RNA Transcription Flashcards
What is transcription?
The process of DNA being copied into RNA
Why does transcription result in one strand of mRNA?
Unlike DNA replication, in transcription, only one strand is being copied
what is an mRNA? Function?
Messenger RNA are Intermediates that carry genetic information from DNA to the ribosomes
What is tRNA? Function?
Transfer RNAs are adaptors between amino acids and the codons in mRNA. Bring in AAs
What is rRNA? Function?
Structural and catalytic components of ribsomes.
What is snRNA? Function?
small nuclear RNAs are structural components of spilceosomes
What is miRNA? Function?
Micro RNAs are short, single-stranded RNAs (20-22bp) that block expression of complementary mRNAs
what is RNAi?
RNA interference. Similar to miRNA and siRNA
What is the structure difference between ribose and deoxy ribose?
Ribose has 2’ hydroxy group and deoxy ribose has 2’ hydrogen group
Transcription vs replication?
Replication is the whole genome and transcription is one gene in the genome
How does RNA pol know what gene to copy?
It will bind to a promoter sequence.
How does RNA pol know when to stop transcribing?
Terminator sequence
What 3 things guide the RNA pol to the DNA?
- direction the replication fork is opening. 2 Promoter region. 3. Can only add bases in a 5’ to 3’ direction
What is a holoenzyme?
Different subunits coming together to perform a specific function.
What are the 5 core subunits of prokaryotic RNA pol?
2 alpha, 1 beta, 1 beta’, 1 omega
Sigma70 is not a core subunit but what is its funciton?
It recognizes the promoter region, specifically the TATA box of a prokaryotic gene
Where is the TATA box in a prokaryotic gene?
In the -10 region
What is a consensus sequence?
Similar but not the same. How the -35 and the -10 regions of the prokaryotic chromosome are.
How many RNA pols do prokaryotes have? Eukaryotes?
Prokaryotes have 1 and eukaryotes have 3
How does eukaryotic RNA pol find the promoter region?
Transcription factors
Does RNA pol need a 3’ OH group?
No it can just start adding bases unlike DNA pol
What are the 3 main phases of translation?
Initiation, elongation, termination
mRNA vs template strand vs coding strand
Since only 1 DNA strand is used for transcription, that strand is called the template strand. The Strand not used for translation is the coding strand. The mRNA sequence will be the same as the coding strand except with uracil since it is complementary to the template strand
Where does RNA pol start copying
Ribonucleoside 5’ triphosphate
What is the major difference between RNA pol in transcription vs DNA pol in replication?
RNA pol doesnt need a primer to start transcribing
What is promoter escape?
The sigma factor dissociates from the holoenzyme to transition from transcription initiation to transcription elongation
What is the transcription bubble?
Approximately 18 bp within the RNA pol where the double strand of DNA is unwound for transcription.
What is rho-independent termination of transcription?
The GC sequence at the end of the transcript that internally base pairs with each other and the series of the uracil at the end of the gene which allows the mRNA to dissociate from the DNA
What is rho-dependent termination of transcription?
Rho proteins have a rho recognition sequence so when RNA pol pauses at a GC rich section Rho moves to the location and unwinds the mRNA from the DNA allowing the RNA pol to dissociate and rho to dissociate
Main difference between eukaryotic and prokaryotic mRNA?
Prokaryotic mRNA can code for multiple genes (polycistronic) because they have operons and eukaryotes are monocistronic. We dont have operons
Where is the TATA box for prokaryotes vs eukaryotes?
Prokaryotic TATA box is -10 region and eukaryotic TATA box is approximately -20 to -30 region
What other regions help guide RNA pol and transcription factors to promoter region?
Octomers and GC rich regions
How do you signal initiation?
Transcription factors need to come together to form the transcription initiation complex
What do enhancer regions do for transcription?
Recruit proteins to bend DNA so the proteins can be closer to the promoter region to help recruit the transcription factors to form the complex and initiate transcription
What is the RNA pol CTD for?
For signaling proteins to come in to add modifications via phosphorylation
When are modifications made to the mRNA?
Modification happen simultaneosly during transcription. The cap is added as soon as there is enough clearance and the poly a tail is added as soon as 3’ end is released.
Why do you need to add a cap to mRNA?
For protection so it doesnt get degraded by exonucleases in the nucleus
Where does RNA pol stop transcription in eukaryotic genes?
Termination sequence, it copies a little after then falls off.
What does cleavage of the mRNA transcript past the termination sequence signal?
Signals for Poly A Adenylase to come and at the
What is the function of the poly A tail on mRNA?
It provides protection from exonucleases, stability, and transport mobility
What are the the 3 eukaryotic mRNA modifications?
5’ cap, 3’ poly A tail, splicing of introns
Do introns serve any purpose?
no, they dont code fron anything. “introns are intruders”
What is the 5’ cap specifically? Why? How does the cap connect to the transcript?
A guanine, easily methylated which protects from exonuclease recognition. 5’ to and helps initiate translation. 5’ triphosphate bridge
How does a transcript become a mature mRNA?
Splicing to remove introns
How does the spliceosome identify intron vs exon?
GU sequence at 5’ end aka E1 splice site and a AG sequence at 3’ end aka E2 splice site
What is a branch site sequence?
7 nucleotide long with an adenine group that forms lariat
What is alternative splicing?
1 original mRNA you can code different protein products depending on which exons you keep or dont keep. 1 or the other, not the same time like polycistronic.
