Parallel sheets are typically large structures; those composed of fewer than five strands are rare. 

Antiparallel sheets may consist of as few as two strands.

TLS Online TPP Program

#Id: 3251

#Unit 3. Fundamental Processes

5-bromouracil induces transitions in both directions, A:T ↔ G:C.

TLS Online TPP Program

#Id: 3254

#Unit 3. Fundamental Processes

Tautomeric forms of the four common bases in DNA.

TLS Online TPP Program

#Id: 3257

#Unit 3. Fundamental Processes

Intercalating agents, such as proflavin, acridine, and ethidium, cause the deletion or addition of a base pair or even a few base pairs.

TLS Online TPP Program

#Id: 3258

#Unit 3. Fundamental Processes

Intercalating agents are flat molecules containing several polycyclic rings that bind to the equally flat purine or pyrimidine bases of DNA, just as the bases bind or stack with each other in the double helix

TLS Online TPP Program

#Id: 3259

#Unit 3. Fundamental Processes

 Ultraviolet light induces the formation of a cyclobutane ring between adjacent thymines

TLS Online TPP Program

#Id: 3261

#Unit 3. Fundamental Processes

g-radiation and X-rays (ionizing radiation) are particularly hazardous because they cause double-strand breaks in the DNA, which are difficult to repair. If left unrepaired, double-strand breaks can be lethal to a cell.