複選題

31. Proteins give cells structure and perform most cellular tasks, thus functions of proteins could be regulated via several different ways. Which of the following descriptions about regulating protein function are CORRECT?
(A) Proteins are regulated at the level of synthesis, degradation or the intrinsic activity.
(B) Proteins are marked for degradation with ubiquitin tag and then degraded within proteasomes or lysosomes.
(C) Ubiquitination of proteins is irreversible.
(D) Phosphorylation and dephosphorylation covalently regulate protein activity.
(E) Protein activity could be regulated by controlling protein location and concentration.

複選題27. Which of the following statements concerning restriction endonucleases is (are) true? (A) They protect bacterial cells from invasion by viruses (bacteriophages). (B) They attack RNA, not DNA. (C) They attack single-stranded sequences only. (D) They can produce "sticky ends". (E) They do not display sequence specificity in their site of attack.

複選題28. Which of the following statement(s) about intracellular second messengers is (are) true? (A) It is a substance that brings about a desired effect in a cell as a result of a hormone binding to its receptor on the cell surface. (B) It is a hormone that affects the DNA of the target cell. (C) It is a specialized form of mRNA. (D) Cyclic ATP can act as secondary messengers. (E) Ca2+ can function as a secondary messenger by controlling the flow of Ca2+ into the cells.

29. When electrical current is applied during a gel electrophoresis procedure, the DNA fragments are separated by (A) electrical charge, positive on one side, negatives on the other. (B) the number of poly-A tails associated with each one. (C) their response to the staining chemicals used during the procedure. (D) the size of the fragments. (E) the enzyme binding activity sites.

30. You are studying the function of a recently identified gene in C. elegans. You have been performing genetic screens for several months in an attempt to isolate loss-of-function mutations in this gene, but unfortunately you have been unsuccessful. Your advisor suggests that you try another approach to eliminate gene function. Which of the following techniques would accomplish this goal? (A) Design a repressor to bind to the operon of this gene. (B) Use a histone deacetylase to induce a transcriptionally inactive state. (C) Use RNA interference to prevent mRNA translation. (D) Use a wild type strain and mutagenize it with a UV light. (E) Use antisense DNA to block RNA transcription.

32. Upon adding more NaCl into a protein solution, the electrostatic interaction between charged groups on the protein surface will be (A) strengthened due to ion exchange. (B) strengthened due to charge induction effect. (C) weakened due to charge induction effect. (D) weakened due to shielding effect. (E) will not be effected.

複選題33. Once transcription is finished and the primary RNA transcript is produced, it must undergo various processing reactions to yield functional RNAs. Which of the following descriptions about pre-mRNA processing are CORRECT? (A) In eukaryotic cells, pre-mRNAs are processed by 5' capping, 3' cleavage, polyadenylation and splicing in the cytoplasm. (B) Spliceosome is a large ribonucleoprotein complex catalyzing two transesterification reactions that joint two exons and remove the intron as a lariat structure. (C) Translation can be repressed by micro RNAs (miRNAs), which form imperfect hybrids with sequences in the 3' untranslated region (UTR) of specific target mRNAs. (D) RNA interference, which probably evolved as an early defense system against viruses and transposons, leads to degradation of mRNAs that form perfect hybrids with short interfering RNAs (siRNAs). (E) Many mRNA are transported to specific subcellular location by sequence-specific DNA-binding protein thus permit production of proteins at specific regions.

複選題34. Which of the following descriptions about eukaryotic cells are CORRECT? (A) Eukaryotic cells gain many advantages from organelle development. (B) Phospholipids are the conserved building blocks of cellular membranes. (C) Eukaryotic cells utilize a similar cycle to regulate their division. (D) The genetic information is carried and passed by the messenger ribonucleic acid (mRNA) in most eukaryotes. (E) Bacteria are eukaryotes and widely used in biology research.

複選題35. Which of the flowing descriptions about gene structure and chromosomal organization are CORRECT? (A) A gene is the entire DNA sequence required for synthesis of a functional protein or RNA molecule, including coding region, control region and intron. (B) Many genes encode functional RNAs that are not translated into proteins but perform significant functions, such as rRNA, tRAN, and snRNAs. Among these are the exception micro RNAs (miRNAs), although up to 1000 in humans, have no any biological significance. (C) Although DNA transposons occur in eukaryotes, retrotransposons generally are much more abundant in vertebrates. (D) Each eukaryotic chromosome contains a single DNA molecular packaged into nucleosomes and folded into a 30-nm chromatin fiber. (E) In eukaryotic cells, the organization of DNA into chromatin allows a mechanism for regulation of gene expression.

複選題36. Which of the flowing descriptions about transcriptional control of gene expression are CORRECT? (A) Gene expression in both prokaryotes and eukaryotes is regulated primarily by mechanisms that control the initiation of transcription. (B) The primary purpose of gene control in multicellular organisms is the execution of precise developmental decisions so that the proper genes are expressed in the proper cells. (C) Enhancers direct binding of RNA polymerase II to DNA, determine the site of transcription initiation, and influence transcription rate. (D) The activity of many transcription factors are indirectly regulated by binding of extracellular proteins and peptides to cell-surface receptors. (E) Epigenetic control of transcription refers to repression or activation that is maintained after cells replicate as the result of DNA methylation or post-translational modification of histones.

複選題37. The advanced fluorescent microscopy not only leads the development of cell biology, but also facilitates the progress of molecular biology. Which of the following descriptions about microscopy are CORRECT? (A) The resolution of light microscope, about 0.2 micro-meter, is limited by the wavelength of light. (B) Confocal microscopy provides better resolution in fluorescent imaging by removing out-of-focus fluorescent signals. (C) Electron microscopy gives better resolution by providing shorter wavelength of illumination source. (D) Total internal refection fluorescence (TIRF) microscopy allows fluorescent sample very close to a coverslip to be seen with great clarity. (E) Super-resolution microscopy allows for detailed fluorescent images at nanometer resolution by using shorter wavelength of light.