L211 Aminoacyl tRNA synthetases

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aa tRNA synthetases, amino acid attachment, anticodons

aa tRNA synthetases

enzymes that charge amino acids to tRNAs. Is the ONLY entity in the cell that "knows" what the genetic code means, whereas tRNAs are just the messengers. They discriminate amino acids and recognize subsets of tRNAs.

single amino acid

In every cell, there must be at least 20 aa tRNA synthetases, which recognize a _______ each and all of the tRNAs to which it can legitimately bind.

3' end

This end and the anti-codon sequence are two recognition sites of tRNAs that are most commonly recognized.

acceptor stem

the 3' end of tRNA where the amino acid is attached; is commonly recognized by aa tRNA synth.

tRNA charging

process done by aa-tRNA synthetase that is very accurate and the ONLY step that insures proper amino acid use during translation.

activation site

site where amino acid is bound in aa-tRNA synthetase in the first step of charging; the pocket is the right SHAPE, SIZW, and CHARGE to match the amino acid.

covalent bond

after the amino acid is bound to aa-tRNA synthetase, it is ________ to the tRNA and the aa-tRNA synthetase proofreads the charged tRNA.

editing site

charged tRNA in another side/pocked of the enzyme that proofreads the amino acid attached.

ester bond

If the wrong amino acid is found attached to the 3' end of the tRNA, the _____ is cleaved, amino acid is released, but not tRNA. The tRNA moves back to the activation site and another amino acid is attached.

proofreading

reduces mischarging events down to once every 10,000 times.

wobble hypothesis

codons with different bases in their third position of the codon (FIRST position of anticodon) can sometimes be recognized by the same tRNA; meaning ONE tRNA can recognize several different codons.

second or first

If two codons code for the SAME amino acid but differ in the nucleotide in their ______ position, they are always encoded by DIFFERENT tRNAs.

flexible

The wobble hypothesis is supported by the fact that a single-stranded anticodon loop is ____ and can "wobble" enough to base pair that would not occur in a helix. The second and first positions, however, are not as flexible and need different tRNAs.

tRNA

During "wobble," instead of not base pairing, the ____ is able to base pair with the codon.

prokaryotic ribosome

Ribosome found in prokaryotes; is 5 times larger than RNAP (2.5 Daltons), is made up of 2/3 rRNAs and 1/3 ribosomal proteins, and has small and large subunits. Is 70S

large subunit

Subunit in prokaryotic ribosome that is 50S. It contains 2 rRNAs and 34 proteins, is CONSERVED between species due to its specific base pairing.

small subunit

Subunit in prokaryotic ribosome that is 30S. It contains one rRNA and 21 proteins.

16S

stem loop created from the large rRNA. Is very specific and folds into a three-dimensional shape.

scaffolding

each large rRNA provides ______ for its subunit, helping position the smaller rRNA and the ribosomal proteins.

aminoacyl

A site; site in ribosome that a tRNA first occupies.

peptidyl

P site; site in ribosome that a tRNA occupies second.

exit

E site; site in ribosome that a tRNA occupies last.

rRNA

structure and function studies of the 70S ribosome revealed that ______ were responsible for ribosome interactions with mRNA and tRNA during trnslation and for catalytic activity during peptide bond formation. (RIBOSOMES CAN ACT AS ENZYMES)

AG

Initiation requires that a ribosome attaches to a region rich with these bases; is near the 5' end of the mRNA, also known as Shine-Dalgarno sequence.

Shine Dalgarno sequence

sequence of mRNA that a ribosome initially attaches to; is near the 5' end of mRNA and is about 10 nucleotides upstream of the initiation codon; acts as a LANDING PAD for ribisome to be positioned in RIGHT PLACE and increases SPECIFICTY of binding site and affinity.

consensus sequence

The Shine-Dalgarno sequence has a weak ___________ because different RNAs are translated at different levels, making less translation. Allows VARIATION in the amount of translation of different mRNAs.

methionine

start codon that is almost always used to start translation. Two tRNAs carry this - one used ONLY for translation process and one to add methionine for ELONGATION.

initiator methionyl tRNA

tRNA that has a chemical group (formal group) attached to amino group of methionine. This happens before it is used for translation initiation, known as fMet-tRNA

formulation

this process gives rise to two met-tRNA structures to tell the two apart and makes the end of the new protein less chemically reactive; stops cleavage of new peptide chain my amino acid.

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