Bacteria Prokaryotic cells

Even the plasma membranes of prokaryotic cells (bacteria) are complex (Figure 9.1). With no intracellular organelles to divide and organize the work, bacteria carry out processes either at the plasma membrane or in the cyto-... 

The situation in bacteria is somewhat different. Prokaryotic cells need not carry out ATP/ADP exchange. Thus, bacteria have the potential to produce approximately 38 ATP per glucose. 

Physically, all these prokaryotes are small, diameter about 1.0 pm and are of rigid, simple shape. They usually have little or no internal structure so that chemical diffusion is relatively rapid. Secondary compartments are rare but vesicles and vacuoles (even nuclei) are found in a very few large bacteria. We shall see that all the prokaryote cells have controlled, autocatalytic, internal metabolism, but are relatively little affected by external circumstances, except by shortage of nutrients. 

Prokaryote Cell or organism lacking a membrane-bound, structurally discrete nucleus and other subcellular compartments. Bacteria are prokaryotes (see also eukaryote). 

If the end goal of cloning is to have a cloned gene expressed in a cell, the entire coding sequence must be doned intact. Furthermore, if a cloned eukaryotic gene is to be expressed in bacteria (to make recombinant proteins), the gene must not contain introns, which could not be processed in a prokaryotic cell. In these cases it is more convenient to done cDNA rather than DNA restriction fragments. 

This drug has a direct amebicidal effect against trophozoites E. histolytica in tissues, and it is not active against cysts in either the lumen or intestinal walls, or in other organs. The mechanism of action of emetine consists of the blockage of protein synthesis in eukaryotic (but not in prokaryotic) cells. It inhibits the process of polypeptide chain formation. Protein synthesis is inhibited in parasite and mammalian cells, but not in bacteria. 

Although all tetracyclines have a similar mechanism of action, they have different chemical structures and are produced by different species of Streptomyces. In addition, structural analogues of these compounds have been synthesized to improve pharmacokinetic properties and antimicrobial activity. While several biological processes in the bacterial cells are modified by the tetracyclines, their primary mode of action is inhibition of protein synthesis. Tetracyclines bind to the SOS ribosome and thereby prevent the binding of aminoacyl transfer RNA (tRNA) to the A site (acceptor site) on the 50S ri-bosomal unit. The tetracyclines affect both eukaryotic and prokaryotic cells but are selectively toxic for bacteria, because they readily penetrate microbial membranes and accumulate in the cytoplasm through an energy-dependent tetracycline transport system that is absent from mammalian cells. 

Topical eukaryotic cells (Fig. 1-7) are much larger than prokaryotic cells—commonly 5 to 100 pm in diameter, with cell volumes a thousand to a million times larger than those of bacteria. The distinguishing characteristics of eukaryotes are the nucleus and a variety of membrane-bounded organelles with specific functions mitochondria, endoplasmic reticulum, Golgi complexes, and lysosomes. Plant cells also contain vacuoles and chloroplasts (Fig. 1-7). Also present in the cytoplasm of many cells are granules or droplets containing stored nutrients such as starch and fat. 

The striking differences between eukaryotic and prokaryotic cells have led to many speculations about the evolutionary relationship of these two great classes of living organisms. A popular theory is that mitochondria, which are characteristic of most eukaryotes, arose from aerobic bacteria. After cyanobacteria had developed and oxygen... 

Many important details have emerged concerning the mechanisms of DNA replication in both bacteria (Prokaryotes) and higher cells (Eukaryotes). These mechanisms are vital in understanding how a cell duplicates its genetic material (DNA), and how this duplication is related to cell division. For these reasons, cells have evolved elaborate mechanisms to ensure that the process of duplication (DNA replication) is error free. This level of control is so important that cells will actually cease cell division if errors become too frequent and wait until the DNA is repaired. 

Generalized representations of the internal structures of animal and plant cells (eukaryotic cells). Cells are the fundamental units in all living systems, and they vary tremendously in size and shape. All cells are functionally separated from their environment by the plasma membrane that encloses the cytoplasm. Plant cells have two structures not found in animal cells a cellulose cell wall, exterior to the plasma membrane, and chloroplasts. The many different types of bacteria (prokaryotes) are all smaller than most plant and animal cells. Bacteria, like plant cells, have an exterior cell wall, but it differs greatly in chemical composition and structure from the cell wall in plants. Like all other cells, bacteria have a plasma membrane that functionally separates them from their environment. Some bacteria also have a second membrane, the outer membrane, which is exterior to the cell wall. 

Schippers A, Neretin LN, Kallmeyer J, Ferdelman TG, Cragg BA, Parkes RJ, Jorgensen BB (2005) Prokaryotic Cells of the Deep Sub-Seafloor Biosphere Identified as Living Bacteria. Nature 433 861... 

Cells are broadly classified as either prokaryotes or eukaryotes. Prokaryotic cells are found in simpler organisms, such as bacteria. They do not have a membrane enclosed nucleus, but their DNA is dispersed in the cytoplasm of the cell. Eukaryotic cells are found in all members of the animal kingdom. Their structures contain distinct membrane encapsulated compartments, such as the nucleus, which contains their DNA, mitochondria and lysomes. These separate compartments are known as organelles. 

Prokaryotes (bacteria and blue-green algae) are the most abundant organisms on earth. A prokaryotic cell does not contain a membrane-bound nucleus. Bacteria are either cocci, bacilli or spirilla in shape, and fall into two groups, the eubacteria and the archaebacteria. 

The peptidoglycan (protein and oligosaccharide) cell wall protects the prokaryotic cell from mechanical and osmotic pressure. A Gram-positive bacterium has a thick cell wall surrounding the plasma membrane, whereas Gram-negative bacteria have a thinner cell wall and an outer membrane, between which is the periplasmic space. 

Structural Organization of the Plasma Membrane. Although our purpose here is not to describe in detail the structure of cell membranes, a brief look at the structure of the plasma membrane will help us to understand the major problems and the role of specific proteolysis related to membrane assembly. All cells—those of bacteria (prokaryotes), higher plants, and animals (eukaryotes)—have plasma membranes, but other distinct internal membranes (88) are found in eukaryotic cells (nuclei, golgi bodies, mitochondria, endoplasmic reticula, and lysosomes). 

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