Question

1a) The genes of eukaryotic cells contain intervening sequences or Introns; in mammals the vast majority of protein encoding genes have introns with some genes containing over 60. Discuss at least two functions of introns in mammalian genes. b) Do prokaryotic cells have introns? Why? (think about your answer in “a”). c) Describe the role (not the mechanism, but more of the basic function) of SnRNPs in the removal of introns from primary mRNA transcripts, i.e. what do the SnRNPs actually do in the splicesome

Answer 1

Answer:                  This question i have to write pointswise,because it's easy to understand you...

a):

• Introns are known to have many functions in eukayotic genome though they donot code proteins.
• Few are direct where as few are indirect in gene expression regulation.
• They are important for regulation of alternative splicing.
• Alternative splicing is a molecular mechanism of producing different proteins from the same gene in a eukaryotic cell.
• Introns contain small or short sequences that are important for efficient splicing, like acceptor, donor and branch points.
• Some Introns are known to enhance the gene expression using Intron mediated enhancement.
• In particular the intron should be present in the transcribed region of the gene for the enhancement to occur, differentiating this from the action of typical transcriptional enhancers.

b):

• The reason that prokaryotic cells don't have introns is the mechanism of translation and transcription are coupled and hence there is no space for splicing if introns are present.
• Also prokaryotic genes are organised into operons and multiple proteins are produced from multiple adjacent genes there is no need of complex regulatory system.

c):

• snRNPs contain proteins and snRNAs also called as small nuclear RNA.
• The snRNA component of the snRNP gives it the specificity to individual introns by recognising the critical signal sequences at 5' 3' and branch sites of the introns.
• Just like ribosome the spliceosome also involves base pairing of the RNA sequence to be spliced with the RNAs of the snRNPs.
• Some proteins are directly involved in splicing the RNA while others are needed for structural binding and attachment of introns.

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