2-Questions : TOPIC #1: RNA splicing: mechanism and importance. Describe the main features of mRNA splicing. Explain the advantagesof mRNA splicingin termsof functional diversity and why these...

Running head BIOMOLECULES: THE AMAZING MOIETIES!
Biomolecules: The Amazing Moieties!
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Biomolecules: The Amazing Moieties!
Biomolecules: The Amazing Moieties
Introduction
There might be identified several characteristics linked with biological molecules which
can be called “amazing”. Such features do not only increase their efficiency, but also make the
biological procedures feasible. For example at one hand, splicing of pre m-RNA transcript
provides versatile nature to a gene in terms of types of products produced by it while on the other
hand, cooperativity can regulate the competence as well as well-timed functioning of a protein.
1. RNA Splicing: Chief characteristics and Importance
Gene Exon 1 Exon 2 Exon 3 Exon 4
(a) hn RNA formation:
1 2 3 4
(b) Alternative Splicing:
m-RNA 1 2 3 1 2 4
Protein A Figure 1 Protein B
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Biomolecules: The Amazing Moieties!
Processing of initially transcribed RNA (hn RNA/pre-mRNA) is a common phenomenon
in eukaryotic genes (and in some prokaryotic ones). Such processing leads towards the formation
of a mature messenger RNA (mRNA) which can further direct the process of protein synthesis
(also known as; translation). Out of several steps of processing, an important one is called as;
RNA splicing that involves removal or "splicing out" of definite sequences which are renowned
as; intervening sequences or introns [figure 1(b)]. Thus; final mRNA contains only expressing
sequences known as; exons. Exons can be linked with each other as a consequence of
splicing procedure.
Key features of Splicing
Splicing can be described as a well- organized process that involves specific signals,
sequences as well as machinery. Chief characteristics of splicing may be identified through
studying the sequence of events that take place to perform the task.
Splicing signal
Most introns initiate from sequence GU and terminate with sequence AG (5' to 3'). These
sites are called as; splice donor and splice acceptor site respectively. There could also be
diagnosed another essential sequence [CU (A/G) A(C/U)], moderately conserved) renowned as;
branch site which is positioned at 20 - 50 bases upstream of acceptor site. (Grabowski et al.,
1985).
Excision of intron as Lariat
2'-OH of an Adenine (A) present at the "branch" point can form a phosphodiester bond
with the first Guanine (G) of intron so that, splicing could be initiated. In fact, splicing can occur
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Biomolecules: The Amazing Moieties!
through a chain of phosphoester transfers which are also known as; transesterification. After
joining of 2’-OH of A with G, the 3'-OH present upstream of the exon can react with the initial
nucleotide present at the downstream position of exon. This results into the removal of intron as
lariat (can be defined as; a circular intermediate) and linkage of two exons through the
phosphodiester transfer technique (Solnick, 1985).
Formation of Functional spliceosome
Small- nuclear RNAs (snRNAs) involved in splicing such as; U1, U2, U4/U6, and U5
snRNAs get linked with proteins to shape small- nuclear ribonucleoprotein particles, or snRNPs.
One class of proteins common to many snRNPs is the Sm proteins. These snRNPs may collect
on the pre-mRNA so that spliceosome...