RNA processing is the modification of primary RNA transcripts into mature RNA molecules. It involves removal of introns through splicing and addition of modifications like 5' capping, 3' polyadenylation tail, and RNA editing. Alternative splicing allows a single gene to produce multiple protein isoforms by selective inclusion or exclusion of exons from the final mRNA.
RNA splicing, in molecular biology, is a form of RNA processing in which a newly made precursor messenger RNA transcript is transformed into a mature messenger RNA. During splicing, introns are removed and exons are joined together.
This presentation is about the transcription machinery that is required for the transcription in eukaryotes. The comparison between the transcription factors involved in prokaryotes and eukaryotes. The initiation of transcription and how it helps in producing a mRNA.
RNA splicing, in molecular biology, is a form of RNA processing in which a newly made precursor messenger RNA transcript is transformed into a mature messenger RNA. During splicing, introns are removed and exons are joined together.
This presentation is about the transcription machinery that is required for the transcription in eukaryotes. The comparison between the transcription factors involved in prokaryotes and eukaryotes. The initiation of transcription and how it helps in producing a mRNA.
Gene regulation in eukaryotes in a nutshell covering all the important stages of gene regulation in eukaryotes at transcriptional level, translation level and post-translational level.
Dna supercoiling and role of topoisomerasesYashwanth B S
supercoiling is one of the important process to condenses the huge amount of DNA to fit inside the histone and its also plays a role during the replication ,transcription etc..,these activities is carried out by an enzyme called topoisomerases.
it describes transcription with simple diagram and animation. its steps and inhibitors are described for both eukaryotes and prokaryotes. it will be easily understood by UG students . post transcriptional modification of all the RNA are also described with diagrams.
Eukaryotic transcription is carried out in the nucleus of the cell and proceeds in three sequential stages: initiation, elongation, and termination. Eukaryotes require transcription factors to first bind to the promoter region and then help recruit the appropriate polymerase.
Gene regulation in eukaryotes in a nutshell covering all the important stages of gene regulation in eukaryotes at transcriptional level, translation level and post-translational level.
Dna supercoiling and role of topoisomerasesYashwanth B S
supercoiling is one of the important process to condenses the huge amount of DNA to fit inside the histone and its also plays a role during the replication ,transcription etc..,these activities is carried out by an enzyme called topoisomerases.
it describes transcription with simple diagram and animation. its steps and inhibitors are described for both eukaryotes and prokaryotes. it will be easily understood by UG students . post transcriptional modification of all the RNA are also described with diagrams.
Eukaryotic transcription is carried out in the nucleus of the cell and proceeds in three sequential stages: initiation, elongation, and termination. Eukaryotes require transcription factors to first bind to the promoter region and then help recruit the appropriate polymerase.
The process by which an RNA copy of a gene is made or it’s a DNA dependent RNA synthesis.
Transcription resembles replication
In its fundamental chemical mechanism
Its polarity (direction of synthesis)
Its use of a template
Transcription differs from replication
It does not requires a primer
It involves only limited segments of a DNA molecule
Within transcribed segments only one DNA strand serves as a template for synthesis of RNA.
1.Definition
2.Transcription is selective
3.Transcription in Prokaryotes
•Initiation
•Elongation
•RNA polymerase vs DNA polymerase
•Termination
4.Transcription in Eukaryotes
•Initiation
•Elongation
•Termination
•Post transcriptional modifications
Transcription and synthesis of different RNAs
Processing of RNA transcript
Catalytic RNA
RNA splicing and Spliceosome
Transport of RNA through nuclear pore
Translation and polypeptide synthesis
Posttranslational modification
Protein trafficking and degradation
Antibiotics and inhibition of protein synthesis.
A hyperlinked and animated PowerPoint presentation on DNA transcription, its stages, units, etc.
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Protein synthesis is the process whereby biological cells generate new proteins. Translation, the assembly of amino acids by ribosomes, is an essential part of the biosynthetic pathway, along with generation of messenger RNA (mRNA), aminoacylation of transfer RNA (tRNA), co-translational transport, and post-translational modification. Protein biosynthesis is strictly regulated at multiple steps. They are principally during transcription (phenomenon of RNA synthesis from DNA template) and translation (phenomenon of amino acid assembly from RNA). The cistron DNA is transcribed into the first of a series of RNA intermediates. The last version is used as a template in synthesis of a polypeptide chain. Protein will often be synthesized directly from genes by translating mRNA. A proprotein is an inactive protein containing one or more inhibitory peptides that can be activated when the inhibitory sequence is removed by proteolysis during post translational modification. A preprotein is a form that contains a signal sequence (an N-terminal signal peptide) that specifies its insertion into or through membranes, i.e., targets them for secretion. The signal peptide is cleaved off in the endoplasmic reticulum. Preproteins have both sequences (inhibitory and signal) still present. In protein synthesis, a succession of tRNA molecules charged with appropriate amino acids are brought together with an mRNA molecule and matched up by base-pairing through the anti-codons of the tRNA with successive codons of the mRNA. The amino acids are then linked together to extend the growing protein chain, and the tRNAs, no longer carrying amino acids, are released. This whole complex of processes is carried out by the ribosome, formed of two main chains of RNA, called ribosomal RNA (rRNA), and more than 50 different proteins. The ribosome latches onto the end of an mRNA molecule and moves along it, capturing loaded tRNA molecules and joining together their amino acids to form a new protein chain.
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Nutraceutical market, scope and growth: Herbal drug technologyLokesh Patil
As consumer awareness of health and wellness rises, the nutraceutical market—which includes goods like functional meals, drinks, and dietary supplements that provide health advantages beyond basic nutrition—is growing significantly. As healthcare expenses rise, the population ages, and people want natural and preventative health solutions more and more, this industry is increasing quickly. Further driving market expansion are product formulation innovations and the use of cutting-edge technology for customized nutrition. With its worldwide reach, the nutraceutical industry is expected to keep growing and provide significant chances for research and investment in a number of categories, including vitamins, minerals, probiotics, and herbal supplements.
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
3. RNA (Ribonucleic Acid)
RNA is much more abundant than DNA
There are several important differences between
RNA and DNA.
The pentose sugar in RNA is ribose, in DNA it’s
deoxyribose.
In RNA, uracil replaces the base thymine (U pairs
with A).
RNA is single stranded while DNA is double
stranded.
4. Primary structure of RNA
A, C, G, and U are
linked by 3’-5’ ester
bonds between
ribose and
phosphate.
5. Secondary structure of RNA
D
A) Single stranded regions
formed by unpaired nucleotides
B) Duplex
double helical RNA (A-form with 11bp per
turn)
C) Hairpin
duplex bridged by a loop of unpaired
nucleotides
D) Internal loop
nucleotides not forming Watson-Crick base
pairs
E) Bulge loop
unpaired nucleotides in one strand,
other strand has contiguous base pairing
F) Junction
three or more duplexes separated by single
stranded regions
G) Pseudoknot
tertiary interaction between bases of hairpin
loop and outside bases
G
A
B
C
D
E
F
7. RNA STRUCTURE: 3 LEVELS OF ORGANIZATION
7
DDobbsISU-BCB444/544X:RNA
Structure&Function
Rob Knight
Univ Colorado
8. RNA TYPES & FUNCTIONS
8
Types of RNAs Function
mRNA - messenger Template for protein synthesis.
rRNA - ribosomal Component of ribosome's (protein synthesis) .
t-RNA - transfer Transfer of amino acid (protein synthesis).
hnRNA - heterogeneous nuclear Precursors & intermediates of mature mRNAs &
other RNAs (Premature mRNA).
scRNA - small cytoplasmic Signal Recognition Particle (SRP)
tRNA processing .
snRNA - small nuclear
snoRNA - small nucleolar
Participate in the splicing and transfer of hnRNA.
rRNA processing/maturation/methylation.
miRNA-micro RNA Usually endogenous, induce degradation of targeted
mRNA. that block expression of complementary mRNAs.
regulation of transcription and translation.
siRNA-small interfering RNA Usually exogenous, induce degradation of targeted
mRNA.
regulation of transcription and translation.
ncRNA-non-coding RNA
(npcRNA, nmRNA, fRNA)
all RNA other than mRNA,functional RNA molecule
that is not translated into a protein. longer than
200nt.
9. Ribosome's are the sites of protein
synthesis.
They consist of ribosomal RNA (65%)
and proteins (35%).
They have two subunits, a large one and
a small one.
Ribosomal RNA
10. Smallest RNA
The existence of tRNA was demonstrated by Hoagland in
1957.
Anticodon loop has 3 nucleotides that function as anticodon.
.
Thymine loop function as the ribosome attachment
region.
The DHU loop serves as the aminoacyl synthetase
recognition region.
Base-pairing involving H bonds.
Transfer RNA(tRNA)
12. MESSENGER RNA (MRNA)
It is a single stranded base for base complementary copy
of one DNA strand& provides information for amino acid
sequence of a polypeptide.
Carries genetic information from nucleus to cytoplasm
(Template of protein synthesis).
Present in two forms:
Active form: actively supports translation.
Inactive form: does not support translation.
.
13. Three main parts:
5’ untranslated region (5’ UTR) or leader sequence
Coding sequence, specifies amino acids to be
translated
3’ untranslated region ( 3’ UTR) or trailer sequence
14. These are catalytic RNAs that mainly participate in the cleavage of
RNA.
They are not true catalysts because they alter their own structure as a
result of catalysis.
Example: 1. RNase P is a common ribozyme that matures tRNA that acts as an
endonuclease.
2. Self-splicing introns.
Clinical applications:-
Used as therapeutic agents in correcting mutant mRNA in human cells and
inhibiting unwanted gene expression.
Kill cancer cells.
Prevent virus replication.
Gene inhibitors.
Gene amenders.
Protein inhibitors.
Immuno stimulatory RNA’s.
Ribozymes
15. Most newly transcribed RNA molecules (primary
transcripts) undergo various alterations to yield the
mature product.
(or)
RNA processing is the collective term used to
describe the molecular events allowing the primary
transcripts to become the mature RNA.
(or)
The process of modification, mainly through cleavage
& or splicing, of primary RNA transcripts so as to
release functional RNA molecules from them.
It is carried out by ribonucleases (RNases) that
cleave RNA.
What is RNA processing……!
16. These RNases not only process the RNA
transcripts, also degrade the tRNA, mRNA,
rRNA, and other RNA molecules as a part of
the normal cellular “Turnover process”.
Turnover process refers to degradation of old
molecules and the synthesis of new
molecules to replace them.
Both exo-and endo ribonuclease participate in
the turnover process.
17. Primary transcript
Mature RNA.
Nucleus or Nucleolus
Cytoplasm
RNAprocessing
Removal of nucleotides
addition of nucleotides
to the 5’- or 3’- ends
modification of certain
nucleotides
18. 1)Remvoal of nucleotides by both endonucleases and
exonucleases.
Endonucleases to cut at specific sites within a
precursor RNA.
Exonucleases to trim the ends of a precursor RNA.
2)Addition of nucleotides to 5’-or 3’-ends of the
primary transcripts or their cleavage products.
Add a cap and a poly(A) tail to pre-mRNA.
3)Modification of certain nucleotides on either the
base or the sugar moiety.
Add a methyl group to 2’-OH of ribose in mRNA
and rRNA.
19. Processing of mRNA
hnRNP
snRNP particles
5’Capping
3’Cleavage
Polyadenylation
Splicing
Pre-mRNA methylation
mRNA PROCESSING
Genetic information is transferred from
genes to the proteins they encode via a
“messenger” RNA intermediate.
20. Characteristics of the Five RNA Polymerases of Eukaryotes
Enzyme Location Products
RNA polymerase I Nucleolus Ribosomal RNAs, excluding 5S
rRNA
RNA polymerase II Nucleus Nuclear pre-mRNAs
RNA polymerase III Nucleus tRNAs, 5S rRNA, and other
small nuclear
RNAs
RNA polymerase IV Nucleus (plant) Small interfering RNAs
(siRNAs)
RNA polymerase V Nucleus (plant) Some siRNAs plus noncoding
(antisense)
transcripts of siRNA target
genes
21. MRNA PROCESSING IN
PROKARYOTES
There is little or no processing of mRNA transcripts in
prokaryotes. In fact, ribosomes can assemble proteins before
mRNA molecules have not yet been completely synthesized.
Prokaryotic mRNA is degraded rapidly from the 5’-end therefore
only be translated for a limited amount of time.
22. DNA
Cytoplasm
Nucleus
EUKARYOTIC MRNA TRANSCRIPTS ARE PROCESSED
Export
G AAAAAA
RNA
Transcription
G AAAAAA
RNA
Processing
mRNA
The mRNA then moves
out of the nucleus
and is translated in
the cytoplasm.
23. mRNA is synthesized by RNA Pol II as longer
precursors (pre-mRNA), the population of
different RNA Pol II transcripts are called
heterogeneous nuclear RNA (hnRNA).
Among hnRNA, those processed to give mature
mRNAs are called pre-mRNAs.
Pre-mRNA molecules are again processed to give
mature mRNAs by 5’-capping, 3’-cleavage and
poly adenylation, splicing and methylation.
Processing of mRNA
24. HNRNP:- HNRNA + PROTEINS
The hnRNA synthesized by RNA Pol II is mainly pre-mRNA
and rapidly becomes covered by proteins to form
heterogeneous nuclear Ribonucleoprotein (hnRNP).
The hnRNP proteins are keep the hnRNA in a single-stranded
form and to assist in the various RNA processing reactions.
25. SNRNP PARTICLES: SNRNA + PROTEINS
Eukaryotic nuclei contain many discreet small RNA
species called small nuclear RNAs(snRNAs) are
rich in the base uracil, which complex with
specific proteins to form snRNPs.
The most abundant snRNP are involved in pre-mRNA
splicing, U1,U2,U4,U5 and U6.
snRNAs are synthesized in the nucleus by RNA Pol II
and have a normal 5’-cap.
29. 5 3
5
5 3
Endonuclease cleavage occurs
about 20 nucleotides downstream
from the AAUAAA sequence.
PolyA-polymerase adds
adenine nucleotides
to the 3end.
Polyadenylation sequence
PolyA tail
AAAAAAAAAAAA....AAUAAA
AAUAAA
AAUAAA
CLEAVAGE/POLYADENYLATION
G/U
30. SPLICING
The process of cutting the pre-mRNA to remove
the introns and joining together of the exons is
called splicing.
It takes place in the nucleus before the mature
mRNA can be exported to the cytoplasm.
Most genes have their protein-coding
information interrupted by non-coding sequences
called “introns”. The coding sequences are then
called “exons”.
Introns: non-coding sequences.
Exons: coding sequences.
32. SPLICEOSOME MEDIATED SPLICING:
All the known introns begin with the dinucleotide GT
and end with the dinucleotide AG this is known as
GT-AG rule
The GT dinucleotide depicts the donor splicing site
and AG dinucleotide depicts the acceptor splicing
site
33. SPLICING – INTRON SEQUENCES
35
5 splice site 3 splice siteBranch site
IntronExon Exon
Py12N PyAGGA/CGGU Pu AGUA UACUUAUCC
Exon n ……A G G U A A G U …Intron …Y N Y Y R A Y …....Y12 N C A G N ….. Exon n+1
64 73 100 100 62 68 84 63 80 80 87 75 100 95 65 100 100
Branch Point
Yeast consensus
35. SPLICING OF PRE-MRNA
This is a
Spliceosome
Composed of five
snRNPs (U1, U2, U4, U5
and U6), other splicing
factors, and the pre-
mRNA being
assembled.
37. All noncoding introns are spliced out of a pre-
mRNA by the Spliceosome.
But not all exons are included in the final mRNA.
mRNA can undergo alternative splicing.
The selective inclusion or exclusion of exons
occur.
From one pre-mRNA can make many different
mRNA(thus different proteins)
>50% of human genes undergo alternative
splicing.
ALTERNATIVE SPLICING
39. HOWEVER, MULTIPLE INTRONS MAY BE SPLICED DIFFERENTLY
IN DIFFERENT CIRCUMSTANCES, FOR EXAMPLE IN DIFFERENT
TISSUES.
1 2 3 5Heart muscle mRNA
1 43 5Uterine muscle mRNA
Thus one gene can encode more than one protein. The proteins are
similar but not identical and may have distinct properties. This is
important in complex organisms
3 5421pre-mRNA
41. RNA EDITING
This is a form of RNA processing in which
the nucleotide sequence of the primary
transcript is altered by either
Changing residues,
Deleting residues,
Inserting residues at specific points
along the molecule
Changing RNA sequence (after transcription).
42. Apolipoprotein-B mRNA in mammalian
intestine and liver
The mammalian liver cells contain apolipoprotein-
B having 4563 amino acids.
While in intestine cells this protein has only
2152 amino acids.
In intestine cells, the codon 2153 is modified in
the mRNA , the C of this codon, CAA, is changed
to U to give rise to the codon UAA, which causes
chain termination.
A guide RNA containing a sequence that is
complementary to the correctly edited mRNA
provides a mechanism of U insertion or deletion.