Download MBBS (Bachelor of Medicine, Bachelor of Surgery) 1st year (First Year) Biochemistry ppt lectures Topic 26 Transcription Notes. - biochemistry notes pdf, biochemistry mbbs 1st year notes pdf, biochemistry mbbs notes pdf, biochemistry lecture notes, paramedical biochemistry notes, medical biochemistry pdf, biochemistry lecture notes 2022 ppt, biochemistry pdf.
Transcription
Objectives
Difference between DNA and RNA synthesis
Chromatin structure and gene expression
Direction of transcription
Promoter
Transcription unit
RNA polymerase
Steps of RNA synthesis
Processing of RNA (mRNA, tRNA, rRNA)
Splicing and clinical implication
Inhibitors
1
Case
? A 24 year old man who is being evaluated as a fol ow up to to a preplacement
medical evaluatio prior to starting his new job.
? He has no significant medical issues. His family history is unremarkable, but he
knows little of the health status of those family members.
? The physical examination was normal. Routine analysis of his blood included the
following results
? RBC 4.8x1066/mm3 (4.3-5.9)
? Hb: 9.6g/dl
? MCV 70microm3 (80-100)
? Serum iron 150 microgram /dl (50-170)
? Based on the data, Hb electrophoresis was performed. The results were as follows
? HbA 90% (96-98)
? HbA2 6% <3
? HbF 4% <2
2
? What is the possible diagnosis?
? What is the pathophysiology?
3
Classes of Eukaryotic RNA
4
Comparison in RNA and DNA synthesis
DNA synthesis
RNA synthesis
Nucleotide
dNTP
NTP
Primer
Yes
No
Length of the
Entire genome
Portion of the
genome to be
genome
copied
Proof reading
Highly effective
Not highly effective
function
Polarity
Yes 5' to 3'
Yes 5'to 3'
Base pairing rule
Adherence
Adherence
5
Transcription Unit
? A transcription unit is defined as that region
of DNA that includes the signals
for transcription initiation, elongation, and
termination.
6
Prokaryotic promoters share two regions of highly
conserved nucleotide sequence
Promoter: A regulatory region o DNA that serves to bind RNA polymerase
I that in turn binds other substances that wil lead to initiation of transcription
7
Adapted from Harper's Biochemistry
RNA polymerase catalyzes the polymerization
of ribonucleotides
8
Adapted from Harper's Biochemistry
Mammalian Nuclear DNA-Dependent
RNA Polymerases
9
The transcription cycle
Adapted from Harper's Biochemistry
bacterial transcription termination signal
11
Adapted from Harper's Biochemistry
Transcription control regions in an mRNA-producing eukaryotic gene
12
Adapted from Harper's Biochemistry
Transcription elements and binding factors
13
Adapted from Harper's Biochemistry
The eukaryotic basal transcription complex
14
Adapted from Harper's Biochemistry
Video on transcription
15
Some of the Mammalian RNA Polymerase I
Transcription Control Elements, Their Consensus
Sequences, and the Factors That Bind to Them
16
Three Classes of Transcription Factors
Involved in mRNA Gene Transcription
17
RNA polymerase I -mediated mRNA gene transcription is cotranscriptional y
coupled to RNA processing and transport.
18
Adapted from Harper's Biochemistry
Modification/processing of mRNA
? Addition of 5' cap
? In nucleus
? Efficient translation initiation
? Protection
? Addition of polyA tail (200)
? Cleaved about 20 nt downstream from AAUAA
recognition sequence
? Poly A polymerase
? Facilitates translation
? Protection
? Splicing
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SPLICING
? Spliceosome:
? Involved in converting the primary transcript into
mRNA
? Consists of
? primary transcript
? five snRNA
? >60 proteins containing conserved RRM (RNA
recognition ) and SR ( serine arginine) protein motif
20
Consensus sequences at splice junctions
PyNPyPyPuAPy
21
Adapted from Harper's Biochemistry
22
Adapted from Harper's Biochemistry
? Video on splicing
23
Mechanisms of alternative processing of mRNA precursors
24
Alternative promoter use in the liver
and pancreatic a-cell glucokinase (GK) genes
25
Adapted from Harper's Biochemistry
Clinical implications of splicing
? Mutation at splice site lead to improper splicing
? At least 20% of al genetic diseases result of
mutation affecting splicing
? Incorrect splicing of -globin mRNA responsible
for thalassemia
? Splice site mutation: exons removed and introns
retained
? Activate cryptic splice site
? In SLE: Antibodies against nuclear protein such as
Sn RNP
26
mRNA Editing
? Change of Coding information at the mRNA level
? the coding sequence of the mRNA differs from
that in the cognate DNA
? Example: apolipoprotein B (apoB) gene and mRNA
? In liver, synthesis of a 100-kDa apoB100.
? In the intestine synthesis of a apoB48
? Cytidine deaminase converts a CAA codon (Glutamine)in the
mRNA to UAA
? Example: glutamine to arginine change in the
glutamate receptor in trypanosome mitochondrial
mRNAs
27
Processing of rRNA
? generated from 45S long precursor molecules called pre-
rRNAs.
? 23S, 16S, and 5S rRNA of prokaryotes are produced from a
single pre-rRNA molecule,
? Eukaryotic 5S rRNA is synthesized by RNA polymerase I I
and modified separately
? pre-rRNAs are cleaved by ribonucleases to yield
intermediate-sized pieces of rRNA
? In eukaryotes, rRNA genes are found in long, tandem arrays
? rRNA synthesis and processing occur in the nucleolus, with
base and sugar modifications facilitated by smal nucleolar
RNAs (snoRNA)
28
Posttranscriptional processing of
eukaryotic ribosomal RNA by
ribonucleases (RNases).
29
Adapted from Lippincotts Biochemistry
Processing of tRNA
? made from longer precursor molecules
? Sequences at both ends of the molecule are removed
and intron is removed from the anticodon loop by
nucleases.
? attachment of CpCpA terminal at the 3 end of the
molecule by the enzyme nucleotidyl transferase.
? modification of bases at specific positions to produce
the "unusual bases" characteristic of tRNA;
methylation, reduction, deamination, and rearranged
glycosidic bonds, nucleotide alkylations
? Methylation in the nucleus, whereas the attachment of
CpCpAOH are cytoplasmic functions
30
Biogenesis of micro (mi) and silencing (si)RNAs
31
Adapted from Harper's Biochemistry
Inhibitors of RNA synthesis
Inhibitor
Source
Mode of action
Rifampicin
Synthetic
Binds to beta subunit of
derivative of
RNA polymerase which is
Rifamycin
inactivated
Alpha amanitin Toxin from
Prevents translocation of
mushroom
RNA pol II
During phospho diester
bond formation
3' ?deoxy
Synthetic
Incorrect entry into chain
adenosine
analog
causing chain termination
32
Summary
? RNA is synthesized from a DNA template by the enzyme DNA
dependent RNA polymerase
? While bacteria contain a single RNA polymerase (2)
there are three distinct nuclear DNA-dependent RNA
polymerases in mammals
? RNA polymerases interact with unique cis-active regions of
genes, termed promoters, in order to form preinitiation
complexes (PICs) capable of initiation. In eukaryotes, the
process of pol II PIC formation requires, in addition to
polymerase, multiple general transcription factors (GTFs),
TFIIA, B, D, E, F, and H.
? Transcription exhibits three phases: initiation, elongation, and
termination
33
Summary
? The presence of nucleosomes can occlude the binding of both
transfactors and the transcription machinery to their cognate
DNA cis-elements, thereby inhibiting transcription
? Most eukaryotic RNAs are synthesized as precursors that
contain excess sequences which are removed-additional
potential steps for regulation of gene expression.
? All steps--from changes in DNA template, sequence, and
accessibility in chromatin to RNA stability and translatability--
are subject to modulation and hence are potential control
sites for eukaryotic gene regulation.
34
MCQ1
? A 1-year-old male with chronic anemia is found to have
-thalassemia. Genetic analysis shows that one of his
-globin genes has a mutation that creates a new splice
acceptor site 19 nucleotides upstream of the normal
splice acceptor site of the first intron. Which of the
following best describes the new mRNA molecule that can
be produced from this mutant gene?
? A. Exon 1 will be too short.
B. Exon 1 will be too long.
C. Exon 2 will be too short.
D. Exon 2 will be too long.
E. Exon 2 will be missing
35
MCQ2
? The base sequence of the strand of DNA used as the
template for transcription is GATCTAC. What is the
base sequence of the RNA product? (Al sequences are
written 5' 3' according to standard convention.)
? A. CTAGATG.
B. GTAGATC.
C. GAUCUAC.
D. CUAGAUG.
E. GUAGAUC
36
MCQ3
? A 4-year-old child who becomes easily tired and has
trouble walking is diagnosed with Duchenne muscular
dystrophy, an X-linked recessive disorder. Genetic analysis
shows that the patient 's gene for the muscle protein
dystrophin contains a mutation in its promoter region. Of
the choices listed, which would be the most likely effect
of this mutation?
? A. Initiation of dystrophin transcription will be defective.
B. Termination of dystrophin transcription will be defective.
C. Capping of dystrophin mRNA will be defective.
D. Splicing of dystrophin mRNA will be defective.
E. Tailing of dystrophin mRNA will be defective.
37
MCQ4
? A mutation to this sequence in eukaryotic mRNA
wil affect the process by which the 3'-end poly-A
tail is added to the mRNA.
A. CAAT
B. CCA
C. GGGGCG
D. AAUAAA
E. TATA A A
38
This post was last modified on 05 April 2022