Science & Technology in Action

1st Edition

DNA - The Secret of Life

Enterprise Ireland

The biology and function of DNA is the subject of this lesson. The concepts of genetic code and replication are examined. The use of base sequences in identification is also covered.
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Contains the full lesson along with a supporting toolkit, including teachers’ notes.

Lesson excerpt

What is DNA?
Deoxyribonucleic acid is better known by its shorter name DNA. The determination of DNA’s structure in 1953 by Francis Crick and Jim Watson is hailed by many to be the most important discovery ever in human history.


DNA is life’s hereditary material, i.e. it holds and passes on the genetic information from parents to offspring. The information carried by DNA directs the construction of each organism, its maintenance, proper functioning and reproduction.

The information is carried in coded form as sequence of specific chemicals called nitrogenous bases. Just as a computer code is a unique sequence of 0s and 1s, so is life’s genetic code a unique sequence of bases.

There are about 2.5 metres of DNA in the nuclear DNA of each human cell. Therefore, we each have about 250 billion kilometres of DNA in our body. Every second we make enough DNA to encircle the equator 3 times. We make about 50 million new cells every second.

What is the structure of DNA?
DNA structure is described as a double helix. It is like a spiral ladder and is composed of two complementary polynucleotide strands held together by hydrogen bonds.

In DNA the sugar is deoxyribose and because there are four different bases – adenine (A), guanine (G), thymine (T) and cytosine (C) - there are four different nucleotides. The nucleotides are PSA, PSG, PST, PSC.

Quiz questions

  1. DNA stands for deoxyribonucleic acid. true
  2. Franklin and Wilkins discovered the structure of DNA. false
  3. DNA is present in nuclei, mitochondria and chloroplasts. true
  4. The genetic information is carried as a sequence of bases in DNA. true
  5. DNA is a single polynucleotide strand. false
  6. DNA and RNA are nucleic acids. true
  7. The bases in DNA are adenine, uracil, guanine and cytosine. false
  8. An alternating sugar phosphate sequence forms the backbone of each DNA strand. true
  9. A gene carries the information for the production of a specific protein. true
  10. Mitosis and meiosis are different types of cell division. false
  11. Meiosis is responsible for our somatic cells being genetically identical. false
  12. DNA profiling is also known as genetic fingerprinting. true