DNA or RNA in different viruses

1
Organization of DNA in Viruses

• DNA or RNA in different viruses
• Single-stranded or double-stranded in different
  viruses
• Circular or linear in different viruses
• Usually one DNA molecule/viral particle
• DNA is packaged into the heads in a very
  compact manner
• DNA is not associated with proteins

l phage
M13
2
Packaging DNA
2-6 um
DNA is about 1.2 mm in length
3
DNA Supercoiling
4
Inheritance of Mitochondrial DNA
5
Mitochondrial Genetic Information
6
Organization of DNA in Eukaryotes

• More DNA per chromosome per cell than
  bacteria
• -E. coli has 1200 micrometers of DNA /cell
• -Humans have 14,000 to 73,000 mm of DNA per
  chromosome
• -46 chromosomes total 2 m of DNA contained
  in 5 mm nucleus
• Nucleosomes
• .Repetitive DNA
• -Only about 5 of the DNA in a human is
  transcribed
• -Certain DNA sequences are present in
  multiple copies
• -Certain sequences are present thousands of
  times

7
Discovery of Nucleosomes

• If chromatin is treated with detergents and
  examined with an electron microscope, you see 100
  angstrom beads on a string (Olins and Olins 1973)

8
Discovery of Nucleosomes

• If you treat chromatin with certain endonucleases
  (micrococcal nuclease), you get DNA pieces that
  are 200 base pairs long or multiples of 200 bases
• Thus, the digestion is not random, but the DNA
  is protected from enzymatic digestion in regions
  200 bases long

9
Description of Nucleosomes

• 2 copies each of H2a, H2b, H3, and H4 to form
  of an octamer with 200 bp of DNA wrapped twice
  around the core
• H1 particles are on the DNA between each
  nucleosome
• DNA associated with nucleosomes forms 11 nm
  fibers
• These coil further into solenoids 30 nm in
  diameter

10
Forther Organization of Chromatin

• The solenoids coil into 300 nm chromatin fibers
• The 300 nm chromatin fibers are coiled into 700
  nm coils
• Which form the metaphase chromatid

11
Heterochromatin vs Euchromatin
12
Heterochromatin vs Euchromatin
Heterochromatin vs Euchromatin

• Heterochromatin describes areas of DNA that
  are genetically inactive. It is involved in
  physical maintenance of chromosome structure.
• Euchromatin describes areas of chromatin
  available for transcription. It is involved in
  gene expression.