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Understanding the Structure and Importance of DNA

In this lesson, we will explore the structure of DNA, focusing on its coiled double helix shape and the four nucleotide bases: adenine, guanine, cytosine, and thymine. We'll discuss how the order of these bases codes for amino acids, highlighting DNA's unique ability to replicate. We will also reflect on the historical significance of DNA's discovery, notably the contributions of Watson, Crick, and Franklin. By the end of the lesson, you will be equipped to describe DNA's structure, explain its coding function, and appreciate its scientific importance.

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Understanding the Structure and Importance of DNA

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  1. Biology B2 Lesson 3: DNA

  2. Connect • On each post-it, write one fact that you think you already know about DNA. • Stick this on your desk. • Collect an exam question.

  3. Connect • DO NOT ANSWER the exam question. • Instead, write your own ‘Walking Talking’ Notes onto it.

  4. What Are We Learning? • By the end of this lesson, you should: • Be able to describe the structure of DNA. • Be able to explain how DNA codes for amino acids. • Consider the importance of the discovery of DNA.

  5. SMSC & RWCM • Cultural: Consider the reasons why some discoveries are more important than others. • Social: Respect the views of others. • Reading: Identify key facts. • Writing: Use key words in the correct context.

  6. Today’s Learning Progress Step 1: Be able to describe the simple structure of DNA and use some key words. Progress Step 2: State the key parts of a DNA molecule. Progress Step 3: Describe the structure and function of DNA Increasing Difficulty

  7. Starting Points • DNA stands for DeoxyriboseNucleic Acid. • Think: • What is the structure of DNA? • Why is DNA so important?

  8. DNA: The Basics • Deoxyribose Nucleic Acid can be descibed as having a coiled double helix shape. • It is unique because it is able to replicate.

  9. DNA: The Basics • Each strand of DNA is made up of a combination of four bases. • The order in which each of these pairs appears is important.

  10. DNA: The Basics • In DNA, there are four bases. These are: • Adenine • Guanine • Cytosine • Thymine

  11. DNA: The Basics • The four bases on one strand line up against the other strand always in the following pairs: • Adenine - Thymine • Guanine - Cytosine

  12. DNA: The Basics • The four base pairs are joined by Hydrogen bonds, which can be easily ‘unzipped’. • What do you know about hydrogen bonds?

  13. DNA: The Basics • Each triplet of bases on one strand of DNA codes for an amino acid. • How many combinations of bases can you come up with in four minutes?

  14. DNA: Task • How many amino acids are there in this section of DNA? Use colours to identify them. • -C-G-C-A-A-T-C-G-T-A-T-A-G-C-G-A-A-C- • What would be the opposite strand of this DNA?

  15. DNA: Task • How many amino acids are there in this section of DNA? Use colours to identify them. • -C-G-C-A-A-T-C-G-T-A-T-A-G-C-G-A-A-C- • What would be the opposite strand of this DNA? • -G-C-G-T-T-A-G-C-A-T-A-T-C-G-C-T-T-G

  16. DNA: The Basic Structure Sugar Hydrogen Bonds Phosphate

  17. Discovering DNA • DNA was first modelled in 1953 by James Watson & Francis Crick. • There is an argument that this was the most important scientific discovery of the the 20th Century. • The Nobel Prize in Physiology or Medicine was awarded in 1962 to Watson, Crick and Maurice Wilkins.

  18. Discovering DNA: Task • Use the information in the text to produce a timeline for the discovery of DNA. • Start with the earliest events. • When you are happy, decide which events were the most significant.

  19. Rosalind Franklin Franklin’s “Photograph 51” Watson & Crick’s ball and stick model

  20. Questions • Which discovery contributed the most to the work of Watson & Crick? • Why was Erwin Chargoff’s work an important contribution to the deduction of the structure of DNA? • Why was the structure of DNA seen as such an important scientific development?

  21. Franklin: A Victim Of Sexism? • Franklin is best known for her work on the X-ray diffraction images of DNA which led to the discovery of DNA double helix. • Her data, according to Francis Crick (Nobel Prize Winner), were "the data we actually used” to formulate Crick and Watson's 1953 hypothesis regarding the structure of DNA. • What do you think about this?

  22. What Are We Learning? • By the end of this lesson, you should: • Be able to describe the structure of DNA. • Be able to explain how DNA codes for amino acids. • Consider the importance of the discovery of DNA.

  23. Reflection • Look at your Post It Note from the beginning of the lesson. • Review what you wrote and comment upon the accuracy of your original comment. • Share one learning point with a neighbour.

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