Question

structural organisations of petromyzon explain?????

Answer 1

Lamprin is a unique structural protein which forms the extracellular matrix of several cartilaginous structures found in the lamprey. Lamprin is noncollagenous in nature but shows sequence similarities to elastins and to insect structural proteins. Here, we characterize the structure and organization of lamprin genes, demonstrating the presence of multiple similar but not identical copies of the lamprin gene in the genome of the lamprey. In at least one species of lamprey, Lampetra richardsoni, the multiple gene copies are arranged in tandem in the genome in a head-to-tail orientation. Lamprin genes from Petromyzon marinus contain either seven or eight exons, with exon 4 being alternatively spliced in all genes, resulting in a total of six different lamprin transcripts. All exon junctions are of class 1,1. An unusual feature of the lamprin gene structure is the distribution of the 3′ untranslated region sequence among multiple exons. A TATA box and cap sequence have been identified in upstream sequences in close proximity to the transcription start site, but no CAAT box could be identified. Sequence and gene structure comparisons between lamprins, elastins, and insect structural proteins suggest that the regions of sequence similarity are the result of a process of convergent evolution

Answer 2

 The head and branchial regions of larval and adult lampreys and hagfish were studied histologically in serial sections. The most remarkable feature in these extant agnathans was the occurrence of large blood‐sinuses. In larval lampreys, blood‐sinuses are well developed in the velum, an organ that functions to introduce water and accompanying food particles from the mouth into the gill and alimentary regions. The sinuses in the velum may act to transduce the force of contraction of velar muscles to the stroke‐like movement of the velum; without these sinuses muscular contractions might simply cause the velum to collapse. In adult lampreys, blood‐sinuses are well developed in the peribranchial space that surrounds the branchial (gill) sac and is surrounded by the branchial pouch. It is possible that the force of contractions of the branchial‐pouch muscles is transduced effectively to the branchial sac via the peribranchial blood‐sinus and facilitates the expiration of water through the external gill pores. If the peribranchial sinus were absent, the muscular contraction might deform the branchial sac in an inappropriate manner. In the hagfish, the blood‐sinus system is also well developed in the velum and peribranchial space, although the peribranchial sinus lies outside the muscular branchial pouch. In agnathans, the blood‐sinus system may function, at least in part, as a kind of hydrostatic skeleton that transduces the force generated by muscular contraction.