Chapter 17

25 July 2022
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The "triplet code" refers to the fact that _________.
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three nucleotides code for a single amino acid
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Gene expression is __________.
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the process by which DNA directs the synthesis of proteins The DNA inherited by an organism leads to specific traits because DNA dictates the synthesis of proteins or, in some cases, just RNA molecules. In other words, proteins are the link between genotype and phenotype. The expression of genes that code for proteins includes two stages: transcription and translation.
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Bacteria can transcribe and translate human genes to produce functional human proteins because __________.
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the genetic code is nearly universal
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Stop codons are unique because they __________.
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do not code for amino acids that allow a releasing factor to bind to the A site of the ribosome
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Because the bacterial cell's DNA is not surrounded by a nuclear envelope, __________ occur(s).
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coupled transcription and translation
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The type of point mutation that results in a premature stop codon is called a _________ mutation.
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nonsense Substitution mutations are usually missense mutations; that is, the altered codon still codes for an amino acid and thus makes sense, although not necessarily the right sense. But a point mutation can also change a codon for an amino acid into a stop codon. This is called a nonsense mutation, and it causes translation to be terminated prematurely; the resulting polypeptide will be shorter than the polypeptide encoded by the normal gene. Nearly all nonsense mutations lead to nonfunctional proteins.
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Eukaryotic processing of the primary transcript includes __________.
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the addition of a 5๊žŒ cap, a 3๊žŒ poly-A tail, and the splicing out of introns
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When RNA is being made, the RNA base _________ always pairs with the base __________ in DNA.
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U; A
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How many nucleotides are needed to code for a protein with 450 amino acids?
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At least 1,350 three times as much or 450 x 3 = 1,350. Because codons are nucleotide triplets, the number of nucleotides making up a genetic message must be three times the number of amino acids in the protein product.
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Which of the following best describes the arrangement of genetic information in a DNA molecule?
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The three-nucleotide words of a gene are arranged in a nonoverlapping series on the DNA template strand. The genetic instructions for a polypeptide chain are written in the DNA as a series of nonoverlapping, three-nucleotide words. The series of words in a gene is transcribed into a complementary series of nonoverlapping, three-nucleotide words in mRNA, which is then translated into a chain of amino acids.
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Polysomes may be defined as __________.
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groups of ribosomes
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An exception to the one gene-one enzyme hypothesis is __________.
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that not all genes code for enzymes; some genes code for structural proteins such as keratin
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One strand of a DNA molecule has the following sequence: 3-AGTACAAACTATCCACCGTC-5. In order for transcription to occur in that strand, there would have to be a specific recognition sequence, called a(n) __________, to the left of the DNA sequence indicated.
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promoter
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The bonds that hold tRNA molecules in the correct three-dimensional shape are __________.
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hydrogen bonds
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Which of the following is a post-translational modification of a polypeptide? The growing polypeptide signals the ribosome to attach to the ER Removal of introns and splicing of exons Complementary base pairing of mRNA and tRNA in the ribosome Formation of a polysome that allows simultaneous formation of many polypeptides from one mRNA transcript Cleavage of a polypeptide into two or more chains
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Cleavage of a polypeptide into two or more chains
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The function of tRNA during protein synthesis is to __________.
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deliver amino acids to their proper site during protein synthesis The message is a series of codons along an mRNA molecule, and the translator is called transfer RNA (tRNA). The function of tRNA is to transfer amino acids from the cytoplasmic pool of amino acids to a growing polypeptide in a ribosome. A cell keeps its cytoplasm stocked with all 20 amino acids, either by synthesizing them from other compounds or by taking them up from the surrounding solution.
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__________ is the synthesis of a polypeptide using information in the mRNA.
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translation During this stage, there is a change in language: The cell must translate the nucleotide sequence of an mRNA molecule into the amino acid sequence of a polypeptide. The sites of translation are ribosomes, molecular complexes that facilitate the orderly linking of amino acids into polypeptide chains.
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Genetic information of eukaryotic cells is transferred from the nucleus to the cytoplasm in the form of __________.
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RNA In a eukaryotic cell, by contrast, the nuclear envelope separates transcription from translation in space and time. Transcription occurs in the nucleus, and mRNA is then transported to the cytoplasm, where translation occurs.
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In eukaryotic cells, a __________ by a __________ targets a growing peptide to the endoplasmic reticulum.
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signal peptide; signal-recognition particle
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RNA molecules that function as enzymes are called __________.
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ribozymes The idea of a catalytic role for the RNAs in the spliceosome arose from the discovery of ribozymes, RNA molecules that function as enzymes. In some organisms, RNA splicing can occur without proteins or even additional RNA molecules: The intron RNA functions as a ribozyme and catalyzes its own excision! For example, in the ciliate protist Tetrahymena, self-splicing occurs in the production of ribosomal RNA (rRNA), a component of the organism's ribosomes. The pre-rRNA actually removes its own introns. The discovery of ribozymes rendered obsolete the idea that all biological catalysts are proteins.
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By bombarding the fungus Neurospora crassa with X-rays, Beadle and Tatum were able to study __________ and characterize enzymes in a __________.
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nutritional mutants; biochemical pathway
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Insertions and deletions are called __________ mutations.
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frameshift
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The TATA box is a __________ that allows for the binding of __________ and __________.
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eukaryotic promoter; transcription factors; RNA polymerase II
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The sickle-cell ฮฒ-globin mutation is an example of a __________.
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missense mutation Substitutions that change one amino acid to another are called missense mutations. Such a mutation may have little effect on the protein: The new amino acid may have properties similar to those of the amino acid it replaces, or it may be in a region of the protein where the exact sequence of amino acids is not essential to the protein's function. Thus, the nucleotide-pair substitutions of greatest interest are those that cause a major change in a protein. The alteration of a single amino acid in a crucial area of a proteinโ€”such as in the part of the ฮฒ-globin subunit of hemoglobin shown belowโ€”can significantly alter protein activity.
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The structures called snRNPs are ________
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part of a spliceosome
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What is the proper order of the following events in the expression of a eukaryotic gene? 1. translation 2. RNA processing 3. transcription 4. modification of protein
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3 2 1 4
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What is a key difference in gene expression between eukaryotic and prokaryotic cells?
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In prokaryotic cells, the mRNA transcript is immediately available as mRNA without processing.
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_________ is the synthesis of RNA using information in the DNA.
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Transcription
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Which of the following catalyzes the linkage between ribonucleotides to form RNA during gene expression?
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RNA polymerase