The Nature of the Genetic Material
- Mendel (1866) - Particulate inheritance
- Weismann (1892) - the germ line theory
- DeVries et al. (1900) - rediscovery of Mendel
- Leads to the chromosomal theory of inheritance
- Morgan (1910) - showed that genes were on chromosomes
- Sturtevant (1913) - linear arrangement of genes
- Griffith (1928) - transformed bacteria
- Avery, Mcleod and McCarty (1944) - DNA is the genetic
material in transformations. This flash animation at "DNA
from the Beginning" describes these experiments:
A
gene is made of DNA
- Hershey and Chase (1952) - phage (T2) genes are
made of DNA. The second half of this flash animation
at "DNA from the Beginning" describes this experiment:
Bacteria
and viruses have DNA too.
- Fraenkel-Conrat and Singer (1955) - reconstituted
TMV - RNA is the genetic material of TMV
- Chargaff (1950) - base composition does vary between
species but A=T and G=C
- Wilken's and Franklin (1953) - DNA is in a helix
(X-ray crystallography)
- Watson and Crick (1953) - a double helix with base
pairing
- strands are antiparallel (they run in
opposite directions)
- There is a free 5' carbon at one end of the
chain and a free 3' carbon at the other end - in
the double helix the 5' end of one chain is at the
same end of the helix as the 3' end of the other
chain
- the bases stack on top of one another on the
inside of the helix, the sugar and phosphate
backbone is on the outside of the helix
- the bases are 3.4 nm apart along the helix and
there are 10.4 bases per one complete turn of the
helix
- a base on one strand hydrogen bonds to a base on
the other strand (A to T and G to C)
- two hydrogen bonds between A and T
- three hydrogen bonds between G and C
- a right-handed helix
- there is a major groove and a minor groove
- the diameter of the helix is 2nm (20 Angstroms)
- This flash animation at "DNA from the Beginning"
describes their work and how to interpret the X-ray
crystal results (also has a nice picture of thier 6
foot tall model):
The
DNA molecule is shaped like a twisted ladder.
Here's a picture of two bases hydrogen bonded together.
Note the distance between the two bases and how the bases
are at right angles to the ribose sugar. Below the first
base pair you can see the next one only with the purine on
the left and rotated a little bit as we go around the helix
Here's a view down the center of the helix. Note that all
of the nitrogenous bases (nitrogen is in blue) are in the
middle while the phosphates (in yellow) are on the outside.
This is a view form the side of the helix, showing the
major groove. Notice how easy it is to see or cantact the
bases in the middle of the helix.
Here's a side view of the minor groove. Note how much
closer together the sugar phosphate backbone is for this
part of the helix.
This document is copyright of
Jeff
Bell
Last Update: Friday, October 27, 2000
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