Animation of the structure of a section of DNA...

Animation of the structure of a section of DNA. The bases lie horizontally between the two spiraling strands. (Photo credit: Wikipedia)

What is a helix?

A helix is a curved spiral, like the wire in a Slinky.

A double helix is two strands wrapped around each other in the curved cylinder, connected by base pairs.

On April 25, 1953, the journal Nature published an article by Francis Crick and James Watson called “The Structure for Deoxyribose Nucleic Acid,” which suggested that the shape of DNA was a double helix.

The most important point in the paper was that the structure “suggests a possible copying mechanism for the genetic material.”

This means that DNA, short for deoxyribonucleic acid, contains the genetic elements that pass down characteristics from parent to child.

Their discovery, what DNA actually looked like, earned them, along with Maurice Wilkins, the 1962 Nobel Prize for Physiology or Medicine.

But, the steps leading up to the discovery go back to 1869.

  • In 1869, physician Friedrich Miescher notices a substance in pus that he found in the nuclei of cells. He named it nuclein.
  • In 1919, Phoebus Levene sees that nuclein is a nucleotide that includes a base, sugar and a phosphate, mistakenlly supposing it a short string of nucleotides strung together, with bases in a fixed order.
  • In 1928, Frederick Griffith’s observations led him to think DNA might hold genetic information
  • In 1937, William Astbury x-ray’d DNA to show a regular structure
  • In 1943, Oswald Avery’s experiments with bacteria led him to suggest DNA, not protein as then thought, as the geneti material for bacteria
  • In 1952, experiments by Alfred Hershey and Martha Chase confirmed that DNA has a role in herdity.

In 1953, Watson and Crick published their ground-breaking paper, based on analyzing x-rays taken first by Rosalind Franklin, then by Franklin and Raymond Gosling.

Franklin was not eligible to share in the Nobel Prize because she died shortly before it was awarded and it only goes to living recipients.

In 1957, Crick hypothesized, later proven correctly, a relationship between DNA, RNA and proteins.

In 1958, the double helix structure was proved in an experiment conducted by Matthew Messelson and Franklin Stahl that showed the two strands in the helix replicated themselves separately.

The double helix structure Crick and Watson discovered means that DNA information is redundant, helping to ensure the passage of  genetic information, like eye color, and the base pair structure reveals a unique sequence of pairs that can be used as a DNA fingerprint.

That’s why we can separate guilty from innocent and determine a baby’s father.

According to The Innocence Project, 305 people have been released from prison after exoneration from DNA evidence since 1989.

Eighteen of them had been sentenced to death.

Do your grandchildren know what we used before DNA to  decide if someone was guilty?

Do your grandchildren think that DNA solves all crimes?

Do you remember Perry Mason?

To your grandchildren’s increasing understanding of how the world works.


Carol Covin, Granny-Guru

Author, “Who Gets to Name Grandma?


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