Ch4 - 4 DNA,RNA,andtheFlowof Information DNA transcription...

Biological Sciences 4087 Chapter
4
DNA, RNA, and the Flow of
Information
DNA RNA Protein
transcription translation

Composition of DNA and RNA
•
2’OH
•
U vs. T
•
Physical
properties
OH- cleavage is hindered by – charge and
by lack of 2’OH

Monomeric Units of DNA and RNA
Nucleoside=adenosine, guanosine, cytidine,
uridine, (deoxyadenosine, etc., thymidine)
Nucleoside 5’triphosphate = 5’
nucleotide triphosphate
3’ deoxy-monophosphate
Polarity of DNA written
5  to 3’

Natural DNAs are long sequences of nucleotides
compacted in the Cell Nucleus
E. Coli genome =  2 chains 4.6
million nucleotides in one
strand
Indian Muntjak: 1 of
3 pairs of
chromosomes > 1
billion nucleotides (>
1 foot length)
Human: 24 chromosomes, > 3
billion nucleotides

X-Ray Diffraction Reveals the Double Helical Structure of
DNA
1.
Coiled chains are
antiparallel
2.
Outside: backbone,
inside bases
3.
Bases perpedicular to
helix axis, 3.4 angstroms/
bp, 10 bps/turn, 36 ° /base
4.
Diameter = 20 angstroms
Rosalind
Franklin

Base stacking
leads to van
der Waals
interaction and
hydrophobic
stabilization
Chargaff 1950:
Amount of A=T
and amount of
G=C
The DNA Double Helix is Held Together by Base
Stacking and Complementarity

Semi-Conservative Replication
•
Grow first generation on 15NH4Cl
•
Switch to 14NH4Cl, What
happens?

Formation of Helical Duplex in DNA can be Monitored
through Absorbance at 260 nm (hypochromism)
DNA is melted in the lab by heat, in the cell by helicases
(during replication and transcription)
Melting (annealing) is reversible
Degree of cross-hybridization (Tm) between different DNAs
indicates the degree of base sequence similarity