The Cell and Its Components  
    Some of the most fascinating activities that take place inside the human body occur within tiny microscopic units called cells.  These units are often described as the body's building blocks and are analogous to the bricks and lumber used to build a house.  Our cells are incredibly diverse.  Each cell type has a specific job that it performs to contribute to the overall structure and well being of the body.  Yet even in the face of this diversity, cells share many characteristics.  Regions found within many cells include the following:


The Cell Membrane
    The outer surface of a human cell is surrounded by a thin, flexible boundary called the cell (plasma) membrane.  This boundary serves to separate the inside of the cell, called the intracellular fluid or environment (ICF) from the outside of the cell, known as the extracellular fluid or environment (ECF) while allowing specific molecules to enter and exit the cell.  The cell membrane is composed of a double layer of phospholipid molecules.  These molecules are considered polar--that means that each part of the phospholipid behaves differently when mixed in various environments.  One part of the molecule will mix with water while the other part of the same molecule will mix with oil.  As a result, the phospholipids form a boundary that prevents watery and oily substances from rushing into or out of the cell.  Scattered throughout the phospholipid bilayer are many membrane proteins.  Some of these proteins extend from one side of the cell membrane to the other.  Other proteins only span part of the width of the phospholipid bialyer.  All of these membrane proteins are essential in the function of the cell.  Some form tiny openings or channels through which molecules and ions can pass.  Others serve as receptors for hormones, neurotransmitters and other important biological chemicals.  A third group functions in cell-to-cell recognition (sort of like a satellite for recieving information).  Click the membrane link to learn more!

The Cytoplasm and Organelles
    The region of the cell contained inside the cell membrane boundary is filled with a semi-solid fluid matrix called cytoplasm.  It has the consistancy of slightly melted Jello!  Suspended within this gel are numerous organelles that serve as the cell's machinery.  These organelles are critical to the cell's survival.  If they are not functioning properly, the cell's life is in jeopardy as is the entire body!
 
 

Organelle Function
Mitochondria sites of ATP (the cell's fuel) synthesis
Ribosome manufactures proteins
Rough endoplasmic reticulum modifies, packages and transports proteins that the cell's ribosomes have just manufactured
Smooth endoplasmic reticulum manufactures lipids & steroids, detoxifies drugs (so they are abundant in liver cells)
Golgi apparatus (also called Golgi bodies) packages, modifies and segregates proteins from export out of the cell (so they are abundant in cells that secrete products such as gland cells)
Lysosomes digests molecules inside the cell (such as invading cells or debris)
Peroxisomes detoxify many toxic compounds (use an enzyme called catalase the break down hydrogen peroxide)
Microtubules & Mircofilaments gives the cell its shape and helps it to bend or move as in muscle contractions
Intermediate filaments stabilize the interior of the cell thereby preventing tearing of the cell
Cilia tiny hairlike structures that move together to propel the cell
Flagella move with whiplike force to propel the cell like an oar on a row boat
Centrioles form the bases of cilia and flagella; are also involved in cell division (which we will discuss at the end of the semester)

For a great 3-D tour of a cell, click the link to the cell's alive website.  This site will provide you with diagrams of the organelles as well as text that summarizes their structure and function.  You can also access a cell quiz and even send "micrograms" (e-cards) to your friends.  Spend some time at this site!  It has lots of good information and great graphics.

The Nucleus
    The largest organelle in the cell is called the nucleus.  It is surrounded by its own membrane, called the nuclear envelope and is filled with semi-solid fluid called nucleoplasm.  This organelle contains the cell's genetic material.  It serves as a critical control center, directing all of the cell's activity.  A cell can survive without out a nucleus (your red blood cells lack a nucleus when they mature) but not for a very long period of time!  And of course, a nucleus is mandatory for cellular reproduction.  Check out the cell's alive site again.  It has information on the nucleus, too.  Also be sure to visit the nucleus site for electron micrographs of the nucleus and its components.