Flashcards in Chapter 14: Translation Deck (95)
Which region of a tRNA molecule binds to amino acids?
The 3′ end of a tRNA molecule contains the amino acid binding site.
A tRNA molecule has a cloverleaf structure that is dictated by base pairing.
The anticodon loop recognizes a complementary mRNA codon.
A tRNA molecule does not contain a codon loop.
Although tRNA molecules contain a variable loop, they do not bind amino acids in this region.
Which of the following statements best describes the function of aminoacyl tRNA synthetase?
It attaches a specific amino acid to a tRNA molecule.
Aminoacyl tRNA synthetase catalyzes the charging reaction that links a specific amino acid to a tRNA molecule.
Aminoacyl tRNA synthetase is an enzyme.
ATP is the energy source in the tRNA charging reaction.
Aminoacyl tRNA synthetase does not synthesize tRNA molecules.
tRNA molecules by themselves do not synthesize proteins.
TRUE or FALSE?
Each aminoacyl tRNA synthetase is specific for one amino acid and a small number of tRNAs.
Think about the mechanisms underlying the charging process.
Each aminoacyl tRNA synthetase enzyme recognizes only one amino acid, but each enzyme can often recognize several tRNAs because there is usually more than one codon for each amino acid.
All of the following are involved in the process of tRNA "charging":
Aminoacyl tRNA synthetase
Ribosomal RNA and ribosomes form the site of protein translation. Transfer RNAs work to bring amino acids to the ribosome. After a tRNA contributes its amino acid to the growing polypeptide chain, it must be "recharged" with a new amino acid. This is done independently of rRNA.
Is rRNA involved in the process of tRNA "charging?"
The ribonucleic acid components known to exist in eukaryotic ribosomes are the following: ___, ___, ___, and ___ .
5.8S, 18S, 28S, and 5S.
A covalently linked combination of an amino acid and a tRNA molecule.
Also referred to as a charged tRNA.
The central paradigm of biochemistry holds that information flows from DNA to RNA to protein. The process of making protein from the mRNA is called translation. Translation is carried out by the ribosome, which binds to the mRNA and binds tRNA, which recognizes the codons on the mRNA and brings the appropriate amino acid with it. The ribosome forms the peptide bond between the new amino acid and the growing peptide chain.
The process of translation, or protein synthesis, is a crucial part of the maintenance of living organisms. Proteins are constantly in use and will break down eventually, so new ones must always be available. If protein synthesis breaks down or stops, then the organism dies.
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
tRNAs associate with sites on the ribosome in the order listed.
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 A site
The following statement concerns peptide bond formation:
It is catalyzed by peptidyl transferase.
It does not use water, nor does it require GTP.
In prokaryotes, the methionine that initiates the formation of a polypeptide chain differs from subsequently added methionines in that _______.
a formyl group is attached to the initiating methionine
This modification is not present on methionine residues added during elongation.
Translation is directly dependent on all of the following associations:
association of the 30S and the 50S ribosomal subunits
complementary base pairing between mRNA and rRNA
complementary base pairing between mRNA and tRNA
Translation is NOT directly dependent on the following association:
complementary base pairing between mRNA and DNA
Transcription, not translation, is dependent on this association.
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
At which site does the charged initiator tRNA bind during protein synthesis?
The initiator tRNAfmet binds to the mRNA codon in the P site of the ribosome. The initiator tRNA is the only one that binds in the P site; all other tRNAs bind the ribosome in the A site.
TRUE or FALSE?
The enzyme EF‑Tu catalyzes the formation of a peptide bond between the amino acid held by the tRNA in the A site and the elongating amino acid chain held by the tRNA in the P site.
Peptidyl transferase is the enzyme that catalyzes the formation of peptide bonds during translation. EF‑Tu is an elongation factor that facilitates the entry of charged tRNAs into the A site.
What event occurs during translocation?
mRNA shifts in the 5' direction along the ribosome.
Translocation is the process by which mRNA shifts by 3 bases in the 5' direction along the ribosome to bring another codon into the A site.
A chromosomal mutation associated with the reciprocal or nonreciprocal transfer of a chromosomal segment from one chromosome to another. Also denotes the movement of mRNA through the ribosome during translation.
The term peptidyl transferase relates to ________.
peptide bond formation during protein synthesis
TRUE or FALSE?
Prokaryotic and eukaryotic ribosomes are structurally and chemically identical.
The following statement is true of translation in eukaryotes:
In eukaryotes, a given mRNA produces only one type of polypeptide chain.
Because the eukaryotic ribosome binds to the cap and not a ribosome-binding sequence, the ribosome cannot bind at any other site on the mRNA and begin translation at an internal site. Some viruses have evolved novel strategies to allow exception to this rule.
Consider the more complex nature of the eukaryotic ribosome and the translational process.
In eukaryotes, transcription takes place in the nucleus and translation takes place in the cytoplasm, after the mature mRNA has been processed.
Protein chains in eukaryotes start with methionine. Only prokaryotes use the formyl derivative.
In eukaryotes, ribosomes bind to the 7-methyl guanosine cap at the 5' end of the mRNA, not to a ribosome binding sequence.
The charged initiator tRNA forms part of the initiation complex and carries methionine.
E site is the exit site at which an uncharged tRNA is ejected from the ribosome.
There is no T site in the ribosome.
A Site is the site at which charged tRNAs complementary to the mRNA codon in the A site enter the ribosome.
The two ribosomal subunits join together to form a complex during translation initiation.
Amino acids are added to the polypeptide chain during elongation.
The polypeptide is cleaved from the terminal tRNA as part of the translation termination.
The Beadle and Tatum experiments were based on all of the following assumptions:
X-irradiation can induce mutations.
auxotrophs fail to grow on minimal media
supplemented media permit growth of auxotrophic strains of Neurospora
The Beadle and Tatum experiments were NOT based on the following assumption:
two strains of auxotrophic Neurospora that grow on minimal medium supplemented with biotin have mutations in the same gene
Since biosynthetic pathways have multiple steps, each catalyzed by a separate enzyme, these two strains would not necessarily have the same mutation.
In their first round of screening, Beadle and Tatum plated spores on minimal medium. The purpose of this screen was to _______.
determine whether any auxotrophic mutants had been generated
Specific deficiencies were tested in subsequent rounds of screening.
Which of the following can be inferred from the Beadle and Tatum experiments?
For a mutation resulting in the production of a defective enzyme involved in a biosynthetic pathway, the compound preceding the corresponding step will accumulate.
The defective enzyme is unable to convert the precursor to the next compound in the pathway. Therefore, the precursor accumulates.