Chapter 14

Life as we know it depends on the genetic code: a set of codons, each made up of three bases in a DNA sequence and corresponding mRNA sequence, that specifies which of the 20 amino acids will be added to the protein during translation. Imagine that a prokaryote-like organism has been discovered in the polar ice on Mars. Interestingly, these Martian organisms use the same DNA → RNA → protein system as life on Earth, except that there are only 2 bases (A and T) in the Martian DNA, and there are only 17 amino acids found in Martian proteins. Based on this information, what is the minimum size of a codon for these hypothetical Martian life-forms? 2 bases 3 bases 4 bases 5 bases 6 bases The answer cannot be determined from the information provided.

What name is given to the process in which a strand of DNA is used as a template for the manufacture of a strand of pre-mRNA? RNA processing gene expression polypeptide formation transcription translation

What name is given to the process in which the information encoded in a strand of mRNA is used to construct a protein? RNA processing gene expression polypeptide formation transcription translation

What name is given to the process in which pre-mRNA is edited into mRNA? RNA processing gene expression polypeptide formation transcription translation

Polypeptides are assembled from _____. hexoses glycerol nucleotides proteins amino acids

RNA processing converts the RNA transcript into _____. a protein DNA a eukaryotic cell mRNA a polypeptide

What is the process called that converts the genetic information stored in DNA to an RNA copy? Translocation Transcription Replication Translation

DNA does not store the information to synthesize which of the following? Messenger RNA Organelles DNA Proteins

Transcription begins at a promoter. What is a promoter? The same as a start codon A site found on the RNA polymerase Part of the RNA molecule itself A site in DNA that recruits the RNA Polymerase

Which of the following statements best describes the promoter of a protein-coding gene? The promoter is part of the RNA molecule itself. The promoter is a nontranscribed region of a gene. The promoter is a site at which only RNA polymerase will bind. The promoter is a site found on RNA polymerase.

What determines which base is to be added to an RNA strand during transcription? The previous base Base pairing between the two DNA strands Base pairing between the DNA template strand and the RNA nucleotides The order of the chemical groups in the backbone of the RNA molecule

Which of the following terms best describes the relationship between the newly synthesized RNA molecule and the DNA template strand? Complementary Identical Covalently bound Permanently base-paired

What happens to RNA polymerase II after it has completed transcription of a gene? It joins with another RNA polymerase to carry out transcription. It is free to bind to another promoter and begin transcription. It begins transcribing the next gene on the chromosome. It is degraded.

Which of these correctly illustrates the pairing of DNA and RNA nucleotides? GTTACG CAATCG GTTACG CAAUGC GTTACG GTTACG GTTACG ACCGTA GTTACG UAACAU

The direction of synthesis of an RNA transcript is _____. 1' —> 5' 5' —> 3' 1' —> 3' 3' —> 5' 2' —> 4'

During transcription in eukaryotes, a type of RNA polymerase called RNA polymerase II moves along the template strand of the DNA in the 3'→5' direction. However, for any given gene, either strand of the double-stranded DNA may function as the template strand. For any given gene, what ultimately determines which DNA strand serves as the template strand? which of the two strands of DNA carries the RNA primer the location of specific proteins (transcription factors) that bind to the DNA the location along the chromosome where the double-stranded DNA unwinds the base sequence of the gene's promoter

After transcription begins, several steps must be completed before the fully processed mRNA is ready to be used as a template for protein synthesis on the ribosomes. Which three statements correctly describe the processing that takes place before a mature mRNA exits the nucleus? A poly-A tail (50-250 adenine nucleotides) is added to the 3' end of the pre-mRNA. A translation stop codon is added at the 3' end of the pre-mRNA. Noncoding sequences called introns are spliced out by molecular complexes called spliceosomes. A cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mRNA. Coding sequences called exons are spliced out by ribosomes.

During RNA processing a(n) _____ is added to the 5' end of the RNA. 3' untranslated region a long string of adenine nucleotides 5' untranslated region coding segment modified guanine nucleotide

During RNA processing a(n) _____ is added to the 3' end of the RNA. 3' untranslated region a long string of adenine nucleotides 5' untranslated region coding segment modified guanine nucleotide

Spliceosomes are composed of _____. snRNPs and other proteins polymerases and ligases introns and exons the RNA transcript and protein snRNPs and snurps

The RNA segments joined to one another by spliceosomes are _____. caps exons snRNPs tails introns

Translation occurs in the _____. cytoplasm lysosome nucleus Golgi apparatus nucleoplasm

Where does translation take place? Ribosome Endoplasmic reticulum Golgi apparatus Nucleus

Which nucleic acid is translated to make a protein? tRNA mRNA rRNA DNA

Which of the following processes is an example of a post-translational modification? Initiation Phosphorylation Elongation Peptide bond formation

Which of the following steps occurs last in the initiation phase of translation? An aminoacyl tRNA binds to the start codon. The large ribosomal subunit joins the complex. The small subunit of the ribosome binds to the 5' cap on the mRNA. A peptide bond is formed between two adjacent amino acids.

At which site do new aminoacyl tRNAs enter the ribosome during elongation? E-site A-site P-site B-site

What is meant by translocation? The ribosome slides one codon down the mRNA. The two ribosomal subunits are joined in a complex. The completed polypeptide is released from the ribosome. The polypeptide chain grows by one amino acid.

True or false. A tRNA with an anticodon complementary to the stop codon catalyzes the reaction by which translation is terminated. True False

What enzyme catalyzes the attachment of an amino acid to tRNA? aminoacyl-tRNA synthetase rubisco dextrinase argininosuccinate lyase nuclease

The tRNA anticodon, GAC, is complementary to the mRNA codon with the sequence _____. CAG CTG GAC CUG TCG

The initiator tRNA attaches at the ribosome's _____ site. A translocation E P Q

Generally speaking, which of the following mutations would most severely affect the protein coded for by a gene? a base substitution at the beginning of the gene a base substitution at the end of the gene a frameshift deletion at the beginning of the gene a frameshift deletion at the end of the gene

Which of the following molecules are produced by transcription? Select all that apply. Ribosomal proteins Messenger RNA Ribozymes

Which of the following molecules is/are produced by translation? Include molecules that are subject to further modification after initial synthesis. Select all that apply. The amino acid glycine RNA polymerase Aminoacyl-tRNA synthetase

Which of the following mutations would likely be most dangerous to a cell? Substitution of one nucleotide for another Deletion of one nucleotide Deletion of three nucleotides

The average length of a transcription unit along a eukaryotic DNA molecule is about 27,000 nucleotide pairs, whereas an averaged-sized protein is about 400 amino acids long. What is the best explanation for this fact? Each amino acid in a protein is encoded by a triplet of nucleotides. Most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides that are not translated. Many genes are subject to alternative RNA splicing.

Which of the following statements about ribozymes is/are correct? Select all that apply. Ribozymes are RNA molecules that function as enzymes. A ribosome can be regarded as one large ribozyme. In some genes, intron RNA functions as a ribozyme and catalyzes its own excision.

The flow of information in a cell proceeds in what sequence? from RNA to DNA to protein from protein to RNA to DNA from DNA to RNA to protein from DNA to protein to RNA from RNA to protein to DNA

Where does RNA polymerase begin transcribing a gene into mRNA? It starts after a certain nucleotide sequence called a promoter. It starts at one end of the chromosome. It looks for the AUG start codon. Transfer RNA acts to translate the message to RNA polymerase. The ribosome directs it to the correct portion of the DNA molecule.

After an RNA molecule is transcribed from a eukaryotic gene, what are removed and what are spliced together to produce an mRNA molecule with a continuous coding sequence? introns ... exons operators ... promoters exons ... introns silencers ... enhancers promoters ... operators

Which one of the following is true of tRNAs? Each tRNA binds a particular amino acid. tRNAs are double-stranded. tRNAs carry special sequences known as codons. There are four types of tRNA. All of the above.

How is translation initiated? The small ribosomal subunit binds to the mRNA. The tRNA bearing methionine binds to the start codon. The large ribosomal subunit binds to the small one. The start codon signals the start of translation. All of the above.

What does a mutagen cause? a change in the sequence of DNA problems with mitosis a reduction in the number of tRNA molecules available for protein synthesis decreased permeability of the nuclear envelope decreased enzyme activity throughout the cell

Which of these is currently considered the best definition of a gene? A gene codes for either a polypeptide or an RNA molecule. A gene codes for a single polypeptide. A gene codes for a single protein. A gene codes for a single enzyme. A gene codes for a particular ribozyme.

In eukaryotic cells, transcription cannot begin until __________. the DNA introns are removed from the template the 5' caps are removed from mRNA the two DNA strands have completely separated and exposed the promoter DNA nucleases have isolated the transcription unit several transcription factors have bound to the promoter

Which of the following is NOT true of a codon? It extends from one end of a tRNA molecule. It is the basic unit of the genetic code. It never codes for more than one amino acid. It may code for the same amino acid as another codon. It consists of three nucleotides.

Which of the following is NOT true of RNA processing? Ribozymes may function in RNA splicing. Nucleotides may be added at both ends of the RNA. RNA splicing can be catalyzed by spliceosomes. Exons are cut out before mRNA leaves the nucleus. A primary transcript is often much longer than the final RNA molecule that leaves the nucleus.

Which component is NOT directly involved in translation? ribosomes mRNA tRNA GTP DNA

Which of the following mutations would be most likely to have a harmful effect on an organism? a single nucleotide insertion downstream of, and close to, the start of the coding sequence a single nucleotide deletion near the end of the coding sequence a single nucleotide deletion in the middle of an intron a nucleotide-pair substitution a deletion of three nucleotides near the middle of a gene

A particular triplet of bases in the template strand of DNA is 5' AGT 3'. The corresponding codon for the mRNA transcribed is 3' UCA 5'. 3' UGA 5'. 3' ACU 5'. 5' TCA 3'. either UCA or TCA, depending on wobble in the first base.

The genetic code is essentially the same for all organisms. From this, one can logically assume which of the following? Different organisms have different numbers of different types of amino acids. The same codons in different organisms translate into the different amino acids. DNA was the first genetic material. A gene from an organism can theoretically be expressed by any other organism. All organisms have experienced convergent evolution.

Which of the following nucleotide triplets best represents a codon? a triplet at the opposite end of tRNA from the attachment site of the amino acid a triplet separated spatially from other triplets a sequence in tRNA at the 3' end a triplet that has no corresponding amino acid a triplet in the same reading frame as an upstream AUG

Which of the following provides some evidence that RNA probably evolved before DNA? DNA polymerase uses primer, usually made of RNA. DNA polymerase has proofreading function. RNA polymerase uses DNA as a template. RNA polymerase does not require localized unwinding of the DNA. RNA polymerase makes a single-stranded molecule.

Which of the following does not occur in prokaryotic gene expression, but does occur in eukaryotic gene expression? RNA polymerase requires a primer to elongate the molecule. mRNA, tRNA, and rRNA are transcribed. RNA polymerase binds to the promoter. A poly-A tail is added to the 3' end of an mRNA and a cap is added to the 5' end. Transcription can begin as soon as translation has begun even a little.

Transcription in eukaryotes requires which of the following in addition to RNA polymerase? ribosomes and tRNA the protein product of the promoter start and stop codons aminoacyl-tRNA synthetase several transcription factors

A part of the promoter, called the TATA box, is said to be highly conserved in evolution. Which of the following might this illustrate? The sequence is transcribed at the start of every gene. The sequence is found in many but not all promoters. The sequence evolves very rapidly. Any mutation in the sequence is selected against. The sequence does not mutate.

What is a ribozyme? an enzyme that uses RNA as a substrate an enzyme that synthesizes RNA as part of the transcription process an enzyme that catalyzes the association between the large and small ribosomal subunits an RNA with enzymatic activity an enzyme that synthesizes RNA primers during DNA replication

During splicing, which molecular component of the spliceosome catalyzes the excision reaction? sugar protein lipid DNA RNA

Alternative RNA splicing is due to the presence or absence of particular snRNPs. increases the rate of transcription. is a mechanism for increasing the rate of transcription. can allow the production of similar proteins from different RNAs. can allow the production of proteins of different sizes and functions from a single mRNA

In an experimental situation, a student researcher inserts an mRNA molecule into a eukaryotic cell after he has removed its 5' cap and poly-A tail. Which of the following would you expect him to find? The cell recognizes the absence of the tail and polyadenylates the mRNA. The mRNA could not exit the nucleus to be translated. The molecule attaches to a ribosome and is translated, but more slowly. The molecule is digested by hydrolytic enzymes because it is no longer protected at the 5' end. The molecule is digested by restriction enzymes in the nucleus.

Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the binding of ribosomes to mRNA. bonding of the anticodon to the codon. bonding of the anticodon to the codon and the attachment of amino acids to tRNAs. shape of the A and P sites of ribosomes. attachment of amino acids to tRNAs.

What is the function of GTP in translation? GTP hydrolyzes to provide energy for making peptide bonds. GTP energizes the formation of the initiation complex, using initiation factors. GTP hydrolyzes to provide phosphate groups for tRNA binding. GTP supplies phosphates and energy to make ATP from ADP. GTP separates the small and large subunits of the ribosome at the stop codon.

There are 61 mRNA codons that specify an amino acid, but only 45 tRNAs. This is best explained by the fact that competitive exclusion forces some tRNAs to be destroyed by nucleases. some tRNAs have anticodons that recognize four or more different codons. the DNA codes for all 61 tRNAs but some are then destroyed. the rules for base pairing between the third base of a codon and tRNA are flexible. many codons are never used, so the tRNAs that recognize them are dispensable.

Which of the following is the first event to take place in translation in eukaryotes? covalent bonding between the first two amino acids elongation of the polypeptide base pairing of activated methionine-tRNA to AUG of the messenger RNA binding of the larger ribosomal subunit to smaller ribosomal subunits the small subunit of the ribosome recognizes and attaches to the 5' cap of mRNA

Which of the following is a function of a signal peptide? to terminate translation of the messenger RNA to signal the initiation of transcription to direct an mRNA molecule into the cisternal space of the ER to translocate polypeptides across the ER membrane to bind RNA polymerase to DNA and initiate transcription

The process of translation, whether in prokaryotes or eukaryotes, requires tRNAs, amino acids, ribosomal subunits, and which of the following? SRP plus chaperones polymerases plus GTP signal peptides plus release factor polypeptide factors plus ATP polypeptide factors plus GTP

When the ribosome reaches a stop codon on the mRNA, no corresponding tRNA enters the A site. If the translation reaction were to be experimentally stopped at this point, which of the following would you be able to isolate? separated ribosomal subunits with a polypeptide attached to the tRNA an assembled ribosome with a polypeptide attached to the tRNA in the P site separated ribosomal subunits, a polypeptide, and free tRNA a cell with fewer ribosomes an assembled ribosome with a separated polypeptide

If a newly made polypeptide is to be secreted from a cell, what must occur before it is secreted? It must be translated by a ribosome that remains free of attachment to the ER. Its signal sequence must cause it to be encased in a vesicle as soon as it is translated. Its signal sequence must be cleaved off before the polypeptide can enter the ER. Its signal sequence must target it to the plasma membrane, where it causes exocytosis. Its signal sequence must target it to the ER, after which it goes to the Golgi.

Why might a point mutation in DNA make a difference in the level of an enzyme's activity? It might substitute a different amino acid in the active site. It might exchange one serine codon for a different serine codon. It might substitute the N-terminus of the polypeptide for the C-terminus. It might result in a chromosomal translocation. It might exchange one stop codon for another stop codon.

Which of the following types of mutation, resulting in an error in the mRNA just after the AUG start of translation, is likely to have the most serious effect on the polypeptide product? a deletion of two nucleotides an insertion of a codon a deletion of a codon a substitution of the first nucleotide of a GGG codon a substitution of the third nucleotide in an ACC codon

A frameshift mutation could result from either an insertion or a deletion of a base. a base deletion only. a base insertion only. a base substitution only. deletion of three consecutive bases.

The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. This results in a nucleotide mismatch. a polypeptide missing an amino acid. a nonsense mutation. a frameshift mutation. a base-pair substitution.

Which of the following mutations is most likely to cause a phenotypic change? a nucleotide substitution in an exon coding for a transmembrane domain a single nucleotide deletion in an exon coding for an active site a duplication of all or most introns a frameshift mutation one codon away from the 3' end of the nontemplate strand a large inversion whose ends are each in the same region between genes

Of the following, which is the most current description of a gene? a DNA sequence that is expressed to form a functional product: either RNA or polypeptide a discrete unit of hereditary information that consists of a sequence of amino acids a unit of heredity that causes formation of a phenotypic characteristic a DNA-RNA sequence combination that results in an enzymatic product a DNA subunit that codes for a single complete protein

In comparing DNA replication with RNA transcription in the same cell, which of the following is true only of replication? The process occurs in the nucleus of a eukaryotic cell. The entire template molecule is represented in the product. It makes a new molecule from its 5' end to its 3' end. The process is extremely fast once it is initiated. It uses RNA polymerase.

The following question refers to the simple metabolic pathway in the figure. According to Beadle and Tatum's hypothesis, how many genes are necessary for this pathway? 3 0 1 2 It cannot be determined from the pathway.

A mutation results in a defective enzyme A. Which of the following would be a consequence of that mutation? an accumulation of C and no production of A and B an accumulation of A and no production of B and C an accumulation of B and C and no production of A an accumulation of B and no production of A and C an accumulation of A and B and no production of C

If A, B, and C are all required for growth, a strain mutant for the gene-encoding enzyme B would be capable of growing on which of the following media? minimal medium supplemented with C only minimal medium supplemented with nutrients A and B minimal medium supplemented with A only minimal medium minimal medium supplemented with B only

Given the locally unwound double strand in the figure, in which direction does the RNA polymerase move? 5' → 3' along the complementary strand 3' → 5' along the template strand 3' → 5' along the complementary strand 5' → 3' along the double-stranded DNA 5' → 3' along the template strand

The dipeptide that will form will be threonine-glycine. cysteine-alanine. alanine-alanine. proline-threonine. glycine-cysteine.

What type of bonding is responsible for maintaining the shape of the tRNA molecule in the figure? peptide bonding between amino acids hydrogen bonding between base pairs covalent bonding between sulfur atoms van der Waals interactions between hydrogen atoms ionic bonding between phosphates

the figure represents tRNA that recognizes and binds a particular amino acid (in this instance, phenylalanine). Which codon on the mRNA strand codes for this amino acid? CAU GUG GUA UUC UGG

A transfer RNA (#1) attached to the amino acid lysine enters the ribosome. The lysine binds to the growing polypeptide on the other tRNA (#2) already in the ribosome. Where does tRNA #2 move to after this bonding of lysine to the polypeptide? exit tunnel A site directly to the cytosol E site P site

During RNA processing a(n) _____ is added to the 3' end of the RNA. 3' untranslated region a long string of adenine nucleotides 5' untranslated region coding segment modified guanine nucleotide