DNA and Replication



After today's lesson you should be able to know:

  • The structure of DNA
  • Role of DNA 


Today's topic is about the human hereditary material known as deoxyribonucleic acid or DNA. It is a long molecule containing the information organisms need to both develop and reproduce. DNA is found in each and every cell in the body and it passes down from parent to child.  The discovery of DNA occurred in 1869 by Swiss-born biochemist Fredrich Miescher. even today after more than 150 years it was discovered exciting research and technology continue to offer a more insight and a better answer as to why it is important. 


  • DNA is a polymer and consists of two strands that are twisted to form a double helix.



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  • The monomers of DNA are known as nucleotides.
  • Each nucleotide consists of a sugar molecule (deoxyribose), a phosphate group and a nitrogenous base.
  • Deoxyribose combines with the phosphate group.
  • One nitrogenous base combine with deoxyribose
  • The sides of the DNA ladder consist of alternating deoxyribose molecules and phosphate groups.
  • There are four types of nitrogenous bases in DNA i.e. Adenine (A), Guanine (G), Cytosine (C) and Thymine (T)
  • Adenine always combines to Thymine • Guanine always combine to Cytosine
  • There are equal numbers of adenine and thymine bases as well as equal numbers of guanine and cytosine bases in a DNA molecule. (A = T and G = C)
  • Nitrogenous bases are joined by weak hydrogen bonds which are easily broken by enzyme action.



  1. Sections of DNA-forming genes carry hereditary information.
  2. DNA contains coded information for protein synthesis.



DNA replication is the process during which a DNA molecule makes an exact copy (replica) of itself. DNA replication takes place during interphase of the cell cycle.

  1. The DNA double helix unwinds
  2. Weak hydrogen bonds between nitrogenous bases break and the two DNA strands unzip
  3. Both DNA strands serves as templates
  4. Free nucleotides in the nucleoplasm are used to build a complementary DNA strand onto each of the original DNA strands (A to T and G to C)
  5. This results in two identical DNA molecules. Each molecule consists of one original and one new strand

Diagram, timeline

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Part II: DNA Structure

Use the links below to learn more about DNA and to explore DNA molecules interactively.

  1. https://www.youtube.com/watch?v=MCKI0PJJ4uA
  2. http://learn.genetics.utah.edu/content/basics/builddna/
  3. http://biomodel.uah.es/en/model4/dna/index.htm

You are now going to build 2 DNA molecules! Before you begin, grab the following materials from the front of the room: 

  • toothpicks, ~50
  • multicolored gumdrops, ~60
  • paper plate, to work on so the table stays clean from loose sugar
  • 1 DNA color key 
  • 2 DNA identity cards
  • blank sheet of paper, for coding notes and sketching
  • pencil

Watch the video below to find out how to build your model: 


Turn your models in.