DNA structure and eukaryotic genome Flashcards
Chemical components of nucleic acids
nitrogenous bases (DNA: AT, GC RNA: AU, GC) CUT the PY and PUR As Gold
ribose or deoxy ribose differs at 2’ with H or OH
Phosphate group
Structure of dsDNA and forces that hold it together
Polynucleotides: nucleotides are held together at a phosphodiester bond connected at the 5’-3’ end (writing sequence)
Nucleic acids have ends, at top of chain theres a 5’ phosphate, at the bottom theres a 3’ OH group
when you put the two strands together: right handed B- form DNA, major (12 A) and minor groove (6A) major groove creates an open space for things to attach
CANCER DRUG: actinomyosin D binds to minor groove to stop transcription/translation
The two strands run in antiparallel fashion (5’-3’ and 3’-5’)
Bases are on the inside and phosphate backbone is on the outside
One twist is 10.5 residues/ 36 A
A::T G:::C
Non B forms of DNA: A is tight and Z is left handed
Complementary Base pairing and stability of DNA hybridization
DNA has lots of - charges on its back bone
2 strands will separate in heat or change in pH and ionic compisition
Denaturation (melting) and Renaturation (annealing)
can be monitored spec at 260 nm causing a hyperchromic shift
Tm: when half of DNA is denatured, and depends on GC content, and ionic composition (need high salt)
linear and circular DNA
B-DNA is flexible and can be supercoiled that can be positive or negative
Supercoiling
Positive supercoiling: tightening the DNA even tighter in the direction that its helix runs in
Negative super coil: twisting opposite the direction the DNA is in, this is favorable bc as it unravels it goes in the original direction, and when its tighly wound it gets knotted- and local unwinding is favorable
Topoisomerases
enzymes that change the topological state of circular DNA, they just change the number of turns
Type 1: create ss brakes to relax the supercoiling doesnt use ATP
Type 2: create ds breaks in DNA to relax 2 super coils but need ATP
