tRNAs, charging reaction, translation in detail -- Lecture 15 Flashcards
structure of a transfer RNA (tRNA):
tRNA molecules (what do they do)
carry amino acids to the ribosome for incorporation into a protein
structure of a transfer RNA (tRNA):
the anticodon associates w/ the codon thru ___
complementary base pairing
structure of a transfer RNA (tRNA):
parts of a tRNA
amino acid
acceptor stem
anticodon loop
anticodon
structure of a transfer RNA (tRNA):
charged tRNA (what is it)
a tRNA w/ an amino acid attached
how does the amino acid get attached to the tRNA to make it a charged tRNA?
thru the tRNA charging reaction
tRNA charging reaction:
aminoacyl-tRNA synthetase (aaRS) enzymes bind to
an amino acid
an ATP
an ‘uncharged’ tRNA (not bound to an amino acid)
tRNA charging reaction:
using the ___, the amino acid is covalently bound to the tRNA ‘charged’
energy from ATP hydrolysis
tRNA charging reaction:
using the energy from ATP hydrolysis, the ___
amino acid is covalently bound to the tRNA ‘charged’
tRNA charging reaction:
there are ___ aaRS enzymes (one for each amino acid)
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what are the phases of translation?
initiation
elongation
termination
phases of translation:
initiation (what happens)
assembly of the ribosome/mRNA/charged-tRNAs
phases of translation:
elongation (what happens)
starts at the ‘Start’ codon (methionine)
amino acids are added until the ‘Stop’ codon
phases of translation:
termination (what happens)
the new protein is released from the ribosome
the ribosome complex disassembles
prokaryotic initiation steps:
1) ___ in the small ribosomal subunit binds the ___ at the ___ (complementary rRNA/mRNA sequences)
rRNA
mRNA
5’ ribosome binding sequence
prokaryotic initiation steps:
2) the ___ binds to the ___ codon (AUG) (methionine)
initiator tRNA
start codon
prokaryotic initiation steps:
3) the ___ subunit joins and initiation is complete
large ribosomal subunit
eukaryotic initiation steps:
1) the ___ subunit + ___ bind to the mRNA 5’ cap
small ribosomal subunit
initiator Met tRNA
eukaryotic initiation steps:
2) the complex scans the mRNA until it finds the ___ codon (AUG)
start
eukaryotic initiation steps:
3) the ___ ribosomal subunit joins the complex and ___ is complete
large
initiation
ribosome tRNA binding sites:
‘P’ site (what is it)
where the initiator tRNA binds
ribosome tRNA binding sites:
‘A’ site (what is it)
where the next tRNA binds carrying the next amino acid to be added to the protein
ribosome tRNA binding sites:
‘E’ site (what is it)
where spent uncharged tRNAs are ejected
elongation overview:
translocation (what is it)
the movement of the ribosome down the length of the mRNA
amino acids are joined by ___ bonds
covalent
proteins are always synthesized in the ___ to ___ direction
N-terminal to C-terminal direction
protein synthesis continues until the ___ codon –> then ___ of translation
‘Stop’
termination
translation termination (steps):
1) release factor (definition)
protein that binds to the stop codon (no tRNAs for the stop codons)
translation termination (steps):
2) the protein is ___ from the ribosome
released
translation termination (steps):
3) the ribosome complex ___
falls apart
(summary) steps in elongation:
initiation complete:
the initiator tRNA is bound to the P site
a new charged tRNA binds to the A site
(summary) steps in elongation:
formation of the peptide bond:
amino acid chain is transferred form the tRNA in the P site to the tRNA in the A site
the tRNA in the P site now has no AA (uncharged)
(summary) steps in elongation:
translocation:
the ribosome moves 1 codon down the mRNA
the uncharged tRNA in the P site shifts to the E site (ejected)
the tRNA in the A site shifts to the P site
a new charged tRNA can now bind to the codon in the A site
