For a couple of decades, biologists knew the nucleus contained DNA and proteins. The prevailing opinion was that the genetic material was proteins, and not DNA. The reason for this belief was that proteins are more complex than DNA. What was the basis of this thinking?
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Proteins have a greater variety of three-dimensional forms than does DNA.
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What does transformation involve in bacteria?
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assimilation of external DNA into a cell
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Cytosine makes up 38% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?
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12%
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Chargaffʹs analysis of the relative base composition of DNA was significant because he was able to show what?
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show that the amount of A is always equivalent to T, and C to G.
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Which of the following can be determined directly from X-ray diffraction photographs of crystallized DNA?
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the diameter of the helix
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Why does the DNA double helix have a uniform diameter?
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Purines pair with pyrimidines
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What kind of chemical bond is found between paired bases of the DNA double helix?
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hydrogen
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It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information in which of the following?
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sequence of bases B) phosphate-sugar backbones
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In an analysis of the nucleotide composition of DNA, which of the following will be found?
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A + C = G + T
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Mendel and Morgan did not know about the structure of DNA; however, which of the following of their contributions was (were) necessary to Watson and Crick?
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the particulate nature of the hereditary material
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Replication in prokaryotes differs from replication in eukaryotes for what reason?
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Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many.
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What is meant by the description ʺantiparallelʺ regarding the strands that make up DNA?
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The 5ʹ to 3ʹ direction of one strand runs counter to the 5ʹ to 3ʹ direction of the other strand.
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Once the pattern found after one round of replication was observed, Meselson and Stahl could be confident of which of the following conclusions?
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Replication is not conservative.
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An Okazaki fragment has what arrangement?
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5ʹ RNA nucleotides, DNA nucleotides 3ʹ
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In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin. Which of the following would you expect as a result of this mutation?
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No replication fork will be formed
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Which enzyme catalyzes the elongation of a DNA strand in the 5ʹ → 3ʹ direction?
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DNA polymerase III
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What determines the nucleotide sequence of the newly synthesized strand during DNA replication?
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the nucleotide sequence of the template strand
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Eukaryotic telomeres replicate differently than the rest of the chromosome. This is a consequence of which of the following?
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Gaps left at the 5ʹ end of the lagging strand because of the need for a 3ʹ onto which nucleotides can attach
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The enzyme telomerase solves the problem of replication at the ends of linear chromosomes by which method?
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adding numerous short DNA sequences such as TTAGGG, which form a hairpin turn
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At a specific area of a chromosome, the sequence of nucleotides below is present where the chain opens to form a replication fork: 3ʹ C C T A G G C T G C A A T C C 5ʹ An RNA primer is formed starting at the underlined T (T) of the template. Which of the following represents the primer sequence?
answer
5ʹ A C G U U A G G 3ʹ
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What is the function of DNA polymerase III?
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to add nucleotides to the end of a growing DNA strand
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You briefly expose bacteria undergoing DNA replication to radioactively labeled nucleotides. When you centrifuge the DNA isolated from the bacteria, the DNA separates into two classes. One class of labeled DNA includes very large molecules (thousands or even millions of nucleotides long), and the other includes short stretches of DNA (several hundred to a few thousand nucleotides in length). These two classes of DNA probably represent what?
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leading strands and Okazaki fragments.
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Which of the following removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3ʹ end of Okazaki fragments?
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DNA polymerase I
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Which of the following separates the DNA strands during replication?
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helicase
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Which of the following covalently connects segments of DNA?
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ligase
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Which of the following synthesizes short segments of RNA?
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primase
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The difference between ATP and the nucleoside triphosphates used during DNA synthesis is that
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the nucleoside triphosphates have the sugar deoxyribose; ATP has the sugar ribose.
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how do the leading and lagging strands differ?
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the leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction.
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What best describes the addition of nucleotides to a growing DNA chain?
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A nucleoside triphosphate is added to the 3ʹ end of the DNA, releasing a molecule of pyrophosphate.
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why does a new DNA strand elongates only in the 5' to 3' direction?
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DNA polymerase can only add nucleotides to the free 3' end.
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What is the function of topoisomerase?
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relieving strain in the DNA ahead of the replication fork.
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What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?
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join Okazaki fragments together
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Which of the following help to hold the DNA strands apart while they are being replicated?
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single-strand binding proteins
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Which would you expect of a eukaryotic cell lacking telomerase?
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a reduction in chromosome length
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Which of the following sets of materials are required by both eukaryotes and prokaryotes for replication?
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double-stranded DNA, 4 kinds of dNTPs, primers, origins
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A typical bacterial chromosome has ~4.6 million nucleotides. This supports approximately how many genes?
answer
4.4 thousand
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When DNA is compacted by histones into 10 nm and 30 nm fibers, the DNA is unable to interact with proteins required for gene expression. Therefore, to allow for these proteins to act, the chromatin must constantly alter its structure. Which processes contribute to this dynamic activity?
answer
methylation and phosphorylation of histone tails
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About how many more genes are there in the haploid human genome than in a typical bacterial genome?
answer
1000x
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In a linear eukaryotic chromatin sample, which of the following strands is looped into domains by scaffolding?
answer
the 30 nm chromatin fiber
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Which of the following statements describes the eukaryotic chromosome?
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It consists of a single linear molecule of double-stranded DNA.
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If a cell were unable to produce histone proteins, which of the following would be a likely effect?
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The cellʹs DNA couldnʹt be packed into its nucleus
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Which of the following statements describes histones?
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Histone H1 is not present in the nucleosome bead; instead it is involved in the formation of higher-level chromatin structures.
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Why do histones bind tightly to DNA?
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Histones are positively charged, and DNA is negatively charged.
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Which of the following represents the order of increasingly higher levels of organization of chromatin?
answer
nucleosome, 30-nm chromatin fiber, looped domain
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