Biology-Dna Essay

3267 WordsFeb 14, 201214 Pages
------------------------------------------------- Hammerhead ribozyme From Wikipedia, the free encyclopedia Hammerhead Ribozyme | | Stylized rendering of the full-length hammerhead ribozyme RNA molecule | Scientific classification | Species: | Catalytic RNA | Hammerhead RNAs are RNAs that self-cleave via a small conserved secondary structural motif termed a hammerhead because of its shape.[1] Most hammerhead RNAs are subsets of two classes of plant pathogenic RNAs: the satellite RNAs of RNA viruses and the viroids. The self-cleavage reactions, first reported in 1986,[2][3] are part of a rolling circle replication mechanism. The hammerhead sequence is sufficient for self-cleavage[4] and acts by forming a conserved three-dimensional tertiary structure. Contents [hide] * 1 Autocatalyst or enzyme? * 2 Species distribution * 3 Chemistry of catalysis * 3.1 Cleavage by phosphodiester isomerization * 3.2 Requirement for divalent metal ions * 3.3 Not a metallo-enzyme * 4 Primary and secondary structure * 4.1 Minimal ribozyme * 4.1.1 Type I & type III hammerhead RNA * 4.2 Full-length ribozyme * 5 Tertiary structure * 5.1 Minimal * 5.2 Structure-function * 5.3 Full-length * 6 Structure and catalysis * 7 Therapeutic applications * 8 References * 9 External links | ------------------------------------------------- [edit]Autocatalyst or enzyme? In the natural state, a hammerhead RNA motif is a single strand of RNA, and although the cleavage is autocatalytic and takes place in the absence of protein enzymes, the hammerhead RNA itself is not a true enzyme in its natural state, as it cannot catalyze multiple turnovers. In vitro hammerhead constructs can be engineered such that they consist of two RNA strands. The strand that gets cleaved can be supplied in excess, and multiple turnover can be

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