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In molecular biology, a polynucleotide (from Ancient Greek πολυς (polys) 'many') is a biopolymer composed of nucleotide monomers that are covalently bonded in a chain. [1] DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are examples of polynucleotides with distinct biological functions.
Exonucleases are enzymes that work by cleaving nucleotides one at a time from the end (exo) of a polynucleotide chain. A hydrolyzing reaction that breaks phosphodiester bonds at either the 3′ or the 5′ end occurs. Its close relative is the endonuclease, which cleaves phosphodiester bonds in the middle (endo) of a polynucleotide chain.
In molecular biology, endonucleases are enzymes that cleave the phosphodiester bond within a polynucleotide chain (namely DNA or RNA).Some, such as deoxyribonuclease I, cut DNA relatively nonspecifically (with regard to sequence), while many, typically called restriction endonucleases or restriction enzymes, cleave only at very specific nucleotide sequences.
In DNA replication, DNA-dependent DNA polymerases make copies of DNA polynucleotide chains. To preserve biological information, it is essential that the sequence of bases in each copy are precisely complementary to the sequence of bases in the template strand. Many DNA polymerases have a proofreading activity. Here, the polymerase recognizes ...
It has sites for amino acid attachment and an anticodon region for codon recognition that binds to a specific sequence on the messenger RNA chain through hydrogen bonding. [32] A diagram of how mRNA is used to create polypeptide chains. Ribosomal RNA (rRNA) is the catalytic component of the ribosomes. The rRNA is the component of the ribosome ...
It then produces an RNA chain, which is complementary to the template DNA strand. The process of adding nucleotides to the RNA strand is known as elongation; in eukaryotes, RNAP can build chains as long as 2.4 million nucleotides (the full length of the dystrophin gene).
Strings of nucleotides are bonded to form spiraling backbones and assembled into chains of bases or base-pairs selected from the five primary, or canonical, nucleobases. RNA usually forms a chain of single bases, whereas DNA forms a chain of base pairs. The bases found in RNA and DNA are: adenine, cytosine, guanine, thymine, and uracil. Thymine ...
Introns and exons are present in both the underlying DNA sequence and the pre-mRNA molecule, therefore, to produce a mature mRNA molecule encoding a protein, splicing must occur. [6] During splicing, the intervening introns are removed from the pre-mRNA molecule by a multi-protein complex known as a spliceosome (composed of over 150 proteins ...