Transcription & Translation Flashcards
Outline the stages of transcription.
INITIATION:
Promoter recognition, transcription initiation factors binds, and RNA pol binds
ELONGATION:
5’ -> 3’ growth of mRNA
TERMINATION:
Sequence dependent end of mRNA production (stop codon read)
What are the different types of RNA in eukaryotes, what are their functions, and in what proportions are they present?
mRNA (~2%)
RNA pol II
100,000s of kinds, few copies of each
rRNA (~80%)
RNA pol I
Few kinds, many copies
tRNA (~15%)
RNA pol III
100s of kinds, very many copies of each
What is the definition of transcription? What are the enzymes, template, and activated substrates used?
Process by which DNA code is transcribed (copied) into an RNA message in the nucleus
Enzyme: RNA pol
Template: DNA (complementary to non-coding strand, therefore a copy of the coding strand)
Activated substrates: NTPs
What is the definition of a promoter? What is a common example of a eukaryotic promoter?
Area of gene upstream of the open reading frame which regulates transcription.
Include sequences for binding of transcription factors and RNA pol, and activators and repressors.
TATA box at -30 in eukaryotes
What is the definition of a transcription factor?
Protein required for recognition by RNA pol of specific stimulatory sequences in eukaryotic genes
How is eukaryotic mRNA post-transcriptionally modified?
Pre-mRNA —-> CAPPING & POLYADENYLATION —–> primary transcript ——> SPLICING
Capping: addition of methyl-guanine cap at 5’ end (prevents degradation of RNA)
Tailing: addition of poly A tail at 3’ end (cleaved from RNA pol by specific endonucleases)
Splicing: non-coding introns removed and exons ligated together
Outline the stages of translation.
INITIATION: AUG codon recognition by special methionyl tRNA in ribosome
ELONGATION: N -> C chain growth using aminoacyl tRNAs
TERMINATION: stop codons read
What is the definition of translation? What are the enzymes, template, and activated substrates used?
Process by which the RNA message is translated into an amino acid code by tRNAs in the cytoplasm
Enzyme: (ribosome) + peptidyl transferase
Template: mRNA
Activated substrates: activated amino acids (GTP)
What is the difference between prokaryotic and eukaryotic ribosomes?
PROKARYOTIC:
30S + 50S = 70S
EUKARYOTIC:
40S + 60S = 80S
What are the important features of tRNA structure? How are tRNAS activated (charged)?
Clover-leaf model
Anticodon loop (determines code translated)
Overhang with OH
Aminoacyl-tRNA synthase + ATP = aminoacyl group bound to OH on overhang by phosphodiester bond (release of H2O)
What is inosine? What are the consequences of tRNAs which will bind to codons containing an inosine?
Inosine = aspecific base (binds to any base)
alanyl tRNA codon 3rd base is inosine (wobble position)
Allows alanyl tRNA to recognise more than one codon
What are the specific steps of elongation in translation? Is GTP needed?
First tRNA in P site, empty A site
Amnoacyl-tRNA binds into A site (GTP needed)
Peptide bond forms between aa in A site (peptidyl transferase)
Translocation of uncharged tRNA from P site, ribosome moves along mRNA, growing peptide chain + charged tRNA moves into P site (GTP needed)
What occurs in termination of translation?
Hydrolysis of bond between growing peptide chain and tRNA overhang.
Peptide chain released from ribosome
What is a polyribosome/polysome? Why are they needed?
RER: non-specific multiple ribosomes which translate mRNA strand
Speeds up translation
What is the difference between eukaryotic and prokaryotic transcription & translation?
Prokaryotes: coupled transcription-translation no post-transcriptional processing different transcription factors short-lived mRNAs simple promoters & ribosomes single RNA pol
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