Polynucleotide, single-stranded

Section 28 14 The nucleotide sequence of DNA can be determined by a technique m which a short section of single stranded DNA is allowed to produce its complement m the presence of dideoxy analogs of ATP TTP GTP and CTP DNA formation terminates when a dideoxy analog is incorporated into the growing polynucleotide chain A mixture of polynucleotides dif fermg from one another by an incremental nucleoside is produced and analyzed by electrophoresis From the observed sequence of the comple mentary chain the sequence of the original DNA is deduced... 

In this method the single-stranded DNA fragment to be sequenced is end-labelled by treatment with alkaline phosphatase to remove the 5 phosphate, followed by reaction with 32P-labelled ATP in the presence of polynucleotide kinase, which attaches 32P to the 5 terminal. The labelled DNA fragment is then divided into four aliquots, each of which is treated with a reagent which modifies a specific base as follows. 

Transfer RNAs are small, single-stranded polynucleotides (70-90 bases long). The tRNA molecule is linked to its specific amino acid in a reaction that is catalysed by the enzyme tRNA-aminoacyl synthetase. It occurs in two stages ... 

A well-extended single-stranded polynucleotide, poly(A)... 

The study demonstrated that single-stranded polynucleotide, such as poly(A), is more flexible than a generic dsDNA. On mica, the long B-DNA binds to mica at many sites and remains intact during drying, while the short DNA binds at fewer sites and settles to an A-DNA structure during dehydration. 

DNA ligase (NAD+) [EC 6.5.1.2] (also referred to as polydeoxyribonucleotide synthase (NAD+), polynucleotide ligase (NAD+), DNA repair enzyme, and DNA join-ase) catalyzes the reaction of NAD+ with (deoxyribo-nucleotide) and (deoxyribonucleotide) to produce AMP, nicotinamide nucleotide, and (deoxyribonucleo-tide)( +m). This forms a phosphodiester at the site of a single-strand break in duplex DNA. RNA can also act as substrate to some extent. 

Secondary structure of DNA consists of two strands of polynucleotides coiled around each there in the form of double helix. The backbone of each strand is sugar-phosphate unit and the base unit of each strand are pointed into the interior of the helix and are linked through H-bonds. G and C are held by three H-bonds, A and T are held by two bonds. Unlike DNA, RNA has a single strand. 

The question of energy transfer is introduced also by the fact that polynucleotides frequently exist not only in single-strand forms but also entirely or partially as double-strand helices in which pyrimidine residues on one chain are hydrogen bonded to purine residues on the other chain. The reactivity of the pyrimidine residue can be strongly affected by the presence of its purine partner. An example of this will be found further on. 

Adds a phosphate to the 5 -0H end of a polynucleotide to label it or permit ligation Adds homopolymer tails to the 3 -0H ends of a linear duplex Removes nucleotide residues from the 3 ends of a DNA strand Removes nucleotides from the 5 ends of a duplex to expose single-stranded 3 ends Removes terminal phosphates from either the 5 or 3 end (or both)... 

Our objective is to understand how the noncovalent interactions responsible for nucleic acid secondary structure (i.e. base stacking and base pairing) affect the photophysics of these multichromophoric systems. Here we describe initial experimental results that demonstrate dramatic differences in excited-state dynamics of nucleic acid polymers compared to their constituent monomers. Although ultrafast internal conversion is the dominant relaxation pathway for single bases, electronic energy relaxation in single-stranded polynucleotides... 

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