What do epigenetic changes involve?
both chemical and structural modifications to the chromatin and DNA
What happens in the cytoplasm in terms of mRNA?
the stability of mRNA is controlled and its translatability
DNA cannot function on its own because-
it can not perform the functions that proteins does, hence the production of proteins
Define transcriptional control-
when and how often a gene sequence is copied into RNA
What is a transcription factor?
they modulate gene expression to turn transcription on or off
What are two categories of transcription factors?
-general (basal)
-specific
What is a general (basal) transcription factor?
they are abundant proteins that assemble on all genes transcribed by RNA polymerase II
what is the function of a general (basal) transcription factor?
-important for basal activity of the promoter
-positions and activates RNA polymerase II at the start of the protein-coding sequence
Why are general transcription factors needed?
priming transcription
Formation of the _____________ complex requires several _________ in addition to RNA polymerase ____
transcription, proteins, II
What is a specific transcriptional factor?
gene regulatory proteins that present in few copies in individual cells.
What is the function of a specific transcriptional factor?
they bind to a specific DNA nucleotide sequence an allowing the genes that they control to be activated or repressed
Why are specific transcription factors needed?
they are designed to bind specific DNA sequences and regulate gene transcription
Transcriptions factors have a-
modular design consisting of at least 2 distinct domains (DNA binding and transcription activating domains)
DNA binding consists of-
the structural notif that recognizes specific DNA sequences
Transcription activating is-
the domain that contracts the transcriptional machinery and accelerates the rate of transcription initiation by accelerating the assemble of the general transcription factors at the promoter site
Specific transcription factors influence the-
number of RNA polymerases that bind to DNA and initiate transcription.
What is a spliceosome
removes noncoding segments (introns) from pre mRNA to make mature mRNA
RNA processing control occurs-
in the nucleus and the subsequent processing is necessary to control the number of mRNA molecules that are translated
why is the addition of the 5' cap structure so important?
- a mRNA to be translated in the cytoplasm
-protects the growing RNA chain from degradation in the nucleus by 5' exonucelases
What do exonucleases do?
degrade RNA
kill RNA primers
5' end of RNA is capped by a
methyl guanosine residue, which protects it from degradation (by 5' exonucleases) during elongation of RNA
The 5' cap also helps-
the transcript binds to the ribosome during protein synthesis.
The addition of a poly(A) tail occurs where?
3' end (abt 200 adenine residues are added)
Why is the polyadenylation reaction important?
it is important from RNA stability and prevents premature degradation at the 3'end
What specifically does the poly(A) tail protect from?
premature degradation by 3' exonucleases.
since introns are noncoding they are
spliced
Since exons are coding they can-
make different protein from one DNA double helix
The splicing of introns occurs because-
the RNA will not leave the nucleus until the post-transcriptional modification are done, this makes mature mRNA
Splice sites are-
present within the gene and delineate the introns
Splice site sequences are found in
pre mRNA
What is alternative splicing?
the ability of genes to form multiple proteins by joining different exon segments in the primary transcript i
mature mRNA exits through the
nuclear pore complex
All transcripts have a ______________ in the cell
finite life time (they get degraded, short life)
The steady-state level of individual RNA species in a cell is determined by:
rate of transcription and rate of decay
what is a half life?
a measure of degrative rate for a certain mRNA, the period it takes to degrade an RNA population to half its initial concentration.
Unstable mRNAS-
usually code for regulatory proteins whose production levels change rapidly in cells
Stable mRNAs-
usually code for housekeeping proteins
What sequence found in the 3' untranslated region (UTR) is a signal for degradation?
AUUUA
The more times AUUUA is present the-
shorter the lifespan of mRNA