DNA is a single molecule, found free in the cytoplasm. Additional DNA is found on one or more rings called plasmids. Type of cell division Mitosis Binary fission. Chromosomal DNA. The DNA of bacterial cells is found loose in the cytoplasm. Plasmid DNA. Bacteria also have small, closed-circles of DNA called plasmids present in their cytoplasm. Bacteria can have one or more flagella singular: flagellum.
Cell wall. Plant and bacterial cell walls provide structure and protection. Most are 0. The cell structure is simpler than that of other organisms as there is no nucleus or membrane bound organelles. Instead their control centre containing the genetic information is contained in a single loop of DNA. Some bacteria have an extra circle of genetic material called a plasmid. The plasmid often contains genes that give the bacterium some advantage over other bacteria.
For example it may contain a gene that makes the bacterium resistant to a certain antibiotic. Bacteria are classified into five groups according to their basic shapes: spherical cocci , rod bacilli , spiral spirilla , comma vibrios or corkscrew spirochaetes. They can exist as single cells, in pairs, chains or clusters.
Bacteria are found in every habitat on Earth: soil, rock, oceans and even arctic snow. Some live in or on other organisms including plants and animals including humans.
There are approximately 10 times as many bacterial cells as human cells in the human body. A lot of these bacterial cells are found lining the digestive system. Some bacteria live in the soil or on dead plant matter where they play an important role in the cycling of nutrients.
Some types cause food spoilage and crop damage but others are incredibly useful in the production of fermented foods such as yoghurt and soy sauce. Whip-like extensions often cover the surfaces of bacteria — long ones, called flagella, or short ones, called pili — and help bacteria move around and attach to a host.
Bacteria can be classified by the composition of their cell walls using a test called the Gram stain, according to the Science Education Resource Center at Carleton College. The test stains Gram-positive bacteria, or bacteria that do not have an outer membrane. Gram-negative bacteria, which do have an outer membrane, don't pick up the stain. For example, S. Delving beneath the cell wall and membrane, bacteria contain cytoplasm, a solution of mostly water and salts.
Within the cytoplasm float the nucleoid, plasmids and tiny protein factories called ribosomes, which are the sites where the cell's genetic instructions are translated into the cell's products. Some antibiotics, like tetracycline, target bacterial ribosomes to prevent them from synthesizing proteins, thus dooming the cell. The cytoplasm of some bacteria may also have little pockets, called inclusions, where nutrients are stored for lean times.
Photosynthetic bacteria, which generate energy from sunlight, may have structures called chromatophores spread throughout their cytoplasm.
These chromatophores hold pigments used in photosynthesis. As some of the oldest life-forms on Earth , bacteria have evolved a dizzying number of ways to survive.
Some bacteria are photosynthetic, while others are master decomposers, breaking down rotting and decaying organic material into nutrients. Some enter symbiotic, or mutually beneficial, relationships with a host more on this later. Most bacteria multiply by a process called binary fission , according to the Cornell University College of Agriculture and Life Sciences.
In this process, a single bacterial cell, called the "parent," makes a copy of its DNA and grows larger by doubling its cellular content. The cell then splits apart, pushing the duplicated material out and creating two identical "daughter" cells. Some types of bacteria, such as cyanobacteria and firmicutes, reproduce via budding. In this case, the daughter cell grows as an offshoot of the parent.
It starts off as a small nub, grows until it is the same size as its parent and then splits off. After binary fission or budding, the DNA found in parents and offspring is exactly the same.
Therefore, bacterial cells introduce variation into their genetic material by integrating additional DNA, often from their surroundings, into their genome. The resulting genetic variation ensures that bacteria can adapt and survive as their environment changes, Live Science previously reported.
There are three ways horizontal gene transfer occurs: transformation, transduction and conjugation. Transformation is the most common process of horizontal gene transfer and occurs when a bacterium absorbs short DNA fragments from the environment through its cell membrane. The DNA fragments are released into the environment by other bacteria. To undergo transformation, a bacterium must be in a state known as competence. Cell wall composition varies widely amongst bacteria and is one of the most important factors in bacterial species analysis and differentiation.
For example, a relatively thick, meshlike structure that makes it possible to distinguish two basic types of bacteria. A technique devised by Danish physician Hans Christian Gram in , uses a staining and washing technique to differentiate between the two forms. When exposed to a gram stain, gram-positive bacteria retain the purple color of the stain because the structure of their cell walls traps the dye.
In gram-negative bacteria, the cell wall is thin and releases the dye readily when washed with an alcohol or acetone solution. Cytoplasm - The cytoplasm, or protoplasm, of bacterial cells is where the functions for cell growth, metabolism, and replication are carried out. It is a gel-like matrix composed of water, enzymes, nutrients, wastes, and gases and contains cell structures such as ribosomes, a chromosome, and plasmids. The cell envelope encases the cytoplasm and all its components.
Unlike the eukaryotic true cells, bacteria do not have a membrane enclosed nucleus. The chromosome, a single, continuous strand of DNA, is localized, but not contained, in a region of the cell called the nucleoid. All the other cellular components are scattered throughout the cytoplasm.
One of those components, plasmids, are small, extrachromosomal genetic structures carried by many strains of bacteria. Like the chromosome, plasmids are made of a circular piece of DNA. Unlike the chromosome, they are not involved in reproduction. Only the chromosome has the genetic instructions for initiating and carrying out cell division, or binary fission, the primary means of reproduction in bacteria. Plasmids replicate independently of the chromosome and, while not essential for survival, appear to give bacteria a selective advantage.
Plasmids are passed on to other bacteria through two means. For most plasmid types, copies in the cytoplasm are passed on to daughter cells during binary fission. Other types of plasmids, however, form a tubelike structure at the surface called a pilus that passes copies of the plasmid to other bacteria during conjugation, a process by which bacteria exchange genetic information.
Plasmids have been shown to be instrumental in the transmission of special properties, such as antibiotic drug resistance, resistance to heavy metals, and virulence factors necessary for infection of animal or plant hosts. The ability to insert specific genes into plasmids have made them extremely useful tools in the fields of molecular biology and genetics, specifically in the area of genetic engineering.
Cytoplasmic Membrane - A layer of phospholipids and proteins, called the cytoplasmic membrane, encloses the interior of the bacterium, regulating the flow of materials in and out of the cell.
This is a structural trait bacteria share with all other living cells; a barrier that allows them to selectively interact with their environment. Membranes are highly organized and asymmetric having two sides, each side with a different surface and different functions. Membranes are also dynamic, constantly adapting to different conditions.
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