Biology Exam 2b

25 July 2022
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question
Meselson and Stahl cultured E. coli for several generations in a medium with a heavy isotope of nitrogen, 15N. They transferred the bacteria to a medium with a light isotope of nitrogen, 14 N. After two rounds of DNA replication, half the DNA molecules were light (both strands had 14N) and half were hybrids (15N-14N). What did the researchers conclude from these results? A Opposite DNA strands are complementary to each other. B The nitrogenous bases in DNA molecules incorporate both 15N and 14N. C DNA replication is semiconservative
answer
C
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DNA is a self-replicating molecule. What accounts for this important property of DNA? A Its two strands are held together by easily broken covalent bonds. B Replication is thermodynamically spontaneous and requires no enzymes. C The nitrogenous bases of the double helix are paired in specific combinations: A with T and G with C.
answer
C
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Nucleotides are added to a growing DNA strand as nucleoside triphosphates. What is the significance of this fact? A Nucleoside triphosphates are more abundant in the cell than nucleotides. B Hydrolysis of the two phosphate groups (P-Pi) and DNA polymerization are a coupled exergonic reaction. C Nucleoside triphosphates are more easily transported in the cell than are nucleotides.
answer
B
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During DNA replication, the leading strand is synthesized continuously, whereas the lagging strand is synthesized as Okazaki fragments. Why is this so? A DNA polymerases can bind to only one strand at a time. B DNA synthesis can take place only in the 5' to 3' direction. C There are thousands of origins of replication on the lagging strand but only one on the leading strand.
answer
B
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Select the most accurate statement describing DNA replication complexes. A DNA and the DNA replication complexes fit together like a lock and key. B DNA replication complexes are grouped into factories, which are anchored to the nuclear matrix. C DNA replication complexes move along a DNA railway track.
answer
B
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Which of these is a difference between a DNA and an RNA molecule? ADNA is usually double-stranded, whereas RNA is usually single-stranded. B DNA contains uracil, whereas RNA contains thymine. C DNA is a polymer composed of nucleotides, whereas RNA is a polymer composed of nucleic acids. D DNA contains five-carbon sugars, whereas RNA contains six-carbon sugars. E DNA contains nitrogenous bases, whereas RNA contains phosphate groups.
answer
A
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Which of these nitrogenous bases is found in DNA but not in RNA? A cytosine B uracil C adenine D guanine E thymine
answer
E
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Nucleic acids are assembled in the _____ direction. A 4' to 5' B 5' to 3' C 1' to 5' D 2' to 3' E 5' to 1'
answer
B
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In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand. A uracil ... cytosine B cytosine ... uracil C cytosine ... thymine D thymine ... cytosine E guanine ... adenine
answer
D
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Short segments of newly synthesized DNA are joined into a continuous strand by _____. A helicase B DNA polymerase C single-strand binding protein D primase E ligase
answer
E
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After DNA replication is completed, _____. A each new DNA double helix consists of one old DNA strand and one new DNA strand B each new DNA double helix consists of two new strands C each of the four DNA strands consists of some old strand parts and some new strand parts there are four double helices D one DNA double helix consists of two old strands and one DNA double helix consists of two new strands
answer
A
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The action of helicase creates _____. A DNA fragments and replication bubbles B primers and replication bubbles C DNA fragments and replication forks D primers and DNA fragments E replication forks and replication bubbles
answer
E
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Why is the new DNA strand complementary to the 3' to 5' strands assembled in short segments? A DNA polymerase can assemble DNA only in the 3' to 5' direction B the replication forks block the formation of longer strands C only short DNA sequences can extend off the RNA primers D it is more efficient than assembling complete new strands E DNA polymerase can assemble DNA only in the 5' to 3' direction
answer
E
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An old DNA strand is used as a _____ for the assembly of a new DNA strand. A source of nucleotides B primer C model D template E complement
answer
D
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The first step in the replication of DNA is catalyzed by _____. A helicase B ligase C single-strand binding protein D DNA polymerase E primase
answer
A
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Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base? A Neither of the two daughter cells would be radioactive. One of the daughter cells, but not the other, would have radioactive DNA. B Radioactive thymine would pair with nonradioactive guanine. C DNA in both daughter cells would be radioactive. D All four bases of the DNA would be radioactive.
answer
D
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The DNA of telomeres has been found to be highly conserved throughout the evolution of eukaryotes. What does this most probably reflect? A the low frequency of mutations occurring in this DNA B the inactivity of this DNA C that mutations in telomeres are relatively advantageous D that the critical function of telomeres must be maintained that new evolution of telomeres continues
answer
D
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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? A sequence of bases B phosphate-sugar backbones C different five-carbon sugars D complementary pairing of bases E side groups of nitrogenous bases
answer
A
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What is meant by the description "antiparallel" regarding the strands that make up DNA? A One strand is positively charged and the other is negatively charged. B Base pairings create unequal spacing between the two DNA strands. C The twisting nature of DNA creates nonparallel strands. D One strand contains only purines and the other contains only pyrimidines. E The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.
answer
E
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During protein synthesis what type of RNA is involved in transcription/RNA processing
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pre-mRNA mRNA snRNA
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During protein synthesis what type of ENa is involved in in translation
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tRNA rRNA
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codon refers to
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DNA nucleotide triplets on the nontemplate strand
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the promoter is
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the DNA sequence where RNA polymerase attaches and initiares transcription
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eukaryotes have three types of RNA polymerase which one synthesizes mRNA
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RNA polymerase @
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operons contain genes for
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enzymes in metabolic pathwasy which are transcribed together
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operators may be under
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negative or positive control
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operators under negative control are inhibited by
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repressors
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operators under positive control are activated by
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catabolite activator protein
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ainactive repressors are called
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repressible operon