Written Comprehensive
Which of the following macromolecules leave the nucleus of a eukaryotic cell through pores in the nuclear membrane?
mRNA
Which of the following molecular structures contain codons?
mRNA
Which of the following molecules are required for the process of translation?
mRNA, tRNA, and rRNA
How are bacteria able to change their patterns of protein synthesis so quickly in response to environmental changes?
mRNAs that are produced are short-lived and degraded within a few minutes of being synthesized.
Use the following information to answer the question.A part of an mRNA molecule with the following sequence is being read by a ribosome: 5′-CCG-ACG-3′ (mRNA). The following charged transfer RNA molecules (with their anticodons shown in the 3′ to 5′ direction) are available. Two of them can correctly match the mRNA so that a dipeptide can form.Which of the following dipeptides will form from this mRNA?
proline-threonine
Which statement about variation is true?
All new alleles are the result of nucleotide variability.
A newly discovered unicellular organism isolated from acidic mine drainage is found to contain a cell wall, a plasma membrane, two flagella, and peroxisomes. Based just on this information, the organism is most likely ________.
a motile eukaryote
Which of the following types of mutation would convert a proto-oncogene into an oncogene?
a mutation that greatly increases the amount of the proto-oncogene protein
Which of the following statements best describes the significance of the TATA box in the promoters of eukaryotes?
It is the recognition site for the binding of a specific transcription factor.
What is the function of the nuclear pore complex found in eukaryotes?
It regulates the movement of proteins and RNAs into and out of the nucleus.
Which of the following properties is associated with a protein that will be secreted from a eukaryotic cell?
Its signal sequence must target it to the ER, after which it goes to the Golgi.
DDT was once considered a "silver bullet" that would permanently eradicate insect pests. Instead, DDT is largely useless against many insects. Which of these would have prevented this evolution of DDT resistance in insect pests?
None of the insect pests would have genetic variations that resulted in DDT resistance.
If the cytoplasm of a cell is at pH 7, and the mitochondrial matrix is at pH 8, then the concentration of H+ ions ________.
is 10 times higher in the cytoplasm than in the mitochondrial matrix.
Which organelle is the primary site of ATP synthesis in eukaryotic cells?
mitochondrion
Which of the following processes occurs during transcription?
RNA is synthesized
Researchers investigating the mechanism of vesicular transport assembled a cell-free system that included microtubule tracks, vesicles, and ATP. However, they observed no movement of transport of vesicles in this system. What were they missing?
motor proteins
At the beginning of this century, there was a general announcement regarding the sequencing of the human genome and the genomes of many other multicellular eukaryotes. Many people were surprised that the number of protein-coding sequences was much smaller than they had expected. Which of the following types of DNA make up the rest of the human genome?
non-protein-coding DNA that is transcribed into several kinds of small RNAs with biological function
A cell with a predominance of rough endoplasmic reticulum is most likely ________.
producing large quantities of proteins for secretion
The reason for differences in the sets of proteins expressed in a nerve and a pancreatic cell of the same individual is that nerve and pancreatic cells contain different ________.
sets of regulatory proteins
Transcription in eukaryotes requires which of the following molecules in addition to RNA polymerase?
several transcription factor
Which of the following processes do normal proto-oncogenes typically exhibit?
They stimulate normal cell growth and division.
A farmer uses triazine herbicide to control pigweed in his field. For the first few years, the triazine works well and almost all the pigweed dies; but after several years, the farmer sees more and more pigweed. Which of these statements explains why the pigweed reappeared?
Triazine-resistant weeds were more likely to survive and reproduce.
Post-translational modifications of proteins may include which of the following processes?
addition of carbohydrates to form a glycoprotein
Which organelle often takes up much of the volume of a plant cell?
central vacuole
Genetic drift produces variation for evolution when ________.
chance events cause allele frequencies to fluctuate unpredictably
Which structure below is independent of the endomembrane system?
chloroplast
Thylakoids, DNA, and ribosomes are all components found in ________.
chloroplasts
A cell with a predominance of smooth endoplasmic reticulum is likely specialized to ________.
synthesize large quantities of lipids
One of the buffers that contribute to pH stability in human blood is carbonic acid (H2CO3). Carbonic acid is a weak acid that, when placed in an aqueous solution, dissociates into a bicarbonate ion (HCO3-) and a hydrogen ion (H+). (See figure.)
the HCO3- to act as a base and remove excess H+ by the formation of H2CO3
Which of the following statements describe the effect of evolution on a population?
increasingly better match between a population and its environment
In bacteria, DNA will be found in ________.
the nucleoid
Why does ice float in liquid water?
Stable hydrogen bonds keep water molecules of ice farther apart than water molecules of liquid water.
Which of the following processes occurs when termination of translation takes place?
A stop codon is reached
Which one of the following structures, if missing, would usually prevent translation from starting?
AUG codon
Of the following anatomical structures, which is homologous to the bones in the wing of a bird?
bones in the flipper of a whale
Melting of ice and this reduced feeding opportunities for polar bears is occurring because of the ____.
Increases in CO2 and other greenhouse gases in the atmosphere.
A solution contains 0.0000001 (10^-7) moles of hydrogen ions (H+) per liter. Which of the following best describes this solution?
Neutral
Use the figure to answer the question.What type of bonding is responsible for maintaining the shape of the tRNA molecule shown in the figure?
hydrogen bonding between base pairs
The following question refers to this table of codons.Refer to the figure. Which of the triplets below is a possible anticodon for a tRNA that transports proline to a ribosome?
3'-GGC-5'
The following question refers to this table of codons.Which of the following sequences of nucleotides are possible in the template strand of DNA that would code for the polypeptide sequence Phe-Leu-Ile-Val?
3'-AAA-GAA-TAA-CAA-5'
In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.1. What is the frequency of individuals with AA genotype?
0.81
How much of 0.5 M glucose (molecular mass 180) is needed to provide 100 mg of glucose?
1.11 mL
What is the hydroxyl ion (OH-) concentration of a solution of pH 8?
10^-6 M
The molar mass of glucose is 180 grams per mole (g/mol). Which of the following procedures should you carry out to make a 1M solution of glucose? In 0.8 liter (L) of water, dissolve _____.
180 g of glucose, and then add more water until the total volume of the solution is 1 L.
One mole (mol) of glucose (molecular mass = 180 daltons) is _____.
180 grams of glucose
Rank the following one-base point mutations with respect to their likelihood of affecting the structure of the corresponding polypeptide (from most likely to least likely). 1. insertion mutation deep within an intron 2. substitution mutation at the third position of a codon in an exon 3. substitution mutation at the second position of a codon in an exon 4. deletion mutation within the first exon of the gene
4, 3, 2, 1
Suppose 64% of a remote mountain village can taste phenylthiocarbamide (PTC) and must, therefore, have at least one copy of the dominant PTC taster allele. If this population conforms to Hardy-Weinberg equilibrium for this gene, what percentage of the population must be heterozygous for this trait?
48%
You have a freshly prepared 0.1 M sucrose (molecular mass 342) solution, which means _____.
6.02 x 10^22 of sucrose molecules or 34.2 g go sucrose is present in the solution.
Which of the following processes occurs in eukaryotic gene expression?
A cap is added to the 5' end of the mRNA.
The genetic code is essentially the same for all organisms. From this, one can logically assume which of the following statements to be true?
A gene from an organism can theoretically be expressed by any other organism.
Which of the following mechanisms is used to coordinate the expression of multiple, related genes in eukaryotic cells?
A given gene may have multiple enhancers, but each enhancer is generally associated with only that gene and no other.
The partial negative charge at one end of a water molecule is attracted to the partial positive charge of another water water molecule. What is this attraction called?
A hydrogen bond
During the elongation phase of translation, which site in the ribosome represents the location where a codon is being read?
A site
A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is ________.
AAA
Cohesion, surface tension, and adhesion are the properties of water molecules that ____.
Are a result of hydrogen bonding.
Which domains of life are classified as prokaryotes?
Bacteria and Archaea
Suppose an experimenter becomes proficient with a technique that allows her to move DNA sequences within a prokaryotic genome. If a researcher moves the promoter for the lac operon to the region between the beta galactosidase (lacZ) gene and the permease (lacY) gene, which of the following results would be most likely?
Beta galactosidase will not be produced.
How does 0.5 M sucrose (molecular mass 342) solution compare to 0.5 M glucose (molecular mass 180) solution?
Both have 3.01 x 10^23 molecules.
The following questions refer to the figure below, which shows an outcrop of sedimentary rock whose strata are labeled A-D.If x indicates the location of fossils of two closely related species, then fossils of their most-recent common ancestor are most likely to occur in which stratum?
C
Which of the following statements best explains why modification or change in an organ or tissue during the lifetime of an individual is not inherited?
Characteristics acquired during an organism's life are generally not passed on through genes.
Which of the following processes would allow the detection of alternative splicing of transcripts from a given gene?
Compare the sequences of different mRNAs made from the given gene.
Which of these conditions are always true of populations evolving due to natural selection?Condition 1: The population must vary in traits that are heritable.Condition 2: Some heritable traits must increase reproductive success.Condition 3: Individuals pass on most traits that they acquire during their lifetime.
Conditions 1 and 2
The following experiment is used for the corresponding question.A researcher discovered a species of moth that lays its eggs on oak trees. Eggs are laid at two distinct times of the year: early in spring when the oak trees are flowering and in midsummer when flowering is past. Caterpillars from eggs that hatch in spring feed on oak flowers and look like oak flowers. But caterpillars that hatch in summer feed on oak leaves and look like oak twigs.How does the same population of moths produce such different-looking caterpillars on the same trees? To answer this question, the biologist caught many female moths from the same population and collected their eggs. He put at least one egg from each female into eight identical cups. The eggs hatched, and at least two larvae from each female were maintained in one of the four temperature and light conditions listed below.In each of the four environments, one of the caterpillars was fed oak flowers, the other oak leaves. Thus, there were a total of eight treatment groups (4 environments × 2 diets).Which of the following is a testable hypothesis that would explain the differences in caterpillar appearance observed in this population?
Differences in diet trigger the development of different types of caterpillars.
Which of the following statements correctly describes the primary difference between enhancers and proximal control elements?
Enhancers are located considerable distances from the promoter; proximal control elements are close to the promoter.
Which of the following is a major difference between prokaryotic cells and eukaryotic cells?
Eukaryotic cells have membrane-bound organelles, while prokaryotic cells do not.
Low humidity in the atmosphere on a hot day _____.
Helps in cooling because water evaporates from the skin faster.
What is the function of the release factor during translation in eukaryotes?
It binds to the stop codon in the A site in place of a tRNA.
Which of the following processes correctly describes alternative RNA splicing?
It can allow the production of proteins of different sizes and functions from a single mRNA.
Which of the following functions does the product of the p53 gene carry out?
It inhibits the cell cycle.
Which of the following statements correctly describes the effect a nonsense mutation would have on a gene?
It introduces a premature stop codon into the mRNA.
Once researchers identified DNA as the molecule responsible for transmitting heritable traits, they asked how information was transferred from the DNA in the nucleus to the site of protein synthesis in the cytoplasm. Which of the following statements correctly describes the mechanism of information transfer in eukaryotes that accomplishes this task?
Messenger RNA is transcribed from a single gene and transfers information from the DNA in the nucleus to the cytoplasm, where protein synthesis takes place.
The following question refers to this table of codons.What amino acid sequence will be generated, based on the following mRNA codon sequence?5′-AUG-UCU-UCG-UUA-UCC-UUG-3′
Met-Ser-Ser-Leu-Ser-Leu
The restriction enzymes of bacteria protect the bacteria from successful attack by bacteriophages, whose genomes can be degraded by the restriction enzymes. The bacterial genomes are not vulnerable to these restriction enzymes because bacterial DNA is methylated. This situation selects for bacteriophages whose genomes are also methylated. As new strains of resistant bacteriophages become more prevalent, this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA. Over the course of evolutionary time, what should occur?
Methylated and nonmethylated strains should be maintained among both bacteria and bacteriophages, with ratios that vary over time.
Hydrophobic substances such as vegetable oil are _____.
Nonpolar substances that repel water molecules.
In a single molecule of water, two hydrogen atoms are bonded to a single oxygen atom by ____.
Polar covalent bonds
Increased atmospheric CO2 concentrations might have what effect on seawater?
Seawater will become more acidic, and carbonate concentrations will decrease.
Use the figure to answer the question.The tRNA shown in the figure has its 3′ end projecting beyond its 5′ end. Which of the following processes will occur at this 3′ end?
The amino acid binds covalently.
Which of the following statements describes a cell that is considered to be differentiated?
The cell produces proteins specific to a particular cell type.
In an experimental situation, a student researcher inserts an mRNA molecule into a eukaryotic cell after she has removed its 5′ cap and poly-A tail. Which of the following processes would you expect her to find to have occurred?
The molecule is digested by enzymes because it is not protected at the 5' end.
Imagine that you've isolated a yeast mutant that contains histones resistant to acetylation. What phenotype would you predict for this mutant?
The mutant will show decreased levels of gene expression.
The cities of Portland, Oregon, and Minneapolis, Minnesota, are at about the same latitude, but Minneapolis has much summers and much colder winters than Portland. Why?
The ocean near Portland moderates the temperature.
The following question is based on information from Frank M. Frey, "Opposing Natural Selection from Herbivores and Pathogens May Maintain Floral-Color Variation in Claytonia virginica (Portulacaceae)," Evolution 58(11), 2004: 2426-37.Claytonia virginica is a woodland spring herb with flowers that vary from white, to pale pink, to bright pink. Slugs prefer to eat pink-flowering over white-flowering plants (due to chemical differences between the two), and plants experiencing severe herbivory are more likely to die. The bees that pollinate this plant also prefer pink to white flowers, so that Claytonia with pink flowers have greater relative fruit set than Claytonia with white flowers. A researcher observes that the percentage of different flower colors remains stable in the study population from year to year. Given no other information, if the researcher removes all slugs from the study population, what do you expect to happen to the distribution of flower colors in the population over time?
The percentage of pink flowers should increase over time.
In bacteria, there are 61 mRNA codons that specify an amino acid, but only 45 tRNAs. Which of the following statements explains this fact?
The rules for base pairing between the third base of a codon and tRNA are flexible.
Members of two different species possess a similar-looking structure that they use in a similar way to perform about the same function. Which of the following would suggest that the relationship more likely represents homology instead of convergent evolution?
The two species share many proteins.
Why are BRCA1 and BRCA2 considered to be tumor-suppressor genes?
Their normal products participate in repair of DNA damage.
If the bacterium Staphylococcus aureus experiences a cost for maintaining one or more antibiotic-resistance genes, what would happen in environments that lack antibiotics?
These bacteria would be outcompeted and replaced by bacteria that have lost these genes.
Which of the following statements correctly describes a characteristic of tumor-suppressor gene?
They encode proteins that help prevent uncontrolled cell growth.
Over long periods of time, many cave-dwelling organisms have lost their eyes. Tapeworms have lost their digestive systems. Whales have lost their hind limbs. How can natural selection account for these losses?
Under particular circumstances that persisted for long periods, each of these structures presented greater costs than benefits.
The questions below refer to the following evolutionary tree, in which the horizontal axis represents time (present time is on the far right) and the vertical axis represents morphological change.Which of these is the extant (that is, living) species most closely related to species X?
V
The following questions refer to the evolutionary tree in the figure below.The horizontal axis of the cladogram depicted below is a timeline that extends from 100,000 years ago to the present; the vertical axis represents nothing in particular. The labeled branch points on the tree (V-Z) represent various common ancestors. Let's say that only since 50,000 years ago has there been enough variation between the lineages depicted here to separate them into distinct species, and only the tips of the lineages on this tree represent distinct species.Which of the five common ancestors, labeled V-Z, is the common ancestor of the greatest number of species, both living and extinct?
Y
Which of the following statements is the most current description of a gene?
a DNA sequence that is expressed to form a functional product: either RNA or polypeptide
A single base substitution mutation is likely to have a less deleterious effect when the base change exhibits which of the following results?
a codon that specifies the same amino acid as the original 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?v
a deletion of two nucleotides
Which of the following statements best describes the characteristics of siRNA?
a double-stranded RNA, one of whose strands can complement and inactivate a sequence of mRNA
An earthquake decimates a ground-squirrel population, killing 98% of the squirrels. The surviving population happens to have broader stripes, on average, than the initial population. If broadness of stripes is genetically determined, what effect has the ground-squirrel population experienced during the earthquake?
a genetic bottleneck
The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. What is the result of this type of mutation?
a polypeptide missing an amino acid
Many crustaceans (for example, lobsters, shrimp, and crayfish) use their tails to swim, but crabs have reduced tails that curl under their shells and are not used in swimming. This is an example of ________.
a vestigial trait
Given what we know about evolutionary biology, we expect to find the largest number of endemic species in which of the following geological features, which have existed for at least a few million years?
an isolated ocean island in the tropics
The cow Bos primigenius (which is bred for meat and milk) has a smaller brain and larger eyes than closely related wild species of ungulates. These traits most likely arose by ________.
artificial selection, because changes in these traits co-occurred with human selection for high milk output and high muscle content
Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the ________.
binding of the anticodon to the codon and the attachment of amino acids to tRNAs
Motor proteins provide for molecular motion in cells by interacting with what types of cellular structures?
components of the cytoskeleton
Which of the following methods is utilized by eukaryotes to control their gene expression that is different from the type of control found in bacteria?
control of both RNA splicing and chromatin remodeling
Which of the following molecules helps to "turn off" genes in a cell?
corepressor
Use the following information to answer the question below.Martin Wikelski and L. Michael Romero (Body size, performance and fitness in Galápagos marine iguanas, Integrative and Comparative Biology 43 [2003]:376-86) measured the snout-to-vent (anus) length of Galápagos marine iguanas and observed the percent survival of different-sized animals, all of the same age. The graph shows the log snout-vent length (SVL, a measure of overall body size) plotted against the percent survival of these different size classes for males and females.Currently the only predators of Galápagos marine iguanas are Galápagos hawks. Iguana body size is not correlated with risk of hawk predation, although small iguanas can sprint faster than large iguanas. If predators (for example, cats) that preferably catch and eat slower iguanas are introduced to the island, iguana body size is likely to ________ in the absence of other factors; the iguanas would then be under ________ selection.
decrease; directional
Which of the following is the most predictable outcome of increased gene flow between two populations?
decreased genetic difference between the two populations
Which of the following is the best modern definition of evolution?
descent with modification
Cotton-topped tamarins are small primates with tufts of long white hair on their heads. While studying these creatures, you notice that males with longer hair get more opportunities to mate and father more offspring. To test the hypothesis that having longer hair is adaptive in these males, you should ________.
determine if hair length is heritable
Which of the following descriptions illustrates phenotype variation caused by environment?
diet of caterpillars changes their morphology
The fact that plants can be cloned from somatic cells demonstrates that ________.
differentiated cells retain all the genes of the zygote
Three-spined stickleback fish (Gasterosteus aculeatus) show substantial heritable variation in gill-raker length related to differences in their diets. Longer gill rakers appear to function better for capturing open-water prey, while shorter gill rakers function better for capturing shallow-water prey. Which of the following types of selection is most likely to be found in a large lake (open water in the middle and shallow water around the sides) with a high density of these fish?
disruptive selection
Refer to the metabolic pathway illustrated. If A, B, and C are all required for growth, a strain that is mutant for the gene-encoding enzyme A would be able to grow on medium supplemented with which of the following nutrient(s)?
either nutrient B or C
The evolution of eukaryotic cells most likely involved ________.
endosymbiosis of an oxygen-using bacterium in a larger bacterial host cell-the endosymbiont evolved into mitochondria
DNA methylation and histone acetylation are examples of which of the following processes?
epigenetic phenomena
Cystic fibrosis is a genetic disorder in homozygous recessives that causes death during the teenage years. If 9 in 10,000 newborn babies have the disease, what are the expected frequencies of the dominant (A1) and recessive (A2) alleles according to the Hardy-Weinberg equation?
fA1 = 0.9700, fA2 = 0.0300
The Dunkers are a religious group that moved from Germany to Pennsylvania in the mid-1700s. They do not marry with members outside their own immediate community. Today, the Dunkers are genetically unique and differ in gene frequencies, at many loci, from all other populations including those in their original homeland. Which of the following mechanisms likely explains the genetic uniqueness of this population?
founder effect and genetic drift
An original section of DNA has the base sequence AGCGTTACCGT. A mutation in this DNA strand results in the base sequence AGGCGTTACCGT. What type of mutation does this change represent?
frameshift mutation
The restriction enzymes of bacteria protect the bacteria from successful attack by bacteriophages, whose genomes can be degraded by the restriction enzymes. The bacterial genomes are not vulnerable to these restriction enzymes because bacterial DNA is methylated. This situation selects for bacteriophages whose genomes are also methylated. As new strains of resistant bacteriophages become more prevalent, this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA. The outcome of the conflict between bacteria and bacteriophages at any point in time results from ________.
frequency-dependent selection
Comparisons of Neanderthal DNA revealed that there are more similarities to non-African DNA than reference sequences from West Africans. Additionally, scientists found that Neanderthal DNA is as closely related to East Asians as to Europeans. This indicates that interbreeding occurred before human migration further east. What process of population genetics generated these results?
gene flow
Where are proteins produced other than on ribosomes free in the cytosol or ribosomes attached to the endoplasmic reticulum?
in mitochondria
After the drought of 1977, researchers hypothesized that on the Galápagos Island Daphne Major, medium ground finches with large, deep beaks survived better than those with smaller beaks because they could more easily crack and eat the tough Tribulus cistoides fruits. A tourist company sets up reliable feeding stations with a variety of bird seeds (different types and sizes) so that tourists can get a better look at the finches. Which of these events is now most likely to occur to finch beaks on this island?
increased variation in beak size and shape over time
Homozygotes with two sickle-cell alleles are selected against because of mortality. However, heterozygotes for sickle-cell allele experience little effects of sickle allele and are more likely to survive malaria. The net effect of this exposure produced evolutionary change in areas where malaria is endemic by ________.
increasing sickle-cell allele frequency
When taken up by a cell, which of the following molecules binds to a repressor so that the repressor no longer binds to the operator?
inducer
What are adaptations?
inherited characteristics of organisms that enhance their survival
Asbestos is a material that was once used extensively in construction. One risk from working in a building that contains asbestos is the development of asbestosis caused by the inhalation of asbestos fibers. Cells will take up asbestos by phagocytosis, but are not able to degrade it. As a result, asbestos fibers accumulate in ________.
lysosomes
According to the central dogma, what is the intermediate molecule involved in the flow of information in a cell that should go in the blank?DNA → ________ → Proteins
mRNA
Cyanide binds with at least one molecule involved in producing ATP. If a cell is exposed to cyanide, most of the bound cyanide is likely to be localized within the ________.
mitochondria
Suppose a young boy is always tired and fatigued, suffering from a metabolic disease. Which of the following organelles is most likely malfunctioning in this disease?
mitochondria
Genetic variation ________.
must be present in a population before natural selection can act upon the population
A proficient engineer can easily design skeletal structures that are more functional than those currently found in the forelimbs of such diverse mammals as horses, whales, and bats. The actual forelimbs of these mammals do not seem to be optimally arranged because ________.
natural selection is generally limited to modifying structures that were present in previous generations and in previous species
Suppose a cell has the following molecules and structures: enzymes, DNA, ribosomes, plasma membrane, and mitochondria. It could be a cell from ________.
nearly any eukaryotic organism
Pseudogenes are ________.
nonfunctional vestigial genes
The higher the proportion of loci that are "fixed" in a population, the lower are that population's ________.
nucleotide variability and average heterozygosity
Which of the following molecules is a protein produced by a regulatory gene?
repressor
In the fractionation of homogenized cells using differential centrifugation, which of the following will require the greatest speed to form pellets at the bottom of the tube?
ribosomes
Which of the following are found in plant, animal, and bacterial cells?
ribosomes
Which of the following is the most common pathway taken by a newly synthesized protein that will be secreted by a cell?
rough ER -> Golgi -> transport vesicle -> plasma membrane
HIV's genome of RNA includes the code for reverse transcriptase (RT), an enzyme that acts early in infection to synthesize a DNA genome off of an RNA template. The HIV genome also codes for protease (PR), an enzyme that acts later in infection by cutting long viral polyproteins into smaller, functional proteins. Both RT and PR represent potential targets for antiretroviral drugs. Drugs called nucleoside analogs (NA) act against RT, whereas drugs called protease inhibitors (PI) act against PR.Which mechanism produces variation for evolution by shuffling existing alleles?
sexual reproduction
Which one of the following conditions would allow gene frequencies to change by chance?
small populations
The liver is involved in detoxification of many poisons and drugs. Which of the following structures is primarily involved in this process and, therefore, abundant in liver cells?
smooth endoplasmic reticulum
Most Swiss starlings produce four to five eggs in each clutch. Starlings producing fewer or more than this have reduced fitness. Which of the following terms best describes this situation?
stabilizing selection
Consider two solutions: solution X has a pH of 4; solution Y has a pH of 7. From this information, we can reasonably conclude that ________.
the concentration of hydrogen ions in solution X is 1000 times as great as the concentration of hydrogen ions in solution Y
How does the primary transcript in the nucleus of a eukaryotic cell compare to the functional mRNA?
the primary transcript is larger than the mRNA
Which of the following processes is the first event to take place in translation in eukaryotes?
the small subunit of the ribosome recognizes and attaches to the 5′ cap of mRNA
In the structural organization of many eukaryotic genes, individual exons may be related to which of the following?
the various domains of the polypeptide product
Gene expression is often assayed by measuring the level of mRNA produced from a gene. What level of the control of gene expression can by analyzed by this type of assay?
transcriptional control
Once a peptide bond has been formed between the amino acid attached to the tRNA in the P site and the amino acid associated with the tRNA in the A site, what process occurs next?
translocation
Under what conditions does the trp repressor block transcription of the trp operon?
when the repressor binds to tryptophan