What are cells? A brief overview on cells.

 Today we will discuss, what are cells?

Cells

Cells are the functional units of life, in which all of the chemical reactions necessary for the maintenance and production of life take place. They are the smallest independent units of life. Structurally speaking, cells are either prokaryotic or eukaryotic. All prokaryotes ("before nucleus") are independent, single-celled organisms ( e.g., bacteria). The word prokaryote describe cells in which DNA is localized in a region but is not bound by a membrane. Table 1.1 summarize some of the more salient characteristics of prokaryotic cell.

              

                          

         All eukaryotes  ("true nucleus") have cells with a membrane-bound nucleus containing DNA (box 1.1). In addition eukaryotic cells contain many other structures called organelles ("little organs") that perform specific functions. Eukaryotic cells also have a network of specialized structure called filaments and tubules organized into the cytoskeleton, which gives shape to the cells and allows intracellular movement.

        All eukaryotic cells have three basic parts ( table 1.1):

1.     The plasma membrane is the outer boundary of the cell. It separates the internal metabolic events from the environment and allows them to proceed in organized, controlled ways. The plasma membrane also has specific receptors for external molecules that alter the cell's function.

2.     Cytoplasm is the portion of the cell outside the nucleus. The semifluid portion of the cytoplasm is called the cytosol. Suspended within the cytosol are the organ

3. The nucleus is the cell control center.                                                                     

     It contain the chromosome and is separated from the cytoplasm by its own nuclear envelope. The nucleoplasm is the semi-fluid material in the nucleus.

                 Because cells vary so much in form and function, no "typical" cells exists.

Table                     Comparison of prokaryotic and eukaryotic cells 1.1

Component                                             Prokaryote                           Eukaryote

Cell wall                                                     Present                              Absent in Animals                                                                                                                    (present in plants)   Centrioles and Microtubules organizing center                  Absent                              Present in animals                                                                                                               (absent in plants)   Chloroplasts                                                Present in some                  present in some                                                                           cells                                       cells   Genetic material                                         Single circular                     Arranged in multiple                                                                     chromosomes                      chromosomes DNA                                                                        of DNA                             Associated with protein   cilia (9+2)                                                  Absent                                   Present in some cells   Cytoskeleton                                              Absent                                 Present in some cells   Endoplasmic                                              Absent                                 Present Reticulum   Flagellum                                                 Often present                       Present in some cells   glycolysis                                              Absent                                   Present   Golgi apparatus                                      Absent                                     Present   Lysosomes                                             Absent                                      Present   Mitochondria                                        Absent                                       Present   Nucleus                                                Absent                                        Present   Plasma membrane                               Present                                        Present   Ribosomes                                           Present                                       Present   Vacuoles                                              Present                                       Present   vesicles                                                Present                                       Present