I believe that answer is neither: "Borrelia burgdorferi resembles other spirochetes in that it is a highly specialized, motile, two-membrane, spiral-shaped bacterium which lives primarily as an extracellular pathogen. One of the most striking features of Borrelia burgdorferi as compared with other eubacteria is its unusual genome, which includes a linear chromosome approximately one megabase in size and numerous linear and circular plasmids."
Curious where you are going with this? You have posed 2 fairly interesting questions. Are you doing private/personal research? I'm sure others on the board are interested in where you are heading with your questions.
Thank you Linda D
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treepatrol
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Prokaryotic cells Prokaryotes are distinguished from eukaryotes on the basis of nuclear organization, specifically their lack of a nuclear membrane. Prokaryotes also lack most of the intracellular organelles and structures that are characteristic of eukaryotic cells (an important exception is the ribosomes, which are present in both prokaryotic and eukaryotic cells). Most of the functions of organelles, such as mitochondria, chloroplasts, and the Golgi apparatus, are taken over by the prokaryotic plasma membrane. Prokaryotic cells have three architectural regions: appendages called flagella and pili--proteins attached to the cell surface; a cell envelope consisting of a capsule, a cell wall, and a plasma membrane; and a cytoplasmic region that contains the cell genome (DNA) and ribosomes and various sorts of inclusions. Other differences include:
The plasma membrane (a phospholipid bilayer) separates the interior of the cell from its environment and serves as a filter and communications beacon. Most prokaryotes have a cell wall (some exceptions are Mycoplasma (a bacterium) and Thermoplasma (an archaeon)). It consists of peptidoglycan in bacteria, and acts as an additional barrier against exterior forces. It also prevents the cell from "exploding" from osmotic pressure against a hypotonic environment. A cell wall is also present in some eukaryotes like fungi, but has a different chemical composition A prokaryotic chromosome is usually a circular molecule (an exception is that of the bacterium Borrelia burgdorferi, which causes Lyme disease). Even without a real nucleus, the DNA is condensed in a nucleoid. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular. Plasmids can carry additional functions, such as antibiotic resistance.
Structure The cell structure of prokaryotes differs greatly from eukaryotes in many ways. The defining characteristic is, of course, the absence of a nucleus or nuclear envelope. Prokaryotes also lack cytoskeletons and membrane-bound cell compartments such as vacuoles, endoplasmic reticulum, mitochondria and chloroplasts. In eukaryotes, the latter two perform various metabolic processes and are believed to have been derived from endosymbiotic bacteria. In prokaryotes similar processes occur across the cell membrane; endosymbionts are extremely rare. Prokaryotes also have cell walls, while some eukaryotes, particularly animals, do not. Both eukaryotes and prokaryotes have structures called ribosomes, which produce protein. Prokaryotes are usually much smaller than eukaryotic cells.
Prokaryotes have a single haploid circular (only exceptionally linear, as in Borrelia burgdorferi ) chromosome, contained within a region called nucleoid, rather than in a membrane-bound nucleus, but may also have various small circular pieces of DNA called plasmids spread throughout the cell. Reproduction is exclusively asexual, through binary fission, where the chromosome is duplicated and attaches to the cell membrane, and then the cell divides in two. However, they show a variety of parasexual processes where DNA is transferred between cells, such as transformation and transduction.
While prokaryotes are nearly always unicelluar, some are capable of forming groups of cells called colonies. Unlike many eukaryotic multicellular organisms, each member of the colony is undifferentiated and capable of free-living. Colonies are formed by organisms that remain attached following cell division, sometimes through the help of a secreted slime layer. http://www.biologydaily.com/biology/Prokaryote
TITLE: Fibroblasts protect the Lyme disease spirochete, Borrelia burgdorferi, from ceftriaxone in vitro. AUTHORS: Georgilis K; Peacocke M; Klempner MS AUTHOR AFFILIATION: Department of Medicine, New England Medical Center, Boston, Massachusetts. SOURCE: J Infect Dis 1992 Aug;166(2):440-4 ABSTRACT: The Lyme disease spirochete, Borrelia burgdorferi, can be recovered long after initial infection, even from antibiotic-treated patients, indicating that it resists eradication by host defense mechanisms and antibiotics. Since B. burgdorferi first infects skin, the possible protective effect of skin fibroblasts from an antibiotic commonly used to treat Lyme disease, ceftriaxone, was examined. Human foreskin fibroblasts protected B. burgdorferi from the lethal action of a 2-day exposure to ceftriaxone at 1 microgram/mL, 10-20 x MBC. In the absence of fibroblasts, organisms did not survive. Spirochetes were not protected from ceftriaxone by glutaraldehyde-fixed fibroblasts or fibroblast lysate, suggesting that a living cell was required. The ability of the organism to survive in the presence of fibroblasts was not related to its infectivity. Fibroblasts protected B. burgdorferi for at least 14 days of exposure to ceftriaxone. Mouse keratinocytes, HEp-2 cells, and Vero cells but not Caco-2 cells showed the same protective effect. Thus, several eukaryotic cell types provide the Lyme disease spirochete with a protective environment contributing to its long-term survival
Prokaryotic Cell Major elements and features of a typical prokaryotic cell: * cell wall - a rigid framework of polysaccharide cross-linked by short peptide chains; provides mechanical support, shape, and protection; it is a porous nonselective barrier that allows most small molecules to pass * cell membrane - 45:55% lipid:protein ratio; bilayer; highly selective and controls the entry of most substances into the cell; important proteins are located in the cell membrane * nucleoid (DNA) - repository of the cell's genetic information; contains a single tightly coiled DNA molecule * ribosomes - sites where proteins are synthesized; consists of a small and a large subunit; a bacterial cell has about 15,000 ribosomes; 35% of a ribosome is protein, the rest is RNA * storage granules - granules where polymerized metabolites are stored (e.g. sugars); when needed the polymers are liberated and degraded by energy-yielding pathways in the cell * cytosol - the site of intermediary metabolism (sets of chemical reactions by which cells generate energy and form precursors necessary for biosynthesis of macromolecules essential to cell growth and function
4/9 Eukaryotic Cell * much larger in size (1,000 to 10,000 times larger than prokaryotic cells) * much more complex * metabolic processes are organized into compartments, with each compartment dedicated to a particular function (enabled by a system of membranes) * possess a nucleus, the repository of cell's genetic material which is distributed among a few or many chromosomes Animal Cell Major elements and features of a typical animal cell: * extracellular matrix - a complex coating which is cell specific, serves in cell-cell recognitions and communication, also provides a protective layer * cell (plasma) membrane - roughly 50:50% lipid:protein ratio; selectively permeable membrane; contains various systems for influx of extracellular molecules (pumps, channels, transporters); important proteins are located here * nucleus - separated from the cytosol by a double membrane; repository of genetic information - DNA complexed with the basic proteins (histones) to form chromatin fibers, the material from which the chromosomes are made * nucleolus - a distinct RNA-rich part of the nucleus where ribosomes are assembled * mitochondria - organelles surrounded by two membranes that differ significantly in their protein and lipid composition; mitochondria are power plants of eukaryotic cells where ATP is produced * Golgi apparatus - involved in packaging and processing of macromolecules for secretion and for delivery of other cellular compartments * endoplasmic reticulum (ER) - the ER is a labyrinthine organelle where both membrane proteins and lipids are synthesized; * ribosomes - organelle composed of RNA and ribosomal proteins; eukaryotic ribosomes are much larger than prokaryotic ribosomes; attached to ER * lysosomes - function in intracellular digestion of certain materials entering the cell; they also function in the controlled degradation of cellular components * peroxisomes - act to oxidize certain nutrients such as amino acids; in doing so they form potentially toxic hydrogen peroxide and then decompose it by means of the peroxy-cleaving enzyme (protein) * cytoskeleton - is composed of a network of protein filaments and it determines the shape of the cell and gives it stability; cytoskeleton also mediates internal movements that occur in the cytoplasm, such as migration of organelles and movement of chromosomes during cell division A word on ribosomes: ribosome consists of two subunits that fit together and work as one to translate the mRNA into a polypeptide chain (side and front view are below)
5/9
6/9 Plant Cell Major elements and features of a typical plant cell (only what differs from the animal cell): * cell wall - consists of cellulose fibers embedded in a polysaccharide and protein matrix; provides protection from the osmotic and mechanical rupture; channels for fluid circulation and for the cell- cell communication pass through the walls * chloroplasts - a unique family of organelles (the plastids) of which the chloroplast is the prominent example; significantly larger than mitochondria; they are the site of photosynthesis, the reaction by which light energy is converted to metabolically useful chemical energy in the form of ATP * mitochondria - a major source of energy in the dark * vacuole - a very large vesicle enclosed by a single membrane; vacuoles grow; they function in transport and storage of nutrients; by accumulating water, the vacuole allows the plant cell to grow dramatically with no increase in cytoplasmic volume
7/9 The Central Dogma of Molecular Biology DNA contains the complete genetic information that defines the structure and function of an organism. Proteins are formed using the genetic code of the DNA. Three different processes are responsible for the inheritance of genetic information and for its conversion from one form to another: 1. Replication: a double stranded nucleic acid is duplicated to give identical copies. This process perpetuates the genetic information. 2. Transcription: a DNA segment that constitutes a gene is read and transcribed into a single stranded sequence of RNA. The RNA moves from the nucleus into the cytoplasm. 3. Translation: the RNA sequence is translated into a sequence of amino acids as the protein is formed. During translation, the ribosome reads three bases (a codon) at a time from the RNA and translates them into one amino acid. In eukaryotic cells, the second step (transcription) is necessary because the genetic material in the nucleus is physically separated from the site of protein synthesis in the cytoplasm in the cell. Therefore, it is not possible to translate DNA directly into protein, but an intermediary must be made to carry the information from one compartment to another.
8/9 Viruses * supramolecular complexes of nucleic acid (DNA or RNA) encapsulated in a protein coat * viruses act as parasites of cells * the protein coat (capsid) serves to protect the nucleic acid * in some instances, it is also surrounded by a membrane * viruses for all types of cells are known * different viruses infect animal and plant cells * viruses infecting bacteria are called bacteriophages (``bacteria eaters'') * often times, viruses cause the lysis (destruction) of cells * in some cases the viral genetic elements may integrate into the host chromosome and become quiescent * some viruses are implicated in transforming cells into a cancerous state, that is, in converting their hosts to an unregulated state of cell division and proliferation * because all viruses are heavily dependent on their host for the production of viral progeny, viruses must have arisen after cells were established in the course of evolution (presumably, the first viruses were fragments of nucleic acid that developed the ability to replicate independently of the chromosome and then acquired the necessary genes enabling protection, autonomy, and transfer between cells.
9/9 -------- Sources: Biochemistry by Reginald H. Garrett and Charles M. Grisham Molecular Biology for Computer scientists by Lawrence Hunter Internet
Eubacteria (see Activity 4B) A Sampling of Diversity Photoautotrophic Eubacteria Cyanobacteria are photosynthetic. Anabaena, by means of heterocysts, can fix nitrogen. Green and purple bacteria use hydrogen sulfide and hydrogen gas as a source of electrons for photosynthesis. Chemoautotrophic Eubacteria Among the most important are the nitrifying bacteria that participate in nitrogen cycling. Their enzymes strip electrons from ammonia for use in generating ATP. Chemoheterotrophic Eubacteria Pseudomonads are major decomposers in the soil. Actinomycetes produce antibiotics; Lactobacillus is used in dairy product conversions;.E. coli makes vitamin K in the human gut; Rhizobium fixes nitrogen on the roots of legumes. Some strains of E. coli can cause serious diarrhea. Some form resistant endospores that can survive harsh environmental conditions; example: Clostridium botulinum (botulism). Borrelia burgdorferi is transmitted by ticks to humans where it causes Lyme disease. Regarding the "Simple" Bacteria Bacteria can sense and respond to light, nutrients, oxygen, toxins, and even magnetic "north." Some imitate multicellular organisms by forming predatory colonies that entrap other microbes and digest them; some even form fruiting bodies that release spores.
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hiker53
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Single celled is the simple answer. All bacteria are single celled. Sometime they gather close together in chains or grape-like clusters, but they are single celled. (I teach life science). Hiker
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Thanks Hiker, I like the short answer too.
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livinlyme
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Hiker, Are you reffering to Bacteria? this statement is true all bacteria are single celled... now what are Protoctista then? they are multicelled and single celled which lack tissue or substantial cellular differentiation.. correct?! a few links to support where I am coming from and where I was heading : http://www.sp.uconn.edu/~bi102vc/102f04/toedt/BacteriaVirusesF2002web.htm
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