Biochem 501: Part IV.2: Nucleic Acid Chemistry and Chromosome Structure
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Which is more stable, DNA or RNA?
- RNA is prone to hydrolysis, resulting in breaking off of nucleotides at the phosphodiester bond
What can cause a DS to become a SS
Heat or solutions conditions such as pH
When heat is added to a DS DNA why does it only split into 2 stands
Strands held together by hydrogen bonds which are broke, Strand itself is held together by stronger covalent bonds
DNA melting temperature effected by:
- Nonpolar solvents (disrupt base stacking)
- Cations (Shield phosphate charges)
- mismatches (destabilize DS form)
DNA denaturement and gene expression
- Denaturement occurs at start of gene before expression
- Lower Tm facilitate denaturement
- Denaturement needed so transcription machinery can access DNA
- DNA denatured during genome replication
How does DNA compact?
What does super-coiling compensate for?
Structural strain from unraveling DNA
- Properties that are unchanged by deformation (such as super-coiling)
- Can only be changed by cleaving and rejoining strands.
What carries out topological changes and why?
Topoisomerases, to relieve strain in DNA
- Have catalytic TYROSINE, catalyzes phosphoryl-transfers
- DNA packaging
- Genome replication
- Chromosome segregation
- Recombination and Repair
- Type I cut one strand, Type II cut both (gyrase)
How a coil is added
- Reaction is a phosphoryl transfer from base-base to base-tyrosine
DNA packaging in eukaryotes
- have DNA associated proteins called histones
- -H1, H2A, H2B, H3, H4 types
- DNA wraps around histone
- -Nucleoprotein complex called nucleosome
- Bacteria lack nucleosomes
Nucleosomes are packaged into:
30 bn Fibers
30 nm Fibers packaged into:
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