From DNA to Protein

From DNA to Protein

Transcription

Translation

The Genetic Code

Sickle Cell Anemia

+ MB+ SH SH Au SH SH SH SH SH SH OH SH pinhole 16

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. • 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. 17

Negative Intercalators Goodinget al. have used 2,6-Disulfonic Acid Anthraquinone (AQDS) as intercalator. AQDSis a anionic intercalator : • 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, 3845. 18

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

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

Anal. Chem. 2003,75, 3845. 21

A OH OH OH OH SH SH SH SH SH SH SH SH SH SH B Ec Ea 22

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

Charge Migration Through theDNA 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

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 Electron Conduction band Valence band Electron Hole Insulator Semiconductor Conductor

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 * Trans. Farad. Soc. 58 ** Radiat. Res. 89

h e- PhotoinducedMethods Donor Acceptor F. D. Lewis, et al., Acc. Chem. Res. 34, 159, 2001. H-A. WagenknechtAngew. Chem. Int. Ed. 42, 2454, 2003 G. B. Schuster, Acc. Chem. Res. 33, 253, 2000.

Key Steps 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.

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

Photoinduced transfer (1) Acceptor [Rh(phi)2phen’] 3+ • 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 15 base pairs Donor [Ru(phen’)2dppz] 2+ Murphy et al. Science 262 (1993)

Means of transfer Tunneling (independent of temperature) kct=k0e-R Hopping (dependent of temperature) kct=k0(T)N- Boon and Barton (illustrations) Curr. Opin. Struct. Biol. 12 (2002) Grozema et al. (theory) J. Am. Chem. Soc. 122 (2000)

From DNA to Protein