Special Examination Test for MCAT in Biology Pt3

Answer Key Part 3 66. E 67. E 68. E 69. C 70. E 71. A 72. D 73. B 74. A 75. B 76. A 77. E 78. D 79. (No Answer Provided) 80. A 81. B 82. B 83. C 84. C 85. E 86. B 87. D 88. B 89. E 90. B 91. 92. 93. 94. 95. 96. 97. 98. 99. 100. 101. 102. 103. C A B E D D A B C B D D E 66. In the inheritance of Down's Syndrome, a balanced translocation carrier is best characterized as A) an individual whose gametes are such that their progeny falls into 3 types: 1/3 will demonstrate Down's Syndrome, 1/3 will be normal, 1/3 will be balanced translocation carriers (assuming that the spouse has a normal karyotype.) B) a person whose parent produced a gamete which had undergone a translocation event such that virtually the whole of chromosome #21 had been translocated to chromosome #14 (a Robertsonian translocation). C) an individual developed from a zygote which was virtually haploid for chromosome #21. D) all of the above E) A and B, but NOT C 67. Which of the following statements correctly describes the organization and contents of eukaryotic chromatin? A) Histones contain large amounts of the basic amino acids lysine, histidine, and arginine, particularly near the N-terminal. B) Histones and DNA are present in approximately equal proportions (by weight) in mammalian chromatin. C) The ratio of proteins to DNA is much higher in eukaryotes than prokaryotes. D) The structure found consists primarily of nucleosomes connected by stretches of linker DNA E) all of the above 68. Which of the following statements is TRUE about the organization and contents of eukaryotic chromatin? A) Nucleosome core particles are composed of approximately 146 DNA base pairs wrapped around a histone octamer. B) In the chromatosome (UV absorbing particle), approximately two full turns of the left-handed superhelix (ca. 165 bp) wrap around the core, and histone H1 is located at sites where DNA enters and leaves the core. C) The term mononucleosome refers to a chromatosome and associated linker DNA, the total DNA content being approximately 200 base pairs. D) At physiological salt concentrations the nucleosomes form a 30 nm solenoidal structure consisting of approximately six nucleosomes per turn. E) all of the above. 69. In E. coli, the enzyme primase functions in DNA replication by A) catalysing the energy-dependent unwinding of the duplex using 2 ATPs per base pair separated B) stabilizing the single-stranded DNA thus formed C) catalyzing polymerization of ribonucleoside 5'-triphosphates to form 3'-5' phosphodiester bonds with a concomitant release of inorganic diphosphate D) catalyzing addition of deoxyribonucleoside to 3' ends of the chains formed in (C) E) catalyzing stepwise excision of ribonucleoside residues from the 5' end and concurrent polymerization of 5'-deoxyribonucleoside triphosphates to form 3'-5' phosphodiester bonds with release of inorganic diphosphate 70. In eukaryotes, a region of nucleic acid that specifies a polypeptide sequence is known as A) an intron B) a cistron C) a structural gene D) all of the above E) B and C, but NOT A 71. Match the following phrase or sentence to the most closely related term: "Amber, ochre and opal (UAG, UAA and UGA, respectively)." A) nonsense codon B) missense codon C) wobble D) competence E) genetic mosaics 72. Match the following phrase or sentence to the most closely related term: "Requirement for bacterial transformation." A) nonsense codon B) missense codon C) wobble D) competence E) genetic mosaics 73. Match the following phrase or sentence to the most closely related term: "Specification of alternate amino acid by a mutant codon." A) nonsense mutation B) missense mutation C) wobble D) competence E) genetic mosaics 74. Consider the following experiment. In 1962 Benzer and colleagues took cysteine, incubated with its cognate tRNA and cysteine tRNA synthetase enzyme, then converted the charged tRNA cysteine to alanine using Raney nickel reaction. The modified aminoacyl tRNA was then used in a cell-free protein-synthesizing system with a template comprised of a random co-polymer of U and G in 5 : 1 ratio. Note that such templates normally lead to abundant incorporation of cysteine (UGU) but not alanine (GCU, GCC, GCA or GCG codons, because there was no C incorporated in the UG copolymer mRNA). This result demonstrated that the translational machinery is unable to distinguish an incorrect from a correct amino acid. The peptides obtained from the above in vitro translation reaction A) incorporated alanine but not cysteine. B) incorporated cysteine but not alanine. C) incorporated both cysteine and alanine. D) incorporated neither cysteine nor alanine. E) Enough information is not given to properly answer the question. 75. Lactose consists of A) two glucose molecules. B) one glucose molecule and one galactose molecule. C) one fructose molecule and one glucose molecule. D) one glucose molecule and one maltose molecule. E) one galactose molecule and one fructose molecule. 76. Sometimes it is found that viruses can transfer genetic material from one bacterial strain to another. This process is called A) transduction B) recombination C) conjugation D) transmission E) mutation 77. Certain strains of E. coli are initially unable to metabolize lactose due to the absence of beta-galactosidase, but when grown continuously on a medium containing lactose they are able to synthesize beta-galactosidase. This is because A) lactose is able to diffuse easily across the cell wall. B) lactose suppresses the metabolism of other substrates. C) at first, E. coli did not require lactose but later developed the need for it. D) Beta-galactosidase is not responsible for lactose metabolism. E) lactose acted as an inducer. 78. Proteins differ from polypeptide chains in that they have well-defined three-dimensional structures which confer biological activities. Which one of the following structures enables polypeptide chains to reverse their direction? A) alpha helix B) gamma helix C) alpha pleated sheet D) beta turns E) None of the above. 79. A long descriptive question about Griffith's 1928 transformation expt (know the experiment, how it was done, and what the conclusion was that DNA is the transforming principal A) B) C) D) E) 80. Which of the following is not one of the four nitrogenous bases of DNA? A) Uracil B) Guanine C) Adenine D) Cytosine E) Thymine 81. When a virus infects a bacterium, the material that enters the bacterium from the virus is A) sulfur B) nucleic acid C) a mutagen D) protein E) both B and D 82. The sequence of bases found in a strand of DNA which served as a template for the synthesis of mRNA is 5'-adenine-guanine-cytosine-thymine-3'. Thus the sequence of bases found in the newly synthesized mRNA is A) 5'-ATCG-3' B) 5'-AGCU-3' C) 5'-TCGA-3' D) 5'-UCGA-3' E) None of the above. 83. DNA and RNA are different from each other in several important respects. Among the differences are their nitrogenous bases. In DNA, the bases are adenine, guanine, cytosine, and thymine. The nitrogenous base not found in RNA is A) guanine B) adenine C) thymine D) cytosine E) uracil 84. This is a technique that separates proteins according to the ability of charged molecules to migrate toward an anode or cathode when placed in an electric field. A) equilibrium gradient centrifugation B) gel filtration C) electrophoresis D) affinity chromatography E) Southern blotting 85. Dimers are formed at the __________ stage of a protein. A) primary B) secondary C) tertiary D) conjugated E) quaternary 86. Specific codons of mRNA have been experimentally found to be recognized by: A) the -CCA stem B) the anticodon loop C) T loop D) D loop E) None of the above 87. "Stop" codons which specify the end of a protein are: I. UAA II. UAG III. UUA IV. UGA A) I only B) I, II and III only C) I and IV only D) I, II and IV only E) I, II, III and IV. 88. Initiator tRNA with an anticodon recognizes and pairs with the initiation codon A) 5'-CAU-3' B) 5'-AUG-3' C) 5'-CUA-3' D) 5'-UUA-3' E) 5'-TAC-3' 89. A baby born in the hospital has a slim chance of survival: he was found to have three copies of chromosome 21. Should he grow to adulthood his abnormality would be known as A) Parkinson's disease B) Sylvan plague C) Bang's disease D) Tsutsugamushi disease E) Down's syndrome 90. Geneticists Watson and Crick are known to have postulated (without evidence, that came later) that because of the arrangement and nature of the nitrogenous bases, DNA replication was probably A) conservative B) semi-conservative C) dispersive D) directional E) None of the above 91. Stability in the helical structure of DNA is maintained by A) carbon bonding B) phosphate bonding C) hydrogen bonding D) ATP E) None of the above 92. A genetic mapping process done in the laboratory which involves the transfer of genetic material from one bacterium to another using a bacteriophage as the carrier is A) transduction B) transcription C) plasmid transfer D) transformation E) None of the above 93. Studies of genes and gene frequencies have shown that individuals do not evolve, but rather populations. This evolution essentially involves a change in the frequencies of: A) genes B) alleles C) mitotic divisions D) recombinance E) All of the above 94. A bacterium which can grow on the most minimal medium and which synthesizes all the essential organic compounds it needs is a/an A) auxotroph B) heterotroph C) organotroph D) chemio-organotroph E) prototroph 95. The material responsible for conferring resistance to antibiotics is the A) F(-) factor B) Hfr factor C) T-DNA plasmid D) R plasmid E) F' factor 96. Inversion, a class of structural variation, is a type of chromosomal abberation in which A) an extra chromosomal segment is included in the haploid pairing of chromosomes. B) a segment of chromosome is removed from one location and is placed at another site on the chromosome. C) chromosomal segments are placed along the chromosome thus causing the formation of new alleles. D) a segment of a chromosome is turned around 180 degrees and is reinserted into the chromosome. E) there is a variation in the chromosome numbers which ranges from the addition or loss of one or more chromosomes to the addition or loss of one or more pairs of haploid sets of chromosomes. 97. The principle that stated that a population remained genetically stable in succeeding generations was the A) Hardy-Weinberg principle B) Darwinian principle C) Mendelian principle D) Avery, McLeod and McCarty principle E) Levine principle 98. In eukaryotes, the DNA duplex is wrapped around protein particles. These structures are referred to as A) solenoids B) nucleosomes C) peroxisomes D) ribosomes E) spliceosomes 99. Which of the following is/are capable of cutting the DNA duplex to relieve twisting forces (torques), and reuniting the DNA strands during replication? A) DNA ligase B) Initiation factor C) Gyrase D) Helix-destabilizing factor E) All of the above. 100. The genetic disorder that is best expressed as (47, 21+) is known as A) Turner's Syndrome B) Down's Syndrome C) Trisomy D) Kleinfelter's Syndrome E) Edward's Syndrome 101. The two strands of a DNA helix unwind and separate when treated by heating or by adding acids or alkalis to a solution of DNA. This unwinding and separation of the double helix is called melting. Single-stranded DNA has a higher absorbancy at 260 nm than double-stranded DNA. Which of the following is or are correct statements based on DNA structure? I. The DNA double helix is a highly cooperative structure. II. DNA double helix with a high GC content melts at a higher temperature. III. The A-T rich regions of DNA melts earlier on heating. IV. A-T base pairs are more stable than the G-C base pairs. A) I, II B) II, III C) III, IV D) I, II, III E) I, II, III, IV 102. X-ray diffraction photographs of a hydrated DNA fiber were taken by Franklin and Wilkins and analyzed by Watson and Crick who proposed a model of DNA structure. Among the following statements, which correctly describes the features of the DNA model? I. Two helical polynucleotide strands running in opposite direction, and coiled with respect to a common axis. II. The purine and pyrimidine bases are located on the inside of the double helix. III. The two polynucleotide strands are held together by hydrogen bonding between adenine and thymine, guanine and cytosine. IV. The base sequence of a polynucleotide strand is restricted by its helical structure. A) I, II B) II, III C) III, IV D) I, II, III E) I, II, III, IV 103. The genetic code is described as "degenerate" because many amino acids are designated by more than one codon. Those codons that specify the same amino acid differ mainly in the third base of the triplet code. Which of the following is or are the biological significance of degeneracy of the genetic code? I. The probability that a codon will mutate to a stop signal is minimized. II. Some mutations at the third base of the triplet codon can be tolerated. III. The same genetic information is allowed to vary in the DNA composition. A) I B) II C) III D) I, II E) I, II, III