複選題

31. Which of the following descriptions about protein synthesis and targeting are correct?
(A) ER (endoplasmic reticulum) targeting of proteins synthesized in the cytosol requires a N-terminus signal sequence.
(B) Cotranslational translocation of proteins into ER lumen requires SRP (signal recognition particle) and the SRP receptor, and this protein translocation is energy-independent.
(C) a-helix of the membrane spanning domains of proteins can function as a topogenic sequence and determine the orientation of the proteins on the membrane.
(D) Most proteins in the mitochondria are encoded and synthesized in the mitochondria, and therefore do not need targeting sequences for mitochondrial localization.
(E) Proper folding of proteins require posttranslational modifications.

複選題27. BrdU is an analog of thymine that can be incorporated into double stranded DNA during  DNA  polymerization in S phase. Unsynchronized cells at various stages of cell cycle are first treate for 2 hours and then cultured in the absence of BrdU for another 4 hours. What would happen to those unsynchronized cells exposure to BrdU?(A) BrdU is incorporated into all the unsynchronized cells. (B) If a cell is labeled by BrdU, only one of the sister chromatins is labeled (C) If a cell is labeled by BrdU, only one strand of DNA is labeled (D) In the 2-hour BrdU pulse, only mitotic cells are labeled (E) In the 2-hour BrdU pulse, only mitotic cells are not labeled

28. The following diagram shows a family pedigree of a disease characterized by muscle weakness from (A) autosomal dominant (B) autosomal recessive (C) sex-linked dominant (D) sex-linked recessive (E) mitochondrial inheritance

29. DNA recombination refers to moving a DNA segment from one to another DNA molecule. This process (A) biogenesis of miRNA (B) linkage mapping human mutations that cause diseases (C) gene targeting, replacing a gene by a mutant allele. (D) tissue specific inactivation of a target gene by the Cre/loxP system. (E) to repair a DNA double strand break

30. Which of the following descriptions about exon, intron, 5' UTR, and 3' UTR is/are NOT correct (A) nonsynonymous mutation is a nucleotide change in exon that changes amino acid sequence of the encoded protein. (B) synonymous mutation is a single nucleotide change in intron that would never cause any change in the amino acid sequence of the encoded protein. (C) although not translated, the nucleotide sequence in the 5' UTR of mRNA corresponds to genomic sequence of exons but not introns. (D) although not translated, mutation in 3' UTR could profoundly affect mRNA stability. (E) mutation in intron sometimes affects protein sequence by introducing mRNA splicing errors.

複選題32. Which of the following about the cell nucleus and nuclear transport are correct? (A) Nucleolus is the major protein synthesis site in the nucleus. (B) Import into and export out of the cell nucleus require a nuclear localizing signal (NLS) and a nuclear export signal (NES), respectively. (C) The cargo-importin complex is cotransported into the nucleus with a GTP-bound Ran. It is the GTP hydrolysis in the nucleus that changes the Ran to the GDP-bound state and releases the cargo into the nucleoplasm. (D) The outer membrane of the nuclear envelope is continuous with the ER. (E) All protein components in the nuclear pore complex (NPC) undergo constant turnover and most have a short half-life.

複選題33. Which of the following approaches may help Michael determine the sequence of protein Q movements between the compartments X, Y and Z? (A) Sit down in front of the microscope, and follow the movements of GFP particles in live, unfixed cultured cells in real time. (B) Add another ligand that competes for the same receptor with protein Q, and measure the difference of GFP signals between compartments X, Y and Z. (C) Add GFP-protein Q to the medium at 4°C. Raise the culture temperature briefly to 37°C to enable endocytosis to occur, and then go back to 4°C again. After this treatment, do the immunostaining-GFP colocalization experiment at different time points. (D) Perform immunoEM to determine the exact localization of protein Q in X, Y or Z. (E) Purify individual intracellular compartments and determine the level of protein Q.

34. Somehow Michael was able to solve his problem, and now he had evidence that protein Q first entered (A) Use cultured fibroblasts that are deficient for Y, and see whether protein Q accumulates in compartment X or compartment Z. The first will indicates protein Q trafficking as X -＞ Z -＞ Y, while the latter will suggest X -＞ Y -＞ Z. (B) Same approach as A, but accumulation in compartment X indicates the order of transport as X -＞ Y -＞ Z, whereas accumulation in compartment Z indicates the order as X -＞ Z -＞ Y. (C) Use RNAi to interfere with the functions or biogenesis of compartments X, Y or Z, and see in which compartment is protein Q trafficking blocked. (D) Collect and homogenize the cells at different time points, and purify compartment Y or Z by density gradient centrifugation. Test whether protein Q exists in the fraction containing Y or Z. (E) Use a radioisotope-labeled protein Q instead of GFP, and measure the radioactivity within compartment Y or compartment Z under light microscopy.

複選題35. Finally Michael worked out the order of protein Q trafficking as X -＞ Y -＞ Z. At the same time, Lisa (A) Sequencing the genomic loci of all the 50 genes is the best way to identify the mutation. (B) Since more than 50 genes are likely to be candidates for the locus harboring this mutation, it is of little help to do traditional genetic mapping. (C) Lisa should perform 2-D gel electrophoresis to identify the mutant protein band. Remove the band from the gel and send it to the mass spectrometry - that is the simplest way to identify the mutation. (D) Do complementation test with individual mutant strains of these 50 genes. A failure to complement will indicate that Lisa's mutation is allelic (i.e., in the same locus) to this mutant. (E) Lisa's mutant could be a dominant, gain-of-function mutation or a recessive loss-of-function mutation.

複選題36. About intracellular signaling, which of the following descriptions is correct? (A) Guanine nucleotide-exchange factors (GEFs) switch the GTPases to GTP-bound forms and inactivate them, whereas GTPases-activating proteins (GAPs) switch the GTPases to GDP-bound states and activate them. (B) Calcium serves as an important second messenger, and the intracellular calcium is primarily stored in endoplasmic reticulum (ER) and the Golgi. (C) Upon activation of G protein-coupled receptors (GPCR), the Ga subunit of G protein dissociates from the receptors and binds to downstream effectors to activate the signaling cascades. (D) GPCR is one of the largest protein families in the genome of metazoan species. (E) GPCRs regulate cAMP- or phospholipase C (PLC)-based signaling pathways, but they do not regulate ion channels.

複選題37. About microtubules, which of the following descriptions are correct? (A) Microtubules are associated with the microtubule-organizing center (MTOC) with their (-) ends, and the (+) ends of microtubules point away from the MTOC. (B) Treadmill (progressive growth) of microtubules requires ATP, with GTP-bound ẞ-tubulins added at the (+) ends of microtubules. (C) Kinesins are microtubule (-)-end-orineted motors, and dyneins are (+)-end-oriented motor proteins. (D) Microtubules go through alternating rescue (growing phase) and catastrophe (shrinking phase), a process known as the dynamic instability. (E) Microtubules determine the shape of a cell but do not function in regulating cellular polarity.