what is sigle stranded and double stranded DNA and RNA
Answers
Answer:
The DNA molecules are not always double stranded helical structures, sometimes they occur in single stranded form called ssDNA.
The DNA molecules are not always double stranded helical structures, sometimes they occur in single stranded form called ssDNA....
The DNA molecules are not always double stranded helical structures, sometimes they occur in single stranded form called ssDNA....ssDNA vs dsDNA – A Comparison Table.
The DNA molecules are not always double stranded helical structures, sometimes they occur in single stranded form called ssDNA....ssDNA vs dsDNA – A Comparison Table.Sl. No. dsDNA ssDNA
The DNA molecules are not always double stranded helical structures, sometimes they occur in single stranded form called ssDNA....ssDNA vs dsDNA – A Comparison Table.Sl. No. dsDNA ssDNA1 Double stranded DNA is linear or filamentous form Single stranded DNA is usually stellate or star shaped
Answer:
ssDNA is a key intermediate in nearly all biochemical reactions involving DNA replication and DNA repair, but there has been a marked absence of techniques for visualizing long ssDNA molecules (Ha, Kozlov, & Lohman, 2012). There are several challenges when trying to work with ssDNA. For example, fluorescence-based microscopy experiments often require intercalating dyes such as YOYO1 to view dsDNA, but YOYO1 can also damage DNA upon laser illumination. This is problematic with ssDNA because even a single nick in the phosphate backbone will cause ssDNA to break away from its attachment to the surface. In addition, dsDNA is stiff and readily stretched by the application of buffer flow, whereas ssDNA has a much shorter persistence length and can also form extensive secondary structure. The much greater force required to stretch out ssDNA is typically inaccessible with the laminar flow systems used for single-molecule imaging.
To prepare ssDNA curtains, long ssDNA molecules are first synthesized by rolling circle DNA replication using phi29 DNA polymerase, and a circular ssDNA template annealed to a biotinylated DNA primer (Gibb, Silverstein, Finkelstein, & Greene, 2012). The ssDNA products of the rolling circle replication assays are then anchored to the bilayer through a biotin–streptavidin linkage and aligned along the leading edges of nanofabricated barriers using buffer flow. The ssDNA cannot be visualized because it is highly compacted and cannot be labeled with intercalating dyes without breaking the ssDNA. To visualize the ssDNA, we use a GFP (green fluorescent protein)-tagged version of a single-stranded eukaryotic DNA-binding protein called replication protein A (RPA), which is itself a key protein that participates in most biochemical reactions involving ssDNA intermediates. RPA binds ssDNA and removes secondary structure, and the RPA-ssDNA filaments are much stiffer than naked ssDNA, allowing the RPA-bound ssDNA to be stretched by buffer flow. The resulting ssDNA curtains are fluorescently labeled with the GFP-tag on RPA. This newest addition to the different types of DNA curtain techniques offers outstanding potential for studying DNA repair reactions such as homologous recombination, where the first intermediate in the physiological pathway is in fact an ssDNA molecule coated with RPA.
Single-Molecule Enzymology: Nanomechanical Manipulation and Hybrid Methods
C.J. Ma, ... E.C. Greene, in Methods in Enzymology, 2017
5 Conclusion and Future Directions
ssDNA curtains provide a powerful experimental platform, enabling new avenues of investigation into the biochemical and biophysical properties of Rad51/RecA–ssDNA presynaptic complexes. These studies offer the potential for new insights into the assembly, stability, and regulation of this crucial HR intermediate, and the procedures described here can be adapted to study many different questions related to HR. Future ssDNA curtains studies may help provide additional insights into the DNA transactions that take place during HR, and may also provide important new clues into the dozens of other proteins that are necessary for HR to take place within living cells. Of particular interest will be work looking at how nucleosomes and chromatin impact the interactions of the Rad51–ssDNA presynaptic complex with dsDNA, and how these interactions are modulated by nucleosome-remodeling proteins and posttranslational histone modifications. In addition, these ssDNA curtain methods can be adapted for studies involving other types of ssDNA-binding proteins, and with additional development it may even be possible to extend these research tools to study of single-stranded RNA substrates.
Targeting Homologous Recombination Repair in Cancer
Henning Willers, ... Lee Zou, in DNA Repair in Cancer Therapy, 2012
Formation of RAD51 Filament
Once ssDNA is generated by resection, it is first recognized by the ssDNA-binding protein RPA. The binding of RPA to ssDNA generates a key structure that recruits the ATR-ATRIP checkpoint kinase (see below), and it removes secondary structures of ssDNA. RPA also inhibits the binding of RAD51 to ssDNA, which needs to be overcome to enable the subsequent steps of HRR.2,3