Gene Expression: Transcription- lecture #19 Flashcards
DNA –> mRNA is what?
transcription
mRNA –> protein is what?
translation
what is the central dogma of biology?
DNA –> mRNA –> protein
descriptor of transcription and translation
what contains information for the amino acid sequence?
genes
are all proteins enzymes?
no, there are diverse functions
one gene can be transcribed into RNA but RNA is not always used to produce protein, why?
RNA thats made can be a dead end/ functional RNA they stop after making RNA cause they only have one job with RNA
what is functional RNA?
rRNA, tRNA
what do many proteins consist of?
many polypeptide subunits
what are polypeptide subunits?
peptide units assembled into protein normally in the quaternary structure
the different structures (primary, secondary, tertiary, quaternary)
what is an example of a peptide subunit?
hemoglobin
how can one gene be used to produce closely related polypeptides?
via alternative splicing
overall what forms RNA in transcription?
DNA template strand of a gene forms RNA
what separates the two DNA strands in transcription?
RNA polymerase
while separating the DNA strands what does RNA polymerase also do? what does it form?
covalently joins nucleotides to one another according to the DNA template forming phosphodiester bonds
what sequence is complementary to the DNA template?
RNA sequence
RNA polymerase can only join nucleotides in what direction? (3’ to 5’) or (5’ to 3’)
5’ to 3’
what is a primer?
RNA
transcription begins at sites on the DNA template called what?
promotors
how does the promotor get initiated?
RNA polymerase attaches and initiates transcription
what ends the transcription in prokaryotes?
terminator sequences
(more complex in eukaryotes because they’re more complicated)
why do we need a terminator in transcription?
or else you’ll create too much information that is not relevant to the protein you want to make
(don’t want to waste energy for no reason!)
what does upstream refer to?
regions before the gene
what does downstream refer to?
regions after the gene
are promoter sequences located upstream or downstream?
always upstream
what is the transcription unit?
the stretch of DNA that is transcribed (before the gene)
how many RNA polymerase do prokaryotes have?
one
how many RNA polymerase do eukaryotes have?
more than one
what assembles mRNA (protein)?
RNA polymerase II
what do RNA polymerase I and III assemble?
RNA that will not be made into protein
what are the 3 stages of transcription?
initiation
elongation
termination
what contains the transcription start point?
promoter region upstream of the gene
what does the promoter extend upstream from the transcriptional start point?
several dozen nucleotides
why does RNA polymerase bind at such a precise location on the promoter?
if its not in the right location you will miss/lose information
what determines where transcription begins and which of the two strands will serve as a template?
RNA polymerase orientation on the promoter
in prokaryotes RNA polymerase binds to what directly?
the promoter, doesn’t need help
what factors mediate the binding of RNA polymerase at the beginning of transcription?
transcription factors
when does RNA polymerase II bind?
once transcription factors are in position on the promoter
what is the process of RNA polymerase called?
transcription initiation complex
what is a TATA box?
series of 4 nucleotides
important in forming the initiation complex
Once the RNA polymerase binds what happens?
DNA unwinds and transcription begins
what happens during elongation?
RNA polymerase keeps moving along the DNA template untwisting the sequence
how many DNA nucleotides of the template are exposed at a time in elongation?
10-20 DNA nucleotides
why does elongation not expose the whole gene at once?
too disorganized
why does elongation not expose the whole gene at once?
too disorganized
elongation adds nucleotides at what end of the growing RNA segment?
3’ end
what does newly synthesized RNA do?
peels away from the DNA template
what happens when the RNA peels away from the DNA template?
double helix reforms
how many nucleotides per second are transcribed in eukaryotes?
40 nucleotides per second
why do many RNA polymerase enzymes work on a DNA template at once?
increases the number of mRNA transcripts produced
increases the amount of protein produced
how does termination occur in prokaryotes?
occurs via a terminator sequence in DNA
(causes the polymerase to detach once it has been transcribed)
how does termination occur in eukaryotes?
RNA polymerase II transcribes a polyadenylation signal on the DNA template (AAAAAA)
where does termination occur in eukaryotes?
pre-mRNA (immature/incomplete mRNA)
when do proteins will cut the mRNA free from the polymerase after how many nucleotides?
10-35 nucleotides after the transcription of this sequence
when does further processing occur after the mRNA is cut?
after the pre-mRNA is released
(processed further to become mature mRNA then become protein)
where is pre-mRNA made and modified?
eukaryotic nucleus
RNA processing modifies what?
5’ end and the 3’ end
interior of the mRNA molecule
what does splicing do?
removes internal segments of the mRNA
what happens to the remaining segments of mRNA do?
they’re joined together
what does the 5’ end of the mRNA transcript recieve?
5’ cap
guanine nucleotide= 5’ cap
what does the 3’ end of the mRNA transcript recieve?
poly-adenine tail
how many adenine nucleotides will be added to the 3’ end?
50-250 adenine nucleotides
new mRNA (mature) is exported from the nucleus and used for what?
used in the cytoplasm for translation
what is apart of the coding section?
mRNA
what do modifications do? (2)
prevent cytoplasmic degradation of the mRNA
allow the ribosome to recognize the mRNA segment and attach
why do we put all these extra groups (modifications) into the mRNA?
because RNA viruses can infect the cell, modifications allow us to self identify RNA
what are untranslated regions (UTR)?
mRNA contains 5’/3’ UTRs
UTR: they are not translated into protein
what do untranslated regions do?
assist ribosome binding
what does RNA splicing do?
removes large chunks of mRNA in the nucleus (before export to cytoplasm)
how many nucleotides are inthe mRNA primary transcript (pre-mRNA)
~27,000
how many nucleotides are in the final mRNA (mature RNA)?
1200 nucleotides
the coding segment gets translated into protein, if the coding segment has 1200 nucleotides how many amino acids will be in the protein product?
1200/3 = 400 amino acids
what are introns?
long non-coding stretches of mRNA that are removed from the primary transcript
what are exons?
interspersed between the coding segments
they stay in the final mRNA
eventually translated into protein
what does RNA polymerase II do?
transcribes the entire DNA gene into pre-mRNA
when do introns get removed?
prior to cytoplasmic export
what is joined together to form the continuous mRNA sequence?
exons
what happens to released introns?
readily degraded
what dictates splicing?
short nucleotide sequences at the start of each intron
what are snRNPs and what do they do?
small nuclear ribonucleoproteins
Recognize the splice sites in pre-mRNA
what are snRNPs comprised of?
small nuclear RNA (snRNA) and proteins
snRNA ~150 nucleotides + protein
where are snRNPs located?
eukaryotic nucleus
what is a splicesome?
snRNPs come together with different proteins forming a splicesome
what do snRNAs do?
catalyze intron removal and are important in recognition of splice sites
what are ribozomes?
RNA with enzyme function
enzymes are normally proteins, this is an exception
what does intron RNA do?
acts to catalyze its own removal
does not require protein
according to sequence complementarity what can ssRNA do?
fold back on itself which provides necessary 3D structure
why is it important for ssRNA to fold back on itself?
forms catalytic activity
what is used in catalysis?
certain RNA bases are specifically used
what does hydrogen bonding ability of RNA do?
allows the molecule to recognize and attach to active site
RNA of spliceosome and RNA of the transcript are what to each other?
complementary to one another
what does 1 gene allow for?
2 or more polypeptides
what is alternative splicing?
removal of different exons creates protein variants
are introns always removed?
yes
why is alternative splicing highly efficient?
allows us to have fewer genes (simplified genome) than we would otherwise require in our genome
the number of proteins that we can produce far outnumbers what?
the number of genes that we encode
what is alternative splicing likely responsible for?
the various domains of a particular protein
what are domains?
different axons give us different domains
look at pic on brainscape folder (domains)
