practice tests from bio
You have inserted the gene for human growth factor into the E. coli lactose operon, replacing the structural genes with the gene for human growth factor. What substance must you add to your culture of bacteria to cause them to produce human growth factor for you? ( Concept 18.1)
Your Answer: allolactose
What is a key difference in gene expression between eukaryotic and prokaryotic cells? ( Concept 17.4)
Your Answer: In prokaryotic cells, the RNA transcript is immediately available as mRNA without processing.
Which of the following statements correctly describes mRNA processing? ( Concept 17.3)
Your Answer: Introns are cut out of the primary transcript, and the resulting exons are spliced together.
The P site of a ribosome does which of the following? ( Concept 17.4)
Your Answer: It holds the tRNA carrying the growing polypeptide chain.
This chapter contains a lengthy discussion of the trp operon involved in regulating the synthesis of tryptophan. In the case of E. coli, the bacterium may need to synthesize tryptophan, or its host, a human, may supply all the tryptophan it needs. Why do both bacteria and humans need tryptophan? ( Concept 18.1)
Your Answer: It is one of the 20 amino acids used by all organisms to synthesize proteins.
Which of the following summaries of protein synthesis is correct? ( Concept 17.4)
Your Answer: Messenger RNA is made on a DNA template, and then amino-acid-bearing transfer RNAs bind to the mRNA through codon-anticodon pairing.
Genetic information of eukaryotic cells is transferred from the nucleus to the cytoplasm in the form of __________. ( Concept 17.1)
Your Answer: RNA
Which of the following catalyzes the linkage between ribonucleotides to form RNA during gene expression? ( Concept 17.2)
Your Answer: RNA polymerase
Which of the following components is required for DNA replication? ( Concept 16.2)
Your Answer: RNA primer
In eukaryotes, which of the following mechanisms operates after transcription, but before translation of mRNA into protein? ( Concept 17.3)
Your Answer: RNA splicing
Once the DNA at the replication fork is unwound by helicases, what prevents the two strands from coming back together to re-form a double helix? ( Concept 16.2)
Your Answer: Single-strand binding proteins bind the unwound DNA and prevent the double helix from re-forming.
One strand of a DNA molecule has the base sequence 5′-ATAGGT-3′. The complementary base sequence on the other strand of DNA will be 3′- __________-5′. ( Concept 16.2)
Your Answer: TATCCA Correct. A always pairs with T, and G with C.
When genes are expressed, they produce __________. ( Concept 17.5)
Your Answer: The second and fourth responses are correct.
Which of the following best describes the arrangement of genetic information in a DNA molecule? ( Concept 17.1)
Your Answer: The three-nucleotide words of a gene are arranged in a nonoverlapping series on the DNA template strand.
When RNA is being made, the RNA base __________ always pairs with the base __________ in DNA. ( Concept 17.1)
Your Answer: U ... A
Who is credited with explaining the structure of the DNA double helix? ( Concept 16.1)
Your Answer: Watson and Crick
Which of the following techniques was most helpful to Watson and Crick in developing their model for the structure of DNA? ( Concept 16.1)
Your Answer: X-ray crystallography
At each end of a DNA replication bubble is __________. ( Concept 16.2)
Your Answer: a replication fork
A geneticist found that a particular mutation had no effect on the polypeptide encoded by the gene. This mutation probably involved __________. ( Concept 17.5)
Your Answer: a silent or neutral mutation
In DNA, the two purines are __________, and the two pyrimidines are __________. ( Concept 16.1)
Your Answer: adenine and guanine ... cytosine and thymine
In prokaryotic genomes, groups of functionally related genes along with their promoters and operators are found together in __________. ( Concept 18.1)
Your Answer: an operon
How many nucleotides are needed to code for a protein with 450 amino acids? ( Concept 17.1)
Your Answer: at least 1,350
The role of DNA polymerases in DNA replication is to __________. ( Concept 16.2)
Your Answer: attach free nucleotides to the new DNA strand
Which of the following types of mutation is LEAST likely to affect the function of the protein corresponding to the gene in which the mutation occurs? ( Concept 17.5)
Your Answer: base-pair substitution
During the replication of DNA, __________. ( Concept 16.2)
Your Answer: both strands of a molecule act as templates
The incorporation of an incorrect base into the DNA during replication __________. ( Concept 16.2)
Your Answer: can be repaired by the mismatch repair system
Unlike prokaryotic DNA replication, replication of eukaryotic chromosomes __________. ( Concept 16.2)
Your Answer: cannot be completed by DNA polymerase
Ultraviolet (UV) radiation is damaging to cells because it __________. ( Concept 17.5)
Your Answer: causes mutations in the DNA
A scientist clones a regulatory gene that is involved in controlling the expression of other genes, and discovers that the regulatory gene encodes an enzyme that acetylates histones. It is likely that this enzyme regulates gene expression by __________. ( Concept 18.2)
Your Answer: causing looser packing of the chromatin at the target gene, thereby enhancing transcription
A bacterium can make the amino acid glycine or absorb it from its surroundings. A biochemist finds that glycine binds to a repressor protein and causes the repressor to bind to the bacterial chromosome, turning off an operon. If it is like other similar operons, the presence of glycine will result in the __________. ( Concept 18.1)
Your Answer: cessation of the synthesis of glycine
Which of the following is a post-translational modification of a polypeptide? ( Concept 17.4)
Your Answer: cleavage of a polypeptide into two or more chains
In eukaryotes, DNA packing seems to affect gene expression primarily by __________. ( Concept 18.2)
Your Answer: controlling access to DNA
Gene expression in bacteria is regulated primarily by __________. ( Concept 18.1)
Your Answer: controlling the transcription of genes into mRNA
The function of tRNA during protein synthesis is to __________. ( Concept 17.4)
Your Answer: deliver amino acids to their proper site during protein synthesis
At one point, as a cell carried out its day-to-day activities, the nucleotides GAT were paired with the nucleotides CUA. This pairing occurred __________. ( Concept 17.4)
Your Answer: during transcription
In a eukaryote, transcription factors called activators may stimulate gene expression by binding to DNA sites called __________. ( Concept 18.2)
Your Answer: enhancers
A point mutation in which a single base pair is inserted or deleted from DNA is called a(n) __________. ( Concept 17.5)
Your Answer: frame-shift mutation
Telomeres __________. ( Concept 16.2)
Your Answer: get shorter with each round of DNA replication
Polysomes may be defined as __________. ( Concept 17.4)
Your Answer: groups of ribosomes translating the same mRNA
During Griffith's experiments with Streptococcus pneumoniae in mice, material from __________ bacteria transformed __________ bacteria. ( Concept 16.1)
Your Answer: heat-killed pathogenic ... living nonpathogenic
After the formation of a replication bubble, which of the following is the correct sequence of enzymes used for the synthesis of the lagging DNA strand? ( Concept 16.2)
Your Answer: helicase, primase, DNA polymerase, ligase
The bonds that hold tRNA molecules in the correct three-dimensional shape are __________. ( Concept 17.4)
Your Answer: hydrogen bonds
The two antiparallel strands of nucleotides that form the DNA double helix are held together by __________. ( Concept 16.1)
Your Answer: hydrogen bonds between nucleotide bases
The control of gene expression is more complex in multicellular eukaryotes than in prokaryotes because __________. ( Concept 18.2)
Your Answer: in a multicellular eukaryote, different cells are specialized for different functions
In a eukaryotic cell, transcription takes place __________. ( Concept 17.1)
Your Answer: in the nucleus
Telomerase __________. ( Concept 16.2)
Your Answer: is an enzyme that lengthens telomeres
Which of the following attributes of DNA is most crucial to its accurate duplication? ( Concept 16.2)
Your Answer: its specific base pairing through hydrogen bonds
During the transcription of a given portion of a DNA molecule __________. ( Concept 17.2)
Your Answer: mRNA is synthesized on only one of the chains
A virus infects a cell and randomly inserts many short segments of DNA containing a stop codon throughout an organism's chromosomes. This will probably cause __________. ( Concept 17.5)
Your Answer: manufactured proteins to be short and defective
The first amino acid inserted into a new polypeptide chain in eukaryotic cells is usually __________. ( Concept 17.4)
Your Answer: methionine
In prokaryotes, the rate of elongation during DNA replication is __________ the rate in eukaryotes. ( Concept 16.2)
Your Answer: much faster than
Which set of enzymes is involved in nucleotide excision repair? ( Concept 16.2)
Your Answer: nuclease, DNA polymerase, and ligase
In the "beads on a string" structure of unfolded chromatin, the "beads" are __________. ( Concept 16.3)
Your Answer: nucleosomes
Monomers for the synthesis of DNA are called __________. ( Concept 16.1)
Your Answer: nucleotides
A base-pair substitution mutation in a germ cell line is likely to have NO effect on phenotype if the substitution __________. ( Concept 17.5)
Your Answer: occurs in an intron
Generally speaking, how many genetic codes are there? ( Concept 17.1)
Your Answer: one
The two strands of a DNA double helix are antiparallel. This means that __________. ( Concept 16.2)
Your Answer: one strand runs in the 5' to 3' direction, and the other runs in the 3' to 5' direction
During translation in a eukaryotic cell, __________. ( Concept 17.4)
Your Answer: polypeptides are synthesized at ribosomes, according to instructions carried by mRNA
The codons AAA, CCC, GGG, and UUU specify the amino acids lysine, proline, glycine, and phenylalanine, respectively. If the base sequence 5′-CCCAAATTTGGG-3′ is present in the coding strand of a stretch of DNA, what polypeptide sequence would be encoded by the corresponding template strand? ( Concept 17.1)
Your Answer: pro-lys-phe-gly
Which of the following statements is FALSE?( Concept 17.2)
Your Answer: In bacteria, proteins called transcription factors enhance the affinity of RNA polymerase to the promoter sites of genes.
As a result of proofreading by DNA polymerases, the overall error rate in the completed DNA molecule is approximately __________. ( Concept 16.2)
Your Answer: 1 error per 10,000,000,000 nucleotides
Consider the following list of events in the expression of a eukaryotic gene. What is their proper sequence? ( Concept 17.4) 1. translation 2. RNA processing 3. transcription 4. modification of protein
Your Answer: 3, 2, 1, 4
DNA polymerase adds nucleotides to the __________ of the leading strands, and to the __________ of the lagging strands (Okazaki fragments). ( Concept 16.2)
Your Answer: 3′ end ... 3′ end
What mRNA codon would be made from the DNA triplet 3′-CGT-5′? ( Concept 17.1)
Your Answer: 5′-GCA-3′
Which one of the following statements is correct? ( Concept 16.1)
Your Answer: Adenine forms two hydrogen bonds with thymine; guanine forms three hydrogen bonds with cytosine.
Enhancers __________. ( Concept 18.2)
Your Answer: All of the listed responses are correct.
In transcription, __________. ( Concept 17.2)
Your Answer: All of the listed responses are correct.
Which of the following considerations was/were important in the choice of viruses and bacteria for early experiments on DNA? ( Concept 16.3)
Your Answer: All of the listed responses are correct.
Which of the following statement(s) about feedback inhibition is/are true? ( Concept 18.1)
Your Answer: All of the listed responses are correct.
Which of the following statements about replication origins is/are correct? ( Concept 16.2)
Your Answer: All of the listed responses are correct.
Which of the following statements is/are correct with regard to individuals with the disorder xeroderma pigmentosum? ( Concept 16.2)
Your Answer: All of the listed responses are correct.
Which of the following statements regarding the structure and function of tRNA is FALSE? ( Concept 17.4)
Your Answer: Although each tRNA consists of a relatively short, single RNA strand, this single strand can achieve a three-dimensional structure by folding back upon itself and forming covalent bonds between complementary bases.
What is the major difference between bacterial chromosomes and eukaryotic chromosomes? ( Concept 16.3)
Your Answer: Bacteria usually have a single circular chromosome whereas eukaryotes have several linear chromosomes.
Who formulated the one gene-one enzyme hypothesis? ( Concept 17.1)
Your Answer: Beadle and Tatum
In a comparison between asexually reproducing bacteria and sexually reproducing multicellular eukaryotes, uncorrected errors in replication are more likely to be transmitted to subsequent generations in bacteria than in multicellular eukaryotes. Which of the following provides the best evidence-based explanation for this difference?( Concept 16.2)
Your Answer: Because they are asexual and single-celled, all uncorrected errors of replication in bacteria are transmitted to subsequent generations. Multicellular eukaryotes typically reproduce sexually, so uncorrected errors are transmitted only if they occur in germ cells that meiotically divide to produce gametes.
Which of the following accurately describes the usual process of transcription for eukaryotic genes? ( Concept 17.3)
Your Answer: Both introns and exons are transcribed, but the RNA transcribed from introns does not leave the nucleus.
What enzyme joins Okazaki fragments? ( Concept 16.2)
Your Answer: DNA ligase
The removal of the RNA primer and addition of DNA nucleotides to the 3' end of Okazaki fragments in its place is carried out by __________. ( Concept 16.2)
Your Answer: DNA polymerase I
Which of the following statements is true? ( Concept 17.1)
Your Answer: Each amino acid in a protein is coded for by three bases in the DNA.
A cell biologist found that two different proteins with largely different structures were translated from two different mRNAs. These mRNAs, however, were transcribed from the same template within the cell nucleus. Which mechanism below could best account for this? ( Concept 17.3)
Your Answer: Exons from the same gene could be spliced in different ways to make different mRNAs.
Which one of the following statements regarding DNA replication is correct? ( Concept 16.2)
Your Answer: Helicases separate the two strands of the double helix, and DNA polymerases then construct two new strands using each of the original strands as templates.
One strand of a DNA molecule has the following sequence: 3′-AGTACAAACTATCCACCGTC-5′. In order for that strand to be transcribed, there would have to be a specific recognition sequence, called a(n) __________, to the left of the DNA sequence indicated. ( Concept 17.2)
Your Answer: promoter
Until Hershey and Chase showed that DNA was the genetic molecule of the phages they studied, what class of molecules was considered the best candidate for carrying genetic information and why? ( Concept 16.1)
Your Answer: proteins because they were thought to be the only molecule with both the variety and specificity of function to account for the array of heritable traits observed
In many cases, more than one codon codes for the same amino acid. Because of this, we say that the code is __________. ( Concept 17.1)
Your Answer: redundant
The experiments of Meselson and Stahl showed that DNA __________. ( Concept 16.2)
Your Answer: replicates in a semiconservative fashion
In general, operons that encode the enzymes of a biosynthetic (anabolic) pathway (such as the trpoperon) are __________, and those encoding the enzymes of a catabolic pathway (such as the lacoperon) are __________. ( Concept 18.1)
Your Answer: repressible ... inducible
In some cases, DNA methylation and removal of acetyl groups from histones (i.e., deacetylation) combine to __________. ( Concept 18.2)
Your Answer: silence certain genes
Cells are able to distinguish proteins destined for secretion or for segregation to specific intracellular compartments from those that will remain in the cytoplasm because __________. ( Concept 17.4)
Your Answer: some proteins, as they begin to be synthesized, contain a signal region that causes the ribosome with its growing polypeptide to attach to the ER and translocate the polypeptide into the lumen (space) of the ER
In an inducible operon, the inducer is often the __________ in the pathway being regulated; the inducer binds to the __________, which then becomes __________. ( Concept 18.1)
Your Answer: substrate ... repressor ... inactive
Bacteria can transcribe and translate human genes to produce functional human proteins because __________. ( Concept 17.1)
Your Answer: the genetic code is nearly universal
In an important experiment, a radioactively labeled bacteriophage was allowed to infect bacteria. In a first trial, the phage contained radioactive DNA, and radioactivity was detected inside the bacteria. Next, phage-containing radioactive protein was used, and the radioactivity was not detected inside the bacteria. These experiments led to the conclusion that __________. ( Concept 16.1)
Your Answer: the genetic material of the phage is DNA
A scientist assembles a bacteriophage with the protein coat of phage T2 and the DNA of phage T4. If this composite phage were allowed to infect a bacterium, the phages produced in the host cell would have __________. ( Concept 16.1)
Your Answer: the protein and DNA of T4
Chargaff found that for DNA __________. ( Concept 16.1)
Your Answer: the ratio of A to T is close to 1:1 and the ratio of G to C is close to 1:1
During translation, amino acid chain elongation occurs until __________. ( Concept 17.4)
Your Answer: the ribosome encounters a "stop" codon
The mRNA codons 5′-CAA-3′ or 5′-CAG-3′ are translated as the amino acid glutamine by __________. ( Concept 17.4)
Your Answer: the same tRNA with the anticodon 3′-GUU-5′
The information in DNA is contained in __________. ( Concept 16.1)
Your Answer: the sequence of nucleotides along the length of the two strands of the DNA molecule
The number of nucleotide bases "read" together on the mRNA to designate each amino acid is __________; this unit is called a(n) __________. ( Concept 17.1)
Your Answer: three ... codon
The unwinding of DNA at the replication fork causes twisting and strain in the DNA ahead of the fork, which is relieved by an enzyme called __________. ( Concept 16.2)
Your Answer: topoisomerase
Both repressible and inducible operons control gene expression at the level of __________. ( Concept 18.1)
Your Answer: transcription
Avery and his colleagues' 1944 experiment showed that DNA __________. ( Concept 16.1)
Your Answer: was the substance that transformed the bacteria in Griffith's experiment