DNA and Its Structure
Importance of DNA
- All cells require instructions to function.
- These instructions are found in DNA (deoxyribonucleic acid).
Components of DNA
- DNA: Contains information that determines inherited characteristics.
- Location: eukaryotic cells: Found in the nucleus.
- Location: prokaryotic cells: Found in the cytosol.
Structure of DNA
- DNA has repeating subunits called monomers or nucleotides.
- Each nucleotide has three main parts:
- Phosphate group
- Sugar (Deoxyribose)
- Nitrogen base
Nitrogen Bases
- Four nitrogen bases in DNA:
- Thymine (T)
- Adenine (A)
- Cytosine (C)
- Guanine (G)
- Bases are categorized into:
- Purines: Adenine and Guanine (two-ring structure)
- Pyrimidines: Cytosine and Thymine (one-ring structure)
Pairing Rules
- Purines pair with pyrimidines:
- Adenine pairs with Thymine (A-T)
- Cytosine pairs with Guanine (C-G)
Structure Details
- DNA forms a double helix due to its slanted shape.
- The double-strand structure:
- Backbone: Alternating sugar and phosphate molecules
- Inside: Nitrogen bases (like rungs of a ladder)
- Hydrogen bonds:
- A-T forms two hydrogen bonds
- C-G forms three hydrogen bonds
Memory Tools
- Purines and Pyrimidines:
- Pyrimidines have a 'y' in their names (Cytosine, Thymine)
- "A-T two" and "C-G three" helps remember hydrogen bonds
Discovery of DNA Structure
- Four scientists credited: Watson, Crick, Wilkins, Franklin
- Note: Rosalind Franklin did not receive the Nobel Prize due to her early death.
- Discovery details:
- Backbone made of alternating sugar and phosphate
- Nitrogen bases form the rungs inside
DNA Complementarity
- Strands of DNA are complementary:
- A always pairs with T
- C always pairs with G
- Knowing one strand allows prediction of the complementary strand.
Labeling a DNA Molecule
- Outside of the molecule: Deoxyribose sugars (pentagon shape) and phosphates (small molecule)
- Inside: Nucleotides with specific pairings (A-T and C-G)
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