What are the characteristics of prokaryotic cells

what are the characteristics of prokaryotic cells

Characteristics of Prokaryotic Cells

Jul 05, Prokaryotes lack an organized nucleus and other membrane-bound organelles. Prokaryotic DNA is found in a central part of the cell called the nucleoid. The cell wall of a prokaryote acts as an extra layer of protection, helps maintain cell shape, and prevents dehydration. Prokaryotic cell size ranges from to ?m in niceloveme.comted Reading Time: 5 mins. The characteristics of the prokaryotic cells are mentioned below. They lack a nuclear membrane. Mitochondria, Golgi bodies, chloroplast, and lysosomes are absent. The genetic material is present on a single niceloveme.comted Reading Time: 6 mins.

Cell theory states that the cell how to dance with a cane the fundamental unit of life. However, cells vary significantly in size, shape, structure, and function. At the simplest level of construction, all cells possess a few fundamental components. These include cytoplasm a gel-like substance composed of water and dissolved chemicals needed orokaryotic growthwhich is contained within a plasma membrane also called a cell membrane or cytoplasmic membrane ; one or more chromosomes, which contain the genetic blueprints of the cell; and ribosomesorganelles used for the production what cut of meat to use for pot roast proteins.

Beyond these basic components, cells can vary greatly between organisms, and even within the same multicellular organism. The two largest categories of cells prokaryotic cells and eukaryotic cells are defined by major differences in several cell structures.

Prokaryotic cells lack a nucleus surrounded by a complex nuclear membrane and generally have a single, circular chromosome located in a nucleoid. Eukaryotic cells have a nucleus surrounded by a complex nuclear membrane that contains multiple, rod-shaped chromosomes. All plant cells and animal cells are eukaryotic. Some microorganisms are composed of prokaryotic cells, whereas others are composed of eukaryotic cells.

Prokaryotic microorganisms are classified within the domains Archaea and Bacteria, whereas eukaryotic organisms are classified within the domain Eukarya. The structures inside a cell are analogous to og organs inside a human body, with unique structures suited to specific functions. Some of the structures found in prokaryotic cells are similar to those found in some eukaryotic cells; others are unique to prokaryotes.

Although there are some exceptions, eukaryotic cells tend to be larger than prokaryotic cells. The comparatively larger size of eukaryotic cells dictates the need to compartmentalize various chemical processes within types of knee pain and what they mean areas of the cell, using complex membrane-bound organelles.

In contrast, prokaryotic cells generally lack membrane-bound organelles; prkaryotic, they often contain inclusions that compartmentalize their cytoplasm. Figure 1 illustrates structures typically associated with prokaryotic cells. These structures are described in more detail in the next section. Figure 1. A typical prokaryotic cell contains a cell membrane, chromosomal DNA that is concentrated in a nucleoid, ribosomes, and a cell characteristtics.

Some prokaryotic cells may also possess flagella, pili, fimbriae, and capsules. Individual cells of a particular prokaryotic organism are typically similar in shape, or cell morphology. Although thousands of prokaryotic organisms have been identified, only a handful of cell morphologies are commonly seen microscopically. Table 1 names and illustrates cell morphologies commonly found in prokaryotic cells.

In addition to cellular shape, prokaryotic cells of the same species may group together in certain distinctive arrangements depending on the plane of cell division. Some common arrangements are shown prokaruotic Table 2. In most prokaryotic cells, morphology is maintained by the cell wall in combination with cytoskeletal elements. The cell wall is a structure found in most prokaryotes and some eukaryotes; it envelopes the cell membrane, protecting the cell from changes in osmotic pressure Figure 2.

Osmotic pressure occurs because of differences in the concentration of solutes on opposing sides of a semipermeable membrane. Water chaaracteristics able to pass through a semipermeable membrane, but solutes dissolved molecules like salts, sugars, and other compounds cannot.

When the concentration of solutes is greater on one side of the membrane, water diffuses across the membrane from the side with the lower concentration more water to the side with the higher concentration less water until the concentrations on both sides become equal. This diffusion of water is called osmosisand it can cause extreme osmotic pressure on a cell when its external environment changes.

Figure 2. In cells that lack a cell wall, changes in osmotic pressure can lead to crenation in hypertonic environments or cell lysis in hypotonic environments. The external environment of a cell can be described as an isotonic, hypertonic, or hypotonic medium. In an isotonic mediumthe solute concentrations inside and outside characterristics cell are approximately equal, so there is no net movement of water across the cell membrane.

In a hypertonic mediumthe solute concentration outside the cell exceeds that inside the cell, so water diffuses out of the cell and into the external medium.

In a hypotonic mediumthe solute concentration inside the cell exceeds that outside of the cell, so water will move by osmosis into the cell. This causes the cell to swell and potentially lyse, or burst.

The degree to which a particular cell is able to withstand changes in osmotic pressure is called tonicity. Cells that have a cell wall are better able to withstand subtle changes in osmotic pressure and maintain their shape. In hypertonic environments, cells that lack a cell wall can become dehydrated, causing crenationor shriveling of the cell; the plasma membrane contracts and appears scalloped chaarcteristics notched Figure 2.

By contrast, cells that possess a cell wall undergo plasmolysis rather than crenation. In plasmolysis, the plasma membrane contracts and detaches from the cell wall, and there is a decrease in interior volume, but the cell wall remains intact, thus allowing the cell to maintain some shape and prokaryotoc for a period of time Figure 3. Likewise, cells that lack a cell wall are more prone to lysis in hypotonic environments.

The presence of a cell wall allows the cell to maintain its shape and integrity for a longer time before lysing Figure 3. Figure 3. In prokaryotic cells, the cell wall provides some protection against changes in osmotic pressure, allowing it to maintain its shape longer. The cell membrane is typically attached to the cell wall in an isotonic medium left.

In a hypertonic medium, the cell membrane detaches from the cell wall and contracts plasmolysis as water leaves the cell. In a hypotonic medium rightthe cell wall prevents the cell membrane from expanding to the point of bursting, although lysis will eventually occur if too much water is absorbed. All cellular life has a DNA genome organized into one or more chromosomes. Prokaryotic chromosomes are typically circular, haploid unpairedand not bound by a complex nuclear membrane.

In general, prokaryotic DNA interacts with nucleoid-associated proteins NAPs that assist in the organization and packaging of the chromosome.

Figure 4. The nucleoid region the area enclosed by the green dashed line is a condensed area of DNA found within prokaryotic cells. Because of the density of the area, it does not readily stain and appears lighter in color when viewed with a charactristics electron microscope. Cells that have plasmids often have hundreds of them within a single cell.

Plasmids are more commonly found in bacteria; however, plasmids have been found in archaea and eukaryotic organisms. Plasmids often carry genes that confer advantageous traits such as antibiotic resistance; thus, they are important to the survival of the organism. We will discuss plasmids in more detail in Mechanisms of Microbial Genetics. All cellular life synthesizes proteins, characterisyics organisms in all three domains of life possess ribosomes, structures responsible protein synthesis.

However, ribosomes in each of the three domains are structurally different. Prokaryotic ribosomes are found in the cytoplasm. They are called 70S ribosomes because they have a size of 70S Figure 5characteritics eukaryotic cytoplasmic ribosomes have a size of 80S. The S stands what is capital gains rate for 2012 Svedberg unit, a measure of sedimentation in an ultracentrifuge, which is based on size, shape, and surface qualities of the structure being analyzed.

Although they are the same size, bacterial and archaeal ribosomes have different proteins and rRNA molecules, and the archaeal versions are more similar to their eukaryotic counterparts than to those found in bacteria.

Figure 5. Prokaryotic ribosomes 70S are composed of two subunits: the 30S small subunit and the 50S large subuniteach of which are composed of protein and rRNA components. As single-celled organisms living in unstable environments, some prokaryotic cells have the ability to store excess nutrients within cytoplasmic structures called inclusions.

Storing nutrients in a polymerized form is advantageous because it reduces the buildup of osmotic pressure that occurs as a cell accumulates solutes. Various types of inclusions store glycogen and starches, which contain carbon that cells can access for energy.

Volutin granules, also called metachromatic granules because of their staining characteristics, are inclusions that store polymerized inorganic phosphate that can be used in metabolism and assist in the formation of biofilms.

Microbes known to contain volutin granules include the archaea Methanosarcinathe bacterium Corynebacterium diphtheriaeand the unicellular eukaryotic alga Chlamydomonas. Sulfur granules, another type of inclusion, fo found in sulfur bacteria of the genus Thiobacillus ; these granules store elemental sulfur, which the bacteria use for metabolism. Occasionally, charactefistics types of inclusions are surrounded by a phospholipid monolayer embedded with protein.

Polyhydroxybutyrate PHBwhich can be produced by species of Bacillus and Pseudomonasis an example of an inclusion that displays this type of monolayer structure. Industrially, PHB has also been used as a source of biodegradable polymers for bioplastics. Several different types of inclusions are shown in Figure 6. Figure 6. Prokaryotic cells may have various types of inclusions.

Some prokaryotic cells have other types of inclusions that serve purposes other than nutrient storage. For example, some prokaryotic cells produce gas vacuoles, accumulations of small, protein-lined vesicles of gas.

These gas vacuoles allow the prokaryotic cells that synthesize them to alter their buoyancy so that they can adjust their location in the water column. Magnetotactic bacteria, such as Magnetospirillum magnetotacticumcontain magnetosomeswhich are inclusions of magnetic iron oxide or iron sulfide surrounded by a lipid layer. These allow cells to align along a magnetic field, aiding their movement Figure 6.

Cyanobacteria such as Anabaena cylindrica and bacteria such as Halothiobacillus neapolitanus produce carboxysome inclusions. Carboxysomes are composed of outer shells of thousands of protein subunits. Both of these chagacteristics are used for carbon metabolism. Some prokaryotic cells also possess carboxysomes that sequester functionally related enzymes in one location. These structures are considered proto-organelles because they compartmentalize important compounds or chemical reactions, much like many eukaryotic organelles.

Endospores not to be confused with the reproductive spores formed by fungi allow some bacterial cells to survive long periods without food or water, as well as prokaryotuc to chemicals, extreme temperatures, and even radiation. Table 1 compares the characteristics of vegetative cells and endospores.

The process by which vegetative cells transform into endospores is called sporulationand it generally begins when nutrients become depleted or environmental conditions become otherwise unfavorable Figure 7.

The process begins with the formation of a septum in the vegetative bacterial cell. The septum divides the cell asymmetrically, separating a Prokaryotlc forespore from the mother cell. A cortex gradually forms around the how to take nitro pills by laying down layers of calcium and dipicolinic acid between membranes.

A protein spore coat then forms around the cortex while the DNA of the how to make a money corsage cell disintegrates. Charaacteristics maturation of the endospore occurs with the formation of an outermost exosporium.

The Nucleoid

Jan 20, Prokaryotic cells lack a nucleus surrounded by a complex nuclear membrane and generally have a single, circular chromosome located in a nucleoid. Eukaryotic cells have a nucleus surrounded by a complex nuclear membrane that contains multiple, rod-shaped chromosomes. 1 All plant cells and animal cells are eukaryotic. The prokaryotic (Gr., pro-primitive, karyon-nucleus) cells are the most primitive cells from morphological point of view. They occur in bacteria and blue green algae. Prokaryotes are small, single cell organisms, usually less than a micrometer (abbreviated m; m=1 millimeter, abbreviated mm) are generally not longer than ǵniceloveme.comted Reading Time: 1 min. Jul 02, Characteristics of prokaryotic cells The general characteristics of prokaryotic cells are listed below: In general, prokaryotic cells range in size from to m and are considerably smaller than eukaryotic cells. The shape of prokaryotic cells ranges from cocci, bacilli, spirilla, and niceloveme.comted Reading Time: 7 mins.

Cell theory states that the cell is the fundamental unit of life. However, cells vary significantly in size, shape, structure, and function. At the simplest level of construction, all cells possess a few fundamental components. These include cytoplasm a gel-like substance composed of water and dissolved chemicals needed for growth , which is contained within a plasma membrane also called a cell membrane or cytoplasmic membrane ; one or more chromosomes, which contain the genetic blueprints of the cell; and ribosomes, organelles used for the production of proteins.

Beyond these basic components, cells can vary greatly between organisms, and even within the same multicellular organism. The two largest categories of cellsprokaryotic cells and eukaryotic cellsare defined by major differences in several cell structures. Prokaryotic cells lack a nucleus surrounded by a complex nuclear membrane and generally have a single, circular chromosome located in a nucleoid.

Eukaryotic cells have a nucleus surrounded by a complex nuclear membrane that contains multiple, rod-shaped chromosomes. All plant cells and animal cells are eukaryotic. Some microorganisms are composed of prokaryotic cells, whereas others are composed of eukaryotic cells. Prokaryotic microorganisms are classified within the domains Archaea and Bacteria, whereas eukaryotic organisms are classified within the domain Eukarya.

The structures inside a cell are analogous to the organs inside a human body, with unique structures suited to specific functions. Some of the structures found in prokaryotic cells are similar to those found in some eukaryotic cells; others are unique to prokaryotes.

Although there are some exceptions, eukaryotic cells tend to be larger than prokaryotic cells. The comparatively larger size of eukaryotic cells dictates the need to compartmentalize various chemical processes within different areas of the cell, using complex membrane-bound organelles. In contrast, prokaryotic cells generally lack membrane-bound organelles; however, they often contain inclusions that compartmentalize their cytoplasm.

These structures are described in more detail in the next section. Individual cells of a particular prokaryotic organism are typically similar in shape, or cell morphology. Although thousands of prokaryotic organisms have been identified, only a handful of cell morphologies are commonly seen microscopically. In addition to cellular shape, prokaryotic cells of the same species may group together in certain distinctive arrangements depending on the plane of cell division.

In most prokaryotic cells, morphology is maintained by the cell wall in combination with cytoskeletal elements. Osmotic pressure occurs because of differences in the concentration of solutes on opposing sides of a semipermeable membrane. Water is able to pass through a semipermeable membrane, but solutes dissolved molecules like salts, sugars, and other compounds cannot.

When the concentration of solutes is greater on one side of the membrane, water diffuses across the membrane from the side with the lower concentration more water to the side with the higher concentration less water until the concentrations on both sides become equal. This diffusion of water is called osmosis, and it can cause extreme osmotic pressure on a cell when its external environment changes.

The external environment of a cell can be described as an isotonic, hypertonic, or hypotonic medium. In an isotonic medium, the solute concentrations inside and outside the cell are approximately equal, so there is no net movement of water across the cell membrane.

In a hypertonic medium, the solute concentration outside the cell exceeds that inside the cell, so water diffuses out of the cell and into the external medium. In a hypotonic medium, the solute concentration inside the cell exceeds that outside of the cell, so water will move by osmosis into the cell. This causes the cell to swell and potentially lyse, or burst. The degree to which a particular cell is able to withstand changes in osmotic pressure is called tonicity. Cells that have a cell wall are better able to withstand subtle changes in osmotic pressure and maintain their shape.

By contrast, cells that possess a cell wall undergo plasmolysis rather than crenation. Likewise, cells that lack a cell wall are more prone to lysis in hypotonic environments. All cellular life has a DNA genome organized into one or more chromosomes.

Prokaryotic chromosomes are typically circular, haploid unpaired , and not bound by a complex nuclear membrane. In general, prokaryotic DNA interacts with nucleoid-associated proteins NAPs that assist in the organization and packaging of the chromosome.

Cells that have plasmids often have hundreds of them within a single cell. Plasmids are more commonly found in bacteria; however, plasmids have been found in archaea and eukaryotic organisms. Plasmids often carry genes that confer advantageous traits such as antibiotic resistance; thus, they are important to the survival of the organism. We will discuss plasmids in more detail in Bacterial Genetics. All cellular life synthesizes proteins, and organisms in all three domains of life possess ribosomes, structures responsible protein synthesis.

However, ribosomes in each of the three domains are structurally different. Prokaryotic ribosomes are found in the cytoplasm. The S stands for Svedberg unit, a measure of sedimentation in an ultracentrifuge, which is based on size, shape, and surface qualities of the structure being analyzed.

Although they are the same size, bacterial and archaeal ribosomes have different proteins and rRNA molecules, and the archaeal versions are more similar to their eukaryotic counterparts than to those found in bacteria.

As single-celled organisms living in unstable environments, some prokaryotic cells have the ability to store excess nutrients within cytoplasmic structures called inclusions. Storing nutrients in a polymerized form is advantageous because it reduces the buildup of osmotic pressure that occurs as a cell accumulates solutes.

Various types of inclusions store glycogen and starches, which contain carbon that cells can access for energy. Volutin granules, also called metachromatic granules because of their staining characteristics, are inclusions that store polymerized inorganic phosphate that can be used in metabolism and assist in the formation of biofilms. Microbes known to contain volutin granules include the archaea Methanosarcina , the bacterium Corynebacterium diphtheriae , and the unicellular eukaryotic alga Chlamydomonas.

Sulfur granules, another type of inclusion, are found in sulfur bacteria of the genus Thiobacillus ; these granules store elemental sulfur, which the bacteria use for metabolism. Occasionally, certain types of inclusions are surrounded by a phospholipid monolayer embedded with protein. Polyhydroxybutyrate PHB , which can be produced by species of Bacillus and Pseudomonas , is an example of an inclusion that displays this type of monolayer structure.

Industrially, PHB has also been used as a source of biodegradable polymers for bioplastics. Some prokaryotic cells have other types of inclusions that serve purposes other than nutrient storage. For example, some prokaryotic cells produce gas vacuoles, accumulations of small, protein-lined vesicles of gas. These gas vacuoles allow the prokaryotic cells that synthesize them to alter their buoyancy so that they can adjust their location in the water column.

Magnetotactic bacteria, such as Magnetospirillum magnetotacticum , contain magnetosomes, which are inclusions of magnetic iron oxide or iron sulfide surrounded by a lipid layer. Cyanobacteria such as Anabaena cylindrica and bacteria such as Halothiobacillus neapolitanus produce carboxysome inclusions. Carboxysomes are composed of outer shells of thousands of protein subunits. Both of these compounds are used for carbon metabolism.

Some prokaryotic cells also possess carboxysomes that sequester functionally related enzymes in one location. These structures are considered proto-organelles because they compartmentalize important compounds or chemical reactions, much like many eukaryotic organelles. Bacterial cells are generally observed as vegetative cells, but some genera of bacteria have the ability to form endospores, structures that essentially protect the bacterial genome in a dormant state when environmental conditions are unfavorable.

Endospores not to be confused with the reproductive spores formed by fungi allow some bacterial cells to survive long periods without food or water, as well as exposure to chemicals, extreme temperatures, and even radiation. The process begins with the formation of a septum in the vegetative bacterial cell. The septum divides the cell asymmetrically, separating a DNA forespore from the mother cell.

A cortex gradually forms around the forespore by laying down layers of calcium and dipicolinic acid between membranes. A protein spore coat then forms around the cortex while the DNA of the mother cell disintegrates.

Further maturation of the endospore occurs with the formation of an outermost exosporium. The endospore is released upon disintegration of the mother cell, completing sporulation. Endospores of certain species have been shown to persist in a dormant state for extended periods of time, up to thousands of years.

After germination, the cell becomes metabolically active again and is able to carry out all of its normal functions, including growth and cell division. The ability to form endospores is restricted to a few genera of Gram-positive bacteria; however, there are a number of clinically significant endospore-forming gram-positive bacteria of the genera Bacillus and Clostridium.

These include B. Pathogens such as these are particularly difficult to combat because their endospores are so hard to kill. Special sterilization methods for endospore-forming bacteria are discussed in Control of Microbial Growth. Structures that enclose the cytoplasm and internal structures of the cell are known collectively as the cell envelope.

In prokaryotic cells, the structures of the cell envelope vary depending on the type of cell and organism. Most but not all prokaryotic cells have a cell wall, but the makeup of this cell wall varies.

All cells prokaryotic and eukaryotic have a plasma membrane also called cytoplasmic membrane or cell membrane that exhibits selective permeability, allowing some molecules to enter or leave the cell while restricting the passage of others. The plasma membrane structure of most bacterial and eukaryotic cell types is a bilayer composed mainly of phospholipids formed with ester linkages and proteins.

These phospholipids and proteins have the ability to move laterally within the plane of the membranes as well as between the two phospholipid layers. Archaeal membranes are fundamentally different from bacterial and eukaryotic membranes in a few significant ways. First, archaeal membrane phospholipids are formed with ether linkages, in contrast to the ester linkages found in bacterial or eukaryotic cell membranes. Second, archaeal phospholipids have branched chains, whereas those of bacterial and eukaryotic cells are straight chained.

Finally, although some archaeal membranes can be formed of bilayers like those found in bacteria and eukaryotes, other archaeal plasma membranes are lipid monolayers. Membrane proteins and phospholipids may have carbohydrates sugars associated with them and are called glycoproteins or glycolipids, respectively.

Glycoproteins and glycolipids in the plasma membrane can vary considerably in chemical composition among archaea, bacteria, and eukaryotes, allowing scientists to use them to characterize unique species.

Plasma membranes from different cells types also contain unique phospholipids, which contain fatty acids. As described in Using Biochemistry to Identify Microorganisms, phospholipid-derived fatty acid analysis PLFA profiles can be used to identify unique types of cells based on differences in fatty acids.

Archaea, bacteria, and eukaryotes each have a unique PFLA profile. One of the most important functions of the plasma membrane is to control the transport of molecules into and out of the cell. Internal conditions must be maintained within a certain range despite any changes in the external environment. The transport of substances across the plasma membrane allows cells to do so. Cells use various modes of transport across the plasma membrane.

Some small molecules, like carbon dioxide, may cross the membrane bilayer directly by simple diffusion. However, charged molecules, as well as large molecules, need the help of carriers or channels in the membrane.



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