Chapter 5: DNA

DNA

  • Made up of 4 nucleotide bases (CGAT) the monomer

  • Polymer = polynucleotide chain

    • two chains twist into double helix

  • Double helix is anti-parallel (face diff directions)

  • Nuculeotide bases/chain is a covalent bonf

  • Thr 2 chains/strands is a hydrogen bond

    • C & G form 3 bonds

    • A & T form 2 bonds

  • Gene: nucleotide sequence needed to make RNA/protein

  • Genome: all DNA in a cell

  • Chromatin: DNA and its associated protein

DNA Packaging

  1. formation of nucleosomes

    • 147 base pairs wraps 1.7 times around a histone

    • Histone: protein complex of 8 polypeptides (positive charge)

  2. Adjacent nucleosomes connect to form chromatic fiber structure

  3. Chormatin fiber structure folds into loops by the SMC Complex (Cohesin)

  4. Condensin proteins form 2nd loop level (inside previous loops)

    • Happens after DNA replication, bur before cell division

  5. Two identical copies of DNA are condensed and held an centromeres

Chromatin remodeling

  • repositioning of nucleosomes in DNA so cell can express genes

  • chromatin remodeling proteins: locally reposition DNA around nucleosomes using energy from ATP

HeteroChromatin: tightly packaged DNA alone chromesomes

  • Transcriptionally inactive = no gene expression occurs

EUchormatin: DNA that is not tightly packages along chromasome

  • Transcriptionally active = gene expression