DNA and RNA Structure
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Nucleotides
Monomers of nucleic acid polymers
dNTP
Deoxynucleoside triphosphate
Difference between purines and pyrimidines
Purines have 2 rings, whereas pyridimines only have 1
Turning uracil into thymine
Methyltransferase adds methyl group to uracil to make it into thymine
Standard form and rare form of pyrimidines
Standard: amino Rare: imino
Standard form and rare form of purines
Standard: keto Rare: enol
Tautomers
Molecules with same molecular formulas, but different bonding/arrangement of atoms Caused by spontaneous proton shift
Base pairing in standard vs. rare forms
Standard forms properly base pair, but rare forms don’t Base pairing between rare forms can cause mutations
Nucleoside
Nitrogenous base and ribose sugar (no phosphate)
Chargraff’s rule
1:1 ratio of A:T and G:C
Periodicity of DNA double helix
10 bp/ 360 degree turn
Space between base pairs in double helix
0.34 nm
Charge of double helix
Negatively charged: phosphate groups on outside
Structure of double helix
Phosphate groups on outside (covalently bound to each other) Nitrogenous bases on inside (H-bonded to each other) Bases are usually on parallel planes 2 strands run antiparallel to one another
Things that cover DNA
Water and proteins
Major and minor grooves
Result of glycosidic bonds Major groove: larger gap than minor groove Proteins usually bind to major groove: more stuff to recognize
Propellor twist
Slight twist in base pair ladder (bases aren’t exactly 180 degrees apart) Results from stress on DNA from protein binding
3 forms of DNA
B-DNA Z-DNA A-DNA
B-DNA
Form of DNA most frequently found in cells Watson and Crick’s model
Z-DNA
Left-handed form of DNA
A-DNA
More compact form of DNA 11 bp/turn Results from reduced humidity
Melting point of DNA depends on…
G:C content Length of dsDNA
Using a spectrophotometer to measure denaturation of DNA
dsDNA has a lower absorbance than ssDNA
Hyperchromicity
Increase in absorbance of a material Occurs when dsDNA is denatured