American Society for Clinical Pathology (ASCP) Technologist in Cytogenetics certification (ASCP CG) Practice Test

How do Quinacrine molecules bind to DNA?

1. Binding to GC rich regions

2. Binding to the AT rich regions

3. Binding to chromatin-associated proteins

4. Binding within the promoter regions

The correct answer is: Binding to the AT rich regions

Quinacrine is a fluorescent dye that intercalates into DNA molecules, and its binding is particularly selective for AT-rich regions of the DNA. The reason it binds selectively to these regions lies in the molecular structure of DNA; AT-rich regions have a different dynamic and stacking pattern compared to GC-rich areas, making them more favorable for the intercalating properties of Quinacrine. The specificity for AT regions corresponds to the presence of adenine and thymine bases, which allow Quinacrine to effectively fit between the bases, thus stabilizing the binding and resulting in the characteristic fluorescence when observed under UV light. This property is utilized in cytogenetics for chromosomal studies, enabling visualization of chromosomal structures and genetic material. In contrast, while GC-rich regions and chromatin-associated proteins are essential aspects of DNA structure and function, Quinacrine's mechanism of action does not predominantly involve them. Additionally, binding within promoter regions is not the primary mode of interaction for Quinacrine, as its affinity is more pronounced in the general context of AT-rich sequences throughout the DNA rather than specifically located in regulatory regions.