Q2-FUN11/Transcription and regulation of gene expression Flashcards
At what steps of transcription does regulation occur at?
- chromatin structure
- transciption initiation
- mRNA stability
- transcript processing
What are the 3 major functions of RNA within the cell?
copying genetic info from DNA, helps make ribosomes, help build new polypeptides
The structure of DNA is _____ while the structure of RNA is _________
DNA is located in the _______ while RNA is located in the _________
What types of RNAs are involved in transcription and translation?
mRNA, rRNA, tRNA
What are snRNAs?
small nuclear RNAs, they function in a lot of nuclear processes, inc. splicing pre-mRNA
What are ncRNAs?
they are non-coding RNAs. They function is a lot of different cellular processes, including
-regulation of gene expression.
- X-chromosome inactivation
- protein transport.
What distinct signals are encoded within the DNA sequence of a gene?
start and stop
Where does transcription start and end at?
it starts at the transcription start site (TSS, located at the end of the promoter region) and ends at the terminator site.
Each gene has a _________ promoter
unique
What are the two types of promoters?
basal promoter element and enhancer element
What is an enhancer?
Enhancers are regulatory DNA sequences that, when bound by proteins called transcription factors, enhance the transcription of a gene.
What is a basal promoter?
it is bound by RNA poly II and basal transcription factors
What is an example of a basal promoter?
TATA box - most common
2-30 base pairs from transcriptional site
can bind basal TFs and RNA poly II
What typically catalyses transcription?
RNA poly II
How does RNA poly II work?
it transcribes one of the 2 DNA strands of the gene. it reads its template from 3’ to 5’ and makes an RNA copy of 5’ to 3’.
It incorportates AGCU when making the mRNA copy of the DNA
What are the 3 stages of transcription?
initiation, elongation, termination
What happens in initiation of transcription?
RNA poly II binds to DNA and unwinds a 17-18 bp segment of the promoter. This segment is called the open complex.
Explain what happens during elongation of transcription.
RNA Pol II moves along the template until it reaches the terminator region. During this phase, an area of DNA under the RNA pol II stays unwounded. This unwounded part is called the transcription bubble and it moved along the DNA.
What 2 things happen during temination?
- transcription continues beyond the protein coding region (3’ UTR)
- endonuclease (enzyme that cleaves mRNA) cleaves abt 20 base pairs beyond the sequence
What is the primary transcript?
What are hnRNAs?
heterogenous nuclear RNA. bulk of transcribed RNAs that hasnt been processed
(processed means hasnt been 5’ capped and no poly A tail)
What are the 2 types of post translational mRNA processing?
5’ capping and 3’ poly A tail
explain 5’ capping.
add a 7-methyl-guanosine residue to the 5’ end of the mRNA.
the mRNA is catalysed by guanylyltransferase (capping enzyme) and then methylated by a methyltransferase enzyme
the 1st and 2nd nucleotides are also methylated
Why is 5’ capping important?
it protects the mRNA from degraded by exonucleases, promotes nuclear export, helps with the recognition of translational machinery
explain the 3’ poly A tail addition to the primary transcript.
after the polyadenylation signal sequence has been recognized (and endonuclease has been recruited and mRNA has been cleaved), Poly(A) polymerase adds abt 40-250 adenines to the cleaved 3’ end
What determines the stability of mRNA?
3’ UTR (untranslated region) sequence determines the stability of mRNA
What is the poly A tail on an mRNA transcript stabilized by?
poly-A binding protein (PABP), binds approx 30 residues
What happens to the poly A tail over its lifetime?
it gets gradually shortened
What happens when the PABP can no longer bind?
the 30 base pairs get degraded
Which part of the mRNA transcript gets spliced out?
introns get spliced out
what carries out the splicing of introns in an mRNA transcript?
spliceosome
what is a spliceosome made out of?
large comple of RNA and proteins, small nuclear RNAs + proteins = small nuclear ribonuceloproteins (snRNPs)
what do snRNP’s do?
the facilitate splicing by located specific seqences at the end of each intron, cutting them out, and rejoining the exons together
explain how snRNP’s work.
Explain differential splicing/exon shuffling.
it is a way for a single primary transcript to be spliced into different mRNAs, by the inclusion of diff sets of exons
https://www.youtube.com/watch?v=JEylX4cQvpg
What are the 2 types of genes?
constitutive genes and inducible genes
Are constitutive genes essential?
yes they are essential and nessessary for life
Are constitutive genes constantly expressed or only on some of the time?
since they are nessessary for life, they are continuously expressed
What are inducible genes?
inducible genes are genes that only need to be turned on some of the time when they are required
What do inducible genes determine?
development and tissue specificity
What do inducible genes allow cells to do?
they allow cells to respond to the environment
Inducible gene expression is controlled by _________________ proteins
transcription factor
what is an example of Inducible gene expression is controlled by transcription factor proteins?
steroid hormones bind to steroid receptor transcription factors. these form a homodimer that finds and binds to certain DNA sequences
transcription factors are proteins that bind to a specific ________ in the gene promoter
DNA sequence
Transcription factors control the rate of ______
transcription
What on the transcription factor determines the rate of transcription?
binding sites
What do miRNAs do?
they are small strands of RNA (20-25 nucleotides) that regulate gene expression
miRNAs are transcribed from _____________
DNA
do miRNAs make proteins?
no they are non-coding RNA
the primary function of miRNA is to ________ gene expression
down regulate
what are the 2 ways miRNA blocks gene expression?
it promotes RNA degradation by binding to complementary sequences in 3’ UTR and induces degradation
it binds to mRNA and blocks translation
