Translation

Which of the following statements about the genetic code is correct? (a) all codons specify more than one amino acid. (b) The genetic code is redundant. (c) All amino acids are specified by more than one codon.(d) All codons specify an amino acid.

The piece of RNA below includes the region that codes the binding site for the initiator tRNA needed in translation. 5′-GUUUCCCGUAUACAUGCGUGCCGGGGGC-3′ Which amino acid will be on the tRNA that is the first to bind to the A-site of the ribosome? (a) methionine (b) arginine (c) cysteine (d) valine

Which amino acid would you expect a tRNA with the anticodon 5′-CUU-3′ to carry? (a) lysine (b) glutamic acid (c) leucine (d) phenylalanine

which of the following pairs of codons might you expect to be read by the same tRNA as a result of wobble? (a) CUU and UUU (b) GAU and GAA (c) CAC and CAU (d) AAU and AGU

From the sequence from the 3′ end of mRNA. 5′-CCGUUACCAGGCCUCAUUAUUGGUAACGGAAAAAAAAAAAAAA-3′ If you were told that this sequence contains the stop codon for the protein encoded by this mRNA, what is the anticodon on the tRNA in the P-site of the ribosome when release factor binds to the A-site? (a) 5′-CCA-3′ (b) 5′-CCG-3′ (c) 5′-UGG-3′ (d) 5′-UUA-3′

A poison added to an in vitro translation mixture containing mRNA molecules with the sequence 5′-AUGAAAAAAAAAAAAUAA-3′ has the following effect: the only product made is a Met-Lys dipeptide that remains attached to the ribosome. What is the most likely way in which the poison acts to inhibit protein synthesis? (a) It inhibits peptidyl transferase activity. (b) It inhibits movement of the small subunit relative to the large subunit. (c) It inhibits release factor. (d) It mimics release factor.

In eucaryotes, but not in procaryotes, ribosomes find the start site of translation by _________________. (a) binding directly to a ribosome-binding site preceding initiation codon (b) scanning along mRNA from the 5′ end (c) recognizing an AUG codon as the start of translation (d) binding an initiator tRNA

A mutation in the tRNA for the amino acid lysine results in the anticodon sequence 5′-UAU-3′ (instead of 5′-UUU 3′). Which of the following aberrations in protein synthesis might this tRNA cause? (a) read-through of stop codons (b) substitution of lysine for isoleucine (c) substitution of lysine for tyrosine (d) substitution of lysine for phenylalanine

Which of the following methods is not used by cells to regulate the amount of a protein in the cell? (a) Genes can be transcribed into mRNA with different efficiencies. (b) Many ribosomes can bind to a single mRNA molecule. (c) Proteins can be tagged with ubiquitin, marking them for degradation. (d) Nuclear pore complexes can regulate the speed at which newly synthesized proteins are exported from the nucleus into the cytoplasm.

Which of the following molecules is thought to have arisen first during evolution? (a) protein (b) DNA (c) RNA (d) All came to be at the same time.

According to current thinking, the minimum requirement for life to have originated on Earth was the formation of a _______________. (a) molecule that could provide a template for the production of a complementary molecule (b) double-stranded DNA helix (c) molecule that could direct protein synthesis (d) molecule that could catalyze its own replication

Ribozymes catalyze which of the following reactions? (a) DNA synthesis (b) transcription (c) RNA splicing (d) protein hydrolysis

You are studying a disease that is caused by a virus, but when you purify the virus particles and analyze them you find they contain no trace of DNA. Which of the following molecules are likely to contain the genetic information of the virus? (a) high-energy phosphate groups (b) RNA (c) lipids (d) carbohydrates

The concentration of a particular protein X in a normal human cell rises gradually from a low point, immediately after cell division, to a high point, just before cell division, and then drops sharply. The level of its mRNA in the cell remains fairly constant throughout this time. Protein X is required for cell growth and survival, but the drop in its level just before cell division is essential for division to proceed. You have isolated a line of human cells that grow in size in culture but cannot divide, and on analyzing these mutants, you find that levels of X mRNA in the mutant cells are normal. Which of the following mutations in the gene for X could explain these results? (a) the introduction of a stop codon that truncates protein X at the fourth amino acid (b) a change of the first ATG codon to CCA (c) the deletion of a sequence that encodes sites at which ubiquitin can be attached to the protein (d) a change at a splice site that prevents splicing of the RNA

Most amino acids can be specified by more than one codon. Each codon specifies only one amino acid.

Ribosomes contain proteins as well as rRNA.

Once proteins are sent to the proteasome, proteases degrade them.

Chaperone proteins provide a place for misfolded proteins to attempt to refold.

Ribosomes are large RNA structures composed solely of rRNA.

Ribosomes are synthesized entirely in the cytoplasm.

rRNA contains the catalytic activity that joins amino acids together.

A ribosome binds one tRNA at a time.

A single procaryotic mRNA molecule can be translated into several proteins.

Ribosomes must bind to the 5′ cap before initiating translation.

mRNAs are not polyadenylated.

Ribosomes can start translating an mRNA molecule before transcription is complete.

Ubiquitin is a small protein that is covalently attached to proteins to mark them for delivery to the proteasome.

Proteases reside in the central cylinder of a proteasome.

Misfolded proteins are delivered to the proteasome, where they are sequestered from the cytoplasm and can attempt to refold.

The protein stoppers that surround the central cylinder of the proteasome use the energy from ATP hydrolysis to move proteins into the proteasome inner chamber.

The initiator _____is underlined on the RNA molecule 5′-GUUUCCCGUAUACAUGCGUGCCGGGGGC-3′. The first tRNA to bind at the _____-site is the second codon of the protein, because the initiator tRNA is already bound to the _________________________ site when translation begins. The codon that follows the binding site for the initiator tRNA is CGU, which codes for _______________________________. In a conventional nucleotide sequences, the ___________ is given reading from 5′ to 3′. The complementary base pairing occurs between antiparallel nucleic acid sequences, and the codon is recognized by the anticodon.

Polyribosomes form because the initiation of translation is fairly___: ribosomes can bind successively to the free __ end of an mRNA molecule and start translation before the first ribosome has had a chance to finish translating the message. Therefore, inhibition of the rate of initiation will tend to ____the number of ribosomes in the ___, and in the extreme case there will be only one ribosome per mRNA. Conversely, increasing the rate of initiation or slowing the rate of elongation would result in an ______ number of ribosomes per polyribosome (up to a maximum point).

Because RNA is known to ______reactions within the cell, because the components of RNA are thought to be more readily formed in the conditions on _____ Earth, and because RNA can contain _______ information, it is the most likely molecule to have arisen first in evolution. The deoxyribose sugar of DNA makes the molecule ___ susceptible than RNA to breakage, because of the lack of the hydroxyl group on carbon 2 of the ribose sugar. DNA is double-stranded and therefore the complementary strand provides a ____ from which damage can be repaired accurately. The use of "T" in DNA instead of "U" protects against the effect of deamination, a common form of damage. Deamination of T produces an aberrant base (methyl C), whereas deamination of U generates C, a normal base. The presence of an abnormal base eases the cell's job of recognizing the damaged strand.

subunits: the _L_ subunit, which catalyzes the formation of the peptide bonds that link the amino acids together into a polypeptide chain, and the _s_ subunit, which matches the tRNAs to the codons of the mRNA. During the chain elongation process of translating an mRNA into protein, the growing polypeptide chain attached to a tRNA is bound to the _P_-site of the ribosome. An incoming aminoacyl-tRNA carrying the next amino acid in the chain will bind to the _A_-site by forming base pairs with the exposed codon in the mRNA. The _p-trans_ enzyme catalyzes the formation of a new peptide bond between the growing polypeptide chain and the newly arriving amino acid. The end of a protein-coding message is signaled by the presence of a stop codon, which binds the _prot_ called release factor. Eventually, most proteins will be degraded by a large complex of proteolytic enzymes called the _prot_______.

A strain of yeast translates mRNA into protein inaccurately. Individual molecules of a particular protein isolated from this yeast have variations in the first 11 amino acids compared with the sequence of the same protein isolated from normal yeast cells, as listed in Figure. What is the most likely cause of this variation in protein sequence? (a) a mutation in the DNA coding for the protein (b) a mutation in the anticodon of the isoleucine tRNA (tRNAIle) (c) a mutation in the isoleucyl-tRNA synthetase that decreases its ability to distinguish between different amino acids (d) a mutation in the isoleucyl-tRNA synthetase that decreases its ability to distinguish between different tRNA molecules

You have discovered a protein that inhibits translation. When you add this inhibitor to a mixture capable of translating human mRNA and centrifuge the mixture to separate polyribosomes and single ribosomes, you obtain the results shown in the figure. Which of the following interpretations is consistent with these observations? (a) The protein binds to the small ribosomal subunit and increases the rate of initiation of translation. (b) The protein binds to sequences in the 5′ region of the mRNA and inhibits the rate of initiation of translation. (c) The protein binds to the large ribosomal subunit and slows down elongation of the polypeptide chain. (d) The protein binds to sequences in the 3′ region of the mRNA and prevents termination of translation.

You have discovered an alien life form that surprisingly uses DNA as its genetic material, makes RNA from DNA, and reads the information from RNA to make protein using ribosomes and tRNAs, which read triplet codons. Because it is your job to decipher the genetic code for this alien, you synthesize some artificial RNA molecules and examine the protein products produced from these RNA molecules in a cell-free translation system using purified alien tRNAs and ribosomes. You obtain the results shown in Table. From this information, which of the following peptides can be produced from poly UAUC? (a) Ile-Phe-Val-Tyr (b) Tyr-Ser-Phe-Ala (c) Ile-Lys-His-Tyr (d) Cys-Pro-Lys-Ala

An extraterrestrial organism (ET) is discovered whose basic cell biology seems pretty much the same as that of terrestrial organisms except that it uses a different genetic code to translate RNA into protein. You set out to break the code by translation experiments using RNAs of known sequence and cell-free extracts of ET cells to supply the necessary protein-synthesizing machinery. In experiments using the RNAs below, the following results were obtained when the 20 possible amino acids were added either singly or in different combinations of two or three: RNA 1: 5′-GCGCGCGCGCGCGCGCGCGCGCGCGCGC-3′ RNA 2: 5′-GCCGCCGCCGCCGCCGCCGCCGCCGCCGCC-3′ Using RNA 1, a polypeptide was produced only if alanine and valine were added to the reaction mixture. Using RNA 2, a polypeptide was produced only if leucine and serine and cysteine were added to the reaction mixture. Assuming that protein synthesis can start anywhere on the template, that the ET genetic code is nonoverlapping and linear, and that each codon is the same length (like the terrestrial triplet code), how many nucleotides does an ET codon contain? (a) 2 (b) 3 (c) 4 (d) 5 (e) 6