Conformations of DNA Flashcards
What is contained in the B conformation and what is its purpose?
Sodium salt of DNA
Stabilizes the DNA
The DNA structure of Watson and Crick represented the ______ of DNA
B Form
When does the B conformation form?
Under conditions of relatively high humidity (92%)
What is the common form of DNA? Why?
B Form
It is very close to the conformation of most DNA in cells
How many base pairs are in the B form per helical turn?
10 per helical turn
What is the pitch of B form DNA?
34Å
Define pitch as it refers to DNA
1 turn of the helix
In the B form, describe the position of the base pairs
Base pairs are perpendicular to the helical axis
The ____________ of DNA changes conformations
Sodium salt
When does DNA assume the A form?
When the humidity surrounding DNA is reduced to 75%
In the A form, describe the position of the base pairs
The base pairs Are tilted about 20 degrees from horizontal
I the A form, how many bass pairs are in a helical turn?
11 per helical turn
In the A form, what is the pitch?
28Å
What is an example that assumes the A form?
DNA-RNA hybrids
What type of helix does A and B DNA form?
Right- handed
What is the structure of Z-DNA?
dsDNA composed of alternating purines and pyrimidines that exists as a left handed helix
What is the pitch of Z-DNA?
46Å
How many base pairs are in a helical turn of Z-DNA?
12 base pairs
In Z-DNA, describe the position of the base pairs
The base pairs have a 9 degree inclination from the helical axis
Where is z-DNA found?
In small proportions in cells
What is the function or purpose of Z-DNA?
It is not yet known
How many forms of DNA are there?
Three
Compare the pitch for the three forms of DNA.
A = 28Å B = 34Å Z = 46Å
Give an example of a sequence of z-DNA
- GCGCGCGCGCGC-
- CGCGCGCGCGCG-
Why was the z-DNA named such?
The backbone appeared to ‘zig-zag’
