Nucleic Acids Flashcards
Components of nucleic acids
Nitrogenous Bases
Sugar (Ribose/Deoxyribose)
Phosphate groups
Backbone of DNA
5’ to 3’ phosphodiester bridge
Importance of Actinomycin D
Slips between base pairs due to ring structure to prevent replication and transcription
Used as an anti-cancer drug and antibiotic
Directionality of strands
Antiparallel (One 5’ to 3’ other is 3’ to 5’)
Orientation of base pairs relative to backbone
Bases are inside of helix and stacked perpendicular to helix axis. This causes resonance to stabolize the double helix
Helical Structure Repeat Length
10.5 Residues, 36 Angstroms
Forces that hold the helix together
Hydrogen bonding between base pairs (A-U < A-T < C-G) 2.9 A
Non B-Form DNA
B-form is average form, A-form is compact, Z-form is expanded, with alternativing pyramidines and purines
Factors to denature DNA helix
Low Salt
Change in pH
High Heat
UV Spec Denaturation
High absorbance at 260 nm for free bases
As temperature increases, 260 nm absorbance increases till saturation, forming sigmoid curve, middle of curve is Tm
Types of DNA topology and cause
Linear, relaxed circular, supercoiled
Supercoiling relieves torsional stress of coiling
Positvie vs Negative Supercoiling
Positive is when it twists even tighter causing the helix to distort and knot
Negative is twisting against thelix which underwinds at low stress and knots into negative supercoils at high stress
Negative supercoils favor local unwinding which is useful for cell processes, therefore it is the default state
Type I Isomerase Properties
- Cleave one strand of DNA
- Passing a segment of DNA through the break
- Resealing the break
- DO NOT need energy donors (ie ATP-independent)
Type II Isomerase Details
Double-stranded breaks, DNA passes through break, ATP reseals DNA (2 ATP to 2 ADP + 2Pi)
Topisomerase Clinical Details
Antibiotics: Coumarins block type II from binding ATP, Quinolones inhibit resealing DNA strand breaks
Chemotherapy: Distinct set of inhibitors for both types
