Chapter 5

True or False: C. Gene expression is the process of duplicating genes during DNA replication.

False. Gene expression is the process of going from gene sequence to RNA sequence, to protein sequence.

5-2 Many of the breakthroughs in modern biology came after Watson and Crick published their model of DNA in 1953. In what decade did scientists first identify chromosomes? (a) 1880s (b) 1920s (c) 1940s (d) 1780s

a

5-19 The manner in which a gene sequence is related to its respective protein sequence is referred to as the _________ code. (a) protein (b) genetic (c) translational (d) expression

b

5-49 When there is a well-established segment of heterochromatin on an interphase chromosome, there is usually a special barrier sequence that prevents the heterochromatin from expanding along the entire chromosome. Gene A, which is normally expressed, has been moved by DNA recombination near an area of heterochromatin. None of the daughter cells produced after this recombination event express gene A, even though its DNA sequence is unchanged. What is this the best way to describe what has happened to the function of gene A in these cells? (a) barrier destruction (b) heterochromatization (c) epigenetic inheritance (d) euchromatin depletion

c

5-18 The complete set of information found in a given organism's DNA is called its ____________. (a) genetic code (b) coding sequence (c) gene (d) genome

d

5-26 The human genome has enough DNA to stretch more than 2 m. However, this DNA is not contained in a single molecule; it is divided into linear segments and packaged into structures called chromosomes. What is the total number of chromosomes found in each of the somatic cells in your body? (a) 22 (b) 23 (c) 44 (d) 46

d

5-4 In a DNA double helix, _____________________. (a) the two DNA strands are identical (b) purines pair with purines (c) thymine pairs with cytosine (d) the two DNA strands run antiparallel

d

5-41 The octameric histone core is composed of four different histone proteins, assembled in a stepwise manner. Once the core octamer has been formed, DNA wraps around it to form a nucleosome core particle. Which of the following histone proteins does not form part of the octameric core? (a) H4 (b) H2A (c) H3 (d) H1

d

5-7 Several experiments were required to demonstrate how traits are inherited. Which scientist or team of scientists obtained definitive results demonstrating that DNA is the genetic molecule? (a) Griffith (b) Watson (c) Crick (d) Hershey and Chase

d

True or False: DNA molecules, like proteins, consist of a single, long polymeric chain that is assembled from small monomeric subunits.

False. DNA is double-stranded. It is actually is made of two polymers that are complementary in sequence.

True or False: Hydrogen bonds between each nucleotide hold individual DNA strands together.

False. Nucleotides are linked covalently through phosphodiester bonds. Hydrogen-bonding between nucleotides from opposite strands holds the DNA molecule together.

True or False: B. All functional DNA sequences inside a cell code for protein products.

False. Some sequences encode only RNA molecules, some bind to specific regulatory proteins, and others are sites where specific chrosomosomal protein structures are built (for example, centromeric and telomeric DNA).

True or False: There are five different nucleotides that become incorporated into a DNA strand.

False. There are four different nucleotides that are used to make a DNA polymer: adenine, thymine, guanine, and cytosine. A fifth nucleotide, uracil, is found exclusively in RNA molecules, replacing thymine nucleotides in the DNA sequence.

True or False: D. Gene sequences correspond exactly to the respective protein sequences produced from them.

False. This statement is false for two reasons. First, genes often contain intron sequences. Second, genes always contain nucleotides flanking the protein-coding sequences that are required for the regulation of transcription and translation.

True or False: The polarity of a DNA strand results from the polarity of the nucleotide subunits.

True

5-10 The DNA from two different species can often be distinguished by a difference in the ______________________. (a) ratio of A + T to G + C (b) ratio of A + G to C + T (c) ratio of sugar to phosphate (d) presence of bases other than A, G, C, and T

a

5-33 The images of chromosomes we typically see are isolated from mitotic cells. These mitotic chromosomes are in the most highly condensed form. Interphase cells contain chromosomes that are less densely packed and __________________________. (a) occupy discrete territories in the nucleus (b) share the same nuclear territory as their homolog (c) are restricted to the nucleolus (d) are completely tangled with other chromosomes

a

5-35 Mitotic chromosomes are _____ times more compact than a DNA molecule in its extended form. (a) 10,000 (b) 100,000 (c) 1000 (d) 100

a

5-38 The classic "beads-on-a-string" structure is the most decondensed chromatin structure possible and is produced experimentally. Which chromatin components are not retained when this structure is generated? (a) linker histones (b) linker DNA (c) nucleosome core particles (d) core histones

a

5-48 Methylation and acetylation are common changes made to histone H3, and the specific combination of these changes is sometimes referred to as the "histone code." Which of the following patterns will probably lead to gene silencing? (a) lysine 9 methylation (b) lysine 4 methylation and lysine 9 acetylation (c) lysine 14 acetylation (d) lysine 9 acetylation and lysine 14 acetylation

a

5-6 Several experiments were required to demonstrate how traits are inherited. Which scientist or team of scientists first demonstrated that cells contain some component that can be transferred to a new population of cells and permanently cause changes in the new cells? (a) Griffith (b) Watson and Crick (c) Avery, MacLeod, and McCarty (d) Hershey and Chase

a

5-3 Mitotic chromosomes were first visualized in the 1880s with the use of very simple tools: a basic light microscope and some dyes. Which of the following characteristics of mitotic chromosomes reflects how they were named? (a) motion (b) color (c) shape (d) location

b

5-36 Interphase chromosomes are about______ times less compact than mitotic chromosomes, but still are about______ times more compact than a DNA molecule in its extended form. (a) 10; 1000 (b) 20; 500 (c) 5; 2000 (d) 50; 200

b

5-43 Stepwise condensation of linear DNA happens in five different packing processes. Which of the following four processes has a direct requirement for histone H1? (a) formation of "beads-on-a-string" (b) formation of the 30 nm fiber (c) looping of the 30 nm fiber (d) packing of loops to form interphase chromosomes

b

5-47 The N-terminal tail of histone H3 can be extensively modified, and depending on the number, location, and combination of these modifications, these changes may promote the formation of heterochromatin. What is the result of heterochromatin formation? (a) increase in gene expression (b) gene silencing (c) recruitment of remodeling complexes (d) displacement of histone H1

b

5-28 The process of sorting human chromosomes pairs by size and morphology is called karyotyping. A modern method employed for karyotyping is called chromosome painting. How are individual chromosomes "painted"? (a) with a laser (b) using fluorescent antibodies (c) using fluorescent DNA molecules (d) using green fluorescent protein

c

5-39 Nucleosomes are formed when DNA wraps _____ times around the histone octamer in a ______ coil. (a) 2.0; right-handed (b) 2.5; left-handed (c) 1.7; left-handed (d) 1.3; right-handed

c

5-42 The core histones are small, basic proteins that have a globular domain at the C-terminus and a long extended conformation at the N-terminus. Which of the following is not true of the N terminal "tail" of these histones? (a) It is subject to covalent modifications, (b) It extends out of the nucleosome core. (c) It binds to DNA in a sequence-specific manner. (d) It helps DNA pack tightly.

c

5-45 Although the chromatin structure of interphase and mitotic chromosomes is very compact, DNA-binding proteins and protein complexes must be able to gain access to the DNA molecule. Chromatin-remodeling complexes provide this access by __________________. (a) recruiting other enzymes (b) modifying the N-terminal tails of core histones (c) using the energy of ATP hydrolysis to move nucleosomes (d) denaturing the DNA by interfering with hydrogen-bonding between base pairs

c

5-8 Which of the following chemical groups is not used to construct a DNA molecule? (a) five-carbon sugar (b) phosphate (c) nitrogen-containing base (d) six-carbon sugar

d

5-9 Which of the following sequences can fully base-pair with itself? (a) 5′-AAGCCGAA-3′ (b) 5′-AAGCCGTT-3′ (c) 5′-AAGCGCAA-3′ (d) 5′-AAGCGCTT-3′

d

True or False: A. Each strand of DNA contains all the information needed to create a new double- stranded DNA molecule with the same sequence information.

true