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Concepts of Genetics, 10e (Klug/Cummings/Spencer/Palladino)
Chapter 14 Translation and Proteins
1) Which of the following are among the major components of prokaryotic ribosomes?
A) 12S rRNA, 5.8S rRNA, and proteins
B) 16S rRNA, 5.8S rRNA, and 28S rRNA
C) 16S rRNA, 5S rRNA, and 23S rRNA
D) lipids and carbohydrates
E) 18S rRNA, 5.8S rRNA, and proteins
2) The term peptidyl transferase relates to ________.
A) base additions during mRNA synthesis
B) peptide bond formation during protein synthesis
C) elongation factors binding to the large ribosomal subunit
D) discontinuous strand replication
E) 5 capping of mRNA
3) The one-gene:one-enzyme hypothesis emerged from work on which two organisms?
A) E. coli and yeast
B) Drosophila and humans
C) Neurospora and Drosophila
D) E. coli and humans
E) All of the answers listed are correct.
4) The chain of adult hemoglobin is composed of 146 amino acids of a known sequence. In comparing the normal chain with the chain in sickle cell hemoglobin, what alteration is one likely to find?
A) valine instead of glutamic acid in the sixth position
B) glutamic acid replacing valine in the first position
C) extensive amino acid substitutions
D) trinucleotide repeats
E) frameshift substitutions
5) The primary structure of a protein is determined by ________.
A) the sequence of amino acids
B) hydrogen bonds formed between the components of the peptide linkage
C) a series of helical domains
D) pleated sheets
E) covalent bonds formed between fibroin residues
6) One form of posttranslational modification of a protein includes ________.
A) removal of introns
B) shuffling of exons
C) removal or modification of terminal amino acids
D) removal of exons
7) Which protein class directly controls many of the metabolic reactions within a cell?
A) structural proteins
B) repressor proteins
C) operator proteins
E) hydrophilic proteins
8) The secondary structure of a protein includes ________.
A) gamma and delta
B) alpha and gamma
C) -helix and -pleated sheet
D) hydrophobic clusters
E) disulfide bridges
9) Side groups of amino acids are typically classified under which of the following?
A) polar, nonpolar
B) linear, circular
C) alpha, omega
D) long, short
E) primary, secondary
10) A protein is 300 amino acids long. Which of the following could be the number of nucleotides in the section of DNA that codes for this protein? (Remember: DNA is double-stranded.)
Section: 14.1, 14.2
11) By their experimentation using the Neurospora fungus, Beadle and Tatum were able to propose the far-reaching hypothesis that ________.
A) prototrophs will grow only if provided with nutritional supplements
B) several different enzymes may be involved in the same step in a biochemical
C) the role of a specific gene is to produce a specific enzyme
D) genetic recombination occurred in Neurospora
E) more than one codon can specify a given amino acid
12) A short segment of an mRNA molecule is shown below. The polypeptide it codes for is also shown:
5-AUGGUGCUGAAG : methionine-valine-leucine-lysine
Assume that a mutation in the DNA occurs so that the fourth base (counting from the 5 end) of the messenger RNA now reads A rather than G. What sequence of amino acids will the mRNA now code for? (You do not need a copy of the genetic code to answer the question.)
Section: 14.1, 14.2
13) During translation, which triplets signal chain termination?
Answer: UAA, UGA, UAG
14) Describe each of the following parameters that relate to the structure and function of tRNA:
(a)four functional domains
(a) The four functional domains are amino acid attachment site, ribosome binding site, anticodon, and aminoacyl synthetase binding site.
(b) The Wobble hypothesis states that the first two positions of the codon are precise in their complementary relationships. However, the third position is less specific.
15) Draw and label the spatial and polarity relationships among the following translational components: ribosome (small and large subunits), growing polypeptide chains, amino acid attachment to tRNA, mRNA, codon, and anticodon.
16) The following drawing represents simultaneous transcription and translation in E. coli.
Answer the questions below the drawing. The direction of the RNA polymerase is given by the arrow.
(a) Is the letter A nearer the 5 or the 3 end of the molecule? ________
(b) Is the letter B nearer the 5 or the 3 end of the molecule? ________
(c)Is the letter C nearer the 5 or the 3 end of the tRNA molecule? ________
(d) What is the S value for the large rRNA that is closest to the letter D? ________
(e) Which terminus (N or C) of the growing polypeptide chain is nearer to the letter E? ________
Answer: (a) 3, (b) 5, (c) 3, (d) 23S, (e) N
17) Knowing that the base sequence of any given messenger RNA is responsible for precisely ordering the amino acids in a respective protein, present two mechanisms by which intrinsic properties of mRNA may regulate the net output of a given gene.
Answer: (a) Final output of a given gene may be influenced by the stability of an mRNA, and stability of an mRNA is determined in part by its base content and sequence. (b) Differential splicing of mRNA (actually mRNA precursors) can influence how much of a given product will be made from a gene.
Section: 14.1, 14.2
18) What are polyribosomes?
Answer: clusters of ribosomes held together by an mRNA
19) Below are several phenomena relating to protein structure. Clearly describe each phenomenon, the conditions under which each occurs, and the probable influence each has on protein structure.
(a) hydrophobic interactions
(b) hydrogen bonds
(c) disulfide bridges
(a) Hydrophobic interactions: These are nonpolar side chains of amino acids that tend to associate to form hydrophobic clusters usually away from the protein surface.
(b) Hydrogen bonds: Such bonds may occur between the components of the peptide bond, the side chains, or a combination of the two. They are responsible for helical and pleated sheet structures of proteins.
(c) Disulfide bridges: Such bonds are formed between two cysteine side chains and, because of their covalent nature, represent relatively strong attractive forces between different (sometimes distant) regions of proteins.
20) Early in the 1900s, Sir Archibald Garrod studied a number of metabolic defects in humans. One particular disorder involved the inability to metabolize homogentisic acid. What is the name of this disorder?
21) Given the following table:
1 2 3 4
Strain A + +
Strain B + + +
Strain C + + + +
Strain D +
where numbers 1 through 4 indicate four supplements that must be added to sustain growth of the organism. Determine a possible metabolic pathway that would give the results seen for the four mutant strains, A through D.
22) The following table presents the effect of different media on the growth response of tryptophan mutations in Salmonella typhimurium (+ = growth, = no growth).
Medium Supplemented with
Strain No Supplement IGP AA IN TRY
trp-8 + + + +
trp-2 + + +
trp-3 + +
(a) Construct the biochemical pathway for the compounds IGP, AA, IN, and TRY based on these data.
(b) Place strains of bacteria (mutations) in the appropriate steps in the pathway.
(c) In bacteria it is often possible to make partial diploid strains. Assume that a diploid strain was made containing the complete genomes of the trp-2 and trp-1 strains. Would this diploid strain be able to grow on the unsupplemented medium? Explain your answer.
(c) Yes, complementation will occur because the trp-2 strain is also trp-1+ and the trp-1 strain is also trp-2+.
23) The histidine locus is complex in Neurospora crassa. Many multiple alleles are known, such as 245, CD-16, 430, and 261, which lack the ability to synthesize the amino acid histidine. Such strains will consequently be unable to grow on minimal medium. Provide an interpretation for the following observations involving these histidine strains of Neurospora.
(a) When heterokaryons are produced (single cells containing nuclei from two different strains), the combination of strains 245 and 261 always produces growth on minimal medium, whereas the combination of strains CD-16 and 245 never produces growth on minimal medium.
(b) When strain 430 is crossed with strain 261, rare ascospores are produced, which can grow on minimal medium.
(a) There are at least two functional domains (complementation groups) in the histidine locus; CD-16 and 245 are in the same domain, whereas 261 is in the other domain.
(b) Rare crossing over between mutation sites in strain 430 and strain 261 produces the wild-type gene.
24) Describe the conceptual basis for constructing biochemical pathways using nutrient supplement experiments with Neurospora.
Answer: The substance, which when added to minimal medium cures the largest number of strains, must be toward the end of the pathway. A supplement that fails to cure many strains must be early in the pathway.
25) Below is a set of experimental results relating the growth (+) of Neurospora on several media (MM = minimal medium). Based on the information provided, present the biochemical pathway and the locations of the metabolic blocks.
MM MM+A MM+B
s111 + +
t60 + + +
26) The problem below relates to the synthesis of several intermediates in the citric acid cycle, which is essential in the production of ATP through aerobic respiration. A set of experimental results relating the growth (+) of Neurospora on several media is given in the table. Based on the information provided, present the biochemical pathway for the substances oxaloacetate, fumarate, malate, and succinate, and the locations of the metabolic blocks produced by the various strains.
MM MM MM MM MM
+ oxaloacetate + fumarate + malate + succinate
l62 + +
l41 + + +
MM = minimal medium
27) Three major types of RNAs are mRNA, rRNA, and tRNA. For each of the conditions below, predict the consequences in terms of the population of proteins being synthesized in a particular cell. What qualitative and quantitative changes, if any, are expected in the individual protein involved (if one is involved) and in the population of proteins in this cell?
(a) An acridine dye-induced mutation (adds or deletes single bases in DNA) leads to an mRNA for one protein-producing gene. The condition is heterozygous in the involved cell.
(b) A deletion (homozygous) that removes approximately half of the rRNA genes.
(a) Population of proteins: Half of the protein products of that gene will be defective, and the other half will be normal. Individual protein: The protein should show multiple amino acid substitutions downstream from the point of the mutation. If a nonsense triplet is introduced, the protein will be shortened in the substituted region.
(b) Population of proteins: There would be an overall reduction in protein synthesis. Individual proteins: All of the proteins would be made in their normal form but at reduced levels.
Section: 14.1, 14.2
28) Phenylketonuria is a recessive metabolic disease caused by the absence of the enzyme phenylalanine hydroxylase. What is the phenotype of the disease, and what causes the phenotype to develop?
Answer: Mental retardation is thought to be caused by the buildup of phenylalanine and its derivatives.
29) Much has been learned about the relationship between genes and gene products through the use of the mold Neurospora. What specific attributes make Neurospora a good organism for such studies?
Answer: knowledge of its biochemistry; its haploid ascospores; relative ease of isolating nutritional mutations
30) Describe the basic structure of normal adult hemoglobin and the abnormality observed in sickle-cell hemoglobin.
Answer: The predominant form of adult hemoglobin is composed of two a and two b chains. In sickle-cell hemoglobin, the sixth amino acid in the b chain is valine instead of glutamic acid.
31) What is the general ethnic distribution of the sickle-cell gene?
Answer: The gene is most common among the African American population.
32) What is the structure of HbF, fetal hemoglobin?
Answer: two and two chains
33) In what ways do the amino acid side chains interact to influence protein function?
Answer: Higher level folding of proteins is dependent on a variety of interactions (ionic, covalent, hydrogen, hydrophobic, hydrophilic, etc.), which determine the functional three-dimensional structure of proteins.
34) Assuming that an amino acid sequence is 250 amino acids long, how many different molecules, each with a unique sequence, could be formed?
35) Regarding the protein structure, how are -pleated sheets arranged and stabilized?
Answer: Several chains run in parallel or antiparallel fashion stabilized by hydrogen bonds formed between components of the peptide linkage.
36) Considering the types of side chains on amino acids and their relationship to protein structure, where are the amino acids with hydrophobic side chains most likely to be located?
Answer: away from the water environment and in the interior portion of the molecule
37) What are two forms of posttranslational modification of proteins?
Answer: removal of terminal amino acids; modification (phosphorylation, glycosylation) of side chains
38) What medical procedures are applied to reduce or avoid potential neurological damage caused by phenylketonuria (PKU)?
Answer: screening of newborns and a low phenylalanine diet
39) Nutritional mutants in Neurospora can be cured by treating the medium with substances in the defective metabolic pathway. What determines whether the mutant strain (auxotroph) is cured by a particular substance?
Answer: The substance needs to be added after the metabolic block in the biochemical pathway.
40) Studies of Neurospora led to the ________ statement, whereas studies of human hemoglobin led to the ________ statement .
Answer: one-gene:one-enzyme; one-gene:one-polypeptide
Section: 14.6, 14.7
41) A procedure that is often used to separate molecules by using their molecular charges is called ________.
42) Electrophoretic separation of HbA from HbS is based on a difference in their ________.
43) Briefly describe what is meant by the term exon shuffling.
Answer: In the 1970s, Walter Gilbert suggested that the functional regions of genes in eukaryotes consist of collections of exons originally present in ancestral genes that are brought together through various recombinational events over time.
44) Assume that a base addition occurs early in the coding region of a gene. Is the protein product of this gene expected to have more or fewer altered amino acids compared with the original gene with a base deletion late in the coding region?
Section: 14.1, 14.2
45) Proteins are composed of strings of nucleotides connected together by 5-3 phosphodiester bonds.
46) The ribonucleic acid components known to exist in eukaryotic ribosomes are the following: 5.8S, 18S, 28S, and 5S.
47) Prokaryotic and eukaryotic ribosomes are structurally and chemically identical.
48) rDNA is the portion of a genome that is involved in the production of ribosomal RNA.
49) The secondary structure of a protein is dependent on polar interactions among the side chains of the amino acids.
50) The primary structure of a protein is composed of the sequence of amino acids in that protein.
51) Sickle-cell anemia is caused by the absence of the alpha chain of hemoglobin.
52) When a metabolic block occurs in a biochemical pathway, it is common for amount of the substance immediately prior to that block to increase.
Section: 14.5, 14.6
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