chapter 40 Flashcards
the 50s subunit of the ribosome is composed of
34 proteins and a 23S RNA and a 5S RNA
the 30S subunit contains
21 proteins and a molecule of 16S RNA
what is the actual catalyst for protein synthesis
ribosomal RNA
what are the 3 tRNA binding sites
1.The A (aminoacyl) site binds the incoming tRNA.
2.The P (peptidyl) site binds the tRNA with the growing peptide chain.
3.The E (exit) site binds the uncharged tRNA before it leaves the ribosome.
what happens at the A site
aminoacyl site binds the incoming tRNA
what happens at the P site
peptidyl site binds the tRNA with the growing peptide chain
what happens at the E site
exit site binds the uncharged tRNA before it leaves the ribosome
what is the polypeptide channel
a tunnel that connects the P site to the back of the ribosome through which the peptide exits the ribosome during synthesis
what is a shine-dalgarno sequence
untranslated region that contains information which directs protein synthesis machinery to the start site
the shine-dalgarno sequence is what rich
purine rich (A and G)
what is the initiator amino acid in most proteins in bacteria
N-formylmethionine
what do initiation factors do
assist in the assembly of protein-synthesizing machinery
what do IF1 and IF3 do
bind the 30s subunit to prevent premature binding to the 50S subunit
what does IF2 do
in cooperation with GTP, delivers fMet-tRNA to the mRNA which is already correctly positioned on the 30S subunit by the SD sequence to form the 30S initiation complex
how does the 70S initiation complex form
50S subunit binds, leading to the hydrolysis of GTP by IF2 and departure of the initiation factors
what is accommodation
If the anticodon pairs with the codon, GTP is hydrolyzed, and EF-Tu-GDP
departs, with the A site now occupied by the appropriate aminoacyl tRNA
what does EF-Tu do
bring the appropriate aminoacyl-tRNA to the A site (with the help of GTP)
what does EF-Ts do
induces release of GDP from EF-Tu which is then replaced by GTP
RECYCLES EF-Tu!!!!!!
what is the peptidyl transferase center and what happens there
peptide bond formation is catalyzed on the 23S (part of the 50S subunit)
is peptide bond formation exergonic
YES, no energy is needed for input
elongation factor G is called what
translocase
what does translocase do
uses the energy of GTP hydrolysis to translocate the mRNA by one codon
what is translocation for dummies
when the guy (translocase) pushes the tRNAs over by one site
the empty tRNA goes to the exit site to prepare to leave, the growing polypeptide chain is bumped over into the P site, and the A site is empty and ready for a new tRNA molecule
what are the 3 stop codons
UAA, UGA, UAG
what recognizes stop codons
release factors
what does release factor 1 do
recognizes UAA/UAG
what does release factor 2 do
recognizes UAA/UGA
what does release factor 3 do
FR1/FR2 release
what do release factors do
RFs recognize stop codons and facilitate the attack of a water
molecule on the ester linkage between the polypeptide chain and
tRNA in the P site, releasing the complete protein.
what do EF-G and ribosome release factor (RRF) do
catalyze the
dissociation for the ribosome, mRNA, and attached tRNA in a
reaction facilitated by GTP hydrolysis.
how is eukaryotic translation more complex than prokaryotic
- ribosomes are larger
- starts with methionine
- initiator codon is always the FIRST AUG from the 5’ end of the mRNA
- mRNA is circular because of interactions between proteins that bind the 5’ cap and polyA tail
- eukaryotes have only 1 release factor
- RNA synthesis occurs in the nucleus in eukaryotes
