Lecture on DNA Structure and Function

Introduction

• Cells require instructions to function properly.
• DNA provides the necessary code for cells.
• DNA stands for Deoxyribonucleic Acid.
  • De: Deoxyribose (type of sugar)
  • N: Nucleic
  • A: Acid

Role of DNA

• Determines inherited characteristics.
• Contains codes for making proteins.
• Found in:
  • Nucleus of eukaryotic cells
  • Cytosol of prokaryotic cells

Structure of DNA

• DNA consists of repeating subunits called nucleotides.
• Nucleotide: Has three main parts:
  1. Phosphate group
  2. Sugar (Deoxyribose)
  3. Nitrogen base

Nitrogen Bases

• Four nitrogen bases in DNA:
  • Adenine (A)
  • Thymine (T)
  • Cytosine (C)
  • Guanine (G)
• Types of bases:
  • Purines (two-ring structure): Adenine and Guanine
  • Pyrimidines (one-ring structure): Cytosine and Thymine
  • Memory aid: Pyrimidines have a 'y' - Cytosine and Thymine both contain 'y'.

Base Pairing Rules

• Purine always pairs with a pyrimidine:
  • Adenine (A) pairs with Thymine (T) (two hydrogen bonds)
  • Cytosine (C) pairs with Guanine (G) (three hydrogen bonds)
  • Memory aid:
    • AT has two straight lines (A and T)
    • CG has curved lines (C and G)
    • Rhyme: "AT two, CG three" for the number of hydrogen bonds

DNA Structure Details

• DNA forms a double helix (spiral shape).
• Scientists credited with discovering the DNA structure:
  • Watson
  • Crick
  • Wilkins
  • Franklin (did not receive Nobel Prize due to premature death)
• DNA backbone: Alternating sugar and phosphate molecules.
• Inside structure: Nitrogen bases form hydrogen bonds.
  • A and T hydrogen-bond together
  • C and G hydrogen-bond together

Complementary Strands

• Strands are complementary due to specific base pairing (A with T, C with G).
• Knowing one strand allows you to predict the complementary strand.

Labeling DNA Molecules

• DNA molecule sides: Deoxyribose sugars (pentagon shape) and phosphates (small molecule).
• Inside the molecule: Bases form pairs according to hydrogen bonds (A-T, C-G).

Conclusion

• Memory aids and structure identification are key for understanding DNA.

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