Ch 18 Protein Synthesis – Flashcards

the synthesis of a polypeptide using the genetic information encoded in an mRNA molecule

a complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm

the place on a ribosome that holds the tRNA carrying the next amino acid to be added to the polypeptide chain

the place on a ribosome that holds the tRNA carrying the growing polypeptide chain

the place on a ribosome where discharged tRNAs leave the ribosome

A sequence in an mRNA that is required for binding bacterial ribosomes. Aka ribosome binding site (RBS)

Amide or peptide

Ester

Phosphodiester

Hydrogen

Hydrogen and van der Waals (noncovalent bonds)

Using polysomes, the cell can produce several protein molecules on a single mRNA molecule. B/c mRNAs have an average lifetime of just a few minutes in the cell, polysomes maximize the number of proteins that can be made per minute.

The fMet-tRNA(fMet) binds directly to the P site during initiation of protein synthesis, positioned there to make the first peptide bond with a second aminoacylated tRNA that is positioned in the A site.

The synthestase recognizes the G-U base pair (b/w G3 and U70) in the amino acid arm of tRNA(Ala).

The mutant tRNA would insert Pro residues at codons that specify Ala. A mutation in tRNA(Pro) that allowed it to be recognized and aminoacylated by ala-tRNA synthetase would have similar effects.

Such changes would insert Pro residues at many inappropriate sites in polypeptides, inactivating many proteins, and thus would be lethal.

exportin and importin

Sequence on mRNA that precedes the start codon, which is complementary to a sequence on the 30S ribosomal subunit.

A complex of a ribosome with an mRNA and the initiating Met-tRNA(i)^Met or fMet-tRNA^fMET ready for the elongation steps

The process by which a partially asembled eukaryotic initiation complex slides along the mRNA until it comes to a start codon

(1) The second of three stages of RNA synthesis in which ribonucleotides are added to the 3? end of the growing RNA molecule. (2) The second of three stages of protein synthesis in which amino acids are added to the C-terminal end of the growing peptide chain.

(1) The third of three stages of RNA synthesis in which the RNA polymerase and the RNA product are released from the DNA template. (2) The third of three stages of protein synthesis in which the ribosome and the peptide product are released from the mRNA template.

Proteins required in the elongation phase of eukaryotic transcription. E.g. eEF1?, eEF1??, eEF2, EF-G, EF-Ts, and EF-Tu.

An enzyme in the ribosome responsible for peptide bond formation during translation.

Third step in elongation. Ribosome moves one codon along mRNA and dipeptide is translocated from A site to the P site. When this occurs again, the empty tRNA will be ejected.

aka *Release Factors* Protein factors required for the release of a completed polypeptide chain from a ribosome; e.g. RF-1, RF-2 and RF-3

aka *termination factors*; Protein factors required for the release of a completed polypeptide chain from a ribosome; e.g. RF-1, RF-2 and RF-3

aka * transfer-messenger RNA* A bacterial RNA that has the properties of tRNA at its 5' end and the properties of an mRNA (incl stop codon) at it's 3' end; When aminoacylated, the 5' end can bind in the A site of a ribosome stalled on a truncated mRNA, and the 3' end can serve as a template for continued Xlation through a termination codon that recruits the termination factors required for proper termination and ribosome recycling.

An amino acid sequence, often at the amino terminus, that signals the cellular fate or destination of a newly synthesized protein.

a protein-RNA complex that recognizes a signal peptide as it emerges from a ribosome and helps direct the ribosome to the endoplasmic reticulum (ER) by binding to a receptor protein on the ER

*FALSE* the "charging" or activation of a tRNA molecule includes the covalent attachment of an amino acid to the 3'-terminal *adenosine* of the tRNA.

*FALSE* The "charging" or activation of a tRNA molecule includes the covalent attachment of the *carboxyl group* of an amino acid to the tRNA. See slide 15/16:25

TRUE

*FALSE* the "charging" or activation of a tRNA molecule includes the covalent attachment of an amino acid to the *3'-terminal* adenosine of the tRNA.

aminoacyl-tRNA synthetase (each amino acid has one, but each synthetase recognizes >1 tRNA)

a translational elongation factor. Initiating 5'-AUG guided to ribosome P site by Shine-Dalgarno sequence: 4-9 purines 8-13 nt upstream of AUG and base-pairs with Py-rich sequence in 16S rRNA

*FALSE* All three sites can be occupied by a tRNA molecule at any given time

*FALSE* Each tRNA that associates with the ribosome must *first* bind in the *A* binding site and *then move to the P* binding site.

TRUE

*FALSE* All tRNAs leave the ribosome through the *E* site.

*FALSE* the N-formyl group to methionine prevents fMet from entering interior positions in a polypeptide

*FALSE* the N-formyl group to methionine prevents fMet from entering interior positions in a polypeptide

TRUE

*FALSE* the N-formyl group to methionine prevents fMet from entering interior positions in a polypeptide

TRUE

TRUE

TRUE

*FALSE* Re: eukaryotic translation initiation, the 40S ribosomal subunit binds *initiation factors before the mRNA*.

TRUE

TRUE

TRUE

*FALSE* ATP is not but *GTP* is an essential component of the bacterial elongation stage of translation

*FALSE* What would make this true?

*FALSE* What would make this true?

TRUE

*FALSE* What would make this true?

TRUE

*FALSE* the protein component of the 30S subunit consists of *21 different proteins*.

TRUE

TRUE

Proline is incorporated during protein synthesis; post-translational processing add the hydroxyl group.

Isoleucyl-tRNA synthetase sometimes catalyzes the addition of valine to tRNA(Ile); valine is similar to but smaller than isoleucine and can readily fit into the synthetase active site. Histaidine has no close structural analogs among the amino acids, greatly lowering the chance that tRNA(His) will be charged with the incorrect amino acid.

Yes. In polypeptide synthesis, removal of the last amino acid added (by hydrolytic cleavage of the last peptide bond to form) would sever the covalent link b/w the polypeptide and the tRNA in the ribosomal P site. This would terminate polypeptide synthesis.

*IF-2*: the 70S ribosome would form, but initiation factors would not be released and elongation could not start. *EF-Tu*: the second aminoacyl-tRNA would bind to the ribosomal A site, but no peptide bond would form. *EF-G*: the first peptide bond would form, but the ribosome would not move along the mRNA to vacate the A site for binding of a new EF-Tu-tRNA.

A tmRNA binds to the A site of the stalled ribosom. Part of its structure acts as an aminoacylated tRNA(Ala), leading to transfer of an Ala residue to the C-terminus of the partially synthesized protein. Another part of the tmRNA structure functions as an mRNA, permitting the addition of 10 additional amino acids to the protein before a stop codon is reached. After the polypeptide is released from the ribosome, the 10 amino acid residues incorporated at its C-terminal end act as a signal for degradation by cellular proteases.

Chloramphenicol inhibits bacterial protein synthesis *and mitochondrial protein synthesis*. The effects on mitochondrial ribosomes give rise to the human toxicity.