Unit 2: Cellular Transport and Trafficking; Cell Cycle and its Regulation - Practice Quiz

1 Which type of transport moves molecules across a membrane against their concentration gradient and requires energy?

2 The pump transports which ions in each cycle?

3 Which molecule can most easily cross a lipid bilayer by simple diffusion?

4 A channel protein that allows only water molecules to pass across the membrane is called a(n):

5 A transporter that moves two different molecules in opposite directions across a membrane is called a(n):

6 Molecules move between the nucleus and cytoplasm through which structure?

7 A short amino acid sequence that directs a protein into the nucleus is called a:

8 Which small GTPase provides directionality to nuclear transport?

9 The receptor proteins that carry cargo through nuclear pores are collectively called:

10 Most proteins imported into mitochondria are synthesized:

11 The protein complex in the mitochondrial outer membrane that imports proteins is the:

12 Protein import into chloroplasts occurs through the TOC and TIC complexes located in the:

13 Proteins destined for mitochondria typically carry a targeting sequence at their:

14 In the secretory pathway, proteins follow which correct order of movement?

15 Which coat protein forms vesicles that transport cargo from the ER to the Golgi?

16 Which coat protein is mainly involved in vesicle formation during receptor-mediated endocytosis?

17 Proteins that mediate the fusion of transport vesicles with their target membranes are called:

18 Which organelle contains hydrolytic enzymes for the breakdown of macromolecules?

19 During which phase of the cell cycle does DNA replication occur?

20 Which enzymes drive progression through the cell cycle by binding to cyclins?

21 A cell maintains a high internal concentration and low internal concentration using the -ATPase. If a drug blocks ATP hydrolysis by this pump, which secondary effect is most likely to occur first?

22 A researcher observes that a solute crosses a membrane down its concentration gradient, shows saturation kinetics at high solute concentration, and requires no ATP. Which transport mechanism best explains these observations?

23 The exchanger in cardiac cells extrudes one ion while importing three ions. This is best classified as:

24 In red blood cells, the band 3 protein exchanges for across the membrane without energy input, and net movement can go either direction depending on gradients. This process is:

25 A protein of kDa lacks a nuclear localization signal (NLS). What is the most likely outcome regarding its distribution?

26 The directionality of nuclear import is maintained by the Ran GTPase system. Which condition holds in the nucleus to promote cargo release from importin?

27 Exportins recognize cargo bearing a nuclear export signal (NES) only when bound to Ran-GTP. Once the complex reaches the cytoplasm, what triggers cargo release?

28 A mitochondrial matrix protein is synthesized in the cytosol with an N-terminal presequence. Which feature of this presequence is essential for its import through the TOM and TIM23 complexes?

29 The import of nuclear-encoded proteins into the mitochondrial matrix requires energy from two sources. These are:

30 Unlike mitochondrial matrix import, protein import into the chloroplast stroma via the TOC/TIC complexes relies primarily on which energy source?

31 Anterograde transport of newly synthesized proteins from the ER to the Golgi apparatus is mediated by which type of coated vesicle?

32 A soluble ER-resident enzyme escapes to the Golgi. How is it retrieved back to the ER?

33 Lysosomal hydrolases are specifically targeted from the trans-Golgi network to lysosomes by which molecular tag?

34 The specificity of vesicle fusion with a target membrane is primarily determined by the pairing of:

35 The activity of cyclin-dependent kinases (CDKs) oscillates through the cell cycle. What primarily controls this oscillation?

36 The spindle assembly checkpoint (SAC) prevents progression from metaphase to anaphase until:

37 Separation of sister chromatids at anaphase is triggered when separase cleaves cohesin. Separase is kept inactive until this point by:

38 A key difference between meiosis I and mitosis is that during meiosis I:

39 In animal cell cytokinesis, the contractile ring that pinches the cell in two is composed mainly of:

40 The retinoblastoma protein (Rb) restrains the transition by binding and inhibiting E2F transcription factors. How is this restraint relieved?

41 In a secondary active transport process, the symporter (SGLT1) moves 2 ions per glucose molecule. If the intracellular glucose concentration is -fold higher than extracellular, what minimum electrochemical gradient (expressed as the ratio of driving force) is theoretically required to sustain uphill glucose accumulation at , assuming membrane potential contribution is embedded in the gradient?

42 The -ATPase undergoes E1/E2 conformational cycling. A mutation locks the pump preferentially in the E2-P (phosphorylated) state with high extracellular affinity but impaired dephosphorylation. What is the most direct consequence?

43 GLUT1 facilitates glucose uptake by alternating access. Which experimental observation would most strongly distinguish a facilitated diffusion carrier from a channel for the same solute?

44 Ran-GTP asymmetry drives directional nucleocytoplasmic transport. If a cell is treated to deplete RanGAP specifically at the cytoplasmic face of the NPC, what is the predicted effect on importin-mediated cargo import?

45 A protein of 82 kDa lacking any classical NLS is found concentrated in the nucleus at steady state. Which mechanism most plausibly explains this without invoking a canonical importin- NLS pathway?

46 The FG-repeat nucleoporins form a selective permeability barrier. According to the selective phase (hydrogel) model, how do transport receptors traverse this barrier?

47 A mitochondrial matrix-targeted protein is engineered to fold rapidly and stably in the cytosol before reaching the TOM complex. What is the most likely outcome regarding its import?

48 TIM23-mediated import into the matrix requires two energy inputs. Which combination correctly identifies both and their roles?

49 Chloroplast protein import via TOC/TIC differs from mitochondrial import in its energy requirement. Which statement correctly captures a key distinction?

50 A protein carries both an N-terminal mitochondrial matrix presequence and, immediately downstream, a hydrophobic stop-transfer sequence. Where will this protein most likely localize?

51 A mutation abolishes the GTPase activity of Sar1 (locking it in the GTP-bound state) in the COPII pathway. What is the most direct consequence for ER-to-Golgi transport?

52 In I-cell disease (mucolipidosis II), lysosomal enzymes are secreted rather than delivered to lysosomes. The primary defect lies in which step?

53 SNARE-mediated fusion requires specific v-SNARE/t-SNARE pairing. NSF/-SNAP function to disassemble cis-SNARE complexes. If NSF is inhibited, what accumulates and why?

54 A soluble ER-resident protein bearing a KDEL sequence is found leaking into the medium at low levels. Which mechanism best explains why most such protein is normally retained despite bulk flow toward the Golgi?

55 The spindle assembly checkpoint (SAC) delays anaphase until all kinetochores are attached. A cell has a single unattached kinetochore. Which molecular event is directly prevented by the active SAC?

56 In meiosis I, sister chromatids must remain attached at the centromere while chromosome arms separate. Which mechanism protects centromeric cohesin from cleavage during meiosis I?

57 The restriction point (R) in G1 is governed by Rb phosphorylation. A cell expresses a mutant Rb that cannot be phosphorylated by Cyclin D-Cdk4/6. What is the predicted phenotype?

58 Cyclin B-Cdk1 (MPF) activity rises abruptly at the G2/M transition. Which positive feedback loop explains the switch-like activation?

59 During cytokinesis in animal cells, positioning of the contractile ring is dictated by the mitotic spindle. Which signaling correctly describes RhoA-based furrow specification?

60 The CFTR chloride channel is an ABC transporter family member that functions as a channel rather than a pump. Which feature explains this unusual behavior?