Transcription Flashcards
information transfers
flow of information from genes to products is characterized by the Central Dogma of Molecular Biology
involves DNA, RNA, proteins
general, special, and unknown transfers
initiation
RNA polymerase binds to the promoter region and separates the two strand of DNA
begins at the +1 site, after the promoter
elongation
RNA polymerase moves along the template DNA in the 3’ -> 5’ direction, adding RNA bases to the 3’ RNA end
unwinded 10 bases as a time
termination
RNA polymerase transcribes a termination region (terminator)
polymerase and transcript are released from the DNA
RNA polymerase
binds to promoter, unwinds DNA, keeps DNA strands separated, adds RNA bases
DNA template
- strand of RNA is produced using DNA as a template
- genes on both sides of the genome, but only one side is a template
- the other side is a coding strand
promoter
transcription initiation site
region of DNA that RNA polymerase recognizes
contains a recognition site to which the RNA polymerase binds
transcription begins downstream of the recognition site, +1 site
termination factors
proteins (rho factors) that end transcription in prokaryotes
ρ binds near the 5’ end of the mRNA and moves along the mRNA as it’s built, towards the RNA polymerase
when RNA polymerase reaches the terminator, ρ catches up to pull the transcript away since the terminator is slower to transcribe
RNA secondary structures
terminate transcription
two-fold symmetry in a sequence causes RNA to form a hairpin fold or loop by base pairing with itself
physically pulls RNA away from DNA
mRNA lifespan
mRNA has a short lifespan
transcription produces many copies of the same mRNA
mRNA is quickly broken down
cytoplasm contains varied and abundant ribonucleases proteins that destroy single-stranded DNA
errors in transcription
transcription is error prone
RNA polymerase does not proofread
mistakes every 10-100 kb
prokaryotic mRNA
transcription and translation occur at the same time
ribosomes bind to the mRNA it is being transcribed
prokaryotic mRNA is not edited
antibiotics
target rho factors
makes cell create abundant mRNA which takes up energy from the cell, which is why rho antibiotics are still used even though still weak
eukaryotic mRNA
transcription and translation happen at separate time and places
transcription occurs in the nucleus, mRNA is edited, mRNA is transported out of the nucleus, translation occurs in the cytoplasm
occurrences between transcription and translation
mRNA splicing
pRNA divided and splicing into multiple mRNAs
ends of mRNA is modified
mature mRNA is transported into the cytoplasm
mRNA silenced by snRNAs and miRNAs
translation can be prevented by translation repressor proteins
5’ cap
added to the 5’ of the pre-mRNA as it is transcribed
chemically modified molecule of GTP
facilitates transport out of nucleus, protects against degradation by RNases, helps mRNA attach to a ribosome
poly-A tail
attached to pre-mRNA, consisting of 100-300 adenine nucleotides
an enzyme cuts the transcript at a polyadenylation sequence, poly-A tail is added to the cut end
assist in transport out of the nucleus and with the stability of the mRNA in the cytoplasm
nuclear hybrid experiment
loops in hybrids form when introns are present
DNA contains some sequences that are absent from the mature mRNA
mRNA splicing
mediated by snRNPs and takes place at consensus sequences
snRNPs bind to splice sites at the end of introns, consensus sequences
snRNPs cut the mRNA at these sites and mediate binding of the ends of the exons
conserved regions
do not vary much between genes within an organism or between organisms
spliceosome
once attached to consensus sequences, snRNPs bind to each other to form a spliceosome
cuts the pre-mRNA at the consensus sequences and joins the ends of exons together
introns are removed and degraded by RNases
snRNPs
small nuclear ribonucleoprotein particles
bind to consensus sequences within pre-mRNA by base pairing
combine enzymatic activity with sequence specificity
alternative splicing
some exons can be spliced out, resulting in different mRNAs from the same genes
generates a protein family from a single gene
happens by accident and causes disease symptoms
