Nucleic Acids, DNA Replication & Repair Flashcards
What is a tautomer?
Structural isomers that can interconvert between different forms quickly
What are nitrogenous bases?
- Aromatic, hydrophobic, Carbon based ring systems
- Purine or pyramidine
A* (Tautomer of Adenine)
H moves from amino group (imino form); binds with C
C* (Tautomer of Cytosine)
H moves from amino group (imino); binds with A
T* (Tautomer of Thymine)
H moves creating alcohol group (enol); binds with G
G* (Tautomer of Guanine)
H moves create alcohol group (enol); binds with T
Common Pyramidine bases
- Cytosine (2-oxy-4-amino pyrimidine)
- Uracil (2-oxy-4-oxy pyrimidine)
- Thymine (2-oxy-4-oxy-5-methyl pyrimidine)
Common Purine Bases
- Adenine (6-amino purine)
- Guanine (2-amino-6-oxy purine)
What is the acid dissociation constant?
o Quantitative measure of the strength of an acid in solution
o Larger pKa = smaller extent of dissociation
What is tautomerism?
Conformational change of Nitrogenous base between its 2 conformational states.
UV Absorption of Nucleotide bases
- Rings of bases made up of alternating single and double bonds.
o Such systems absorb in the UV spectrum - Each of 4 nucleotide bases has a slightly different absorption spectrum
o Spectrum of DNA is the average of them - A pure DNA solution appears transparent to the eye
o Absorption doesn’t become measurable until 320nm
o Peak at about 260nm followed by a dip between 220 and 230
o Then solution becomes opaque in the far UV range. - When DNA helix is denatured to become single stranded – absorbance is increased about 30%.
o Called HYPERCHROMIC EFFECT
o Reflects interaction between electronic dipoles in stacked bases of native helix.
What is a nucleoside?
Comounds formed when a nitrogenous base is linked to a pentose sugar
What is the structure of nucleosides?
- Base linked to sugar via glycosidic bond (N9 in purines; N1 of pyrimidines)
- Carbon of the glycosidic bond is anomeric.
- All beta formations
- Named by adding -idine to root name of pyrimidine (cytidine), and -osine to root name of purine (adenosine).
- Conformation can be syn or anti
o Rotation around the glycosidic bond is sterically hindered; syn goes left over sugar molecule; anti goes right (forms ‘S’)
o Pyrimidines usually anti and not syn as the 2’-O atoms sterically hinders the ring position above the ribose.
Nucleoside triphosphates
- More than 1 P group attached
• Hydrolysis of phosphoanhydride bonds releases energy (Like in ATP)
- Cyclic nucleotides are signal mols and regulators of cellular metabolism and reproduction.
What is a nucleotide?
Nucleoside bonded to phosphate group C5 of pentose sugar