From DNA to Protein

Transcription

Translation

The Genetic Code

Sickle Cell Anemia

OH SH + Au SH pinhole 16 SH MB +

Barton and co-workers showed that the electron transfer was not sufficiently sensitive to the dynamic motions of a G-A mismatch to perturb the electronic coupling through the bases; hence, the mismatch was not detected. To solve this problem, they used an electrocatalytic system that coupled ferricyanide as an oxidant to recycle the reduced form of MB (leucomethylene blue) back to MB. The electrocatalysis amplified the sensitivity to the base motions and allowed the G-A mismatch to be detected. 17

Gooding et al. have used 2,6-Disulfonic Acid Anthraquinone (AQDS) as intercalator. AQDS is a anionic intercalator : Negative Intercalators The greater sensitivity of the AQDS to electronic perturbations could infer that the AQDS is less well electronically coupled with the base stack than the MB, as inferred by the low rate of electron transfer. Anal. Chem. 2003, 75,

SH OH SH OH SH OH SH OH + SH pinhole 19

SH OH SH OH SH OH SH OH SH OH SH OH AQDS 20

Anal. Chem. 2003, 75,

A SH OH SH OH SH OH SH OH B EaEa EcEc 22

Sensors and Actuators B, 111–112, 2005, 515. If there was a mismatch in the duplex, the electron transfer was either completely diminished or greatly reduced. 23

Charge Migration Through the DNA Double Helix

Introduction The charge-transport in DNA have intrigued: chemists Physicists biologists The striking similarity of the π-stacked array of DNA bases to π-stacked solid-state conductors has prompted the suggestion that DNA might efficiently facilitate charge transport.

Charge transfer in DNA Charge mobility in DNA has consequences for: DNA damage, which dictates biological damage from: Radiation UV, Light Chemicals Nanoscale electronic devices

Page  17 Charge Transfer through DNA  Less than a decade after discovering of structural features of DNA double helix, the first experiments to answer how charge can be transported through DNA chains were carried out. But  This question is still debated-Does DNA act as:  An insulator,  A semiconductor  Or a molecular wire???

Insulators, semiconductors and conductors Energy Insulator Conduction band Valence band SemiconductorConductor Electron Hole

The early years Eley and Spivey (1962) * : Conduction in DNA arises from thermally excited electrons on the paired bases, which traverse along the  -stacks of the DNA bases Gregoli, Olast and Bertinchamps (1982) ** : Charge migration occurs via the stacked bases, but may be hindered by interfering factors ** Radiat. Res. 89 * Trans. Farad. Soc. 58

Page  20 Photoinduced Methods h Donor Acceptor e-e- F. D. Lewis, et al., Acc. Chem. Res. 34, 159, H-A. Wagenknecht Angew. Chem. Int. Ed. 42, 2454, 2003 G. B. Schuster, Acc. Chem. Res. 33, 253, 2000.

Page  22 Key Steps 1.Covalent labeling of the DNA with redox-active probes. 2. Photochemical initiation of the charge transfer process. 3. Spectroscopic or electrochemical detection of the charge transfer processes or analysis of irreversible DNA products yielded by the charge transfer reaction.

Page  23 Charge transport can occur through DNA over at least short distance Positive charge (hole) transport: Nucleobase guanine is the carrier of positive charge. Electron transport: Thymine and cytosine are the charge carriers? Hole or electron??????

Page  24

Photoinduced transfer (1) Donor [Ru(phen ’ ) 2 dppz] 2+ Acceptor [Rh(phi) 2 phen ’ ] 3+ Murphy et al. Science 262 (1993) 15 base pairs Hybridization of DNA strands, each intercalated with metal complex Ru-complex luminesces, but not when connected to Rh-complex via DNA  DNA is a conductor

Means of transfer Tunneling (independent of temperature) Boon and Barton (illustrations) Curr. Opin. Struct. Biol. 12 (2002) Hopping (dependent of temperature) k ct =k 0 e -  R k ct =k 0 (T)N -  Grozema et al. (theory) J. Am. Chem. Soc. 122 (2000)