Download MBBS Biochemistry PPT 26 Transcription Lecture Notes

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

19

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