Topic 2 Flashcards
Avery MacLeod
Transformative element = DNA
Hershey-Case
bacteriophage labeled with DNA has radioactive progeny
Mono/dinucleotides
redox rxn, energy transfer, intracellular signalling, biosynthetic reaction
examples of mon/dinucleotides
NAD+/NADPH, ATP, GTP, cAMP
polynucleotides
storage and code genetic info, as enzymes
examples of polynucleotides
DNA/RNA, RNA enzymes, riboenzyme
Nucleotides are..
make up nucleic acids, high energy molecules (NTP and electron carriers)
Nucleotide composition (dAMP)
phosphate, nitrogen containing aromatic base, deoxyribose sugar
Pyrimidine
1 ring, 2 N at 1 and 3
Uracil
pyrimidine, 2 carboxyl, 2 amide, 6 H-bonds
Thymine
pyrimidine, 2 carboxyl, 2 amide, 1 methyl, 6 H-bonds
Cytosine
pyrimidine, 1 carboxyl, 3 amide, 6 H-bonds
Purine
2 rings, N at 1, 3, 7, 9, start numbering N farthest from smaller ring
Adenine
purine, 4 amide, 1 amide branch, 6 H-bonds
Guanine
purine, 1 carboxyl, 1 amide branch, 8 H-bonds
RNA bases
GACU
DNA bases
CAGT
Nucleoside
5C sugar bound to:
N1 in pyrimidine
N9 in purine
RNA 5C sugar
ribose
DNA 5C sugar
deoxyribose
Naming nucleosides
purine ends in -osine
pyrimidine ends in -idine
ribose no prefix
deoxyribose add deoxy-
Nucleotides
5C sugar connected to phosphate with phosphodiester bond
naming nucleotides
ribose/deoxyribose name, 5’ mono/di/triphospahte
Ribose
5C sugar, OH at C1 (up), C2 (down), C3(down), OCH2 at C4
Deoxyribose
5C sugar, OH at C1 (up), H at C2 (down), C3(down), OCH2 at C4
Phosphoester bond
phosphate ester, link carbons to phosphates
Phosphodiester bond
2 phosphate ester bonds, links 2 different carbons
Phosphoanhydride
link 2 phosphates together
Structure of nucleic acids
direction 5’ to 3’
primary structure of nucleic acids
order of monomers in a polymer ex. 5’ AGTC 3’
Backbone
net charge comes from phosphate
polar
backbone in RNA is more polar > contains 2’ OH (H-bonds)
Phosphates attached to a single C
mono- di- tri-
Phosphates attached to multiple C
bis- tris-
Hydrolysis of phosohodiester
phosphodiesterase
DNA is more stable than RNA because….
doesn’t have a second OH that can spontaneously hydrolyze in alkaline (pH > 10) conditions
how does cytosine turn into uracil
deanimates the 4C
Properties of the Bases
- heterocyclic
- aromatic
- planar
- poorly soluble in water
- hydrophobic
sugar phosphate backbone polar or non polar?
POLAR
hyperchromicity
increase in absorbance
ex. when DNA or RNA denatures
A260/A20 DNA
1.8-1.95
A260/A20 protein
<1
used to measure conc of nucleic acids
A260 and Beer Lamberts Law
Secondary structure of DNA
dna forms double helix through H-bonds (non-covalent)
Chargaff’s Rule
A=T C=G
DNA (B-form)
structure in aqueous environment hydrophobic core polar exterior bases excluded from H2O rib/deoxyrib exposed to H2O H bonds in base pairing ~10 bp per turn
Base-stacking
primarily Van der Waals
also hydrophobic forces
anti parallel
right handed twist
DNA denaturation
ds to ss
disruption of base stacking and H-bonds
essential for transcription and translation
changes in absorption
Tm
midpoint of melting
characteristic of base composition and solvent conditions
Hypochromicity
Low absorbance ex. ds DNA
Renaturation
reformation of DNA, nucleation and zippering
which bonds in base pairing are stronger and why?
GC triple bonds and more H bonds
More GC =
higher Tm
A260/280 ratio RNA
~2.1
RNA secondary structure
H-bonded base pairs
2’ OH group
Helical
Hydrophobic/ van der Waal
RNA base pairing
intrastrand
DNA base pairing
interstrand
low salt = Tm
decreases, double helix destabilizes
high salt = Tm
increases, stabilizes helix
pH increases = Tm
decreases