How many bases in a heical turn?
hbeernin at med.uvm.edu
Tue Aug 15 08:17:40 EST 1995
Billy Li (billyli at hkuxa.hku.hk) wrote:
: Sorry for an easy question. I have read from Kornberg that there are 10
: bases in a helical turn. My supervisor insists that it is a bit more than
: 10, perhapseven 11. My guess is that for different types of DNA (A, B
: and Z) the numbers are slightly different. Anyone has the exact
: numbers please.
: Please email or post.
: Thanks in advance.
: Billy Li, email: billyli at hkuxa.hku.hk
: Assistant Lecturer,
: Department of Statistics,
: University of Hong Kong.
: Tel: (852) 28591987 Fax: (852) 28589041
both you and your supervisor are right:
It depends on the type of DNA, and how the structure was determined
(e.g. x-ray or NMR). In addition, it depends on the base sequence. In
general, average values are used for most purposes. These are as follows:
A-DNA B-DNA Z-DNA
bases/turn ~11 ~10.4 ~12
Rotation/bp(deg) 32.7 34.6 30
Rise 0.23nm 0.33nm 0.38nm
These values were taken from Dickerson et.al., Science 216:475-485 (1982).
For a general class, these values are fine. If you are doing structural
modeling or determination, however, you may want something a bit more
"The worst monotonous drone coming from a lectern or the most eye-splitting
textbook written in turgid English is nothing in comparison to the
psychological Sahara that starts right in your bedroom and spurns the
-Joseph Brodsky, from "In praise of Boredom"
delivered as a commencement address at Dartmouth College.
Hans T.H. Beernink, Department of Biochemistry, University of Vermont
hbeernin at protein.med.uvm.edu
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