Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS
SAF Archives  search ask the scientists in the classroom cool science

Eat Less -- Live Longer

The Clock of Life

Wisdom of the Worms

How to Make a Nose

Use It or Lose It

Viewer Challenge
in the classroom

Never Say Die:
The Clock of Life

Is old age inevitable? Research at the cellular level has always demonstrated that the aging process cannot be stopped. But startling new research suggests there may be a way to turn back the genetic clock. If cells could be made immortal, might the aging process be delayed indefinitely? The tips of our chromosomes may provide clues to immortality.

Curriculum Links
National Science Education Standards
Activity: Animating Cell Division



cell structure, DNA



(Please visit the Subject-Area Search feature on this website for related Frontiers shows and activities!)


5-8: Structure and Function in Living Systems; Reproduction and Heredity
9-12: The Cell; The Molecular Basis of Heredity; Matter; Energy and Organization in Living Systems
5-8, 9-12: Understandings About Science and Technology
5-8: Personal Health; Science and Technology in Society
9-12: Personal and Community Health; Science and Technology in Local, National and Global Challenges
5-8: Science as a Human Endeavor; Nature of Science; History of Science
9-12: Science as a Human Endeavor; Nature of Scientific Knowledge; Historical Perspectives


The basic unit of all life is the cell. The nucleus of each cell contains the chromosome made of DNA -- the twisted, double strands of deoxyribonucleic acid that carry genetic information. Genes are made up of portions of these DNA strands. Each of us has 23 pairs of chromosomes and more than 100,000 genes.

Cells reproduce through cell division, or a process called mitosis. The cell divides into two identical cells, each containing the same genetic information stored in the original chromosome. With each cell division, a protective cap on the end of the chromosome, called a telomere, gets shorter. After about 50 divisions, the telomere is so short that the cell stops dividing and may die or start to malfunction.

What if there were a way to keep the telomere from shortening? If cells could go on dividing forever, the organism might theoretically live a very long time.

As you'll see in this episode of Frontiers, by restoring the cell's ability to continue dividing, cells could be maintained in a perpetually youthful state. Telomerase might become this century's Fountain of Youth. We'll meet geneticists who have activated the enzyme telomerase, extended the telomeres and the life span of certain cells -- in effect, rejuvenating them.

Before scientists could understand the biochemistry of the genes, they had to learn how cells divide and reproduce. In this activity you will create a flipbook that will animate the process of mitosis.


  • tag board or blank index cards
  • circular object with a diameter of about 8 cm
  • colored pencils
  • scissors
  • string
  • hole punch
  1. Cut tag board into at least 20 rectangles, each 10 x 15 cm. Or use index cards.

  2. Use a circular object or a stencil to draw circles on each piece of tag board at the exact same spot, close to one end. Leave a few cards blank.

  3. Draw the stages of mitosis on each of the cards. To create a smooth animation, make only small changes between each of the stages. Be sure to show how cells change during and after telophase.

  4. Use the hole punch to make three holes along the side of each card opposite the cell drawing. Place the cards in order of the stages of mitosis, from interphase through telophase. Bind the cards together using string.

  5. Flip through the book quickly.


    Explain what happens in each stage of mitosis. You'll find useful resources online, such as Cells Alive!, which features animations of cell processes at, or the Biology Project, an interactive resource found at

    Not all cells continue to divide throughout life. Research the different kinds of cells in our bodies and their functions.

    Brainstorm applications of an "immune system boost." Would you want to try this procedure, if it were available?


Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.