D Bacterial cell walls are similar in function to the cell walls of many protists, fungi, and plants. In an attack upon a gram-negative bacterium that has a slimy cell covering, what is the correct sequence of structures penetrated by B. This is because bacteria that encounter such an environment. Because of this, which of the following is correct?
A Some antibiotics can block protein synthesis in bacteria without effects in the eukaryotic host. C Translation can occur at the same time as transcription in eukaryotes but not in prokaryotes. E Prokaryotes are able to use a much greater variety of molecules as food sources than can eukaryotes.
C Prokaryotic cells have multiple chromosomes, "packed" with a relatively large amount of protein. D The prokaryotic chromosome is not contained within a nucleus but, rather, is found at the nucleolus. Which of these questions stems from this observation, plus an understanding of eukaryotic origins? C If chloramphenicol inhibits prokaryotic ribosomes, should it not also inhibit mitochondrial ribosomes?
If this bacterium readily performs conjugation involving a copy of this plasmid, then the result should be. C Prokaryotes exchange some of their genes by conjugation, the union of haploid gametes, and transduction. D The persistence of bacteria throughout evolutionary time is due to their genetic homogeneity in other words, sameness. E Genetic variation in bacteria is not known to occur, because of their asexual mode of reproduction. This experiment subjected bacteria to the same gene transfer mechanism as occurs in.
They are, however, no longer able to lead independent lives because most genes originally present on their chromosome have moved to the nuclear genome. Which phenomenon accounts for the movement of these genes?
What was the basis for dividing prokaryotes into two domains? What is likely to be true of this species? You suspect that the fish has been contaminated by the extreme halophile, Halobacterium.
Which of these features of cells removed from the surface of the fish, if confirmed, would support your suspicion? One kind is a spirochete that propels its host through the termite gut. A second type of bacteria synthesizes ATP, some of which is used by the spirochetes. The locomotion provided by the spirochetes introduces the ATP-producing bacteria to new food sources.
Which term s is are applicable to the relationship between the two kinds of bacteria? If this bacterium gains access to the inside of a leaf, however, it causes a fatal disease in the plant. Once the plant dies, the bacterium and its offspring decompose the plant. What is the correct sequence of ecological roles played by the bacterium in the situation described here? Use only those that apply. Which of these methods should be least effective at inhibiting bacterial growth?
Consequently, assuming that nothing is done to counter the reduction of intestinal bacteria, a hospital patient who is receiving broad-spectrum antibiotics is most likely to become.
Which role typically does not involve a symbiosis? Sign in. Campbell Biology Chapter Helpfulness: 0. Set Details Share. A Bacterial cell walls differ in molecular composition from plant cell walls. B Cell walls prevent cells from bursting in hypotonic environments. C Cell walls prevent cells from dying in hypertonic conditions.
E Cell walls provide the cell with a degree of physical protection from the environment. This is because bacteria that encounter such an environment A undergo death by plasmolysis. B are unable to metabolize the glucose or fructose, and thus starve to death.
C experience lysis. D are obligate anaerobes. E are unable to swim through these thick and viscous materials. B an external covering provided by the plasma membrane. C a complex "motor" embedded in the cell wall and plasma membrane. D a basal body that is similar in structure to the cell's centrioles. E a membrane-enclosed organelle with motor proteins. Furthermore, unlike eukaryotic chromosomes, most prokaryotic genomes are organized into polycistronic operons, or clusters of more than one coding region attached to a single promoter , separated by only a few base pairs.
The proteins encoded by each operon often collaborate on a single task, such as the metabolism of a sugar into by-products that can be used for energy Figure 3. The organization of prokaryotic DNA therefore differs from that of eukaryotes in several important ways.
The most notable difference is the condensation process that prokaryotic DNA molecules undergo in order to fit inside relatively small cells. Other differences, while not as dramatic, are summarized in Table 1. Abbott, A. Lyme disease: Uphill struggle. Nature , — doi Ahnert, S. How much non-coding DNA do eukaryotes require? Journal of Theoretical Biology , — Bendich, A. Prokaryotic and eukaryotic chromosomes: What's the difference? Bioessays 22 , — Bradley, M.
Effects of Fis on Escherichia coli gene expression during different growth stages. Microbiology , — Cairns, J. The chromosome of Escherichia coli.
Intracellular location of the histonelike protein HU in Escherichia coli. Journal of Bacteriology , — Endy, D. Modelling cellular behaviour. Ferdows, M. Proceedings of the National Academy of Sciences 86 , — Fraser, C. Genomic sequence of a Lyme disease spirochaete, Borrelia burgdorferi. Hinnebusch, B.
The bacterial nucleoid visualized by fluorescence microscopy of cells lysed within agarose: Comparison of Escherichia coli and spirochetes of the genus Borrelia. Jacob, F. Genetic regulatory mechanisms in the synthesis of proteins. Journal of Molecular Biology 3 , — Mason, D. Nuclear division as observed in live bacteria by a new technique. Journal of Bacteriology 71 , — link to article. Minsky, A. Nucleosomes: A solution to a crowded intracellular environment.
Murphy, L. Isolation and characterization of spermidine nucleoids from Escherichia coli. Journal of Structural Biology , — Rice, P. Cell 87 , — Robinow, C. The bacterial nucleoid revisited. Microbiology and Molecular Biology Reviews 58 , — Sandman, K. HMf, a DNA-binding protein isolated from the hyperthermophilic archaeon Methanothermus fervidus , is most closely related to histones. Proceedings of the National Academy of Sciences 87 , — Diversity of prokaryotic chromosomal proteins and the origin of the nucleosome.
Cellular and Molecular Life Sciences 54 , — Sauvonnet, N. Pilus formation and protein secretion by the same machinery in Escherichia coli.
EMBO Journal 19 , — doi Sinden, R. Chromosomes in living Escherichia coli cells are segregated into domains of supercoiling. Proceedings of the National Academy of Sciences 78 , — Snyder, L. Molecular Genetics of Bacteria , 2nd ed. Trucksis, M. The Vibrio chol erae genome contains two unique circular chromosomes.
Proceedings of the National Academy of Sciences 95 , — Willenbrock, H. Chromatin architecture and gene expression in Escherichia coli. Genome Biology 5 , Yasuzawa, K. Histone-like proteins are required for cell growth and constraint of supercoils in DNA. Gene , 9—15 Chromosome Mapping: Idiograms. Human Chromosome Translocations and Cancer. Karyotyping for Chromosomal Abnormalities.
Prenatal Screen Detects Fetal Abnormalities. Synteny: Inferring Ancestral Genomes. Telomeres of Human Chromosomes. Chromosomal Abnormalities: Aneuploidies. Chromosome Abnormalities and Cancer Cytogenetics. Copy Number Variation and Human Disease.
The length of a genome varies widely, but is generally at least a few million base pairs. Prokaryote cell nucleoid : Prokaryote cell right showing the nucleoid in comparison to a eukaryotic cell left showing the nucleus.
The nucleoid can be clearly visualized on an electron micrograph at high magnification, where it is clearly visible against the cytosol. Sometimes even strands of what is thought to be DNA are visible. The nucleoid can also be seen under a light microscope. The latter two constituents are likely to be mainly messenger RNA and the transcription factor proteins found regulating the bacterial genome. Proteins helping to maintain the supercoiled structure of the nucleic acid are known as nucleoid proteins or nucleoid-associated proteins, and are distinct from histones of eukaryotic nuclei.
In contrast to histones, the DNA-binding proteins of the nucleoid do not form nucleosomes, in which DNA is wrapped around a protein core.
Instead, these proteins often use other mechanisms, such as DNA looping, to promote compaction. A genophore is the DNA of a prokaryote. It is commonly referred to as a prokaryotic chromosome. The genophore is compacted through a mechanism known as supercoiling, but a chromosome is additionally compacted through the use of chromatin. The genophore is circular in most prokaryotes, and linear in very few.
The circular nature of the genophore allows replication to occur without telomeres. Genophores are generally of a much smaller size than Eukaryotic chromosomes. A genophore can be as small as , base pairs Mycoplasma genitalium. Many eukaryotes such as plants and animals carry genophores in organelles such as mitochondria and chloroplasts. These organelles are very similar to true prokaryotes. DNA supercoiling refers to the over- or under-winding of a DNA strand, and is an expression of the strain on that strand.
Supercoiling is important in a number of biological processes, such as compacting DNA. Additionally, certain enzymes such as topoisomerases are able to change DNA topology to facilitate functions such as DNA replication or transcription.
Mathematical expressions are used to describe supercoiling by comparing different coiled states to relaxed B-form DNA. Note that the helical nature of the DNA duplex is omitted for clarity.
Adding or subtracting twists, as some enzymes can do, imposes strain. If a DNA segment under twist strain were closed into a circle by joining its two ends and then allowed to move freely, the circular DNA would contort into a new shape, such as a simple figure-eight. Such a contortion is a supercoil. The simple figure eight is the simplest supercoil, and is the shape a circular DNA assumes to accommodate one too many or one too few helical twists.
The two lobes of the figure eight will appear rotated either clockwise or counterclockwise with respect to one another, depending on whether the helix is over or underwound. For each additional helical twist being accommodated, the lobes will show one more rotation about their axis.
Instead, global contortions of a circular DNA, such as the rotation of the figure-eight lobes above, are referred to as writhe. The above example illustrates that twist and writhe are interconvertible. The twist is the number of helical turns in the DNA and the writhe is the number of times the double helix crosses over on itself these are the supercoils.
Extra helical twists are positive and lead to positive supercoiling, while subtractive twisting causes negative supercoiling. Many topoisomerase enzymes sense supercoiling and either generate or dissipate it as they change DNA topology.
DNA of most organisms is negatively supercoiled. In part because chromosomes may be very large, segments in the middle may act as if their ends are anchored. As a result, they may be unable to distribute excess twist to the rest of the chromosome or to absorb twist to recover from underwinding—the segments may become supercoiled, in other words.
In response to supercoiling, they will assume an amount of writhe, just as if their ends were joined.
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