What are the three strands of DNA?
Parts of a DNA Strand Nucleotides themselves are comprised of three joined parts: a sugar molecule, a phosphate group, and a nitrogenous base. The sugars of one nucleotide link to the phosphates of the adjacent nucleotide to form the exterior of the DNA strand, known as the sugar-phosphate backbone.
Is there triple-stranded DNA?
Triple-stranded DNA (also known as H-DNA or Triplex-DNA) is a DNA structure in which three oligonucleotides wind around each other and form a triple helix.
What does triple helix DNA mean?
A DNA triple helix is made up of three separate DNA strands, each oriented with the sugar/phosphate backbone on the outside of the helix and the bases on the inside of the helix.
How triplex DNA is formed?
A DNA triplex is formed when pyrimidine or purine bases occupy the major groove of the DNA double Helix forming Hoogsteen pairs with purines of the Watson-Crick basepairs.
Can DNA have a triple helix?
DNA can form multi-stranded helices through either folding of one of the two strands or association of two, three, or four strands of DNA. In 1986, it was demonstrated that a short (15-mer) mixed-sequence triplex-forming oligonucleotide (TFO) formed a stable specific triple helical DNA complex [3].
Who thought DNA was a triple helix?
Pauling
In the early 1950s, many scientists were racing to discover the structure of DNA. Pauling proposed a triple helix structure with the bases on the outside, but James Watson and Francis Crick ultimately disproved his idea with their famous double helix model.
Is triplex DNA pyrimidine rich?
While pyrimidine TFOs preferentially form triplexes with T–A duplex-rich TTS, purine TFOs form triplex structures with G–C-rich TTS. The complementary sequence recognition code of purine and pyrimidine TFOs increases the specificity and regulatory potential of TFO containing RNA molecules.
What is Tetraplex DNA?
Tetraplex DNA has a quadruple-stranded structure, which is formed by the folding of the single-stranded DNA through the formation of a G-quartet. Tetraplex DNA structure is known to occur in oncogenes, such as c-Myc, or in the telomere region, where this acts as a regulating lifetime gene.
What causes triple helix?
A triple helix is formed after the binding of a third strand to the major groove of a duplex DNA through Hoogsteen base pairing. Pyrimidine-rich and purine-rich sequences can form stable triplex structures as a consequence of the formation of A–T–A and C+–G–C triplets (Fig. 8.5).
What would a triple helix do?
These structures can induce transcriptional repression and site-specific mutagenesis or recombination. Triplex-forming oligonucleotides (TFOs) can bind to duplex DNA in a sequence specific fashion with high affinity, and can be used to direct DNA-modifying agents to selected sequences.
Is it possible to have a triple helix DNA?
Based on the way a double-stranded DNA helix is formed, a triple-stranded helix would not be possible. Because this happens to both single strands of the original double-stranded helix, you end up with two new double-stranded helices when you started with just one.
Why can DNA not be a triple helix?
DNA is only read as a double helix, so a triple helix would be a disadvantage. Also, all the enzymes (cellular proteins that act as ‘machines’) need the DNA to be in a double helix to recognize their substrate (landing spot) to do their work.
How does the third strand of triple stranded DNA bind?
In triple-stranded DNA, the third strand binds to a B-form DNA (via Watson–Crick base-pairing) double helix by forming Hoogsteen base pairs or reversed Hoogsteen hydrogen bonds.
When did scientists discover triple stranded DNA structures?
Triple-stranded DNA structures were common hypotheses in the 1950s when scientists were struggling to discover DNA’s true structural form.
How is a triple stranded DNA helix recognized?
The PNA-DNA-PNA triplex helix is able to be recognized by the cell’s own DNA repair mechanism, which sensitizes the surrounding DNA for homologous recombination.
How are TFOs used to form triple stranded DNA?
Triplex forming oligonucleotides (TFO) TFOs are short (≈15-25 nt) nucleic acid strands that bind in the major groove of double-stranded DNA to form intramolecular triplex DNA structures. There is some evidence that they are also able to modulate gene activity in vivo.