Q&A Hero

Q: The β chain of adult hemoglobin is composed of 146 amino acids of a known sequence. In comparing the normal β chain with the β 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

Q: 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 pathway 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

Q: 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.

Q: 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

Q: The term peptidyl transferase relates to ________.A) base additions during mRNA synthesisB) peptide bond formation during protein synthesisC) elongation factors binding to the large ribosomal subunitD) discontinuous strand replicationE) 5-² capping of mRNA

Q: A short segment of an mRNA molecule is shown below. The polypeptide it codes for is also shown:5-²-AUGGUGCUGAAG-3-²: methionine-valine-leucine-lysineAssume that a mutation in the DNA occurs so that the fourth base (counting from the 5"² 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.)A) methionine-valine-leucine-lysineB) methionine-lysine-leucine-lysineC) methionine-leucine-leucine-lysineD) methionine-valine-methionine-lysineE) methionine-methionine-leucine-lysine

Q: 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.) A) 3 B) 100 C) 300 D) 500 E) 1800

Q: A 5-²-cap describes the addition of a base, usually thymine, to the 5"² end of a completed peptide.

Q: A 3-² poly-A tail and a 5-²-cap are common components of prokaryotic RNAs.

Q: RNA processing occurs when amino acids are removed from nascent proteins.

Q: Transcription factors function to help move ribosomes along the mRNA.

Q: An intron is a section of an RNA that gets spliced out.

Q: Heterogeneous nuclear RNA is a primary transcript in eukaryotes that is processed prior to involvement in translation.

Q: Messenger RNA is usually polycistronic in eukaryotes.

Q: The triplet AUG is commonly used as a start codon during translation.

Q: The enzyme polynucleotide phosphorylase is capable of generating a random assembly of ribonucleotides.

Q: The code is nonoverlapping, meaning that, assuming "standard translation," a given base participates in the specification of one and only one amino acid.

Q: In eukaryotes, which three factors appear to encourage the specific association of RNA polymerase(s) to a specific region of DNA?

Q: What is meant by the term heterogeneous nuclear RNA (hnRNA)?

Q: Describe a difference between the RNA polymerases of eukaryotes and prokaryotes.

Q: Regarding the efficient initiation of transcription by RNA polymerase II, which specific "upstream" signals appear to be involved?

Q: Describe how the sigma subunit (factor) of E. coli RNA polymerase participates in transcription.

Q: What is polycistronic mRNA?

Q: In the context of molecular genetics, how does one reconcile the terms overlapping genes and nonoverlapping code?

Q: Referring to the genetic code, what is meant by "wobble"?

Q: The finding that virtually all organisms use the same genetic code provides the basis for declaring that the code is universal. Name at least two exceptions to such universality.

Q: List four base triplets that are clearly responsible for punctuation (initiation, termination).

Q: There is some indication that the code is in some way ordered; a certain pattern exists. Describe an observation that supports this view.

Q: What is meant by punctuation in terms of the genetic code?

Q: Describe the function of N-formylmethionine in prokaryotes.

Q: Of the following three types of nucleic acidsDNA, mRNA, tRNAwhich is most likely to contain modified bases?

Q: The relationship between codon and anticodon can be characterized as involving ________.

Q: A base at the first position of an anticodon on the tRNA would pair with a base at the ________ position of the mRNA.

Q: "Breaking the genetic code" has been referred to as one of the most significant scientific achievements in modern times. Describe (in outline or brief statement form) the procedures used to break the code.

Q: What two experimental procedures allowed deciphering of the ordered triplet assignments of the genetic code?

Q: Suppose that in the use of polynucleotide phosphorylase, nucleotides A and C are added in a ratio of 1A:5C. What is the probability that an AAA sequence will occur?

Q: From the late 1950s to the mid-1960s, numerous experiments using in vitro cell-free systems provided information on the nature of the genetic code. Briefly outline significant experiments in the determination of the genetic code.

Q: What is a nonsense mutation?

Q: Sidney Brenner argued that the code was nonoverlapping because he considered that coding restrictions would occur if it were overlapping. A second major argument against an overlapping code involved the effect of a single nucleotide change. In an overlapping code, how many adjacent amino acids would be affected by a point mutation? In a nonoverlapping code, how many amino acid(s) would be affected?

Q: Describe the direction of information flow in living systems. Use appropriate, scientific terms in your description.

Q: In which cellular organelle do the three posttranscriptional modifications often seen in the maturation of mRNA in eukaryotes occur? A) nucleus B) cytoplasm C) mitochondrion D) lysosome E) Golgi

Q: If one compares the base sequences of related genes from different species, one is likely to find that corresponding ________ are usually conserved, but the sequences of ________ are much less well conserved. A) exons; introns B) introns; exons C) introns; chaperons D) chaperons; exons E) introns; proteins

Q: Which of the following two terms relate most closely to split genes?A) 5-²-cap, 3-²-poly-A tailB) introns, exonsC) elongation, terminationD) transcription, translationE) heteroduplex, homoduplex

Q: An intron is a section of ________. A) protein that is clipped out posttranslationally B) RNA that is removed during RNA processing C) DNA that is removed during DNA processing D) transfer RNA that binds to the anticodon E) carbohydrate that serves as a signal for RNA transport

Q: It has been recently determined that the gene for Duchenne muscular dystrophy (DMD) is more than 2000 kb (kilobases) in length; however, the mRNA produced by this gene is only about 14 kb long. What is a likely cause of this discrepancy? A) The exons have been spliced out during mRNA processing. B) The DNA represents a double-stranded structure, whereas the RNA is single-stranded. C) There are more amino acids coded for by the DNA than by the mRNA. D) The introns have been spliced out during mRNA processing. E) When the mRNA is produced, it is highly folded and therefore less long.

Q: Which of the following contains the three posttranscriptional modifications often seen in the maturation of mRNA in eukaryotes?A) 5-²-capping, 3-²-poly(A) tail addition, splicingB) 3-²-capping, 5-²-poly(A) tail addition, splicingC) removal of exons, insertion of introns, cappingD) 5-²-poly(A) tail addition, insertion of introns, cappingE) heteroduplex formation, base modification, capping

Q: When considering the initiation of transcription, one often finds consensus sequences located in the region of the DNA where RNA polymerase(s) binds. Which of the following is a common consensus sequence? A) TATA B) GGTTC C) TTTTAAAA D) any trinucleotide repeat E) satellite DNAs

Q: The relationship between a gene and a messenger RNA is that ________. A) genes are made from mRNAs B) mRNAs are made from genes C) mRNAs make proteins, which then code for genes D) all genes are made from mRNAs E) mRNA is directly responsible for making Okazaki fragments

Q: The genetic code is fairly consistent among all organisms. The term often used to describe such consistency in the code is ________. A) universal B) exceptional C) trans-specific D) overlapping E) none of the above

Q: What is one particular function that the codons (UAA, UGA, or UAG) serve during protein synthesis? A) UAA, UGA, and UAG are initiator codons, not termination codons. B) They allow the mRNA to assume a variety of linear conformations. C) These triplets cause frameshift mutations, but are not involved in termination. D) They provide a substrate for the addition of the initiator amino acid. E) They act in chain termination.

Q: When examining the genetic code, it is apparent that ________. A) there can be more than one amino acid for a particular codon B) AUG is a terminating codon C) there can be more than one codon for a particular amino acid D) the code is ambiguous in that the same codon can code for two or more amino acids E) there are 44 stop codons because there are only 20 amino acids

Q: What is the initiator triplet in both prokaryotes and eukaryotes? What amino acid is recruited by this triplet? A) UAA; no amino acid called in B) UAA or UGA; arginine C) AUG; arginine D) AUG; methionine E) UAA, methionine

Q: What is the name given to the three bases in a messenger RNA that bind to the anticodon of tRNA to specify an amino acid placement in a protein? A) protein B) anti-anticodon C) cistron D) rho E) codon

Q: In 1964, Nirenberg and Leder used the triplet binding assay to determine specific codon assignments. A complex of which of the following components was trapped in the nitrocellulose filter? A) ribosomes and DNA B) free tRNAs C) charged tRNA, RNA triplet, and ribosome D) uncharged tRNAs and ribosomes E) sense and antisense strands of DNA

Q: Significant in the deciphering of the genetic code was the discovery of the enzyme polynucleotide phosphorylase. What is this enzyme used for? A) manufacture of synthetic RNA for cell-free systems B) ribosomal translocation C) peptide bond formation D) production of ribosomal proteins E) degradation of RNA

Q: When scientists were attempting to determine the structure of the genetic code, Crick and coworkers found that when three base additions or three base deletions occurred in a single gene, the wild-type phenotype was sometimes restored. These data supported the hypothesis that ________. A) the code is triplet B) the code contains internal punctuation C) AUG is the initiating triplet D) the code is overlapping E) there are three amino acids per base

Q: A class of mutations that results in multiple contiguous (side-by-side) amino acid changes in proteins is probably caused by which of the following type of mutation? A) frameshift B) transversion C) transition D) base analog E) recombinant

Q: The genetic code is said to be triplet, meaning that there ________. A) are three amino acids per base in mRNA B) are three bases in mRNA that code for an amino acid C) may be three ways in which an amino acid may terminate a chain D) are three "nonsense" triplets E) none of the above

Q: Each human contains an identical set of VNTRs.

Q: In contrast with euchromatin, heterochromatin contains more genes and is earlier replicating.

Q: In situ hybridization allows one to "visualize" the location of labeled RNA or DNA in a tissue or cell.

Q: Telomerase is an enzyme involved in the replication of the ends of eukaryotic chromosomes.

Q: Viral genomes are always linear, double-stranded DNA.

Q: The E. coli chromosome is circular and double-stranded DNA.

Q: Chromosomal regions that represent evolutionary vestiges of duplicated copies of genes that have underdone sufficient mutations to render them untranscribable are called ________.

Q: Briefly describe the makeup of VNTRs (variable number tandem repeats).

Q: Approximately how much of the mammalian genome is composed of repetitive DNA?

Q: How do VNTRs relate to DNA fingerprinting?

Q: What is meant by SINE in terms of chromosome structure? By LINE? Why are they called "repetitive"?

Q: Briefly state what is meant by repetitive DNA.

Q: In the formation of nucleosomes, one histone class, H1, is not directly involved, yet it does associate with DNA to form higher level chromosomal structures. Where does this histone (H1) associate?

Q: When native chromatin is digested with micrococcal nuclease, what significant result occurs?

Q: What are histones, and how are they arranged in nucleosomes?

Q: What similarities do bacterial chromosomes have with eukaryotic chromosomes?

Q: In instances in the eukaryotic genome, DNA sequences represent evolutionary vestiges of duplicated copies of genes. What are such regions called and what are their characteristics?

Q: What are minisatellites and microsatellites?

Q: List the components of a nucleosome.

Q: Compare and contrast the chromosome structure of viruses, bacteria, and eukaryotes.

Q: Describe the basic structure of a nucleosome. What is the role of histone H1?

Q: What is unusual about the amino acid composition of histones? How is the function of histones related to the amino acid composition? Of which histones are nucleosomes composed?