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.
Relatively few bacteria are parasites or pathogens that cause disease in animals and plants. Bacteria reproduce by binary fission. In this process the bacterium, which is a single cell, divides into two identical daughter cells. Binary fission begins when the DNA of the bacterium divides into two replicates.
The bacterial cell then elongates and splits into two daughter cells each with identical DNA to the parent cell. Each daughter cell is a clone of the parent cell. When conditions are favourable such as the right temperature and nutrients are available, some bacteria like Escherichia coli can divide every 20 minutes.
This means that in just seven hours one bacterium can generate 2,, bacteria. Bacteria that create their own energy, fueled by light or through chemical reactions, are autotrophs. Capsule - Some species of bacteria have a third protective covering, a capsule made up of polysaccharides complex carbohydrates. Capsules play a number of roles, but the most important are to keep the bacterium from drying out and to protect it from phagocytosis engulfing by larger microorganisms.
The capsule is a major virulence factor in the major disease-causing bacteria, such as Escherichia coli and Streptococcus pneumoniae. Nonencapsulated mutants of these organisms are avirulent, i.
Cell Envelope - The cell envelope is made up of two to three layers: the interior cytoplasmic membrane, the cell wall, and -- in some species of bacteria -- an outer capsule.
Cell Wall - Each bacterium is enclosed by a rigid cell wall composed of peptidoglycan, a protein-sugar polysaccharide molecule. The wall gives the cell its shape and surrounds the cytoplasmic membrane, protecting it from the environment. It also helps to anchor appendages like the pili and flagella, which originate in the cytoplasm membrane and protrude through the wall to the outside.
The strength of the wall is responsible for keeping the cell from bursting when there are large differences in osmotic pressure between the cytoplasm and the environment. 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. While some bacteria cause diseases in humans, many types of bacteria are benign, and even beneficial.
All living things can be divided into five kingdoms: animals, plants, fungi, protists--single-celled organisms, such as amoeba, which are more complex than bacteria--and monera. Bacteria belong to kingdom Monera, which can be further divided into archaea and bacteria. All living things can be divided into two types of cells: prokaryotes and eukaryotes. Eukaryotic cells have a nucleus and other cell structures that are bound by a distinct membrane. Bacteria, as prokaryotic cells, lack these internal membrane-bound structures.
This distinction is considered to be one of the most important of all biological classifications. Bacteria are single-cell organisms. Bacteria are microscopic, usually 0. Unlike a human muscle cell or blood cell, a bacterial cell is a self-sufficient living being. While bacteria sometimes live together in large numbers, they are generally not dependent on one another for survival, and they do not perform specialized tasks.
Bacteria are usually one of three shapes: rod, sphere or spiral.
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