Prokaryotic cell chromosomes

Prokaryotic cells have only a single membrane, the plasma membrane or cell membrane. Because they have no other membranes, prokaryotic cells contain no nucleus or organelles. Nevertheless, they possess a distinct nuclear area where a single circular chromosome is localized, and some have an internal membranous structure called a mesosome that is derived from and continuous with the cell membrane. Reactions of cellular respiration are localized on these membranes. In photosynthetic prokaryotes such as the cyanobacteria,... 

In terms of evolutionary biology, the complex mitotic process of higher animals and plants has evolved through a progression of steps from simple prokaryotic fission sequences. In prokaryotic cells, the two copies of replicated chromosomes become attached to specialized regions of the cell membrane and are separated by the slow intrusion of the membrane between them. In many primitive eukaryotes, the nuclear membrane participates in a similar process and remains intact the spindle microtubules are extranuclear but may indent the nuclear membrane to form parallel channels. In yeasts and diatoms, the nuclear membrane also remains intact, an intranuclear polar spindle forms and attaches at each pole to the nuclear envelope, and a single kinetochore microtubule moves each chromosome to a pole. In the cells of higher animals and plants, the mitotic spindle starts to form outside of the nucleus, the nuclear envelope breaks down, and the spindle microtubules are captured by chromosomes (Kubai, 1975 Heath, 1980 Alberts et al., 1989). 

DNA contains the genetic information transmitted to each daughter cell when cells divide. The DNA usually exists in the form of nucleoprotein (DNA-protein) complexes called chromosomes. A prokaryotic cell contains a single chromosome. Prior to cell division this chromosome duplicates and segregates so that an identical complement of DNA goes to each of two newly formed daughter cells. 

Eukaryotic cells are more complex than prokaryotic cells and usually contain more DNA, which is partitioned between several chromosomes. In both prokaryotes and eukaryotes, almost all cells of the same organism contain the same number of chromosomes. In eukaryotes most of the chromosomes are localized in the nucleus. Thus the DNA is isolated from the main body of the cytoplasm—a unique feature of eukaryotes and the primary distinction between prokaryotes and eukaryotes. Some organelles, notably the mitochondria and the chloroplasts, contain a single circular chromosome. 

Potentized homeopathic drugs are capable of producing effects on both prokaryotic and eukaryotic cells. Prokaryotic cells are usually smaller in size (1 - 10 pm) than eukaryotic ones (5 - 100 pm). Membrane-bound organelles like mitochondria, endoplasmic reticulum, Golgi complexes etc. are present in eukaryotic cells but absent in prokaryotic ones. While eukaryotic cells have nucleus containing DNA with histone and non-histone proteins in chromosoms, prokaryotic cells have no nucleus and their DNA with non-histone proteins lies in nucleoid without any membranous envelope. However, both types of cells are covered by plasma membrane with some common features. 

Large group of organisms that do not have organelles enclosed in cell membranes and have DNA in both a chromosome and circular plasmids. They have a protein and complex carbohydrate cell wall over a plasma membrane. Although eukaryotic and prokaryotic cells are structurally different, their basic biochemical processes are similar. Volume 1(1, 2), Volume 2(3). 

Eukaryotic cell— A cell whose genetic material is carried on chromosomes inside a nucleus encased in a membrane. Eukaryotic cells also have organelles that perform specific metabolic tasks and are supported by a cytoskeleton which runs through the cytoplasm, giving the cell form and shape. In contrast, the more primitive prokaryotic cells are smaller than eukaryotes, and have no nucleus, distinct organelles, or cytoskeleton. 

The nucleus is a large membrane-bound cell organelle which houses the chromosomes and which occupies roughly 10% of the volume of all eukaryotic cells. The nucleus is separated from the rest of the cell and the cytoplasm by a double membraue known as the nuclear envelope. The outer layer of the nuclear membrane is studded with small openings called nuclear pores, which allow for the controlled movement of selected molecules in and out of the nucleus. Most of a eukaryotic cell s DNA is found in the chromosomes of the nucleus, while a very small amount of DNA is present in the mitochondria. All plant and animal cells with a nucleus and known as eukaryotic cells, (meaning true nucleus) while bacterial cells which lack a nucleus are known as prokaryotic cells. 

DNA (section 2.4.1) than eukaryotic RNA (section 2.4.2). The result will be the construction of a collection of cloned DNA fragments propagated in bacteria that is called the genomic library. This library should contain representatives of every sequence in the chromosome of a prokaryotic cell and every expressed gene in the case of a eukaryotic cell. The final step consists of the screening of every recombinant clone to identify the required gene(s). 

Microbial cell structure is varied with a tremendous diversity in size and shape. Prokaryotic cells typically contain a cell wall, 70s ribosomes, a chromosome that is not membrane bound, various inclusions and vacuoles, and extrachromosomal DNA or plasmids. Eukaryotic microorganisms are equally varied with a variety of forms many are photosynthetic or harbor photosynthetic symbionts. Many eukaryotic cells contain prokaryotic endosymbionts, some of which contain their own set of plasmids. Given the variety of eukaryotic microorganisms, they have been labeled protists, since they are often a mixing of algal and protozoan characteristics within apparently related groups. 

Organisms (excluding viruses) can be broadly separated into prokaryotes and eukaryotes on the basis of cellular structure. Prokaryotic cells contain no nuclear membranes and their DNA is not arranged in chromosomes. Eukaryotic cells always contain a nuclear membrane and their DNA is usually in chromosomal form. There are other differences between the two cell types but these are the most useful general distinguishing features. The prokaryotes comprise all bacteria (including cyanobacteria) and are therefore unicellular (also termed the Monera). All other organisms are eukaryotes, either unicellular (the Protista) or multicellular. 

Most of the DNA in eukaryotic cells is located in the nucleus, extensively folded Into the familiar structures we know as chromosomes (Chapter 10). Each chromosome contains a single linear DNA molecule associated with certain proteins. In prokaryotic cells, most or all of the genetic Information resides... 

The replicon model used to describe the regulation of DNA synthesis in prokaryote cells has influenced many concepts of the same process in eukaryote cells. Since the basis of this discussion will center around the limitations of the replicon model as applied to eukaryotes, several terms will be emphasized here. The term "replication unit used here refers to any stretch of DNA in a eukaryote chromosome which is replicated by the efforts of one growing point. The growing point is defined as any one site on a parental, double-standard DNA molecule where enzymatic activity results in the replication of both strands of parental DNA. 

The region in a replication unit where DNA synthesis is initiated will be referred to as the initiation site. It is stressed that initiation sites in both prokaryote and eukaryote chromosomes are deoxynucleotide sequences no other structural linkers provide this site. This is well illustrated in prokaryote cells where DNA synthesis is initiated at a genetically defined site in the DNA (Caro and Berg, 1969 Makover, 1968 Mosig and Werner, 1969). Similarly in eukaryote cells, the establishment of a heritable pattern of replication of DNA molecules through each S phase combined with the demonstration that contiguous DNA molecules contain multiple replication units, indicates that a component(s) of the initiation mechanism must be able to select a deoxynucleotide sequence as the site of initiation of DNA synthesis. 

Prokaryotic cells (e.g. bacteria) contain a single chromosome which is a large closed circular double-stranded DNA molecule, often folded or supercoiled. Electron microscopy has proved invaluable for direct observations of this kind. 

Nucleoid The large, circular DNA molecule of a prokaryotic cell, along with its associated proteins also sometimes called the bacterial chromosome. It is supercoiled and forms a dense mass within the cell, and the term Nucleoid is often used for the cell region occupied by this mass. 

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