabinogalactan, and mycolic acid.
Cell envelope construction
The cell envelope is made up of cell walls, cell membranes, and outer membranes.
The gram-positive bacterial cell envelope covers the cell wall, the cytoplasmic membrane, and the capsule.
The gram-negative bacterial cell envelope covers the cell wall, the cytoplasmic membrane, the outer membrane, the periplasmic area, and the capsule.
Bacteria do not have a cell wall composed of Peptidoglycans.
Bacteria that do not have a cell wall are made up of peptidoglycans. The forced intracellular bacterium in the family Chlamydiaceae has an unusual morphology because its infectious forms do not have significant levels of peptidoglycan on the walls of their cells. Instead, extracellular forms of these gram-negative strains rely on a layer of disulfide bond cysteine-rich cytoplasmic proteins and outer membranes, similar to the peptidoglycan layer in other non-gram-containing bacteria, to maintain structural integrity. . Disulfide cross bond is absent in the internal forms of bacteria, making this form mechanically brittle.
Bacterial class mollicutes do not have cell walls in cell envelopes. Mycoplasma and ureaplasma are the most common pathogenic bacteria in this group. L-bacteria are a type of bacterium that does not have cell walls but is produced by active bacteria.
Parts of the Cell Envelope
The bacterial cell wall consists mainly of three layers, the glycocalyx, the cell wall, and finally the plasma membrane. The structure of the glycocalyx varies from one species to another. A loose-like shell is called a slime layer, while a solid and thick layer is called a capsule. Also, the plasma membrane is a thin, thin layer that joins the outer part of the cell. The formation of plasma membranes remains the same even in eukaryotes.
It contains another membrane-like structure, the mesosome. Mesosome is an extended part of this plasma membrane. They assist in DNA replication, cell formation, and cell proliferation.
Another part of the bacterial cell wall is the pill, a long structure made of pilin protein. Also, there is another small bristle-like fiber, the fimbriae. It helps the germs to attach to different parts of the body.
Bacterial cells also include various flagella structures. Specifically, the bacterial flagellum is divided into three sections, the filament, the hook, and the basal body.
The cell wall of gram-positive bacteria includes the cell wall, the cytoplasmic membrane, and the capsule.
The cell wall of gram-negative bacteria includes the cell wall, the cytoplasmic membrane, the outer membrane, the periplasmic space, and the capsule.
Cell Envelope Functions
Here are the key functions of the cell envelope:
The bacterial cell wall not only keeps the cell membrane healthy and prevents it from exploding or crumbling but, as noted in the case of moving bacteria, forms filamentous extensions called flagella.
The cell membrane also controls the transport of substances inside and outside the cell.
A special structure known as the mesosome is formed by the expansion of the plasma membrane into the cell wall. These extensions are usually in the form of vesicles, tubules, and lamellae. They help the cell to perform various functions, such as cell wall reconstruction, DNA replication, distribution of daughter cells, respiration, fluid, and so on.
Bacteria do not have a cell wall composed of Peptidoglycans.
Bacteria that do not have a cell wall are made up of peptidoglycans. The forced intracellular bacterium in the family Chlamydiaceae has an unusual morphology because its infectious forms do not have significant levels of peptidoglycan on the walls of their cells. Instead, extracellular forms of these gram-negative strains rely on a layer of disulfide bond cysteine-rich cytoplasmic proteins and outer membranes, similar to the peptidoglycan layer in other non-gram-containing bacteria, to maintain structural integrity. Disulfide cross bond is absent in the internal forms of bacteria, making this form mechanically brittle.
Bacterial class mollicutes do not have cell walls in cell envelopes. Mycoplasma and ureaplasma are the most common pathogenic bacteria in this group. L-bacteria is a type of bacterium that does not have cell walls but is produced by active bacteria.
Parts of the Cell Envelope
The bacterial cell wall consists mainly of three layers, the glycocalyx, the cell wall, and finally the plasma membrane. The structure of the glycocalyx varies from one species to another. A loose-like shell is called a slime layer, while a solid and thick layer is called a capsule. Also, the plasma membrane is a thin, thin layer that joins the outer part of the cell. The formation of plasma membranes remains the same even in eukaryotes.
It contains another membrane-like structure, the mesosome. Mesosome is an extended part of this plasma membrane. They assist in DNA replication, cell formation, and cell proliferation.
Another part of the bacterial cell wall is the pill, a long structure made of pilin protein. Also, there is another small bristle-like fiber, the fimbriae. It helps the germs to attach to different parts of the body.
Bacterial cells also include various flagella structures. Specifically, the bacterial flagellum is divided into three sections, the filament, the hook, and the basal body.
The cell wall of gram-positive bacteria includes the cell wall, the cytoplasmic membrane, and the capsule.
The cell wall of gram-negative bacteria includes the cell wall, the cytoplasmic membrane, the outer membrane, the periplasmic space, and the capsule.
Also read: Important Topic Of Biology: Cell Membrane
FAQs
“What is an Activity Cell Envelope?
The cell envelope is the outer layer of bacterial cells, and it serves a variety of purposes including cell protection, contact with the outside world, cellular preservation, cell stability and stability, and cell fluctuations, growth, and division. Its functions include protecting cells, maintaining cell structure, and facilitating cell development and metabolism. Carbohydrate-based macromolecules and carbohydrates are important components of a cell envelope, and they play a key role in all these processes, whether Gram-positive, negative, mycobacterial, or archaeal. [/sc_fs_faq]
Q. Which Eukaryotic and Prokaryotic Cell have a Plasma membrane?
Ans: The plasma membrane, a double layer of lipids that separates the inner cell of the cell from the outside, is found in both prokaryotic and eukaryotic cells. Phospholipids, which are special lipids, make up a large portion of this double layer.
The phospholipid is composed of two hydrophobic tails, a water-repellent oil, and a hydrophilic, water-loving head. Phospholipids form a structure with two layers naturally, with their hydrophobic tails facing inward and their hydrophilic heads facing outwards. Many biological membranes contain this dual-strength structure, known as the phospholipid bilayer.
What is the difference between a positive E Coli gram and a negative gram?
Escherichia coli is a gram-negative, rod-shaped virus. Creatures with warm blood have it in their lower intestines. E Coli is generally harmless. E. coli is an active anaerobic bacterium that is Gram-negative and rod-shaped. Theodor Escherich was the first to develop the virus in 1885. Most species of E. coli are found in parts of the intestines of humans and animals as natural plants. However, certain types of E. coli have evolved into E. pathogenic cold due to harmful substances found in plasmids, transposons, bacteriophages, and/or islands of pathogenicity. Serogroups, pathogenicity methods, clinical symptoms, and risk factors can all be used to classify E. pathogenic cold. [/sc_fs_faq]
Q. What is the use of Gram Stain?
Ans: Gram staining is a bacteriological laboratory method that divides bacteria into two groups based on the physical characteristics of their cell walls (gram-positive and gram-negative). Because these bacteria produce a variety of reactions that do not follow their own evolutionary collection, Gram staining is not used to distinguish archaea, earlier archaebacteria.
Some organic matter is gram-variable (meaning they can be contaminated or bad), while others are invisible because even Gram dyes will not be used to lubricate them. In the modern biological or molecular biological laboratory, genetic sequences and other molecular mechanisms, which are much clearer and more instructive than distinct pollutants, are used for multiple detections.
To know more visit Important Topic of Biology: Egestion
