Cell Structure: Part 1

There are many many different kinds of cells.  They vary in size, shape, function and composition.  A "general" cell is discussed here.

There are three main regions of the cell:  The cell membrane, the cytoplasm, and the nucleus.
 

The cell membrane is like the skin of the cell; it envelops the cytoplasm and nucleus, keeping the contents of the cell separated from the exterior.  The cell membrane also plays a role in regulating exchange with the external environment.  The cell membrane is composed of two layers of phospholipid molecules (molecules consisting of a various configurations of lipid/fat and phosphate).  The hydrocarbon tails of the phospholipid molecules face inward, towards each other, and the fatty heads "line" the outside of the membrane. 

Specialized proteins are embedded in the cell membrane.  These proteins may serve as receptors, channels through which outside material may pass, carrier molecules and more.  
 

The cytoplasm is a gel-like substance located between the cell membrane and the nucleus.  The gel provides an environment for chemical reactions to occur.  This means that the cytoplasm is vital for cell reproduction and function because both are dependent upon chemical reactions.    

Specialized structures called organelles are located in the cytoplasm.  There are several types of organelles, each differing in structure and function.  The most important organelles are the mitchondrion, the ribosome, the golgi apparatus, the endoplasmic reticulum, and the lysosome. 
 

The nucleus is located at the center of the cell.  It determines the function and structure of the cell.  The nucleus consists of a nuclear membrane that encloses the nucleoplasm (similar to the gel like substance of the cytoplasm).  The nucleus contains DNA in the form of chromatin.  It also contains the nucleolus.  The nucleolus is a dense area of RNA and is also responsible for ribosome synthesis.