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Models of Eukaryotic Cell

Eukaryotes are organisms composed of one or many complex cells containing nuclei. All animals, plants, fungi, and single-celled protists are eukaryotes; they contain complex cellular structures and comparatively large genomes. Scientists employ a number of models to simplify the eukaryotic cell and explain its basic structure and function. The distinction of eukaryotes from more primitive prokaryotic cells -- bacteria -- was first made in the mid-20th century as it became clear that these two classes of organisms had very distinct types of cells.
  1. The Schematic Cell

    • The nucleus is a large organelle within the eukaryotic cell that contains all of the cell's genetic information.

      The most basic cell model is the schematic cell; this is simply a graphical representation showing the different internal structures of the cell. Often, these schematics will be specific to a subset of eukaryotes, such as an animal or plant cell. The schematic cell contains an outer cell membrane and may also contain a cell wall. The internal structure of the cell is buttressed by a cytoskeleton and interspersed with numerous organelles; these organelles include the nucleus, endoplasmic reticulum, golgi complex, mitochondria and ribosomes. Other structures such as chloroplasts and vacuoles may also be included.

      The schematic model is often used by students who are just starting to learn about the cell and how its different parts interact. It is a convenient way to divide the cell into parts to make learning about each individual part easier.

    Models of the Cell Membrane

    • The outer membrane of the cell is an enormously complex mass of fatty molecules, called phospholipids, interspersed with various proteins and cholesterol. The first model of the cell membrane approaching biology's current understanding was Singer and NIcolson's fluid mosaic model. In this model, the outer membrane of the cell is a thin, double-layered sheet of phospholipid molecules. This sheet is fluid and the constituent molecules are constantly moving about. Various proteins are embedded in the membrane, providing molecular function, physical structure, and selective pores for materials to cross.

      More recently, the lipid raft model has amended the fluid mosaic model. According to this model, the membrane proteins are embedded within thick "rafts" of lipid molecules surrounded by a region of shorter molecules that contain no proteins. These lipid rafts appear the be the functional units of the cell membrane and help keep the proteins localized.

    Modelling the Cell Cycle

    • The chromosomes of eukaryotic cells must duplicate and then carefully separate for successful cell division to occur.

      Due to the complex internal structure of the eukaryotic cell, successful division requires an intricate regulatory system. The presence of numerous genetic and other molecular regulators makes mathematical models extremely helpful in understanding how the cell divides. These models generally consist of a "wiring diagram" which illustrates how the different regulatory processes involved in cell division operate. For instance, the activation and inactivation of various cyclin proteins (proteins important in triggering stages of division) occupy different slots of the diagram. Once the diagram is set up and different parameters are set, the model predicts how the cell should divide in different situations and whether that division is tenable over a long period of time.

    Intra-Organelle Modeling

    • Gene expression is one of the most complex and closely-regulated aspects of cell function.

      Due to the complexity of individual organelles, cell biologists produce specialized models for them. For instance, the nucleus and mitochondria both undergo complex internal and external regulation that is crucial for the cell's survival. The nucleus is by far the most complex organelle; it contains all of the genetic information of the organism. At any given time, some of the DNA within the nucleus is tightly-wound and inactive, while other DNA is loosely-wound and active. A complex cascade of molecules makes sure the appropriate molecules are constantly entering and leaving the nucleus.

      By modeling how the different components of the nucleus interact, cell biologists can make predictions, such as which genes will be activated when a given signaling system is turned on. Computational models of nuclear molecules, such as transcription factors of micro-RNAs, illustrate how genes within the cell behave and interact.


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