Cell , biological nucleus

Claude Bernard was the first to suggest that the cell nucleus was concerned with synthetic reactions, a view sustained by later experiments with amoebae. If amoebae were transected, only the nucleated halves could continue the syntheses essential for growth. Observations by Flemming (late 19th century) on the behavior of nuclei during fertilization and cell division are the basis of modem cell biology. 

Nucleus (1) In chemistry, the central body of an atom, made up of positively charged protons and electrically neutral neutrons. Virtually all of the mass of an atom is in the nucleus. (2) In biology, in living cells the nucleus is a dense area, within a membrane, containing the genetic material (DNA). 

Figure 28.15. Transcription and Translation. These two processes are closely coupled in prokaryotes, whereas they are spacially and temporally separate in eukaryotes. (A) In prokaryotes, the primary transcript serves as mRNA and is used immediately as the template for protein synthesis. (B) In eukaryotes, mRNA precursors are processed and spliced in the nucleus before being transported to the cytosol for translation into protein. [After J. Darnell, H. Lodish, and D. Baltimore. Molecular Cell Biology, 2d ed. (Scientific American Books, 1990), p. 230.]...

The life of a cell depends on thousands of chemical interactions and reactions exquisitely coordinated with one another in time and space and under the influence of the cell s genetic instructions and its environment. How does a cell extract critical nutrients and information from its environment How does a cell convert the energy stored in nutrients into work (movement, synthesis of critical components) How does a cell transform nutrients into the fundamental structures required for its survival (cell wall, nucleus, nucleic acids, proteins, c3Aoskeleton) How does a cell link Itself to other cells to form a tissue How do cells communicate with one another so that the organism as a whole can function One of the goals of molecular cell biology Is to answer such questions about the structure and function of cells and organisms In terms of the properties of Individual molecules and Ions. 

Karin M. (1994) Signal transduction from the cell surface to the nucleus through the phosphorylation of transcription factors. Curr. Opinion Cell Biology. 6 415. 

Fig. 8. Electronmicrograph of a hepatocyte from an adult liver incubated for 30 minutes for glucose-6-phosphatase activity. The deposits of enzyme reaction are evenly distributed throughout the endoplasmic reticulum. N, nucleus nm, nuclear membrane rm, rough membranes of the endoplasmic reticulum sm, smooth membranes m, mitochondria [Courtesy of the Journal of Cell Biology (Leskes et al., 1971).]...

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). 

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