DNA 3 Flashcards
single bonds are very
flexible
nucleic acids have many… per monomer
torsions
regarding the backbone and sugar, which torsion angle is the same
delta and V3
torsion angles in the backbone
alpha
beta
gamma
delta
epsilon
zeta
glycosidic torsion angle
X
sugar torsion angles
V0
V1
V2
V3
V4
which torsion angle differs between the pyrimidines and the purines
the glycosidic torsion angle X
sugars pucker because of
tetrahedral carbons
endo and exo are defined with respect to
the orientation of the base at C1
the central dihedral defines the
torsion angle
cis and syn are
interchangeable
anti and trans are
interchangeable
between -30 and +30 degrees, it is considered
cis or syn
between 30 and 90 degrees, it is considered
+syn
+gauche
between -30 and -90 degrees it is considered
-syn
-gauche
between 150 and -150 (210) degrees it is considered
trans or anti
idealized envelopes and twist forms have a precise
nomenclature
E^3 means
Endo
the 3’ carbon is pulled up
E^2 means
Endo
the 2’ carbon is pulled up
^3↓2T means
Twist
the 3’ carbon is pulled up and the 2’carbon is pulled down
o on top
^3T↓2
Twist
the 3’ carbon is pulled up and the 2’carbon is pulled down
o on bottom
North puckers inducate
A-form DNA
RNA/DNA
South puckers indicate
B-Form DNA
DNA not RNA
northern blots are for
RNA
southern blots are for
DNA
the pucker is controlled by the underlying
potential energy surface
the potential energy surface has
two distinct maxima and is connected by a broad low trough
the sugar pucker, base pairing, and base stacking are all in tension with the
phosphate-phosphate repulsions
what does salt do to the phosphate-phosphate repulsions
lowers the repulsion exponentially
DNA is polymorphic meaning
there is more than one structure
DNA structure depends on what external variables
salt concentration
humidity
temperature
etc.
three major polymorphs of DNA
A form
B form
Z form
what form of DNA is right handed
A form and B form
what form of DNA is left handed
Z form
what form of DNA has the largest diameter
A form
what form of DNA has the smallest diameter
Z form
what form of DNA has the fewest base pairs per turn
B form with 10.5
what form of DNA has the largest number of base pairs per turn
Z form with 12
What form of DNA has the highest degree of base tilt
A form with 20 degrees
what form of DNA has the highest helix rise per base pair
A form DNA
Sugar pucker conformation for A form DNA
C-3’ endo
sugar pucker conformation for B form DNA
C-2’ endo
sugar pucker conformation for Z form DNA
C-2’ endo for pyrimidines
C-3’ endo for purines
glycosyl bond conformation for A form DNA
Anti
glycosyl bond conformation for B form DNA
anti
glycosyl bond conformation for Z form DNA
anti for pyrimidines
syn for purines
what form of DNA has less deep grooves and the bases are strongly inclined on the vertical helix axis
A form DNA
what form of DNA is chromosomal DNA
A form DNA
A form DNA is found under what conditions
high salt
low humidity
double stranded RNA is close to what form of DNA
A form DNA
what form of NDA is more open and stretched out exposing the bases in the grooves
B form DNA
what form of DNA is most useful for proteins to read and process
B form DNA
under what conditions id B form DNA found
lower salt concentration
high humidity
DNA changes shape with respect to
salt concentration
what happens to DNA with zero salt
DNA does not form a dimer
given the same number of base pairs, what form of DNA is the longest and which is the shortest
longest is Z form
shortest is A form
what happens when A form DNA and B form DNA attach
a kink or bend is made in the DNA due to proteins present
what plays a major role in nucleic acid stabilization
base pi-stacking
the stacking geometry usually … the rings to avoid both sterics and to allow for … to be in proximity to each other
staggers
unlike charges
how the bases stack depends strongly on the … orientation as well as…
3’-5’
Pu-Py vs Py-Pu vs Py-Py vs Pu-Pu stacking
forming duplexes is often called
hybridization
true hybridization requires
using two dissociated (melted) samples and mixing them.
replication involves
unwinding, duplication and rehybridization (renaturing).
there are many base pairing possibilities due to
the number of hydrogen bonding groups
triple helices
major groove binding
base triplet specific
high salt requirement
quadruplex
usually G-quartet
loops of 3-4 bases
binds ions specifically in the core
triplets of bases are reasonably
stable
regions of triplex DNA can occur in natural settings as in what structure
H-helix
G-quartets are very
stable
G-quartets are the basis for the
crystal packing of pure guanine and telomers
the center of a G-quartet is full of
oxygens so it us very electron rich with lone pairs
G-tetrads can form in
any G-rich sequence
one strand or multiple stands
what does it take to dissociate a G-tetrad
12M LiCl and boiling
in regards to G-tetrads, what is the topology like
the bases can be syn or anti and the stands can either be parallel or antiparallel.
the loops between the G-tetrad are usually
T’s