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DNA Structure

  • Discovery of DNA Structure

    • Watson and Crick, with Rosalind Franklin's major contribution, determined that DNA has a double helix structure.

    • Importance of shape: Understanding DNA’s shape is essential to understanding its function.

  • DNA Composition

    • DNA is a polymer made of nucleotides.

    • Components of Nucleotide:

      • Phosphate group

      • Sugar (deoxyribose)

      • Four nitrogenous bases: adenine (A), thymine (T), guanine (G), cytosine (C).

DNA Bonding & Base Pairing

  • Structural Features of DNA

    • Strands held together by weak hydrogen bonds, analogous to a zipper.

    • Base pair complementarity:

      • A pairs with T, and G pairs with C.

      • This specificity is critical for the double helix’s proper formation.

  • Chargaff's Rules

    • The percentage of A equals T, and G equals C due to base pairing.

    • Improper pairing leads to structural failure in DNA.

DNA Replication

  • Mechanism of Replication

    • During DNA replication, hydrogen bonds break, unzipping the strands.

    • Each strand serves as a template to synthesize a new complementary strand.

    • Results in two identical DNA strands.

  • Chromosome Structure

    • Each chromosome consists of a single long DNA molecule, coiled around proteins (histones).

    • Chromatin is not visible during interphase because it is unwound.

    • DNA is further compacted during cell division through supercoiling.

Importance of Nucleotide Sequence

  • Significance of Nucleotide Order

    • The arrangement of nucleotides encodes genetic information to synthesize proteins.

    • Sequencing DNA enables the reading of nucleotide orders, crucial for understanding genetic instructions.

Proteins and Amino Acids

  • Protein Basics

    • Proteins are polymers made of amino acids (20 different types).

    • The sequence of amino acids determines a protein's shape and function.

  • Understanding Amino Acids

    • An amino acid consists of:

      • An amino group

      • A carboxyl group

      • An R group (variable side chain with unique characteristics).

    • Only 20 amino acids are used to build proteins, although thousands exist.

    • Nine of these are essential and must be obtained through diet (complete proteins contain all essential amino acids).

Peptide Bonds

  • Formation of Peptide Bonds

    • Bonds form between the amino group of one amino acid and the carboxyl group of another, releasing a molecule of water (dehydration synthesis).

    • Example: Formation of aspartame from aspartic acid and phenylalanine.

Protein Structure Levels

  • Levels of Protein Structure

    • Primary Structure: Order of amino acids in a chain.

    • Secondary Structure: Local folding due to interactions between amino acids, forming alpha helices and beta sheets.

    • Tertiary Structure: Overall 3D shape formed by interactions between side chains (R groups).

    • Quaternary Structure: Multiple polypeptides assembling into a larger functional protein.

Examples of Protein Structures

  • Visualizing Protein Structures

    • Insulin's primary structure consists of a specific sequence of amino acids.

    • Secondary structures can be alpha helices or beta sheets, while tertiary structure represents the full fold of the protein.

    • Quaternary structure examples include proteins like gliadins and glutenins, significant in food structure and properties.