transcript
- Slide 1
- Anum kamal(BB-307-016) Umm-e-Habiba(BB307-035)
- Slide 2
- Gene splicing Gene splicing is the removal of introns from the
primary trascript of a discontinuous gene during the process of
Transcription. Gene splicing is a post-transcriptional modification
in which a single gene can code for multiple proteins.
- Slide 3
- Gene splicing is an important source of protein diversity. One
gene can lead to different mature mRNA molecules that generate
multiple functional proteins. Thus, gene splicing enables a single
gene to increase its coding capacity.
- Slide 4
- Introns: The areas of the gene that are spliced out are
representing noncoding regions that are intervening sequences also
known as introns. Exons: The DNA that remains in the processed RNA
is referred to as the coding regions and each coding regions of the
gene are known as exons.
- Slide 5
- Slide 6
- There are two phenomenons by which gene splicing occur one is
natural i.e. 1. Post transcriptional modification. 2. Artificially
or by chemical agent used generally in recombinant technology.
- Slide 7
- History of gene splicing: Berg was the first scientist to
splice together segments of DNA from different organisms and his
work was published in a landmark paper in the Proceedings of the
National Academy of Science in 1972.
- Slide 8
- Gene Splicing Mechanism There are several types of common gene
splicing events. 1. Exon Skipping: In which exons are included or
excluded from the final gene transcript leading to extended or
shortened mRNA variants. The exons are responsible for producing
proteins that are utilized in various cell types for a number of
functions.
- Slide 9
- 2.Intron Retention: In which an intron is retained in the final
transcript. In humans 2-5 % of the genes have been reported to
retain introns. It leads to a demornity in the protein structure
and functionality.
- Slide 10
- 3.Alternative 3' splice site and 5' splice site: Alternative
gene splicing includes joining of different 5' and 3' splice site.
Two or more alternative 5' splice site compete for joining to two
or more alternate 3' splice site. Introns are first cut at their 5'
end and then at their 3' end.
- Slide 11
- Slide 12
- Spliceosomes The molecules or molecular complexes that actually
splice RNA in the cellular nucleus are called spliceosomes. The
spliceosome is an enzymatic complex.
- Slide 13
- Structure of spliceosomes Spliceosomes are made of small
sequences of RNAs bound by additional small proteins. The small
RNAs which make up the spliceosome are small nuclear RNAs
(snRNA's). The snRNAs combine with proteins to comprise, small
nuclear ribonuclearprotein particles. The absence of individual
snRNP components can inhibit splicing.
- Slide 14
- Slide 15
- Alternative splicing A single gene can be processed to create
numerous gene products, or proteins and this process is referred to
as alternative splicing. In eukaryotes information can be stored
much more economically. Several proteins can be encoded by a single
gene, thus allowing a more varied proteome from a genome of limited
size.
- Slide 16
- Alternative splicing was first observed in the late 1970s. In
humans, over 80 % of genes are alternatively spliced. Alternate
splicing is used to create the five antibody-types from the same
gene. Alternate splicing controls sex determination in Drosophila
melanogaster flies. The gene Tra encodes a protein that is
expressed only in females.
- Slide 17
- Slide 18
- Alternative splicing and disease over 60% of human disease
causing mutations affect splicing rather than directly affecting
coding sequences. Cancerous cells show higher levels of intron
retention than normal cells, but lower levels of exon
skipping.
- Slide 19
- Splicing out introns Most introns begin with the nucleotide
sequence G-T and end with the sequence A-G. Are described as
conforming to the GT-AG rule. Within the intron is another highly
conserved sequence this region (called the branch site) is the area
that connects to the 5' end of the intron as it is cut and then
curls around to form a lariat shape. which is removed from the
maturing RNA.
- Slide 20
- mRNA splicing mechanism Splicing of mRNA is performed by
spliceosome, containing snRNPs designated U1 U2 U4 U5 U6 (U3 is not
involved in mRNA splicing).
- Slide 21
- Slide 22
- Slide 23
- Self-splicing Self-splicing occurs for rare introns that form a
ribozyme, performing the functions of the spliceosome by RNA alone.
There are three kinds of self-splicing introns. Group I Group II
Group III
- Slide 24
- Slide 25
- Other splicing events
- Slide 26
- tRNA splicing tRNA (also tRNA-like) splicing is another rare
form of splicing that usually occurs in tRNA. The splicing reaction
involves a different biochemistry Ribonucleases cleave the RNA and
ligases join the exons together.
- Slide 27
- Protein splicing Proteins can also undergo splicing. The
biomolecular mechanisms is different, but principle is the same.
Inteins instead of introns, are removed. The remaining parts,
called exteins instead of exons. Protein splicing has been observed
in all sorts of organisms, including bacteria, archaea, plants,
yeast and human.
- Slide 28
- Common errors Mutation of a splice site resulting in loss of
function of that site. Mutation of a splice site reducing
specificity. Displacement of a splice site, leading to inclusion or
exclusion of more RNA than expected, resulting in longer or shorter
exons.
- Slide 29
- Applications of gene splicing Using gene-splicing technology,
vaccines have been produced. Another application of gene spicing
technology is related to the gene involved in Vitamin B production.
Human insulin-producing genes have been spliced into plasmids.
- Slide 30
- THANK YOU MAY ALLAH BLESS U ALL