cell wall outer layer
What have we learned so far in terms of cell layers? All cells have a cell membrane. Most bacteria have cell walls. But bacteria may or may not have several additional layers. If present, they are found outside cell membranes and cell walls.
a bacteriumcapsuleIt is the polysaccharide layer that completely envelops the cells. It is well organized and tightly packed, which explains its resistance to staining under the microscope. The capsules protect cells from a variety of different threats, such as desiccation, hydrophobic toxic substances (i.e. detergents), and bacterial viruses. The capsules may enhance the ability of bacterial pathogens to cause disease and may provide protection from phagocytosis, the engulfment of white blood cells called phagocytes. Lastly, it can help cling to surfaces.
a bacteriummucus layerSimilar to the capsule, it is usually composed of polysaccharides and completely surrounds the cells. It also protects against various threats such as desiccation and antibiotics. It can also adhere to surfaces. So, how is it different from capsules? The mucus layer is a loose, disorganized layer that peels off easily from the cells that formed it, rather than firmly bound capsules around the bacterial cell wall.
Some bacteria have highly organized layers composed of secreted proteins or glycoproteins that self-assemble into a matrix on the outside of the cell wall. this regular structureS layerAnchored in the cell wall, although it is not considered an official part of the bacterial cell wall. S-layers have very important functions for the bacteria that possess them, especially in terms of growth and survival and cell integrity.
The S layer helps maintain the overall rigidity of the cell wall and surface layer as well as cell shape, which is important for reproduction. The S layer protects cells from ionic/pH changes, osmotic pressure, harmful enzymes, bacterial viruses, and predatory bacteria. They can provide cell adhesion to other cells or surfaces. For pathogenic bacteria, they can provide protection from phagocytosis.
structures outside the cell wall
Bacteria can also have structures on the outside of the cell wall, often associated with the cell wall and/or the cell membrane. The building blocks of these structures are usually manufactured inside the cell and then secreted across the cell membrane and cell wall for assembly on the outside of the cell.
Edge (sing. Edge)
piliare filamentous appendages that protrude from cells, usually dozens or hundreds of them. they consist ofyour batteryproteins and are used by cells to attach to surfaces. They are especially important for pathogenic bacteria, which use them to attach to host tissues.
Pili (sing. pilin)
relatedVery similar to pilus (some textbooks use the terms interchangeably) in that they are filamentous appendages that extend from the cell and are made of the protein pilus. Pili are also used to attach to surfaces and host cells such asNeisseria gonorrhoeaeThe cells use pili to grab the sperm cells and pass them on to the next human host. So why do some researchers bother to distinguish pili from pili?
Pili are usually longer than pili, with only 1-2 pili on each cell, but this does not seem to be sufficient to distinguish the two structures. This actually comes down to the fact that some specific pili are involved in functions other than attachment. thiscommon fungal hairParticipation is calledconjugate, which allows the transfer of a short piece of DNA from a donor cell to a recipient cell. thisType IV pilifunction in an unusual movement calledtwitching movement, the pili attach to a solid surface and then contract, pulling the bacteria forward in jerky movements.
Flagella (aka flagella)
Bacteria's motility is usually determined by what is known asflagellum. Bacterial flagella differ in composition, structure, and function from eukaryotic flagella, which utilize microtubules as flexible whip-like tails. Bacterial flagella are rigid in nature and operate more like a propeller on a boat.
Bacterial flagella are composed of three main components:
- thisfilament– Elongated appendages extending from the cell surface. filaments made of proteinflagellinand is hollow. Flagellin is transcribed in the cytoplasm and then transported across the cell membrane and cell wall. Bacterial flagellar filaments grow from their tips (unlike the hair on the head), adding more and more flagellar units to lengthen until they reach the correct size. Flagellin units are guided into place by protein caps.
- thishook- This is a bend coupler that connects the filament to the flagellar motor.
- thisengine– Rotary motors spanning cell membranes and cell walls, and additional components for Gram-negative outer membranes. The motor has two parts:Substrate, which provides the rotation, andstator, which provides the torque required for rotation to occur. The matrix consists of a central axis surrounded by protein rings, two for Gram-positive bacteria and four for Gram-negative bacteria. The stator consists of the following partsagainst proteinSurrounds a ring embedded in the cell membrane.
Diagram of the base of the flagella. By LadyofHats (Own work) [Public domain] via Wikipedia Commons
Bacterial motility usually involves the use of flagella, although there are some other possibilities (such as the use of type IV pili for twitching motility). But certainly the most common type of bacterial movement isswim, this is done by using flagella or flagella.
The rotation of the flagellar basal body occurs due to proton dynamics, in which protons accumulated on the outside of the cell membrane are driven through pores in the Mot protein, interacting with charges in the ring protein as they pass through the membrane. This interaction causes the matrix to rotate and turn the filaments extending from the cells. Rotation speeds of up to 200-1000 rpm and speeds of up to 60 cell lengths/sec (for comparison, cheetahs move at a maximum of 25 cell lengths/sec).
Rotation can occur atClockwise (CW)or aCounterclockwise (CCW)Orientation, produces different results for cells. Bacteria will move forward, called "running, "when there is a counter-clockwise rotation, and random reorientation, called "roll," when there is a clockwise rotation.
Some spiral-shaped bacteria, calledSpirochetes, using ascrew powerDue to its unusual morphology and flagellar conformation. These Gram-negative bacteria have specialized flagella that attach to one end of the cell, extend through the periplasm, and then attach to the other end of the cell. when theseinner flagellaWhen rotated, they apply a twist to the entire cell, creating a bending motion that is particularly effective for burrowing through viscous liquids.
sliding powerJust what it sounds like, a slower, more graceful movement than the other forms introduced so far. Certain filamentous or bacillus species have gliding motility that do not require the use of flagella. Although more than one mechanism has been identified, it does require the cell to be in contact with a solid surface. Some cells rely on mucus propulsion, in which secreted mucus pushes the cell forward, while others rely on surface layer proteins to pull the cell along.
Now that we have understood the basics of bacterial flagellar motility and the mechanism of bacterial swimming, let's combine these two topics and talk aboutChemotaxisOr any other kind of tax (just not mine). Chemotaxis is the movement of an organism towards or away from a chemical substance. You can also havePhototaxis, in which the organism responds to light. In chemotaxis, favorable substances such as nutrients are calledattract, while substances that have adverse effects on cells (such as toxins) are calledinsect repellent. In the absence of attractants or repellants, cells will undergo "random walk’, which alternates between tumbling and running, ultimately accomplishing nothing. In the presence of some type of gradient, the cell’s motion will become biased, causing the bacteria to move toward the attractant and away from any attractant over time. Repellants. How did this happen?
First, let's cover how bacteria know which direction to go. Bacteria rely on protein receptors embedded in their membranes calledchemoreceptor, to bind a specific molecule. Binding often results in the methylation or phosphorylation of chemoreceptors, which trigger complex protein pathways that ultimately affect the rotation of the flagellar motor. Bacteria involvedtime perception, they compare the concentration of the substance with the concentration obtained a few seconds (or microseconds) ago. In this way, they gather information about the direction of the substance's concentration gradient. Swim (determined by CCW flagellar rotation) became longer and tumbling (determined by CW flagellar rotation) decreased as bacteria approached higher concentrations of attractant. Sometimes, the bacteria still move away from the attractant in the wrong direction because tumbling causes the cells to randomly reorient, but it doesn't last long in the wrong direction. the result of "biased random walk"allows cells to quickly move up a gradient of attractant (or down a gradient of repellant).
bacterial movement. By Brudersohn (Own work (Original: Own creation)) [CC BY-SA 2.0 de], via Wikimedia Commons
capsule, mucus layer, S layer, pilus/pilus, pilus, pilus/pilus, conjugative pilus, conjugation, type IV pilus, twitching motility, flagella/flagellate, silk, flagellin, hook, motor, Substrate, Stator, Mot Protein, Swimming, Clockwise (CW), Counterclockwise (CCW), Running, Tumbling, Helicoid, Spiral Motion, Internal Flagella, Gliding Motion, Chemotaxis, Phototaxis, Attractant, Repellent, Random Walks, chemoreceptors, time sensing, biased random walks.
- What are the components and functions of the capsule and the mucus layer? When are they produced? How does the capsule or mucus layer increase the bacteria's chances of survival in different environments?
- What are pili and pili? What are their composition and function? What is the size of the bacterial flagella? How are they arranged on bacterial cells? How common are flagella in bacteria?
- What are the basic components of bacterial flagella? How is it different from the flagella found in eukaryotes? How do bacterial flagella grow and how are proteins transported across membranes? How do they cause movement? How does this movement differ from eukaryotic flagella?
- How do bacterial flagella attach to the body? How do the 2 inner rings create movement and what is the dynamics of movement? What is the purpose of the 2 outer loops in the matrix of Gram bacteria? What can replace gram+?
- How is inner flagella different from flagella? What types of bacteria are they found in? In what ways are they more effective than flagella?
- What is Chemotaxis? How does the direction of flagella's rotation affect how bacteria move? What do we know about the chemotaxis mechanisms of membrane-bound proteins and chemotactic mediators? How long do chemotactic stimuli last? Why is this important to the phenomenon?
Exploratory Questions (Optional)
- How to use the chemotaxis of microorganisms to solve the problem of environmental pollution?
Structure of a typical bacterium. The numbered parts are: (1) pilus, (2) plasmid, (3) ribosome, (4) cytoplasm, (5) cytoplasmic membrane, (6) cell wall, (7) capsule, (8) nucleoid, and (9) flagellum (Source: LadyofHats [Public domain] via Wikimedia Commons).
The principal surface layers are capsules and loose slime, the cell wall of Gram-positive bacteria and the complex cell envelope of Gram-negative bacteria, plasma (cytoplasmic) membranes, and mesosomal membrane vesicles, which arise from invaginations of the plasma membrane.What structure could a bacteria use to adhere to a surface? ›
Fimbriae are thin filamentous appendages that extend from the cell, often in the tens or hundreds. They are composed of pilin proteins and are used by the cell to attach to surfaces. They can be particularly important for pathogenic bacteria, which use them to attach to host tissues.
Gram-positive bacteria are surrounded by many layers of peptidoglycan (PG), which form a protective shell that is 30–100 nm thick (Silhavy et al. 2010). The PG layers are covalently modified with carbohydrate polymers including wall teichoic acids (WTAs) or functionally related anionic glycopolymers as well as CPS.What is the structure of the cell surface? ›
The structure of the cell surface may be thought of as three-layered, with a central plasma membrane to which certain macromolecular components are attached on the outer face (the exoskeleton) and other components on the inner face (the membrane cytoskeleton).What is the surface area of bacteria cell? ›
A range of diameters 0.65-0.66µm, lengths 1.8-2.15µm, volumes 0.55-0.66µm^3 and surface ares 3.8-4.42 µm^2 is given in table.What structures are only found in bacteria? ›
Answer and Explanation: The correct answer is b. capsule. The capsule forms the outer layer of the bacterial cell - it is found outside the cell wall for an extra layer of protection, given that these organisms are single-celled and free-living in their environment.What is surface bacteria? ›
Bacteria attached to surfaces often exist as biofilms, which play several protective roles. The extracellular polymeric substance (EPS) secreted by cells in biofilms that are attached to surfaces provides protection from mechanical damage and shear caused by fluid flow.What is bacteria structure and function? ›
Bacteria are prokaryotic unicellular organisms. They have a relatively simple cell structure compared to eukaryotic cells. They also do not possess any membrane-bound organelles such as a nucleus. However, do they possess genetic material (DNA or RNA) in the intracellular space called the nucleoid.What is the structure of Gram positive and Gram-negative bacteria? ›
Gram-negative bacteria are surrounded by a thin peptidoglycan cell wall, which itself is surrounded by an outer membrane containing lipopolysaccharide. Gram-positive bacteria lack an outer membrane but are surrounded by layers of peptidoglycan many times thicker than is found in the Gram-negatives.
Gram positive bacteria have a thick peptidoglycan layer and no outer lipid membrane whilst Gram negative bacteria have a thin peptidoglycan layer and have an outer lipid membrane.What is the surface charge of Gram-negative bacteria? ›
Gram-negative bacteria have a high negative charge on their surface because of lipopolysaccharides. At neutral pH, the majority of bacterial cells have a net negative charge as a result of the existence of peptidoglycan, which is abundant in carboxyl and amino groups.What are the six structures in an animal cell? ›
The organelles of an animal cell include the nucleus, mitochondria, ribosomes, lysosomes, vacuoles, endoplasmic reticulum, and Golgi apparatus.What are the major structures and characteristics of bacteria? ›
Bacteria are like eukaryotic cells in that they have cytoplasm, ribosomes, and a plasma membrane. Features that distinguish a bacterial cell from a eukaryotic cell include the circular DNA of the nucleoid, the lack of membrane-bound organelles, the cell wall of peptidoglycan, and flagella.What are the major structures of a bacterial membrane? ›
The bacterial cell envelope consists of a capsule, a cell wall and a cytoplasmic membrane. This structure allows the passage of bacterial nutrients and excreted products, while acting as a barrier to harmful substances such as antibiotics.What are 5 characteristics of bacteria? ›
Five characteristics of bacteria include being unicellular, prokaryotic, microscopic, lacking a nucleus, and having a plasma membrane. These traits are shared by all bacteria.