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Inner World of the Cell

Structure in a Cell

Cell Organelles Moleculartracks The structure of an eukaryote cell is shown in Figure 04, in which the cell organelles are often likened to the various utilities within a city. There is library for the nucleus, power plants for the mitochondria, garbage disposal for lysosomes, post office for Golgi complex, ... Table 01 gives a brief description and its function for each of the organelles. However, this is not a complete picture. It has glossed over the role of molecular tracks and the molecular motors running on these tracks.

Figure 04 Cell Organelles

Figure 05 Molecular Tracks [view large image]

Without these molecular tracks (Figure 05), the cell would be a shapeless blob and all the material inside would be wandering aimlessly. As discussed below, there are two kinds of visible tracks -
the microtubule and the actin, each one is accompanied with a particular motor. The actin also provide a scaffold to support the cell membrane, and the microtubule is critical (providing the spindle) in cell division.

Cytosketeton Network of protein filaments Structural support; cell movement No
Flagella(cilia, microvilli) Cellular extensions Motility or moving fluids over surfaces Yes
Centrioles Hollow microtubules Moving chromosomes during cell division No
Plasma membrane Lipid bilayer in which proteins are embedded Regulates what passes into and out of cell; cell-to-cell communication Yes
Endoplasmic reticulum Network of internal membranes; forms compartments and vesicles Rough type processes proteins for secretion and synthesizes phospholipids; smooth type synthesize fats and steroids No
Nucleus Structure bounded by double membrane; contains chromosomes Control center of cell; directs protein synthesis and cell reproduction No
Golgi complex Stacks of flattened vesicles Modifies and packages proteins for export from cell; forms secretory vesicles No
Lysosomes Vesicles derived from Golgi complex that contain hydrolytic digestive enzymes Digest worn-out mitochondria and cell debris; play role in cell death No
Autophagy Vesicles to collect debris within the cell Malfunction causes accumulation of cell damage leading to diseases and aging (see Malfunction of Autophagy) No
Mitochondria Bacteria-like elements with inner membrane Battery of the cell by ATP synthesis; site of oxidative metabolism No
Chromosomes (during cell division) / Chromatins Long threads of DNA that form a complex with protein Contain hereditary information Yes
Nucleolus Site of rRNA synthesis Assembles ribosomes No
Ribosomes Small, complex assemblies of protein, often bound to ER Site of protein synthesis Yes

Table 01 Cell Structure

PKC - Absence or presence in prokaryotic cells.

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