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Midterm Practice Exam - Aleksander Jeremic...

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BISC 3320

Midterm Exam

Name: Katherine Shek

Spring 2021 Important guidelines: Teamwork is NOT allowed during the exam! Making copies, distribution and/or sharing of the exam is strictly prohibited and will be considered violation of academic integrity. Following completion of this course every student will need to discard or permanently delete hard and electronic copies of the midterm and final exams.

Questions 1-33 (2 points each) Questions 34-35 (12 points each) The plot of End Plate (acetylcholine-evoked) current (I) as a function of membrane potential (V) is shown below (Graph 1). One can see that the current-voltage relation is almost linear, and that the reversal potential (Vr) is close to zero. Based on the known equilibrium potentials for calcium (+60 mV), sodium (+50mV), potassium (-85mV) and fact that the Ach channel relative conductance for gK:gNa:gCa are: 1:1:0. 2, analyze the graph and answer questions 1-3. I

V

Graph 1. 1. At Vm= -25mV the current is: (A) (B) (C) (D)

zero inward outward none of the above

2. With membrane potential clamped at +50mV the Ach-evoked synaptic current consists of: (A) (B) (C) (D)

Sodium current Potassium and calcium currents Sodium, potassium and calcium currents Sodium and calcium currents

3. The Ach-evoked synaptic currents at the motor end plate with the membrane potential clamped at -90mV mV will consist of: 1

(A) (B) (C) (D)

Sodium current Potassium current Sodium, potassium and calcium currents Sodium and calcium currents

Large nerve fibers in vertebrates are wrapped in myelin sheets formed by glial cells. Myelin sheets insulate nerve fibers to regulate propagation of action potential. Answer questions 4-7 regarding the role of myelin in the neurotransmission. 4. What will be the consequence of demyelination (loss of myelin) on the efficacy of action potential propagation and neurotransmission? (A) Large increase in the magnitude of inhibitory postsynaptic potentials (IPSP) are expected (B) Length constant (λ) will decrease and reduction in neurotransmitter release will occur (C) Neurons will produce larger action potentials to compensate for that change (D) There will be no effect on the postsynaptic cell 5. Myelinated axons with relatively large internal diameter (Daxon~0.7) will propagate action potentials faster than axons with small internal diameter (Daxon0.3) due to: (A) Large membrane resistance (B) Large internal resistance (C) Low internal resistance (D) Both A and C 6. If the myelin content in a nerve fiber increases from 10% to 30% this should: (A) (B) (C) (D)

Boost propagation of action potential due to increase in longitudinal resistance Decrease propagation of action potential due to increase in longitudinal resistance No change in action potential propagation is expected Boost propagation of action potential due to increase in membrane resistance

7. Myelinated axons with large internal diameter propagate action potentials faster as compared to nonmyelinated axons with small internal diameter. This is due to: (A) (B) (C) (D)

Increase in membrane resistance Increase in internal resistance Decrease in internal resistance Both A and C

8. The sodium-potassium ATPase exhibits 3:2 stoichiometry and hence it is an example of: (A) (B) (C) (D)

Primary neutral transport Primary electrogenic transport Secondary neutral transport Secondary electrogenic transport

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9. Neuronal communication through chemical synapse is slower than in electrical synapse due to: (A) (B) (C) (D)

absence of gap junctions presence of synaptic cleft synaptic delay All of the above

10. At both excitatory and inhibitory synapses, the direction of current flow is determined by: (A) (B) (C) (D)

The ion concentration gradient The electrical gradient across the membrane Both A and B pH

11. Action potential will be generated in the postsynaptic cell following activation of the ionotropic receptor with the following reversal potential: (A) Vr = -50mV (B) Vr = -85mV (C) Vr = -10mV (D) Vr = -70mV 12. Activation of ionotropic receptors on the postsynaptic membrane mediates: (A) (B) (C) (D)

Direct chemical synaptic transmission Indirect chemical synaptic transmission Both A and B Electrical synaptic transmission

13. Metabotropic receptors regulate channel activities in the postsynaptic cells: (A) (B) (C) (D)

directly by allowing ion flux through metabotropic channels indirectly by recruiting G-proteins directly by allowing ion flux through ionotropic channels by some other mechanism

14. Characteristics of phospho-lipase A2 signaling pathway is/are: (A) (B) (C) (D)

Generation of cyclic-AMP, protein kinase A activation, and channels phosphorylation Generation of cyclic-AMP, protein phosphatase activation, and channels phosphorylation Formation of inositol-triphosphate (IP3) Conversion of arachidonic acid into active metabolites that modulate channel activity

15. G-protein-mediated signaling in cells will be prolonged by: (A) Binding of GDP to -subunit (B) Addition of a non-hydrolyzable form of GTP (C) Addition of ATP (D) Increased rate of hydrolysis and conversion of GTP to GDP by G-subunit 16. The term synaptic integration refers to: 3

(A) (B) (C) (D)

Direct exchange of electric potentials between neurons Integrated action of action potentials in a presynaptic cell Integration of metabolic activities in presynaptic and postsynaptic cells Summation of presynaptic inputs at a postsynaptic cell

17. At peripheral synapses such as NMJ, the size of postsynaptic potentials depends on: (A) (B) (C) (D)

Quantum content Quantum size Expression of connexons Both A and B

18. At central synapses, the size of postsynaptic potentials will increase due to: (A) (B) (C) (D)

Increase in a quantum content Increase in a quantum size Both A and B Synaptic integration

19. Inhibition of connexons function should affect: (A) (B) (C) (D)

Direct chemical synaptic transmission Indirect chemical synaptic transmission Electrical synaptic transmission both A and B

20. The inhibition of voltage-gated K-channels will have a disruptive effect on: (A) (B) (C) (D)

Resting membrane potential Action potential in neurons Reversal potential Action potential in glia cells

21. The chemical synaptic transmission will be blocked by: (A) (B) (C) (D)

Inhibition of voltage-gated calcium channels Closure of chloride channels Activation of Na/K pump Closure of connexons

22. Ion flux through a voltage-gated channel is determined by: (A) (B) (C) (D)

Channel permeability Electrical gradient across the membrane Concentration gradient across the membrane All of the above

23. Channel’s gating properties is determined by: 4

(A) Channel primary structure (B) Channel secondary structure (C) Channel tertiary structure (D) Channel quaternary structure 24. The ion fluxes through the channels coupled to activation of metabotropic receptors will be affected by: (A) Change in temperature (B) Change in intracellular pH (C) Change in ATP intracellular levels (D) Change in GTP intracellular levels The current-voltage (I-V) plot (Fig. 2A) for potassium channel (peak late current) and for sodium channel (peak early current), and their respective conductances (Fig. 2B) are provided below. Analyze both graphs and answer questions 25-27. Figure 2A

Figure 2B

I

V

25. One may see that as voltage (V) becomes more positive, the potassium (K+) current becomes progressively larger (Fig. 2A). A main reason for the increase in K+ current at negative membrane potentials (Vm  0mV) is: (A) (B) (C) (D)

The increase in driving force The increase in potassium conductance The increase in sodium conductance The increase in K+ equilibrium potential (EK becomes more positive)

26. A main reason for the increase in K+ current at positive membrane potentials (Vm  20mV) is: (A) The increase in driving force (B) The increase in sodium current (C) The increase in potassium conductance (D) The increase in Na+ equilibrium potential (ENa becomes more negative) 27. Taking into an account EK and ENa one may predict that at high positive potentials (Vm +50mV) electrochemical gradients for these two ions will move: 5

(A) (B) (C) (D)

sodium inside the cell and potassium outside of the cell potassium inside the cell and sodium outside of the cell sodium and potassium outside of the cell sodium and potassium inside the cell

28. A selective inhibition of the voltage-dependent potassium channels by TEA in neurons will: (A) Block depolarization of the membrane (B) Stimulate repolarization of the membrane (C) Increase neuron’s excitability (D) Prolong repolarization of the membrane following the induction of action potential 29. A structural analysis of an unknown membrane-associated protein revealed a presence of four -helical repeats within its transmembrane domain. Based on this specific protein topology one may predict that protein is: (A) (B) (C) (D)

An enzyme Ionotropic receptor Metabotropic receptor Transporter

30. N-terminal domain of this unknown protein likely serves as: (A) (B) (C) (D)

Pore opening domain Ligand binding site GTP-binding site Second messenger interacting site

31. Likewise, C-terminal domain of this protein likely serves as: (A) (B) (C) (D)

Pore opening domain Ligand binding site GTP-binding site Regulatory domain

32. The phosphorylation of its C-terminal domain will: (A) Prevent binding of the ligand to this transmembrane protein (B) Stimulate protein`s enzymatic activity (C) Modulate protein`s transport activity (D) Have no effect on protein’s signaling activity 33. In general, the low intrinsic GTP-ase activity of G-proteins favors: (A) Prolonged G-protein signaling activity (B) G-protein degradation (C) No change in cellular response (D) Termination of G-protein signaling activity

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34. Describe the terms listed below and explain how they contribute sequentially to generation and propagation of action potential, neurotransmitter release and/or vesicle recycling in neurons. Please be specific. - Resting Potassium Channels - Voltage-dependent Sodium, Potassium and Calcium Channels - Axon hillock and Nodes of Ranvier - Endocytosis and Kiss-Run mechanisms of vesicle recycling at the axon terminal

Ana c t i o np ot e n t i a li sc ha r a c t e r i z e db yaf a s tr i s ea n df a l li nv o l t a g ea c r o s sac e l l me mb r a n e . I to nl yo c c u r si ft h et h r e s h o l di sr e a c h e dg oi n gf r o ma b o u t7 0mV( r e s t i n gme mb r a n e p o t e n t i a l )t oa b ou t+4 0mV. Ani n flu xo fp o s i t i v ei on sl e a d st ot h eo p e ni n gofv o l t a g ed e p e n d e n t Na +c h a n n e l s . Th i so p e n i n ga l l o wsf ora ni nflu xr u s ho fNa +wh i c hl e a d st od e p o l a r i z a t i o n ( g e n e r a t e db yl oc a lg r a d e dp o t e n t i a l ) . Th i si sf o l l o we db ya ne fflu xo fK+i o n st h r o u g hv o l t a g e g a t e dK+c ha n ne l sa l l o wi n gf o rr e p o l a r i z a t i ont oe s t a bl i s hr e s t i ngme mb r a n ep o t e n t i a l .Fol l o wi n g t her e p o l a r i z a t i o ni sh y p e r p ol a r i z a t i o nwh e r er e s t i n gp o t a s s i umc h a n n e l sa r eo p e n( l e a k c h a n ne l s )a n ds o meK+v o l t a g ec h a n n e l sa r es t i l lo pe na l l o wi n gf o rmo r ee fflu xofi o n s . Ma k i n g t hec e l lmo r en e g a t i v et ha nt h er e s t i n gme mb r a nep o t e n t i a l( 8 5 mV) . Th i sp e r i o di sd e fin e da st he r e f r a c t o r yp e r i o dwh i c hi st h et i mef r a mei nwh i c hv o l t a g ed e p e n de n tNa / Kc h a n n e l sa r e n ’ t r e s po n s i v ea n dc a n n o tp r o d u c ea n o t h e ra c t i o np o t e nt i a l . On c et h eAPi sg e ne r a t e d,i tc a npr o p a g a t ei ne i t h e rd i r e c t i o nb u to n c ei tg o e s , i tc a n ’ tg o b a c kwa r d s .K+e fflu xvi av o l t a g ed e p e nd e n tKc h a nn e l sr e s u l t si nr e p o l a r i z a t i o na nd h yp e r p o l a r i z a t i o n , p r e v e n t i n ga n o t h e rAP . Ac t i o np ot e n t i a l st r a v e li no n l yo n ed i r e c t i o nd o wna n a x o nb e c a u s eNa +c h a n n e l si nt h en e ur o na r et e mp or a r i l yi n a c t i v ea f t e rt h eAPg e n e r a t i o n . On c ea nAPi sg e ne r a t e di tp r o p a g a t e sf r o mt h ec e l lbo d ya n dt h ea x o nh i l l o c ka c r o s st he a x o nt ot h ea x o nt e r mi n a l . Th ea x o no nan e u r o ni ss u r r o un d e db ymy e l i ns he a t h s( s c h wa n nc e l l s ) wh i c hp r e v e n tt h el e a ko fi o n sa c r o s st h eme mb r a n e .Th i si n s u l a t i o ni n c r e a s e st heme mb r a n e r e s i s t a n c ewh i c hi nt u r ni nc r e a s e st h es pe e dofc o nd u c t i o n . I nb e t we e nt h e s emy e l i ns h e a t h sa r e g a p sc a l l e dn od e so fr a n vi e r . Then o d e so fr a n v i e ra l l o wf o ra c t i o npo t e n t i a lt oq u i c kl yt r a v e l d o wnt h ea x o n . Wi t h ou tt h e s ebr e a k so fmy e l i ns h e a t h, t h ea c t i o np o t e n t i a lwo u l dn o t t r a v e la s q ui c k l y Ther e l e a s ea n dr e t r i e v a lo fne u r ot r a n s mi t t e r swi l loc c u ri nt wowa y s . Th efir s ti swh e n s y n a p t i cv e s i c l e swi l lf u s ewi t ht h eme mb r a n ea n dt h ewho l ec o nt e n twi l lb er e l e a s e df r o mt h e v e s i c l e .Th e r ewi l lb et o t a l f u s i onwi t ht h epr e s y n a pt i cme mb r a n ehe r e . Th es e c on dop t i oni s Ki s sa n dRu n( mo r ee ffic i e nta n de c on o mi c a l )wh i c hi swh e nt h es y n a p t i cv e s i c l et o uc h e st h e me mb r a n ea n dt e mp o r a r yf u s e s , r e l e a s e st h es o meo fv e s i c l ea n dd e f u s e sb a c ki n t ot h ec e l l .

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3 5 . De finea nde x p l a i ni nwo r d ss i mi l a r i t i e sa n dd i ffe r e n c e sb e t we e nd i r e c ta n di n d i r e c ts y na p t i c t r a n s mi s s i o n . I ny o u re x p l a n a t i o na l s oi n c l u d eb e l o wl i s t e dt e r msa n dd e s c r i beh o wt h e y c o nt r i bu t et os y n a p t i ct r a n s mi s s i on .Ag a i n, b es pe c i fic . -I o no t r o p i cr e c e p t o r sa n dme t a b o t r op i cr e c e p t o r s -EPSPa n dI PSP -Hy p e r p o l a r i z a t i o na n dd e p o l a r i z a t i o n -Sy n a p t i cde l a ya n ds y n a p t i ci n t e gr a t i o n The r ea r et wot y p e so fd i r e c ts y n a p t i ct r a ns mi s s i o n , e l e c t r i c a la n dc h e mi c a l .Ma n yo ft he p o s t s y na p t i cr e c e p t o r sa r ei o no t r o p i cr e c e p t o r swh e r er e c e p t o r sa r ec h a n n e l st h e ms e l v e s . Bi nd i n g o ft r a n s mi t t e r ss h i f t sc h a n n e l sf r o mc l o s e dt oo pe ns t a t e( r a r e l yl e a d i ngt oc l o s i n g ) . Th i sa l l o ws t heflu xo fi o n si na n dou to ft h ec e l l . Fo re x a mp l e , Ac hr e c e p t o ra l l o wsf o rt h eflu xofc a t i o n s . Th i si sf a s ta n da l l o wsf o ra na l mo s ti mme d i a t er e s p o n s ef r omt h ec h a n n e l . El e c t r i c a l t r a n s mi s s i o nma k e su p1 0 % oft r a n s mi s s i o n .Th i sr e s ul t si nav e r yf a s tp os ts y n a pt i cr e s p o n s evi a g a pj u n c t i on s . Th e ya r ea l s ov e r ye ffic i e n t ,ma i n t a i n i n ga b o u t1 / 4 t ho ft hep o t e n t i a lf r o mt h e p r e s y n a p t i cc e l l . Na +o rCa +c a ne a s i l ypa s sb yd i ffu s i o nf r o mp r e s y n a p t i ct op o s t s yn a p t i c . Th i s t yp eo ft r a ns mi s s i o ni sv e r ymu c hpr e s e n ti ni n v e r t e b r a t e swh e r er e fle x e sa r er e q u i r e da si ti sv e r y s i mp l e . Ch e mi c a lt r a n s mi s s i onma k e su pa b o ut9 0 %o ft r a n s mi s s i o n .De p o l a r i z a t i o noft h e p r e s y n a p t i cn e r v et r i g g e r sr e l e a s eo fn e ur o t r a n s mi t t e rwhi c ho p e n si o nc h a n n e lr e c e p t o r so nt h e p o s t s y na p t i cc e l lc a u s i n ge i t h e ri n hi bi t i o no re x c i t a t i o n . Thea d v a n t a g eo fac h e mi c a li st h a td e p e n d i n go nt het y p eo fn e u r o t r a n s mi t t e rr e l e a s e d a n dr e c e p t o r se x p r e s s e do nt h es u r f a c ewi l ld e t e r mi newh e t h e ry o ug e td e p o l a r i z a t i o no r h yp e r p o l a r i z a t i o n . Th usy o uc a nmod u l a t et h ep os t s yn a p t i cr e s p o n s e .Th i so c c u r swh e nt h e n e ur o t r a n s mi t t e ra c t i v a t e sp o s t s y na p t i cr e c e p t o r s( i on o t r o p i cr e c e p t o r s ) . Sy n a p s e sc a nb ee i t h e r e x c i t a t o r yf o re x a mp l ea c e t y l c h o l i n ei nt h es k e l e t a ln e u r o mu s c u l a rj u n c t i o no ri n h i b i t o r yf o r e x a mpl et h eg l y c i n eorGABAr e c e p t or .AnEPSPi swhe nt h ede p ol a r i z a t i o ni ss t r o n ge n o u g ht o g e n e r a t ea nAPwhe r eI PSPs t o p st h epr o c e s sb yc a u s i n gh y p e r p o l a r i z a t i o n . I nt e r mso fdi r e c t p o s t s y na p t i ci nh i b i t i on ,t h er e l e a s eo fGABAo rg l y c i n ei si nh i b i t o r ya l l o wi n gf o rt h ei n flu xo f o n l yc l -l e a d i n gt oh y p e r p o l a r i z a t i o n .Th i sma k e si th a r d e rt oi n v o k ea na c t i o np o t e n t i a l . Th e r e l e a s eo fNTi sr e s po n s i b l ef o rs y n a p t i cd e l a y , wh i c hi st h et i mi n go ft h eAPf r o mp r e s yn a p t i c c e l lt op o s t s y n a p t i cc e l l .Syn a p t i ci n t e g r a t i o nd e s c r i b e sh o wt h ei n pu to fp r e s y n a p t i cc e l l sa d d s t o g e t h e rb e f o r et h eg e n e r a t i o no fa nAP .The only way of activating an AP in the brain is via synaptic integration meaning since the number or receptors is limited on the surface, there needs to be a lot of presynaptic inputs.

I ni n d i r e c ts yn a p t i ct r a n s mi s s i o n,n e u r o t r a n s mi t t e r sc a nb i n dt ome t a b o t r o pi cwh i c ha r e n o tc h a n n e l st h e ms e l v e sa n dc a n ’ ta l l o wf o rflu xo fi on s .Ra t h e rt h e r ea r ec e r t a i nme d i a t o r ss uc h a si n t r a c e l l u l a rs e c o n dme s s e n g e r s( l i k eGp r o t e i n s )t h a tb e l on gt oGp r o t e i nc o up l e dr e c e p t o r s . Th eGp r o t e i nt h e nmu s tb i n dt ot h eGp r o t e i nc ou p l e dr e c e p t o rt oa l l o wf o rt h efluxo fi o n s . Th i s p r o c e s si ss l o we rb e c a u s et he r ea r ei nt e r me d i a t e sa ndi tt a k e st i met oa c t i v a t eGp r o t e i no r i nc r e a s et h el e v e lo fs e c o n dme s s e n g e r s .Th ea d v a n t a g e sa r es i g n a la mp l i fic a t i o nwh e r eb i n d i n g o fas i gn a ll i g a n dc a nc r e a t ea nda c t i v a t eanu mb e ro fd i ffe r e n tGpr o t e i n swh i c hi nt u r na c t i v a t e s 8

ma n ye v e nt h o u s a n d so fs e c o n dme s s e n g e r swh i c hb i n dt oi o nc h a nn e l s . An o t h e ra d v a n t a g ei s n e ur o mo d ul a t i o nwh e r ei n d i r e c tt r a ns mi s s i o nc a nmodu l a t edi r e c t t r a n s mi s s i on , e i t h e re nh a nc i n g o rde c r e a s i n ga c t i v a t i o n .

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