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Molecular & Cell Biology > Electrochemical Gradients > Flashcards

Electrochemical Gradients Flashcards

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1
Q

What is the dynamic equilibrium vapor pressure?

A

Vapour pressure when is a dynamic equ between condensation & evaporation: H20(l) –> H2O(g)

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2
Q

What is needed to maintain homeostasis?

A

Energy

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3
Q

Features & role of ER?

A

• Rough or smooth
• Site of protein synthesis

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4
Q

What happens at the Golgi complex?

A
  • Cell secretions packaging
  • Vesicles bud off & move to
    cell memb
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5
Q

What is the role of lysosomes?

A

Break down materials using enzymes

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6
Q

What is the role of peroxisomes?

A

Breaks down materials using ROS (reactive O2 species)

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7
Q

Structure of mitochondrial memb - what happens at each layer?

A

Double layer
1st = allows material passage
2nd = ox phos - make energy

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8
Q

What are glycolipids essentially?

A

Protein anchors

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9
Q

What are sphingomyelin & cholesterol essentially?

A

Lipid rafts

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10
Q

How do lipids arrange in bilayer?

A

-Non-polar tails align towards lipids (hydrophobic)
-Polar head align towards water (hydrophilic)

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11
Q

Describe how the plasma membrane can move.

A

Phospholipids can move laterally (back and forth) & rotate - but rarely flip from inner to outer/outer to inner leaflets

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12
Q

What is within ECF?

A
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13
Q

Where are: Na+, K+, Ca2+, Mg2+, Cl-, Phosphates, HCO3-, H+, Glucose, AAs, protein - concentrations higher - ICF or ECF?

A

Concs in mM

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14
Q

What are ion gradients based on?

A

Charge (electrical) & the ion in question (chemical) = electrochemical grad

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15
Q

Rank the 3 transporters from fastest to slowest.

A

1 = pores
2 = ion channels/solute carriers
3 = ATPases

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16
Q

Methods of transport in ion channels/solute carriers?

A

-Symport (co-transporter)
-Antiport (counter-transporter)
-Uniport

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17
Q

Methods of transport in ATPases?

A

Pumps:
-P-type
-F-type
-V-type
-ABC transporters

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18
Q

How do aquaporins work?

A

Usually open when inserted in memb – but can regulate some pores via protein-protein interactions

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19
Q

What does regulation of aquaporins mean?

A

Controlling the availability (number of available) aquaporins in memb

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20
Q

Types of aquaporins?

A

Different tissues have different subtypes of aquaporin

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21
Q

How to regulate aquaporins?

A

Aquaporins stored in cell, in vesicles
-For rapid inc in no. on plasma memb = signal directs vesicles to fuse w/ plasma memb
-Longer term - can get prot syn - can be regulated e.g., by AVG (arginine vasopressin) - leads to signalling pathways

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22
Q

Example of an ion channel?

A

Nicotinic acetylcholine receptor - nAChR

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23
Q

What is needed for transport to occur via ion channels?

A

Conc grad established across memb

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24
Q

What is an ion channel?

A

-Limited permeability (permeable pathway only open for limited time)
-Need activator to open
.Volt-gated (e.g., in nerves - open once reach certain voltage)
.Ligand-gated (e.g., 1 or 2 ligands - conf change in shape)
.Other (e.g., stretch, mechanical-activated)

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25
Q

How are ion channels selective?

A

Have selective filter - open in presence of certain ions
-May be e.g., anions/cations
-May be only K+

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26
Q

How do voltage-gated ion channels work?

A

Open at certain voltage

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27
Q

How do ligand-gated channels work?

A

Ligand binds. = conf. change in shape & opens

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28
Q

What family is the nicotinic acetylcholine receptor ion channel a part of?

A

Cys-loop superfamily of inotropic recs

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29
Q

How are nicotinic acetylcholine receptors activated?

A

Require 2 ACh to bind to both alpha subunit ACh binding pockets

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30
Q

What does activation of nicotinic acetylcholine receptors cause?

A

Alters selective filter - allowing Na+ flux across memb

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31
Q

Role of nicotinic acetylcholine receptors?

A

-Primary channel to engage muscle contraction
-Also v. important in ganglionic function

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32
Q

Location of nicotinic acetylcholine receptors?

A

-Just outside spinal cord – sympathetic
-OR close to organs – parasympathetic
-Located in synapses

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33
Q

How do ATPases work?

A

-Using energy to move/pump substance
= primary active transport
–> elect grad established - used to move substance
= secondary active transport

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34
Q

Where are ATPases?

A

-Cell memb
-Intracellular memb

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35
Q

What is a electrogenic pump?

A

Moves unequal no.s of ions in/out plasma memb –> creates conc & electrical grads

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36
Q

How do ABC transporters work - include example?

A

-Use ATP hydrolysis
-e.g., = CFTR
—> regulates Cl- movement
-CFTR opens when 2 ATP bind to their associated binding domains & are hydrolysed

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37
Q

Give an example of a P-type pump ATPase.

A

Na+/K+ ATPase

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38
Q

Outline the basic stages of the Na+/K+ ATPase.

A

-3Na+ bind to pump
-ATP hydrolysis
-3Na+ extruded
-2K+ bind
-Loss of the inorganic phosphate
-ATP binding
-2K+ enter

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39
Q

Give the more complex stage process of the Na+/K+ ATPase.

A

-Spontaneous change from E1-P to E2-P from stage 3–>4
-Stage 6–>7 Pi is lost from E2 form of pump!

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40
Q

Why is the ATPase method of transport the slowest?

A

Involves a multi/many step process

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41
Q

Give an example of a solute carrier.

A

SGLT1 (Na+/glucose co-transporter)

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42
Q

Give the stages of how a SGLT1 (Na+/glucose co-transporter) works.

A

-Solute binds to site in carrier prot
-Conf change in shape of carrier prot = reveals hydrophilic path to opposite memb side
-Solute released
(also get in other direction)

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43
Q

What is needed for both ion channels and solute carriers to work?

A

Conc grad established across memb for primary transport substance OR the cotransporter molecule

44
Q

What are the 3 types of solute carries (defined in terms of direction & no. of solutes/ions being moved?

A

-Symport (co-transporter)
-Antiport (counter-transporter)
-Uniport

45
Q

Which one of the 3 types of solute carriers is SGLT1?

A

Symport (co-transporter)

46
Q

When might a molecule not be able to pass through cell memb?

A

-Not non-polar or hydrophobic/lipophilic enough

47
Q

What is faster - simple diffusion or via solute carrier?

A

Solute carrier

48
Q

What mode of transport is involved in carrier-mediated transport?

A

Facilitated diffusion

49
Q

When does facilitated diffusion occur fastest?

A

At lower concs

50
Q

So, why use solute carriers?

A

-When molecule isn’t non-polar or lipophilic enough to pass cell memb
-Faster (especially at lower concs)
–> do have max speed though as rate of diffusion cannot exceed Vmax (max speed of transport) even when substrate conc inc. - plateaued/max diff rate reached

51
Q

Where are SGLT1 found?

A

GI tract

52
Q

How does SGLT1 work?

A

-Na+ conc grad established - lower conc int than ext (across apical memb)
-Na+/K+ pump enhances Na+ grad (moves Na+ out cell)
-SGLT1 co-transports 2Na+ for each glu/gal (split into these by lactase - from lactose)
–> so glu/gal moved from lumen into cytoplasm (along with Na+ to allow this)

53
Q

Why is the SGLT1 solute carrier important?

A

For glu absorption in Si & reabsorption (lesser than abs) in proximal convoluted tubule of kidney

54
Q

Where else might SGLT1s be found besides GI tract, & what do they do here?

A

Renal tubule - for glu reabsorption (so not lost from body)

55
Q

When might glucose NOT move from tubule lumen space, into renal cell, into blood?

A

In diabetics

56
Q

What happens to blood glucose transport in diabetics?

A

-Have high blood glu conc
-So get ‘eclipsed’ Vmax - as have limited no. of SGLT1 (rate of diffusion has plateaued - reached max)
-So can’t reabsorb all glu @ renal tubule = urinated out (why get glu in diabetic urine)

57
Q

What is Vm (memb potential)?

A

Difference in electrical potential/voltage between int & ext of cell

58
Q

How is Vm (memb potential measured)?

A

-Electrode put in cell
-Ion cons int vs ext & how charges are balanced

59
Q

How does an electrode measure voltage difference across cell membrane?

A

-If had 1 side of ICF/ECF with balanced charge so balanced electrical grad (cations = anions) - but chem grad not balanced - get movement of certain types/’species’ of ion from one side to other –> creates electrochemical grad as now charge isn’t balanced
*Movement of ions between ICF & ECF = registered by electrode

60
Q

What 4 ions are responsible for establishing an electrochemical gradient?

A

Cl-
Ca2+
K+
Na+

61
Q

What direction do the 4 ions that set up the electrochemical gradient move in?

A

Cl- = in
Ca2+ = in
K+ = out
Na+ = in

62
Q

How is memb potential calculated?

A

Nernst equation

63
Q

What are the individual ion equilibrium potentials?

A
64
Q

How is the total memb potential calculated?

A

Potential of each ion based on its conc int & ext = equilibrium potential

65
Q

What is hyperkalaemia & what does it cause?

A

-Insufficient K+ efflux in resting memb pot
-Will get inc memb pot (less -ve)

66
Q

What is hypokalaemia & what does it cause?

A

-Excess K+ efflux in resting memb pot
-Will get dec memb pot (more -ve)

67
Q

Effect of altering either intracellular or extracellular K+ concentration?

A

Substantial effects on resting memb pot & so ability of neurons & muscle cells to reach action potential threshold

68
Q

Effect if changing ion concentrations in ECF (e.g., plasma)?

A

Alters equilibrium pot for that ion & potentially alters memb pot

69
Q

What is the value for membrane potential, roughly?

A

-70mV

70
Q

What is depolarisation - how is it caused (generally)?

A

More +ve mem pot - as Im (direction of current flow across memb changes) - Na+ in (inward current)

71
Q

What is repolarisation - how is it caused (generally)?

A

More -ve memb pot - as Im (direction of current flow across memb changes) - K+ out (outward current)

72
Q

Explain process of an action potential - basic.

A

-Na+ channels open once threshold reached = influx (as higher conc ext than int) = depolarisation
-Na+ channels close
-K+ channels open = efflux (as higher conc int than ext) = repolarisation
(inc Vm past threshold can = AP)

73
Q

Where are voltage gated Na+ & K+ channels involved in action potential currents?

A
74
Q

Structure of voltage gated Na+ channel?

A

-x1 alpha subunit
-x2 beta subunits
-S4 segments of alpha subunit = voltage sensitive (i.e., involved in ‘deciding when to open’)

75
Q

Structure of voltage gated K+ channel?

A

-x4 alpha subunits
-x4 beta subunits
-S4 segments of alpha subunits = voltage sensitive (i.e., involved in ‘deciding when to open’)

76
Q

Name the 3 methods available to ions to move across cell membrane (as can’t directly cross)?

A

-Gap junctions
-Memb transporters
-Ion channels

77
Q

Why can’t ions move directly through phospholipid bilayer?

A

As lipid part of cell memb has high electrical voltage

78
Q

Name the 2 characteristics of ion channels?

A

-Selectivity (on no. & type of ions let through)
-Gating

79
Q

Name 3 ways channels can be gated.

A

-Mechanically gated
-Ligand gated
-Voltage gated

80
Q

Why do electrically cells (neurones, myocytes) have higher Vm (membrane potentials) than other cells at rest?

A

Have more K+ channels open at rest (so = -30mV instead of -60mV)

81
Q

What is Na+/K+ ATPase pump used for?

A

Establishing conc grads of Na+ & K+ for resting pot & graded pots & action pots

82
Q

What is meant by the Na+/K+ ATPase pump being slightly electrogenic?

A

Causes slight change in memb pot (from 5mV –> 12mV)

83
Q

What is meant by the equilibrium potential for an ion?

A

Memb pot where net flow through any open channels is 0 (i.e., chemical & electrical forces are in balance)
(e.g., for K+ = -ve charge across memb required to oppose movement of K+ down its conc grad)
No electrochemical gradient - as electrical & chemical forces = equilibrated/balanced

84
Q

How to calculate resting membrane potential?

A

Account for RELATIVE contribution of each channel type - expressed in terms of permeability (P)

85
Q

Structure of glycerophospholipids?

A

Hydrophilic head & x2 hydrophobic tails

86
Q

How do glycerophospholipids arrange?

A

In bilayer

87
Q

What does the structure of the phospholipid bilayer cause?

A

Limits ion/charged molecule passage

88
Q

What molecules can move across phospholipid bilayer via simple diffusion?

A

Gases (e.g., some neurotransmitters) & small amphiphilic compounds (e.g., most general anaesthetics)

89
Q

Role of membrane proteins?

A

For passage of charged molecules across memb

90
Q

Name 3 types of membrane proteins that enable charged molecules to cross the membrane?

A

-Gap junctions (large pores between 2 ad cells - ions and small molecules can pass through) (including ATP)
-Electrical synapses (specialized form of gap junction)
-Memb transporters (pumps) - integral memb prots - mediate facilitated diff or active transport of ions & other small molecules across memb
-Channels

91
Q

What are the 2 types of active transport?

A

-Primary
-Secondary

92
Q

What is primary active transport?

A

Uses energy source - often ATP

93
Q

What is secondary active transport?

A

Uses ion grads established by primary active transport processes

94
Q

What are the 3 types of membrane transporters & say what they do?

A

-Uniports (move 1 molecule)
-Symports (move multiple molecules in 1 direction)
-Antiports (move multiple molecules in opposite directions)
= ALL ACTIVE TRANSPORT PUMPS!!!

95
Q

What do channels do?

A

Allow water OR ions to flow rapidly through a water-filled pore

96
Q

Compare channels vs pumps?

A
97
Q

What allows depolarisation & repolarisation to occur?

A

Cell memb’s permeability to certain ions & no.s of those ions

98
Q

Give the concentrations of certain ions (Na+, K+, Cl-, ca2+) in the intracellular & extracellular environment

A
99
Q

What is happening at resting membrane potential?

A

No active stimuli

100
Q

What measures membrane potential?

A

Microelectrode

101
Q

What happens at resting potential (-70mV)?

A

No stimuli so:
-x3 Na+ out & 2K+ in (using Na+/K+ ATPase pump) & K+ leak channels = K+ diffuses out
-Memb = polarised

102
Q

What happens during depolarisation?

A

Is a stimuli so:
-Voltage gated Na+ channels open = diffuses in
-If threshold reached = ALL Na+ channels open = more Na+ diffuses in
-Generated AP moves along memb to depolarise all
-Memb = depolarised

103
Q

What happens during repolarisation?

A

-Voltage gated Na+ channels close
-Voltage gated K+ channels opne = diffuses in
–> so -ve charge in cell regained
-Memb = repolarised

104
Q

What happens during hyperpolarisation?

A

Memb = more -ve than @ resting pot - refractory period - CANNOT generate another AP as memb = recovering
(THEN –> after Na+ build up in cell - efflux when Na+/K+ pump restarts)

105
Q

What decides membrane potential?

A

-Direction of current
+ve ion influx = depolarised memb
+ve ion efflux = re/hyper-polarised memb

Molecular & Cell Biology (4 decks)

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