GIVEN SELECTION (1) PDF - Biology Past Paper

SELECTION: 1. What enzyme is depicted in the following schematic drawing? 3' 5' 5' A. DNA polymerase B. RNA polymerase C. Ribosome D. Reverse transcriptase...

SELECTION: 1. What enzyme is depicted in the following schematic drawing? 3' 5' 5' A. DNA polymerase B. RNA polymerase C. Ribosome D. Reverse transcriptase E. Topoisomerase Answer: B Feedback: The enzyme synthesizes RNA using one of the DNA strands as template. 2. Each aminoacyl-tRNA synthetase activates a certain amino acid by attaching it to its corresponding tRNA(s) through a high-energy linkage... A. between the amino group of the amino acid and the 3' hydroxyl group of the tRNA. B. between the amino group of the amino acid and the 5' hydroxyl group of the tRNA. C. between the carboxyl group of the amino acid and the 3' or 2' hydroxyl group of the tRNA. D. between the carboxyl group of the amino acid and the 5' hydroxyl group of the tRNA. E. between the amino group of the amino acid and the 3' or 2' hydroxyl group of the tRNA. Answer: C Feedback: The amino group of the amino acid is free and will serve as the attacking group in the formation of the peptide bond on the ribosome. The carboxyl group, on the other hand, forms a high-energy and susceptible ester bond with the tRNA in preparation for that same reaction.  3. On the ribosome, the mRNA is read from..., and the polypeptide chain is synthesized from... A. 5' to 3'; C- to N-terminus. B. 5' to 3'; N- to C-terminus. C. 3' to 5'; C- to N-terminus. D. 3' to 5'; N- to C-terminus. Answer: B Feedback: During translation elongation, the ribosome translocates on the mRNA from the 5′ end to the 3′ end in consecutive sets of three nucleotides. The polypeptide is concomitantly elongated at its C-terminus by addition of individual amino acids. 4. An elongating ribosome is bound to appropriate tRNAs in both the A and the P sites and is ready for peptidyl transfer. What happens next? A. The carboxyl end of the polypeptide chain is released from the P-site tRNA and joined to the free amino group of the amino acid linked to the A-site tRNA. B. The amino end of the polypeptide chain is released from the P-site tRNA and joined to the free carboxyl group of the amino acid linked to the A-site tRNA. C. The carboxyl end of the amino acid is released from the A-site tRNA and joined to the free amino group of the polypeptide chain linked to the P-site tRNA. D. The amino end of the amino acid is released from the A-site tRNA and joined to the free carboxyl group of the polypeptide chain linked to the P-site tRNA. Answer: A Feedback: In the fundamental reaction of protein synthesis, a peptide bond is formed between the carboxyl group at the end of a growing polypeptide chain and a free amino group on an incoming aminoacyl-tRNA. 5. Indicate whether each of the following transport processes occurs via the mechanisms described as gated transport (G), transmembrane transport (T), or vesicular transport (V). Your answer would be a five-letter string composed of letters G, T, and V only, e.g. VTTTG. ( ) Import into nucleus ( ) Export from nucleus ( ) Import into mitochondria  ( ) Return from Golgi to ER ( ) Return from ER to cytosol Answer: GGTVT Feedback: While nuclear traffic uses gated transport, transport into the endoplasmic reticulum (and back) and into mitochondria, plastids, and peroxisomes is carried out using transmembrane translocators. Finally, proteins can move between the various membrane-enclosed organelles of the intracellular membrane system, as well as to and from the plasma membrane, by vesicular transport. Feedback: The outer nuclear membrane is continuous with the inner nuclear membrane, but has different proteins and is associated with ribosomes. The endoplasmic reticulum lumen is continuous with the perinuclear space between the nuclear membranes. Since assembly of ribosomal protein and RNA takes place inside the nucleus, the protein components have to be imported before the assembled subunits can be exported back to the cytoplasm. 6. A schematic drawing of the secretory and endocytic pathways is presented below. Indicate which component in the drawing (A to J) corresponds to each of the following. Your answer would be a 10-letter string composed of letters A to J only, e.g. HICDJABFGE. Lysosomes are the principal site of cellular digestion. They … A. normally maintain a pH of about 2.0 to 2.5. B. contain F-type ATPases that pump protons into the organelles. C. contain heavily glycosylated membrane proteins. D. are homogeneous in size and shape. E. All of the above.  J I A H B C D E F G ( ) Early endosome ( ) Late endosome ( ) ER ( ) Lysosome ( ) cis Golgi cisterna ( ) medial Golgi cisterna ( ) trans Golgi cisterna ( ) cis Golgi network (CGN) ( ) trans Golgi network (TGN) ( ) Secretory vesicle Answer: HIAJCDEBFG 7. The telomerase enzyme in human cells … A. has an RNA component. B. extends the telomeres by its RNA polymerase activity. C. polymerizes the telomeric DNA sequences without using any template. D. removes telomeric DNA from the ends of the chromosomes. E. creates the “end-replication” problem. Answer: A Feedback: Telomerase uses its RNA component as a template to polymerize DNA sequences at the chromosome ends to solve the “end-replication” problem. 8. A replication fork is shown schematically below. The strand labeled A is called the … strand. A 3ʹ 5ʹ B Answer: lagging Feedback: Strand A is extended 5′-to-3′ (from right to left) whereas the fork moves in the opposite direction; therefore, the strand should be polymerized discontinuously 9. Which of the time points (A to E) in the following schematic drawing of the mammalian cell cycle represents the restriction point? E D A C M G2 G1 S B Answer: B Feedback: Under favorable conditions and in the presence of signals to grow and divide, cells in early G1 (or G0) progress through a commitment point near the end of G1 known as Start (in yeasts) or the restriction point (in mammalian cells). 10. Which division in meiosis is more similar to mitosis? In which division do sister chromatids separate from each other? A. Meiosis I; meiosis I B. Meiosis I; meiosis II C. Meiosis II; meiosis I D. Meiosis II; meiosis II Answer: D Feedback: Meiosis II resembles mitosis, in which sister chromatids segregate during anaphase. 11. A form of a gene that has a slightly different sequence than other forms of the same gene but encodes the same type of an RNA or protein, is called a(n) a) locus. b) allele. c) homologous chromosome. d) heterozygote. e) homozygote. Answer: b 12. The attachment point on the chromosome for spindle microtubules is the a. telomere. b. centromere. c. origin of replication. d. sister chromatid. e. allele. Answer: b 13. Diploid cells are cells with a. a single set of chromosomes. b. circular chromosomes. c. two sets of chromosomes. d. many sets of chromosomes. e. three sets of chromosomes Answer: c 14. Which of the following occurs during prometaphase? a. The chromosomes align in a single plane. b. DNA is replicated. c. Microtubules attach to the kinetochores. d. Mitotic spindles form. e. The two sister chromatids separate. Answer: c 15. In Mendel’s peas, yellow seeds are dominant to green. A pure-breeding yellow plant is crossed with a pure-breeding green plant. All of the offspring are yellow. If one of these yellow offspring is crossed with a green plant, what will be the expected proportion of plants with green seeds in the next generation? a. 0% b. 25% c. 50% d. 75% e. 100% Answer: c 16. Which of the following chromosome constitutions would never lead to a viable human baby being born? a. XXX b. XYY c. XO (O = the absence of a second chromosome) d. YY e. XXY Answer: d 17. In humans, blood types A and B are codominant to each other and each is dominant to O. What blood types are possible among the offspring of a couple of blood types AB and A? a) A, B, AB, and O b) A, B, and AB only c) A and B only d) A, B, and O only e) A and AB only Answer: b 18. Two parents are phenotypically normal, but one of their four biological children has a typical autosomal recessive trait. The other three children are phenotypically normal. It is very likely that a. the affected child is a girl. b. the affected child is a boy. c. the trait was expressed by one of the grandparents of the children. d. the parents are both heterozygous for the trait. e. if the affected child eventually marries a phenotypically normal spouse, all of the their children will have the trait. Answer: d 19. Which of the following statements is incorrect concerning an X-linked recessive trait in humans? a)An affected man often has phenotypically normal parents. b)All the sons of an affected woman will be expected to be affected. c)An affected woman almost always has an affected mother. d)An affected man usually has a mother who carries the recessive allele. e)A phenotypically normal woman whose father was affected is likely to be heterozygous for the condition. Answer: c 20. Recombination occurs through a. crossing over and chromosome interference. b. chromosome interference and independent assortment. c. somatic-cell hybridization and chromosome interference. d. complete linkage and chromosome interference. e. crossing over and independent assortment. Answer: e 21. Hershey and Chase determined whether DNA or protein was the genetic material in bacteriophages. What isotope did they use to label the viral protein? 14 a. C 15 b. N 18 c. O 32 d. P 35 e. S Answer: e 22. Which of the following has repetitive DNA and heterochromatin? a) Telomere b) Centromere c) Mitochondria d) Chloroplast e) a and b Answer: e 23. Which of the following enzymes do NOT aid in unwinding of DNA for replication? a. Helicase b. Single-stranded binding proteins c. Primase d. Gyrase e. Topoisomerase Answer: c 24. If the following DNA strand were used as a template, what would the sequence of an RNA be? 5′ GTACCGTC 3′ a. 5′ GUACCGUC 3′ b. 5′ GACGGTAC 3′ c. 5′ CAUGGCAG 3′ d. 5′ GACGGUAC 3′ e. 5′ GUCGGUAC 3′ Answer: d 25. Which of the following correctly describes nonsense mutations? a. They cause a nonfunctional amino acid to replace a functional amino acid. b. They change the nucleotide sequence of a gene but do not change the sequence of the resulting protein. c. They result in the insertion or deletion of a small number of nucleotides to the DNA. d. They convert a codon for a particular amino acid within a gene into a stop codon. e. They cannot revert or back mutate to wild-type.  Answer : d 26. The amino acid serine has an amino group, a carboxyl group, and a hydroxyl group. Which of the following better represents the structure of this amino acid at neutral pH? A B C H O H O H O H3N+ C C O– H3N+ C C NH2 H3N+ C C O– CH3 OH CH2 OH D H O E H O H O H3N+ C C H H2N C C N C C H OH OH H OH Answer: C