Transcript RNA polymerases

Gene Structure
and Transcription
J a v a d
F a s a
J a m s h i d i
U n i v e r s i t y
o f
M e d i c a l
S c i e n c e s ,
N o v e m b e r
2 0 1 5
How Cells Read Their Genome?
How cells decode and use the information in their genomes?
The DNA in genomes uses RNA as an intermediary
Transcription  Translation (Central Dogma)
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From DNA to Protein
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Gene
Unit of DNA that contains the information to specify synthesis of a
single polypeptide chain or functional RNA
The vast majority of genes are protein coding genes
There are many other genes which don’t code proteins
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Transcription
DNA 
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Transcription
 RNA
DNA Strands
Sense or Non-template
Antisense or Template strand
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Gene Structure
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Gene Structure
Transcription region
5´UTR and 3´UTR
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Translated region
Upstream, Downstream
Promoter
Gene Expression
The process by which information from a gene is used in the synthesis of a
functional gene product
This could be a protein or some functional RNA
The difference between various cells in a specific organism is due to
difference in gene expression
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Expression with Different Efficiencies
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Transcription Principals
Transcription begins with the opening and unwinding of a small portion of the DNA
double helix
One of the two strands of the DNA double helix acts as template
The RNA nucleotide sequence is determined by the complementary base-pairing
Catalyzed by RNA polymerases, add rNTPs
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Transcription Principals
Always 5´3´
RNA polymerases can start an RNA chain without a primer
About one mistake for every 104 nucleotides
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Transcription of two genes under the electron microscope
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Different Directions of Transcription
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RNA Splicing
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Alternative Splicing
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Capping
After 20 to 30 nucleotides have been transcribed
Protect the RNA transcript from degradation by
endogenous cellular exonucleases
Facilitate transport of the mRNA to the cytoplasm and
attachment to the ribosomes
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Polyadenylation
Approximately 200 adenylate residues-the so-called poly(A) tail-are added to the mRNA,
Facilitates nuclear export and translation
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TYPE OF RNA
FUNCTION
mRNAs
messenger RNAs, code for proteins
ribosomal RNAs, form the basic structure of the
ribosome and catalyze protein synthesis
rRNAs
tRNAs
transfer RNAs, central to protein synthesis as adaptors
between mRNA and amino acids
snRNAs
small nuclear RNAs, function in a variety of nuclear
processes, including the splicing of pre-mRNA
snoRNAs
small nucleolar RNAs, used to process and chemically
modify rRNAs
miRNAs
microRNAs, regulate gene expression typically by
blocking translation of selective mRNAs
siRNAs
small interfering RNAs, turn off gene expression by
directing degradation of selective mRNAs and the
establishment of compact chromatin structures
Other noncoding RNAs
function in diverse cell processes, including telomere
synthesis, X-chromosome inactivation, and the
transport of proteins into the ER
Transcription Initiation in Eukaryotes
Transcription Initiation in Eukaryotes Requires Many Proteins
RNA Polymerase II Requires General Transcription Factors (TFIIs)
Eukaryotic transcription initiation must deal with the packing of DNA
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Structures of Prokaryotic And Eukaryotic mRNA Molecules
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Steps leading from gene to protein in eukaryotes and bacteria
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