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Chapter 20 Molecular Genetics Lesson 1 - Structure of DNA
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  • 1. Chapter 20 Molecular Genetics Content • The Structure of DNA • The Role of DNA in Protein Synthesis • Genes • Genetic Engineering and Medical Biotechnology
  • 2. Lesson Objectives
    • At the end of this lesson, you should be able to:
    • (a) outline the relationship between DNA, genes and chromosomes
    • (b) state the structure of DNA in terms of the bases, sugar and phosphate groups found in each of their nucleotides
    • (c) state the rule of complementary base pairing
  • 3. Recap
  • 4. DNA
    • Deoxyribonucleic acid ( DNA ) is a molecule that carries genetic information
    • This information is important for cellular functions e.g. cell division and cell differentiation
    • Without DNA, cells would not be able to carry out these vital functions
    • Almost all cells contain DNA inside their nuclei
  • 5. How is DNA organised in cells?
    • Each DNA molecule consists of 2 parallel strands twisted around each other forming a double helix
    • A molecule of DNA is wrapped around proteins ( histone proteins) to form a single chromatin thread
    • During cell division, chromatin threads coil tightly into chromosomes inside the nucleus
  • 6.  
  • 7. How DNA is packed into a chromosome
  • 8. Basic Unit of DNA
    • is called a nucleotide
    • A nucleotide is made up of
    • Deoxyribose (a sugar)
    • A phosphate group
    • A nitrogen-containing base ( ATGC )
    • A denine
    • T hymine
    • G uanine
    • C ytosine
  • 9. 4 types of nucleotides linked to form a polynucleotide instead of thymine double ring structure single ring structure
  • 10. Nucleotides are the building blocks of DNA
    • Each gene is made up of a sequence of nucleotides
    • The sequence of nucleotides can vary
    • This results in many different genes
    • Since there are 4 different bases and hence 4 different nucleotides, for a gene made up of n nucleotides, there are 4 n different combinations of nucleotides
  • 11. Complementary base pairing between polynucleotides
    • Adenine (A) always binds with thymine (T)
    • Cytosine (C) always binds with guanine (G)
    • A denine
    • T hymine
    • G uanine
    • C ytosine
  • 12. A DNA molecule
    • is made up of 2 polynucleotide chains
    • running in opposite directions ( anti-parallel )
    • The bases of one chain are bonded to those of the opposite chain according to the rule of base pairing
    • A-T = 2 hydrogen bonds
    • G-C = 3 hydrogen bonds
  • 13.  
  • 14. A DNA molecule
  • 15. Create a DNA model worksheet