Unit 5: Transporters in the Biological system - Practice Quiz

1 Which type of membrane transport moves ions down their electrochemical gradient without using ATP?

2 A key structural difference between channels and transporters is that channels typically:

3 Compared with transporters, ion channels generally allow ion movement that is:

4 The -ATPase is best classified as a:

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

6 Which property allows ion channels to conduct only specific ions?

7 Voltage-gated ion channels open primarily in response to changes in:

8 Which region of a voltage-gated channel acts as the voltage sensor?

9 The rapid rising phase of a neuronal action potential is caused mainly by the opening of:

10 The state in which a voltage-gated channel cannot reopen immediately even if depolarized is called:

11 Which ion channel is chiefly responsible for repolarizing the neuronal membrane after an action potential?

12 The term 'gating' in ion channels refers to:

13 Channelrhodopsins are light-sensitive proteins that function as:

14 The chromophore that absorbs light in rhodopsins is:

15 The technique that uses light to control the activity of neurons expressing rhodopsins is called:

16 Bacteriorhodopsin functions in the cell as a light-driven:

17 When channelrhodopsin-2 (ChR2) is illuminated with blue light, the expressing neuron typically undergoes:

18 The characteristic internal arrangement of microtubules in a eukaryotic cilium is described as:

19 The motor protein that generates movement in cilia and flagella is:

20 The bending movement of cilia and flagella results from:

21 A researcher observes that a membrane transport process shows saturation kinetics (a maximum rate that cannot be exceeded even at very high substrate concentrations) and can be competitively inhibited. Which transport mechanism does this most likely represent?

22 Ion channels typically conduct – ions per second, while transporters move roughly – ions per second. What is the primary structural reason for this large difference in throughput?

23 The -glucose cotransporter (SGLT) in the intestinal epithelium moves glucose into the cell even against its concentration gradient. What powers this uphill glucose movement?

24 Which statement best distinguishes primary from secondary active transport?

25 During an action potential, voltage-gated channels inactivate rapidly, but voltage-gated channels do not inactivate as quickly. What is the functional consequence of this timing difference?

26 The voltage sensor of a voltage-gated ion channel is located primarily in which region?

27 The channel selectivity filter conducts far better than the smaller . What explains this counterintuitive selectivity?

28 In a voltage-clamp experiment, a neuron is depolarized and held at a constant positive voltage. The inward current rises then decays to near zero within a few milliseconds despite the maintained depolarization. This decay is due to:

29 Using the Nernst equation, at with and , the equilibrium potential for is approximately:

30 A toxin binds the extracellular mouth of voltage-gated channels and physically blocks the pore (like tetrodotoxin). What is the expected effect on an axon's action potential?

31 Bacteriorhodopsin and channelrhodopsin both use retinal and absorb light, yet they function differently. What is the key functional distinction?

32 In optogenetics, expressing channelrhodopsin-2 (ChR2) in a neuron and illuminating it with blue light typically causes:

33 To silence neurons optogenetically, researchers often use halorhodopsin. What does halorhodopsin do upon light activation?

34 The -ATPase moves 3 out and 2 in per ATP hydrolyzed. Why is this pump described as electrogenic?

35 In the photocycle of bacteriorhodopsin, absorption of a photon causes retinal to isomerize. This isomerization is best described as:

36 The classic axoneme of eukaryotic cilia and flagella has which arrangement of microtubules?

37 Ciliary bending is generated when dynein arms on one doublet walk along the adjacent doublet. Why does this sliding produce bending rather than telescoping apart?

38 Which motor protein powers the movement of the eukaryotic axoneme, and what is its energy source?

39 A key difference between bacterial and eukaryotic flagella is the mechanism of movement. The bacterial flagellum moves by:

40 In primary ciliary dyskinesia, defective dynein arms impair ciliary beating. Besides respiratory problems, patients may show situs inversus (reversed organ placement). This link suggests that:

41 In a Hodgkin-Huxley analysis, the conductance is described as . If a mutation removes the inactivation gate while leaving activation intact, which functional consequence is most directly expected?

42 The gating charge movement of a voltage sensor produces a measurable gating current that precedes ionic current. Which observation best distinguishes a genuine gating current from a leak or capacitive artifact?

43 The selectivity filter of voltage-gated channels contains the signature sequence TVGYG. Why can this filter conduct near the diffusion limit yet strongly exclude ?

44 A voltage-gated channel shows a Boltzmann activation curve with a slope factor mV. Assuming at ( mV), what is the effective gating valence ?

45 During the relative refractory period of a neuron, a larger-than-normal stimulus is required to fire an action potential primarily because:

46 Consider a cell with intracellular mM, extracellular mM, and mV at ( mV). What is the approximate electrochemical driving force on ()?

47 Which criterion most fundamentally distinguishes a channel from a transporter (carrier) at the mechanistic level?

48 The cotransporter (SGLT) accumulates glucose against its gradient. This is thermodynamically possible because:

49 For the -ATPase moving 3 out and 2 in per ATP, why is this pump described as electrogenic and what is its direct membrane effect?

50 In the alternating-access model, a uniporter (e.g., GLUT1) reaches a maximal transport rate at saturating substrate. The rate-limiting step at saturation is typically:

51 Bacteriorhodopsin and channelrhodopsin both contain retinal and absorb light, yet they are functionally distinct. The key difference is:

52 In optogenetics, a neuroscientist wants to silence (hyperpolarize) neurons with light. Which tool and mechanism is appropriate?

53 The photocycle of bacteriorhodopsin involves all-trans to 13-cis retinal isomerization. What is the direct functional role of this isomerization?

54 Compared with wild-type channelrhodopsin-2, engineered 'step-function opsins' (e.g., with a C128 mutation) show greatly prolonged open times. The primary optogenetic advantage is:

55 A light-driven proton pump moves against a of 2 units plus a membrane potential of 120 mV (inside negative, opposing outward pumping is not relevant here; consider work to move out). Roughly how much energy per proton must the photon supply to overcome the electrochemical gradient at ? (Use mV per pH unit.)

56 The '9+2' axoneme generates bending through dynein activity. Sliding of adjacent outer doublets is converted into bending rather than telescoping because:

57 For coordinated bending, dynein arms on opposite sides of the axoneme cannot be simultaneously active. What ensures this asymmetric, switched activity?

58 A eukaryotic flagellum and a bacterial flagellum both produce motility but are fundamentally different. Which statement correctly contrasts them?

59 Intraflagellar transport (IFT) is essential for building and maintaining cilia. Loss of anterograde IFT (kinesin-2 dependent) would most directly cause:

60 Primary cilia (9+0, immotile) differ functionally from motile cilia (9+2). What is the principal role of primary cilia and the structural reason for their immotility?