slides 16 - translation

what is translation?

reading the mRNA made during transcription and assembling amino acids in the sequence indicated by the mRNA

what all does translation require?

• amino acids

• activation of amino acids

• specific tRNAs

• ribosome

• mRNA

what is the first step in translation?

activation of amino acids

what is a codon?

triple base sequence corresponding to a particular amino acid or stop

what is an anticodon?

the complement of the codon; a region on the tRNA which recognizes the codon

what is the start codon?

AUG

what does AUG correspond with?

Met

proteins synthesized in the ribosome always start with what?

Met

Met is usually cleaved off when?

during post-translational processing

in the transfer RNA structure, where is the anticodon located?

loop at the bottom of cloverleaf tRNA which base pairs with the codon

in the transfer RNA structure, the anticodon is what to the codon?

antiparallel

what is the acceptor stem in tRNA structure?

segment at the top of the cloverleaf tRNA which attaches to the amino acid during charging

what kind of sequence is the acceptor stem?

CCA

in the ribosome binding to the mRNA, what is the Shine-Delgarno sequence?

attachment sequence in the mRNA which align the ribosome for efficient and accurate attachment

what are ribosomes?

enzymes which catalyze protein synthesis by properly aligning the mRNA and respective tRNAs

what is the structure of the prokaryotic ribosome (70S)?

• contains over 50 proteins and at least 3 RNAs

• two subunits

what are the two subunits?

• 50 S (large)

• 30 S (small)

what is the overall end result of initiation?

formation of 70S initiation complex

what is the first step in initiation?

30S subunit of the ribosome binds mRNA, initiator tRNA, and initiation factors 1,2,3 (IF-1,2,3)

what does initiator tRNA carry?

N-formylmethionine

activation by binding for the formyl groups is essential for what?

initiation

what do IF3 and IF1 do?

they are thought to help free the 30 S subunit

what does IF2 do?

it is a G-protein which is associated with the charged initiator tRNA

what is the second step of initiation?

5 end of mRNA is bound by the 30 S subunit

how is proper alignment assured?

by binding to the shine-delgarno sequence

where is the initiator tRNA placed?

next to the P site

the 30S complex has increased affinity for what?

for the 50S subunit

what is step 3 of initiation?

• binding of the 50S subunit

• release of IF3

what are the 3 binding sites in the ribosomal complex?

• P site

• A site

• E site

what is the P site?

“peptidyl site” because this is the site in which the extended peptide will ultimately “end up”

what is the A site?

“aminoacyl site” because this is the binding site for the incoming amino acid

what is the E site?

“exit site” because it is the site where the “empty” tRNA molecule with exit

what is the first step in elongation?

AA-tRNA binding

where is the polypeptide chain attached?

to a tRNA in the P site

where is the next tRNA with corresponding next amino acid put?

aligned for entry into the A site with the help of the elongation factor ER-Tu (a G protein)

where is the tRNA delivered?

to the A site

what is step 2 of elongation?

peptide bond formation

what does the release of EF-Tu allow for?

proofreading twice before the amino acid is added to the growing peptide

the existing polypeptide chain in the in the P site is moved where?

it is transferred to the amino acid in the A site and a peptide bond is formed

what enzyme is needed to complete this task?

a component of the 50S subunit called peptidyltransferase

what is the 3rd step of elongation?

translocation

what does the translocation process involve?

switching from a P site A site situation to a hybrid PA site

translocation happens with the help of another G protein, which is?

EF-G

the empty tRNA is transferred to what site?

the E site

the extended peptide is transferred where?

P site

what is the 4th step of elongation?

tRNA release. the empty tRNA is release

are there any tRNA stop molecules?

NO

what protein causes tRNA to stop growing?

proteins called release factors (RFs) recognize and bind stop codons in the A site

how many different RFs are known?

3

how do RFs do this process?

they are G proteins which utilize the hydrolysis of GTP to release the growing peptide from the tRNA