Genetics chapter 9

Which region of a tRNA molecule binds to amino acids?

3′ end

A tRNA in the P site of the ribosome will enter the ________ site after translocation of the ribosome.

E

Ribosomal subunits are large complexes composed of numerous polypeptides and at least one rRNA molecule. Which subunits include three rRNA molecules? See Section 9.1 (Page 316) .

Eukaryotic large subunits

________ helps control ribosome formation and binding of the initiator tRNA.

Initiation factor protein

Which of the following statements best describes the function of aminoacyl tRNA synthetase? It synthesizes tRNA molecules. It attaches a specific amino acid to a tRNA molecule. It helps tRNA synthesize proteins. It provides the energy required to attach a specific amino acid to a tRNA molecule. Submit

It attaches a specific amino acid to a tRNA molecule.

How does the eukaryotic ribosomal small subunit recognize the start codon on the mRNA? It performs an ATP hydrolysis within the small subunit once it encounters a Met-tRNA already bound to the AUG. It binds an Met-tRNA to the first AUG codon after the Kozak sequence. It undergoes a conformational charge that recruits other proteins when it hydrogens bonds to the correct tri-nucleotide sequence. It binds an Met-tRNA to the first AUG codon it encounters. It wraps the mRNA strand to bring initiation enhancer proteins into the vicinity of the start codon. Submit

It binds an Met-tRNA to the first AUG codon after the Kozak sequence.

If the first nucleotide in a codon is mutated to a different nucleotide, what would be the effect on the encoded protein?

It depends on what the changed nucleotide is.

The preinitiation complex forms in bacteria when the start codon is recognized through binding of 16srRNA and what region of mRNA?

Shine-Dalgarno sequence

Which units that describe the speed of sedimentation of a substance during centrifugation are ribosomal subunits measured in?

Svedberg units (S)

Each aminoacyl tRNA synthetase is specific for one amino acid and a small number of tRNAs. T/F

T

How might a single base INSERTION into the second codon of the coding sequence of a gene affect the amino acid sequence of a protein encoded by the gene? The mutation may have no effect on amino acid sequence. A single amino acid could change. A single extra amino acid would be present in the protein. The amino acid sequence would be altered. All of the above are possible outcomes. Submit

The amino acid sequence would be altered.

How does the eukaryotic initiation complex locate the correct start codon? The correct start codon is the formyl-ATG, which will encode for fMet in the protein. The pre-initiation complex moves the ribosome through the 3' UTR, scanning for the Kozak sequence. The true start codon is the first ATG encountered downstream of the Shine-Dalgarno sequence. The initiation complex moves the small ribosomal subunit through the 5' UTR, scanning for the start AUG. The correct start codon is the first ATG encountered downstream of the Kozak sequence. Submit

The initiation complex moves the small ribosomal subunit through the 5' UTR, scanning for the start AUG.

Which of the following best describes the first step in the formation of the translation initiation complex?

The small ribosomal subunit binds to an mRNA sequence near the 5' end of the transcript

What does it mean for two codons to be synonymous?

They encode the same amino acid.

In the process of translational initiation in bacteria, where does the initiator tRNA first bind to the ribosome? See Section 9.2 (Page 321) . To the partial P site on the small ribosomal subunit Submit To the partial A site on the small ribosomal subunit To the partial A site on the large ribosomal subunit To the partial P site on the large ribosomal subunit

To the partial P site on the small ribosomal subunit Submit

What is the final step of translational initiation in both bacteria and eukaryotes? See Section 9.2 (Page 321) . Binding of the intact ribosome to the 5' cap on the mRNA Union of the large subunit with the small subunit to form the intact ribosome Binding of GTP to the intact ribosome Binding of the initiator tRNA to the AUG start codon Submit

Union of the large subunit with the small subunit to form the intact ribosome

In bacteria, the methionine that initiates the formation of a polypeptide chain differs from subsequently added methionines in that _______. the initiating methionine is not an amino acid a formyl group is attached to the initiating methionine incorporation of the initial methionine does not require a tRNA its tRNA anticodon is not complementary to the AUG codon Submit

a formyl group is attached to the initiating methionine

What would you expect to find bound to the stop codon at the A site? an uncharged tRNA a charged tRNA with the anticodon ATC a translation release factor a charged tRNA with the anticodon TAG Nothing binds to a stop codon, which is why the peptide is released. Submit

a translation release factor

What are the three phases of translation?

initiation, elongation, termination

Thanks to flexible base pairing, the wobble nucleotides in anticodons can be one or more of the standard RNA nucleotides or which modified nucleotide?

inosine (I)

The Shine-Dalgarno sequence in bacteria ________. is a purine-rich consensus sequence found in the 16S rRNA subunit is a region of the tRNA molecule involved in formation of charged tRNAs is a purine-rich consensus sequence found in the 5' UTR of the mRNA is a consensus sequence involved in the termination of translation is a pyrimidine-rich consensus sequence found in the 3' UTR of the mRNA

is a purine-rich consensus sequence found in the 5' UTR of the mRNA

When a peptide bond is formed between two amino acids, one is attached to the tRNA occupying the P site and the other _______. is attached to the tRNA occupying the E site is attached through hydrogen bonds to the mRNA is free in the cytoplasm is attached to the tRNA occupying the A site Submit

is attached to the tRNA occupying the A site Submit

Binding of what protein initiates translation-termination events that result in polypeptide release and dissociation of ribosomal subunits?

release factor (RF)

During elongation, which location on the ribosome is the charged tRNA is recruited to?

A site

What is a charged tRNA? See Section 9.2 (Page 321) . A tRNA that carries a specific amino acid A tRNA that is bound to an initiation factor (IF) An ionic form of a tRNA A tRNA that is bound to the small ribosomal subunit Submit

A tRNA that carries a specific amino acid

What normally binds to an open A site on the ribosome? See Section 9.1 (Page 316) . An empty tRNA after its amino acid has been added to the polypeptide chain The 3' UTR (untranslated region) of the mRNA A tRNA that carries the next amino acid to be added to the polypeptide chain The initiator tRNA that carries the first amino acid in the polypeptide chain

A tRNA that carries the next amino acid to be added to the polypeptide chain

In eukaryotes, the initiation factor proteins eIF1A and eIF3 join with ________ to form the preinitiation complex. elongation factors peptidyl transferase the P site of a ribosome charged tRNAMet

charged tRNAMet

Translation in bacteria is directly dependent on all of the following associations except _______.

complementary base pairing between mRNA and DNA

What is the cellular location of the stages of translation in bacteria and eukaryotes? membrane for bacteria and cytosol and rough ER for eukaryotes cytosol for bacteria and nucleus for eukaryotes cytosol for bacteria and eukaryotes cytosol for bacteria and cytosol, mitochondrion, and plastid for eukaryotes nucleoid for bacteria and rough ER for eukaryotes Submit

cytosol for bacteria and cytosol, mitochondrion, and plastid for eukaryotes

Many antibiotics cause mispairing between codons and anticodons. What fatal effect would this mispairing have on the cell? defective protein synthesis abnormalities in membrane transport abnormalities in vesicular transport defective pre-mRNA synthesis

defective protein synthesis

A mutagen has introduced a frame-shift mutation by adding one nucleotide base. Which of the following could be a reversion mutation for this particular mutant?

deleting 1 base or adding 2 bases

Sidney Brenner demonstrated that the triplet code is, in fact, nonoverlapping. Assuming a nonoverlapping code, how many complete codons would the following sequence encode before encountering a stop codon? 5' - AUGCGAUUAUAGUGC - 3'

3

Once elongation is underway, tRNAs involved in the process occupy a series of sites on the complexed ribosome. The occupation of sites occurs in the following order.

A Site, P Site, E Site

How many different aminoacyl-tRNA synthetases can be found in a given organism's cells?

At least 20, or more depending on the organism

Which of the following steps in translation is NOT facilitated by elongation factors? See Section 9.2 (Page 321) . Translocation of the ribosome along the mRNA Recruitment of charged tRNAs to the A site Formation of peptide bonds between sequential amino acids Binding of initiator tRNA to the AUG start codon Submit

Binding of initiator tRNA to the AUG start codon Submit

Eighteen of the amino acids have two or more synonymous codons. Which two amino acids are the exceptions?

Met and Trp

During translation initiation in bacteria, the amino acid on the initiator tRNA is ________. acetylated methionine (Met) IF-1 N-formylmethionine (fMet) added using ATP as the energy source

N-formylmethionine (fMet)

In the unlikely event that a tRNA has been charged with the wrong amino acid, which high-fidelity enzyme most likely caused the incorrect charging? peptidyl transferase DNA polymerase III DNA polymerase I aminoacyl peptidase aminoacyl synthetase

aminoacyl synthetase

Elongation factors translocate the ribosome in the 3' direction by a distance of

one codon.

If you were designing an antibiotic that inhibits peptide bond formation, what enzyme would you target? 8-oxo-dGDP phosphatase peptidyl transferase glycoside hydrolase tRNA synthetase

peptidyl transferase

Bacteria group their genes such that they share a single promoter and the mRNA transcript synthesizes several different polypeptides. Collectively, these are referred to as ________ mRNAs, which are part of the operon system. polyadenylated polycistronic processed monocistronic

polycistronic

A polycistronic mRNA contains multiple ________. promoters Kozak sequences polypeptide-producing sequences Shine-Dalgarno sequences mRNAs

polypeptide-producing sequences