Just as the last century saw a great series of discoveries about our universe, this same period witnessed an enormous development in our understanding of the basic unit of life, the cell.

My reference is a small but idea packed book “How We Live and Why We Die: The Secret Lives of Cells” by embryologist Lewis Wolpert, an emeritus professor of biology at University College London.

  Wolpert maintains that if we consider size, cells of living beings are the most complicated systems in the known universe. Let’s focus on human cells, of which you, dear reader have about 10 trillion (1 followed by 13 zeroes).

All the different types of human or animal cells have a common plan. There is a thin, but flexible outer wall or membrane. Inside is the cytoplasm, the gooey inside full of structures and molecules in motion.

Within each cell are several hundred sausage shaped mitochrondria, which churn out adenosine triphosphate (ATP), the energy currency of the cell.

A typical human cell has a billion ATP molecules; all are used up and replaced every two minutes. The many millions of proteins within a cell are complex, twisted chains; some act as machines, cutting up molecules while other proteins construct molecules.

The nucleus or control center of each cell is a flattened disk that stores the genetic material or cell blueprints in the form of tiny twisted staircases called DNA (Deoxy Ribonucleic Acid).

Every human cell has 2 meters of DNA tightly coiled within the nucleus. The only human cells that lack a nucleus or genetic plan are red blood cells, manufactured by your bone marrow at the rate of 2 million cells per second. These cells that carry oxygen to all parts of your body have a lifetime of 120 days.

Other cells need to be replaced even more frequently. Your skin, whether you are a senior citizen or a child, consists of dead skin cells. On the average, your skin is replaced a thousand times during your lifetime.

The cells lining your intestines must be replaced each week. The secret to regenerating these cells are stem cells that lie underneath. Typically, a stem cell underneath your skin will divide, one cell becoming a fresh skin cell while the other remains a stem cell. If there is a need for new skin tissue (a nasty cut), a stem cell may divide with both halves remaining stem cells.

These stem cells “know to form” the appropriate replacement cells. A stem cell from an embryo is “pluripotent,” being able to form any kind of human cell.

As research with embryonic stem cells has become unacceptable to Catholics and fundamental Christians, Wolpert suggests transplanting the nucleus of a human cell (from underneath your skin) into a fertilized cow egg or ovum (while removing the cow cell’s nucleus). Then this cell will act as an embryonic human stem cell for your needs.

Each cell has a plan that allows it to die (apoptosis). If a cell is cut off from oxygen or glucose, the interior scaffolding of the cell will collapse and white blood cells will move in and devour the cell in a way that the neighboring cells are not affected.

Each cell relies on sodium pumps to move sodium out of the cell, so that the interior potassium concentration is about twenty times higher. But if the sodium inside a cell is allowed to build up, water will flow into the cell, causing the cell to burst.

Each cell has small pockets of digestive enzymes called lysosomes. These pockets will move near to any discarded or broken cell components and release their enzymes.

EVENING SKIES THIS WEEK: This Wednesday is the start of summer, when the sun’s direct rays travel farthest north (latitude 23.5 degrees).

All through the summer and fall, the amount of sunlight each day will drop. This change in daylight is due to the tilt of our Earth’s axis.

At the start of summer, our northern hemisphere is tipped most towards the sun. At the start of winter, our hemisphere is tipped most away from the sun.    

On June 5, the planet Venus passed in front of the sun. Venus’ rapid motion has now moved it to a large enough angle to the sun so it can now be seen low in the eastern dawn, rising about an hour before the sun.

On Tuesday, the moon will swing from the morning to the evening side of the sun (New Moon).  By June 21, the moon will have moved to a large enough angle from the sun to be seen low in the 9:30 p.m. western dusk. Above and to the right of the moon is the innermost planet Mercury.

By next Saturday, the evening moon will appear half full in the southwestern sky. Above and to the right of the moon will be the planet Mars.

Bob Doyle invites any readers comments and questions. E-mail him at rdoyle@frostburg.edu . He is available as a speaker on his column topics.