Lecture 4: DNA transcription 1) What is the central dogma of molecular biology 2) What are the steps involved in transcribing a primary RNA transcript? 3) How does eukaryotic post- transcriptional processing convert a primary transcript into messenger RNA? 4) Write notes on promoters, enhancers and transcription factors
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Lecture 4: DNA transcription 1) What is the central dogma of molecular biology 2) What are the steps involved in transcribing a primary RNA transcript?
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Lecture 4: DNA transcription
1) What is the central dogma of molecular biology
2) What are the steps involved in transcribing a primary RNA transcript?
3) How does eukaryotic post-transcriptional processing convert a primary transcript into messenger RNA?
4) Write notes on promoters, enhancers and transcription factors
Central dogma of molecular biology
Transcription
DNA directed RNA synthesis
What is the biological significance?Allows selective expression of genes Regulation of transcription controls time,
place and level of protein expression
Basic structure of a geneBasic structure of a gene
Regulatory region coding region
E:\Lessons\5-4_Transc-Transl-b3\Transc-Transl.swf
Transc-Transl.htm
Transcription Transcription is the mechanism by which
a template strand of DNA is utilized by
specific RNA polymerases to generate
one of the three different types of RNA.
Types of RNA
1) Messenger RNA (mRNA)This class of RNAs are the genetic coding templates used by the translational machinery to determine the order of amino acids incorporated into an elongating polypeptide in the process of translation.
2) Transfer RNA (tRNA)This class of small RNAs form covalent attachments to individual amino acids and recognize the encoded sequences of the mRNAs to allow correct insertion of amino acids into the elongating polypeptide chain.
Types of RNA…..
This class of RNAs are assembled, together with numerous ribosomal proteins, to form the ribosomes. Ribosomes engage the mRNAs and form a catalytic domain into which the tRNAs enter with their attached amino acids. The proteins of the ribosomes catalyze all of the functions of polypeptide synthesis
3) Ribosomal RNA (rRNA)
Where does transcription take place?
Step 1: transcribing a primary RNA transcript
Step 2: modification of this transcript into mRNA
Transcription in eukaryotes
Step 1 - overview
A.Initiation
B.Polymerisati
on
C.
Termination
A) RNA polymerase binds to promoter & opens helix
B) De novo synthesis using rNTPs as substrate
Chain elongation in 5’-3’ direction
C) stops at
termination signal
A) Initiation: ENZYME
RNA polymerase holoenzyme
an agglomeration of many different factors that together direct the synthesis of mRNA on a DNA template
Has a natural affinity for DNA
Initiation: SIGNAL
specific DNA sequences called promoters
1) Region where RNA polymerase binds to initiate
transcription
2) Sequence of promoter determines direction of
RNA polymerase action
3) Rate of gene transcription depends on rate of
formation of stable initiation complexes
PROMOTERSProkaryotes
Near 5’ end of operons Pribnow box – consensus sequence TATAAT
Fig 29-10: Voet and Voet
PROMOTERSEukaryotes
Near 5’ end of genes Recognised by RNA pol II Consensus promoter sequence for
RNA polymerase Enzymes that catalyse the formation of RNA using DNA as a template De novo synthesis using rNTP as substrates 1960 – J Hurwitz & S Weiss
(RNA)n + rNTP = (RNA)n+1 + Ppi
Antibiotics such as Rifampicin / rifamycin B inhibit RNA polymerase activity