L5 Flashcards
methionine
new proteins always start with it, prokayotes have methylated methioloine (like chloroplasts and mitochondria)
protein backbone
nitrogen carbon NCCNCCN
nucleic acid backbone
oxygen phosphorus carbon OPOCCCOPOCCC
first time
- They Fed a lot of Uracil to a polynucleotide phosphatase, making a lot of
UUU codons - Had 20 E. coli, gave each a different radioactive amino acid
- Then Phenylalanine was synthesized by the bacteria
- Now they know UUU codes for Phe
- The same can be done with AAA and CCC
second time
- They put A and C together in different ratios and saw what amino acids got
synthesized - Based on these ratios and the ratios in which the amino acids are made,
they can theorize the order of nucleotides, and for which one they code - 6 amino acids were found using the A and C method, this means all other
amino acids need at least one G or U in the codon - G and U together did not work (because it makes a stop codon), but they
didn’t know that
ribosomes consistency
65% rna and 35% protein, together make particle weight of 70S
proteins start with
methionine, AUG
methionine in prokayotes
and mitochondria and chloroplasts, is always formylated, not in eukaryotes
inosine
Deamination of adenosine makes inosine, found in trna anticodon, can base pair with a c and u
uracil
can base pair with a and g and I
EF-Tu
he ‘chaperone’ for any tRNAs loaded with an
amino acid. EF-Tu ensures that the loaded tRNA is properly bound
to the mRNA and placed in the active site of the ribosome. Then it
hydrolyses its GTP to GDP and the ribosome can couple the growing
chain to the new tRNAAA
prokaryote translation
mrna can be used by ribosomes as soon as it exits the rna polymerase, both take place in cytoplasm
eukaryote translation
transcription in nucleus, translation in cytoplasm, mrna must be transported out of the nucleus to be translated
first elongation step
-The tRNA that carries aa2 fits into the A site of the
ribosome as a complex with EF-TuGTP.
-If tRNAaa2 is bound correctly to ribosome A site
mRNA triplet, EF-Tu will hydrolyse the GTP and let
go of the tRNA.
- EF-TuGDP will later be recycled to the GTP bound
form by its guanosine exchange factor EF-Ts. Then,
as a new EF-TuGTP it can bind a new tRNA loaded
with an amino acid until it releases it in the
ribosome.
second elongation step
-the RNA of the ‘large’ ribosomal
subunit catalyses the formation of a
peptide bond between the carboxyl
end of the growing protein bound to
the tRNA in the P (peptidyl) site and
the amino end of the newly bound
tRNAaa in the A (aminoacyl) site.
- The tRNA in the P site is now without
amino acids at its 3’ end.
third elongations step
- If all is in order, the ribosome
should translocate along the mRNA
to the next codon. This is done with
the help of the EF-G GTPase. - The ‘empty’ tRNA in the P site exits
though the E site, the polypeptide
bound to the tRNA moves from the A
site to the P site and the next tRNAaa
can bring the correct aa in the A site.
EF - G
ribosome translocate, promotes the translation step in bacterial protein syntheis,
puromycin
forms a peptide-puromycin bond in the a site of ribosomes, the production of short incomplete proteins is toxic to cells
chloraphenicol
inhibits peptidyl transfer (prokaryotic specific)
cycloheximide and neomycin
eukaryote specific, inhibit translocation
streptomycin
prokaryote specific, inhibitis initiation