Single polynucleotide chains

RNA also differs from DNA in that there are not the same regularities in the overall composition of its bases and it usually consists of a single polynucleotide chain. There are different types of RNA, which fulfill different functions. About 80% of the RNA in a cell is located in the cytoplasm in clusters closely associated with proteins. These ribonucleoprotein particles specifically are called ribosomes, and the ribosomes are the sites of most of the protein synthesis in the cell. In addition to the ribosomal RNA (rRNA),... 

There are a greater variety of RNA forms, with molecular weights in the range 25,000 to several million. Most RNAs contain a single polynucleotide chain, but this can fold back on itself to form double-helical regions containing A U and G C base pairs. 

The W-C DNA structure is a right-handed helix as one looks down either axis of the molecule and the helix rotates in a clockwise direction. This conformation of DNA is called B-DNA and is the form found in solution and inside cells. The double helix is stabilized by a number of forces, including hydrophobic interactions and van der Waals forces, which also help stabilize single polynucleotide chains. Collectively, these two forces are known as stacking interactions because of their contribution to the stacked arrangement of the bases in DNA. 

Base pairing also has an important structural function. It is responsible for the joining of two complementary DNA chains (or, exceptionally, RNA, in certain viruses) into the celebrated double helix. It also causes single polynucleotide chains (mostly RNA) to bundle up into complex, three-dimensional arrangements. This property accounts for the many functions accomplished by RNA molecules, as opposed to DNA, which is essentially inert chemically and has as its sole functions to serve as a repository of genetic information and as a template for the transfer of this information in replication and transcription. 

RNA (ribonucleic acid) A nucleic acid found mainly in the cytoplasm and involved in protein synthesis. It is a single polynucleotide chain similar in composition to a single strand of DNA except that the sugar ribose replaces deoxyribose and the pyrimidine base uracil replaces... 

Figure 2 (leU)- A 24-residue 7-turn helix representing a single polynucleotide chain in the proposed structure for nucleic acid. The phosphate groups are represented by tetrahedra, and the ribofuranose groups by dashed arcs connecting them. 

The enzyme (mol wt 109,000) is a single polynucleotide chain with a single disulfide bond and a single sulfhyd-ryl group. It contains 0.6 phosphorous atoms per protein molecule. 

After extraction, the RNA obtained from mammalian ribosomes separates into two groups—a 28 S and an 18 S RNA. The 28 S is derived from the two-thirds portion, and the 18 S from the one-third portion of the ribosome. Whether or not each of these two RNA s constitutes a single polynucleotide chain is not certain, but if they do, the molecular weight of the 28 S would be about twice that of the 18 S (1.2 x 10 and 0.6 x 10, respectively). Similarly, extraction of nucleic acid from ribosomal segments of E. coli yields 23 S and 16 S RNA base composition studies show significant differences between the two types of RNA. 

C below the Tm of duplex AAV DNA. These duplex linear monomers did form duplex circular monomers and hnear dimers when exposed to annealing conditions. Thus, anneahng of intact linear AAV single polynucleotide chains led to the formation of two types of duplex linear monomers (1) those without cohesive single-stranded termini, and (2) those with cohesive single-stranded termini. 

Fig. 6. Electron micrographs of hydrogen-bonded single-stranded circles formed when purified linear heavy AAV single polynucleotide chains are exposed to annealing conditions. The arrows point to the projections observed on such single-stranded circles...

The current model of the purified DNA is that it is a linear single polynucleotide chain containing a limited number of nucleotide sequence permutations, the start points of which occur within a region representing less than 6% of the genome, and also containing a terminal nucleotide sequence repetition (either inverted, natural, or both). 

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