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Linear Chromosome
A linear chromosome is a chromosome which is linear in shape, and contains terminal ends. In most eukaryotic cells, DNA is arranged in multiple linear chromosomes. In contrast, most prokaryotic cells generally contain a singular circular chromosome. However, linear chromosomes are not limited to eukaryotic organisms; some prokaryotic organisms have linear chromosomes as well, such as ''Borrelia burgdorferi''. In fact, experiments in which the circular chromosomes of prokaryotic organisms have been linearized have demonstrated that some prokaryotes can maintain viability even with linear chromosomes. In general, the factors which led to the evolution of linear chromosomes in eukaryotes are not well understood. One potential selective pressure in favor of linear chromosomes relates to the size of an organism's genome: linear chromosomes may make transcription and replication of large genomes easier. In an organism with a very large genome, circular chromosomes could potentially cause p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are the histones. These proteins, aided by chaperone proteins, bind to and condense the DNA molecule to maintain its integrity. These chromosomes display a complex three-dimensional structure, which plays a significant role in transcriptional regulation. Chromosomes are normally visible under a light microscope only during the metaphase of cell division (where all chromosomes are aligned in the center of the cell in their condensed form). Before this happens, each chromosome is duplicated ( S phase), and both copies are joined by a centromere, resulting either in an X-shaped structure (pictured above), if the centromere is located equatorially, or a two-arm structure, if the centromere is located distally. The joined copies are now called si ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eukaryotic Cells
Eukaryotes () are organisms whose Cell (biology), cells have a cell nucleus, nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the Three-domain system, three domains of life. Bacteria and Archaea (both prokaryotes) make up the other two domains. The eukaryotes are usually now regarded as having emerged in the Archaea or as a sister of the Asgard (archaea), Asgard archaea. This implies that there are only Two-domain system, two domains of life, Bacteria and Archaea, with eukaryotes incorporated among archaea. Eukaryotes represent a small minority of the number of organisms, but, due to their generally much larger size, their collective global biomass (ecology), biomass is estimated to be about equal to that of prokaryotes. Eukaryotes emerged approximately 2.3–1.8 billion years ago, during the Proterozoic eon, likely as Flagellated cell, flagellated phagotrophs. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prokaryotic Cells
A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connections". Pearson Education. San Francisco: 2003. In the two-empire system arising from the work of Édouard Chatton, prokaryotes were classified within the empire Prokaryota. But in the three-domain system, based upon molecular analysis, prokaryotes are divided into two domains: ''Bacteria'' (formerly Eubacteria) and ''Archaea'' (formerly Archaebacteria). Organisms with nuclei are placed in a third domain, Eukaryota. In the study of the origins of life, prokaryotes are thought to have arisen before eukaryotes. Besides the absence of a nucleus, prokaryotes also lack mitochondria, or most of the other membrane-bound organelles that characterize the eukaryotic cell. It was once thought that prokaryotic cellular components within the cytopla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Circular Chromosome
A circular chromosome is a chromosome in bacteria, archaea, mitochondria, and chloroplasts, in the form of a molecule of circular DNA, unlike the linear chromosome of most eukaryotes. Most prokaryote chromosomes contain a circular DNA molecule – there are no free ends to the DNA. Free ends would otherwise create significant challenges to cells with respect to DNA replication and stability. Cells that do contain chromosomes with DNA ends, or telomeres (most eukaryotes), have acquired elaborate mechanisms to overcome these challenges. However, a circular chromosome can provide other challenges for cells. After replication, the two progeny circular chromosomes can sometimes remain interlinked or tangled, and they must be resolved so that each cell inherits one complete copy of the chromosome during cell division. Replication The circular bacteria chromosome replication is best understood in the well-studied bacteria ''Escherichia coli'' and ''Bacillus subtilis''. Chromoso ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Borrelia Burgdorferi
''Borrelia burgdorferi'' is a bacterial species of the spirochete class in the genus ''Borrelia'', and is one of the causative agents of Lyme disease in humans. Along with a few similar genospecies, some of which also cause Lyme disease, it makes up the species complex of ''Borrelia burgdorferi'' sensu lato. The complex currently comprises 20 accepted and 3 proposed genospecies. ''B. burgdorferi'' sensu stricto exists in North America and Eurasia and until 2016 was the only known cause of Lyme disease in North America. ''Borrelia'' species are Gram-negative. Microbiology ''Borrelia burgdorferi'' is named after the researcher Willy Burgdorfer, who first isolated the bacterium in 1982. ''Borrelia burgdorferi'' is a microaerophile, requiring small amounts of oxygen in order to undergo glycolysis and survive. Like all other ''Borrelia'' sps., this bacterium is also gram-negative and a spirochete. Borrelia colonies are often smaller, rounded, and white with an elevated center. ''B. b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Evolutionary Pressure
Any cause that reduces or increases reproductive success in a portion of a population potentially exerts evolutionary pressure, selective pressure or selection pressure, driving natural selection. It is a quantitative description of the amount of change occurring in processes investigated by evolutionary biology, but the formal concept is often extended to other areas of research. In population genetics, selective pressure is usually expressed as a selection coefficient. Amino acids selective pressure It has been shown that putting an amino acid bio-synthesizing gene like ''HIS4'' gene under amino acid selective pressure in yeast causes enhancement of expression of adjacent genes which is due to the transcriptional co-regulation of two adjacent genes in Eukaryota. Antibiotic resistance Drug resistance in bacteria is an example of an outcome of natural selection. When a drug is used on a species of bacteria, those that cannot resist die and do not produce offspring, while th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as regulatory sequences (see non-coding DNA), and often a substantial fraction of 'junk' DNA with no evident function. Almost all eukaryotes have mitochondria and a small mitochondrial genome. Algae and plants also contain chloroplasts with a chloroplast genome. The study of the genome is called genomics. The genomes of many organisms have been sequenced and various regions have been annotated. The International Human Genome Project reported the sequence of the genome for ''Homo sapiens'' in 200The Human Genome Project although the initial "finished" sequence was missing 8% of the genome consisting mostly of repetitive sequences. With advancements in technology that could handle sequenci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
