What does DNA look like?

Tom Goddard
June 9, 2010
Demo for Celsius and Beyond summer camp

No microscope is powerful enough to see the DNA helix, so we look at models.

Watson & Crick model made from metal rods, 1953.

A dream "home" computer imagined in 1950 when DNA structure solved. Molecular visualization was 20 years in the future.
Today molecule models are usually viewed on computers.
  • Small double-stranded DNA in Chimera, 1BNA.
  • Representations: slabs, sphere, ball and stick, stick, wire, surface.
  • Standard atom colors: white carbon, blue nitrogen, red oxygen, orange phosphorous.
  • Which one does it really look like?
  • Sphere style is maybe most realistic.
  • Fly down axis (ctrl-middle button drag).
DNA in cells is wrapped around a spool (PDB 1AOI) called a nucleosome.
  • Just 2 turns are wrapped on each spool.
  • Millions of spools are in each chromosome.
DNA spools are stacked to make filaments.
Electron microscopy -- fly chromosome tomography.
  • Maximum intensity projection.
  • Rock.

Dividing cells seen with light microscopy.

  • show time series, stereo glasses.
  • Fly (drosophila) has 4 pairs of chromosomes, but one pair is too small to see.
  • Reduce z size to 0.15 um for better appearance.
  • yuri...cmm colors each cell, but apparently with 0.5 um z grid, color range 10
  • arms.cmm colors chromosomes of one cell, color range 1, z grid 0.15 um.
  • use "cache 30 renderings" to improve speed.

Show virus paper strip RNA, explain human DNA paper strip would fill entire room tightly packed.