L10 - translation Flashcards
what is translation
the process of translating mRNA to amino acids
how was the genetic code deciphered
- synthesised poly - U mRNA and added to tube with everything required for transcription (ribosomes, AAs)
- only one AA radiolabelled per tube
- incubated the filtered to wash off unbound AAs
- radioactive signal significantly higher for phenylalanine for the poly - U strand
- repeat with other poly base combinations
- different combinations eg ACC , the order could not be known for sure so to combat this the synthetic DNA was made in proportions and then calculated. eg 75% A and 25% C
what is start codon and AA
in P and E
AUG
MET in eukaryotes
fMET in prokaryotes
how was the genetic code for codons such as ACC deciphered?
different combinations eg ACC , the order could not be known for sure so to combat this the synthetic DNA was made in proportions and then calculated. eg 75% A and 25% C
CCC would be : 0.25 x 0.25 x 0.25 = 1.5%
what is required for translation
ribosome
tRNA
what transcribes tRNA in Eukaryotes
DNA pol 3 in
where is rRNA transcribed
nucleolus
describe tRNA structure
internal base pairing clover leaf structure unusual bases (D) ends with CCA at 3' end that attaches to AA each contains 1 anticodon
how many tRNA molecules are there and what does this mean for its bonding to the codon
- 22 tRNAs and 61 AA codons
- means some tRNAs recognise more than 1 codon (wobble pairing)
explain wobble pairing mechanism
the first 2 bases in codon match, but the 3rd is less critical so can follow non watson crick base pairing without altering AA sequence
what is the bond between tRNA and AA
ester
what happens to tRNA when AA attaches
tRNA becomes charged (activated)
can tRNA attach any AA?
no , it can only attach the AA that is appropriate for its anticodon
what are aminoacyl-tRNA-synthetases
enzymes that ‘load’ tRNA with correct AA
how is the correct AA attached to tRNA?
by aminoacyl - tRNA - synthetases
how is the tRNA for phenylalanine written
tRNA phe
how is the activated tRNA for phenylalanine written
phe - tRNA phe
describe prokaryote ribosome structure
70s complex
small subunit - 30s
-contains 16s rRNA
large subunit - 50s
what happens at A site of ribosome
new AAs delivered by tRNA
what happens at P site
where new polypeptide chain forms
what happens at E site
where tRNA leaves ribosome
explain process of translation initiation (prokaryotes)
- initiation factors (IF1 and IF3) bind to small subunit
- this complex then binds to mRNA
- first tRNA (start codon) (fMet - tRNA fmet) enters P site in complex with IGF2-GTP
- 16s rRNA binds to shine delgarno sequence in 5 ‘ UTR region of the mRNA to line up the first AA with the AUG start codon
- large subunit binds
- GTP hydrolysis
- IFs and GDP + Pi leave released
define UTR
untranslated region
what is shine delgarno sequence and its function
prokaryotes
sequence in 5’UTR region of mRNA
lines up start codon of mRNA (AUG) to first activated tRNA (fmet - tRNA fmet)
define process of translation elongation
- next tRNA binds to EF-Tu - GTP (elongation factor) and enters A site
- if anticodon is complimentary to codon, conformational change causes GTP hydrolysis
- EF-Tu , GDP + Pi released
- peptidyl transferase process (new AA is placed underneath the pp)
- EF-G - GTP binds to ribosome, GTP hydrolysis causes a shape change moving the ribosome along
- original tRNA leaves through E site
ribosome now only has P site occupied
explain peptidyl transferase process
new AA is placed ‘underneath’ PP chain
NH2 group from new AA attacks carbonyl group of existing AA forming peptide bond
what happens if the tRNA anticodon isnt complimentary to the mRNA codon
the tRNA will just diffuse away
explain process of translation termination
- stop codon presented by mRNA
- release factor (RF1 , RF2) mimics shape of tRNA and enters A site with a h2o molecule
- pp is hydrolysed from the final tRNA using h2o molecule
- ribosome disassembles using IF3 and ribosomal recycling factor
how does ribosome disassemble during translation termination
using IF3 and ribosomal recycling factor
how is old tRNA released from ribosome once a new AA has been added
- EF-G - GTP binds to ribosome, GTP hydrolysis causes a shape change moving the ribosome along
- original tRNA leaves through E site
ribosome now only has P site occupied
define polycistronic
an mRNA strand that may encode several proteins
are prokaryotes or eukaryotes polycistronic
prokaryotes
eukaryote mRNA only encodes 1 protein
