Double-strand nucleotides

Cellular protein biosynthesis involves the following steps. One strand of double-stranded DNA serves as a template strand for the synthesis of a complementary single-stranded messenger ribonucleic acid (mRNA) in a process called transcription. This mRNA in turn serves as a template to direct the synthesis of the protein in a process called translation. The codons of the mRNA are read sequentially by transfer RNA (tRNA) molecules, which bind specifically to the mRNA via triplets of nucleotides that are complementary to the particular codon, called an anticodon. Protein synthesis occurs on a ribosome, a complex consisting of more than 50 different proteins and several stmctural RNA molecules, which moves along the mRNA and mediates the binding of the tRNA molecules and the formation of the nascent peptide chain. The tRNA molecule carries an activated form of the specific amino acid to the ribosome where it is added to the end of the growing peptide chain. There is at least one tRNA for each amino acid. 

Another class of DNA-binding proteins are the polymerases. These have a nonspecific interaction with DNA because the same protein acts on all DNA sequences. DNA polymerase performs the dual function of DNA repHcation, in which nucleotides are added to a growing strand of DNA, and acts as a nuclease to remove mismatched nucleotides. The domain that performs the nuclease activity has an a/P-stmcture, a deep cleft that can accommodate double-stranded DNA, and a positively charged surface complementary to the phosphate groups of DNA. The smaller domain contains the exonuclease active site at a smaller cleft on the surface which can accommodate a single nucleotide. 

Figure 28.4 A representation of semiconservative DNA replication. The original double-stranded DNA partially unwinds, bases are exposed, nucleotides line up on each strand in a complementary manner, and two new strands begin to grow. Both strands are synthesized in the same 5 - 3 direction, one continuously and one in fragments.

Dicer represents the key enzyme in the RNAi pathway. Dicer is also known as Helicase with RNAse motif, heRNA, Helicase-moi, K12H4.8-like, or KIAA0928. Dicer produces cleaves long double-stranded RNA into small pieces of about 21-23 nucleotides. These so-called siRNA duplexes produced by the action of Dicer contain 5 -phosphates and free 3 -hydroxylgroups... 

Recently, the related phenomenon of RNA interference (RNAi) has attracted much attention [5]. RNAi occurs when a short (generally 21 nucleotides in length) double-stranded RNA (dsRNA) catalyticaUy represses the translation of a fully complementary mRNA sequence. The process appears to proceed via a complex formed between the antisense RNA strand and a protein with RNase activity [6]. Upon binding to the target mRNA sequence, the ribonucleoprotein complex initiates cleavage of the mRNA transcript thus preventing translation of intact protein. After dissociation from the truncated mRNAs, the ribonucleoprotein complex is free to act on other intact mRNAs. Such small interfering RNAs (siRNAs) have... 

C13-0090. One nucleotide and its hydrogen-bonded partner in double-stranded DNA is called a duplex. Identify the duplex formed by guanine and draw its structure. 

Subjecting cells to oxidative stress can result in severe metabolic dysfunctions, including peroxidation of membrane lipids, depletion of nicotinamide nucleotides, rises in intracellular free Ca ions, cytoskeletal disruption and DNA damage. The latter is often measured as formation of single-strand breaks, double-strand breaks or chromosomal aberrations. Indeed, DNA damage has been almost invariably observed in a wide range of mammalian cell types exposed to oxidative stress in a number... 

Deoxyribose nucleic acid (DNA) Comprises a backbone with four nucleotide bases, adenine, cytosine, guanine and thymine, bound to it. The genetic information in all cells is encoded in this genome of double-stranded DNA, comprising 3 billion base pairs located in the chromosomes. 

Base pair (bp) The four nucleotides in the DNA contain the bases adenine (A), guanine (G), cytosine (C), and thymine (T). Two bases (adenine and thymine or guanine and cytosine) are held together by weak bonds to form base pairs. The two strands of human DNA are held together in the shape of a double helix by those bonds between base pairs. For example, the complementary nucleic acid base sequence to G-T-A-C that forms a double-stranded structure with the matching bases is C-A-T-G. 

DNA (deoxyribonucleic acid) A double-stranded molecule held together by weak bonds between base pairs of nucleotides that encodes genetic information. The base sequence of each single strand can be deduced from that of its partner since base pairs form only between the bases A and T and between G and C. 

DNA DNA (deoxyribonucleic acid) is a double-stranded helix of nucleotides... 

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