Background Information: In the nervous system, the brain processes information b
ID: 195276 • Letter: B
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Background Information: In the nervous system, the brain processes information by transmission of electrical and chemical signals through a network of neurons. These signals travel through synapses which connect two neurons. Neuroligins are cell-adhesiorn molecules that function to connect two neurons at synapses and mediate proper signalling across the synapse. Interestingly, neuroligin function has been linked to autism spectrum disorder (ASD) which is primarily manifested by delayed development and deficiency in social interaction and communication in patients. Mutations in genes encoding neuroligins have been identified in ASD patients. The molecular mechanism of how neuroligins function in ASD has been investigated using mouse models. The mouse gene NL3 encodes a neurolignin. Aberrant NL3 gene function in mice results in synaptic dysfunction and a diverse range of abnormal behavior including a subset that resembles ASD patients. A striking phenotype of NL3 mutant mice is increased repetitive behavior compared to wild type/normal mice. There are two alleles of the mouse NL3 gene. One allele (referred as"or wild type) produces NL3 protein which results in the synthesis of neuroligins for synaptic function. In contrast, the other allele (referred as "-") does not produce any NL3 mRNA (and hence no NL3 protein) resulting in an inability to produce neuroligins. Question: Closer examination of the two alleles of the mouse NL3 gene reveals no changes in nucleotide sequence in the transcriptional unit. This observation indicates that the difference in nucleotide sequence between the two alleles must not occur within the transcriptional unit. Provide two possibilities where nucleotide changes could occur on the chromosome for the allele that does not produce any NL3 mRNA and explain why. (4 marks)Explanation / Answer
Most probable change occure in the chromosomal genes responsible for m-RNA processing and spicing .because from above case if both wild and mutant type genes transcribed and have same nucleotide sequence but mutant type doesn't code proteins it means functionality of m-RNA attained by processing like polyadnylation ,5'capping and splicing whichis hampered in mutant type.
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