TOPIC 3 - TRANSCRIPTION AND TRANSLATION Flashcards
(22 cards)
Prokaryotes
transcription
initiation
Promoter sequences upstream of start
sigma factor recognises and brings polymerase
Prokaryotes
transcription
elongation
RNA polymerase unwinds, template strand read 3’ to 5’, ribonucleotide triphosphate added, 2 phosphates released provides energy for bond formationq
Prokaryotes
transcription
termination
Intrinsic terminator produces hairpin, instability of AU back tracks but pin causes dissociation
Rho terminator Rut sequence is transcribed, Rho binds follows RNA up to polymerase and causes dissociation
codons are read in a…
5’ to 3’ direction
Start codon
AUG
also codes for methionine
Stop codon
UAA
UAG
UGA
What is degenaracy
refers to some amino acids being able to be coded for by more than one codon. Change in 3rd base
Structure of ribosome
2 units
small subunit (30S prom, 40S euk) binds
large subunit (50S prok, 60S euk) ribozyme activity
Activation of amino acids
aminoacyl synthetase brings amino acid to tRNA and remains attached. Amino acid added at 3’ end
Amino acid activation equation
Amino acid + tRNA + ATP –> Aminoacyl-tRNA + AMP + PPi.
What is wobble binding
refers to the anticodon of tRNA being able to tolerate a mismatch of the 3rd nucleotide in a codon.
Prokaryote
translation
initiation
Within RBS, 16S rRNA complimentary to shine delgrano sequence a bit before first codon.
codon lined up with P site, IF3 blocks E, IF1 blocks A, IF2 binds to small subunit + recruits fmet for first codon
Eukaryote
translation
initiation
Complex od eIFs binds to 5’ cap and polyA tail to ensure integrity. mRNA recruited to ribosome, scanned for start codon.
Translation
elongation
A site = decodes, tRNA enters
P site = peptidyl transferase activity, chain shifts from P tRNA to A tRNA
E site = after chain shift, tRNAs move up, tRNA in E site ejected
Translation termination
Release factor enters A site when stop codon read causing dissociation
prokaryotic polyribosome
multiple ribosomes move along strand of mRNA all at one time
eukaryotic polyribosome
5’ cap binds to IF4E and PolyA tail binds to IF4G allowing ends to be held close together, forming spiral shape, ribosomes then attach
Prokaryotic post translation events
Removal of formyl group on fmet
Amino acid modifications
Eukaryotic post translational events
Proteolytic maturation
Complex folding process
Amino acid modification
Endoplasmic Reticulum post translational event
translation stalled by signal sequence binding to unfinished peptide. Cut off in ER and translation resumes into the ER. Other signals transport to GA, lysosomes and plasma membrane. If travelling out of membrane and get stuck = membrane bound proteins
What are chaperones
2 hydrophobic cavities covered by a GroES cap that help proteins fold into 3º structure. require ATP
What are proteasomes
Degrade proteins by recognising polyubiquitinated attachment to proteins. ATP driven
