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Block Two Cell Signaling > Pumps, Transporters, Channels > Flashcards

Pumps, Transporters, Channels Flashcards

1
Q

disulfide bond on glycosylation site

A

makes it more compact

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2
Q

Plasma membrane permiability

A
  • hydrophobic and small polar molecules (H2O) can pass lipid bilayer ions and larger polar molecules can not
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3
Q

organelle membranes

A

allow compartmentalization of cellular functions

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4
Q

challenge for the cell

A

maintaining concentration gradient against leaky pores and water efflux, this takes energy

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5
Q

along solute gradient

A

spontaneous

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6
Q

against solute gradient

A

requires energy driving it

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7
Q

osmosis

A

hypertonic, isotonic, hypotonic

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8
Q

hypertonic

A

more ions outside cell so water goes out

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9
Q

isotonic

A

equilibrium so = water going in and out

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10
Q

hypotonic

A

more ions inside than outside so water goes into cell

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11
Q

electrochemical gradient

A

chemical gradient creates membrane potential b/c ions trying to flow in; more efficient to move pos molecules across gradient than negative

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12
Q

membrane potential

A

outside of cell diff concentration than inside of cell

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13
Q

simple difusion

A

molecule just crosses plasma membrane

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14
Q

passive transport

A

go through channel mediated or transport mediated passage

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15
Q

active transport

A

use energy to move molecule against concentration gradient

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16
Q

passive transport

A
  1. Simple diffusion (along a gradient)
  2. Osmosis (hydrostatic pressure)
  3. Facilitated diffusion (protein mediated) Diffusion facilitated by channels and solute carriers, allows molecules to pass otherwise impermeable membrane along their concentration gradient
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17
Q

Carrier

A

transmembrane proteins that expose solute binding site; transport involves conformational changes that exposes solute binding site to other side of membrane where solute is released

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18
Q

channels

A

pore forming transmembrane protein that allow flux of solute molecules to cross membrane; allows rapid transport bc weak pore interaction with molecule ; open and close via conformational changes in inner helices that line the pore

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19
Q

ionophores

A

channel forming protein that allows ion to cross membrane by sheathing its charge; found in microorganisms; work for passive transport

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20
Q

Rumensin

A

used in beef and dairy to improve growth rates and prevent coccidiosis (ionophore)

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21
Q

ion channels used for

A

passive fast transport
have selective hydrophobic pore
provide pathway for charged ions to penetrate hydrophobic cell membrane; ions can pass passively through water filled pore formed by channel

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22
Q

Different modes of ion channel regulation

A
  • voltage gated channels
  • ligand gated channels
  • mechanically gated channels (affected by things like stress)
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23
Q

Why don’t small ions like Na+ pass through K+ channel

A

b/c channel is highly selective for K+; selectivity filters read radius and charge of ion and only if its right ion does it go through
- when K+ goes through ion dehydrated when entering filter and electrostatic interactions w/ water are replaced by carbonyl oxygen atoms lining pore, oxygen atoms spaced too far apart to strip Na+ ions of water molecules in K+ channel so they can’t enter

24
Q

Mechanosenstive channels

A

controled by mechanics, react to hight of membrane, stress on membrane ect.

25
Q

Voltage- gated channels

A

wide transmembrane helices that read membrane potential via voltage sensor

26
Q

voltage gated cat ion channels

A

composed of four highly similar segments clusters around central pore; loop btwn 2 membrane spanning domains makes pore
- cell depolarizes and positively charged AAs move within charged voltage fields -> conformational change and gating of channel

27
Q

voltage gated anion channels

A

cl-; mediate hyperpolarizatoin of muscle and nerve

28
Q

3 states of ion channel

A
  1. Closed
  2. Inactivated
  3. Open
    change in membrane voltage opens channel allowing ions to permeate, channel inactivates while cell depolarized bc separate inactivation particle binds to vestibule; membrane depolarizes and voltage gate closes and inactivation peptide binding is relieved
29
Q

Ligand gated ion channels

A

Neurotrasmitter-relsease triggers channel opening (chemical signal -> electrical signal)

  • opened by binding of one or more ligands to external channel surface
  • mediate excitatory and inhibitory postsynaptic potentials
  • channels also gated by intracellular ligands and mechanical stimuli
  • transport can be triggered by second messengersr biding
30
Q

Acetylcholine receptor

A

at neuromuscular junction; ligand-gated channel; binding of two acetylcholine molecules opens the channel that has relatively broad selectivity for cations

31
Q

interplay of multiple channel systems

A

multiple channels work together from chem signals -> electrical signals

32
Q

Transporters

A
  • require large conformational changes
  • can work with or against gradient where channels can only go in passive direction
  • stronger interaction with substrate so works slower than channels
33
Q

Basic principles of transporter fx

A
  1. Strong interaction with substrate on one side
  2. Reversible conformational change (with and without substrate)
  3. Exposure of substrate binding site on opposite side of bilayer and release of substrate
  4. “Alternate Access” model (open on 1 side close open on other)
34
Q

Transporters (carriers) vs channels

A

Transporters Channels
- strong interaction w - weak interaction with
cargo cargo
- slow transport - rapid transport
-can work bidirectional - unidirectional (only
(w/ or against gradient) along a gradient)

35
Q

Active transport

A

requires energy to transport molecules against electrochemical; gradient (energy in form of ATP or light); these transporters aka pumps

36
Q

3 ways of driving active transport

A
  1. Coupled Transporter
  2. ATP driven pump
  3. Light- Driven Pump
37
Q

Coupled transport

A

aka co-transport; use energy stored in electrochemical gradient

38
Q

ATP driven pump

A

consumes 1 ATP molecule per cycle; this is facilitated by energy ATP consumption

39
Q

Light-Driven pump

A

facilitated by light

40
Q

Uniporter

A

passive or active transport; regulation by voltage, stress, or ligand

41
Q

symport

A

Active transport; 2 molecules transported in same direction (ie from 1 side of membrane to other)

42
Q

antiport

A

Active transport; molecules transported in opposite direct w/ respect to membrane

43
Q

Na+ coupled glucose transporter

A

Uses Na+ gradient to transport glucose (Na+ binds increasing affinity for glucose and allowing both to be transported)

  • cooperative binding sites
  • undergoes conformational change upon transport
  • toggles between several states

** Still active transport (secondary) bc still uses ATP bc will eventually have to pump Na+ out of cytosol w/ ATP driven pump

44
Q

Primary active transport and secondary active transport both

A

Use energy to relocate substrates across membranes; transport against concentration gradient

45
Q

primary active transport

A

ATPases (consuming energy in form of ATP)

46
Q

Secondary active transport

A

coupled to Na+ (plasma membrane) or H+ (bacterial and organelles) co-transport using energy stored in electrochemical gradient
- Na+ and H+ will subsequently be pumped out of cytosol by ATP-driven Na+ or H+ pumps that maintain Na+ or H+ gradient across cell membrane

47
Q

Trans-celluar transport of glucose

A

Gut -> Blood

Gut has low glucose gradient so use Na+ powered symporter to cross into interstitum from gut lumen
Blood has low glucose concentration so passive transport into blood + Na+/K+ pump to maintain cellular [Na+] which uses ATP

48
Q

Sodium pump

A

restores Na+ and K+ gradient across plasma membrane by moving Na+ and K+ against concentration gradients via antiporter; driven by ATP hydrolysis (~1/3-2/3 cellular energy consumption dedicated to maintaining this gradient)
Pumping directions:
Na+ inside cell -> outside
K+ outside cell -> inside
* also called Na+ pump, Na+/K+ pump and ATPase
* without this pump Na+ and Cl- would leak into cell -> swelling

49
Q

P-type transport ATPases mechanism

A

Overall mechanism applies to
Na+/ K+ pump
Ca2+ pump
H+ pump

In Na+/ K+ example
sodium binds ATP hydrolyzes -> conformational change -> sodium release on other side -> K+ binds -> dephosphorylaion -> K+ released on other side

50
Q

P-type transport ATPases

A
  1. Na+/ K+ antiporter for maintenance of cellular [Na+]/[K+]
  2. Ca2+ ATPase; removal of Ca2+ from cytosol after signaling; Steep [Ca2+] gradient across plasma membrane (or SR/ ER)
  3. H+/K+ pumps; avid secretions in stomach
51
Q

Ca2+ gradient

A
  • maintained by two systems in plasma membrane
  • antiporter system (Na+ driven Ca2+ exchange) and Ca2+ pump
  • Structure Ca2+ pump:
  • unphosphorylated- Ca2+ binding cavity exposed to cytosol
  • phosphorylated- Ca2+ released on luminal side
52
Q

Ca2+ storage

A

stored in ER/ SR so intracellular Ca2+ pumped by Ca2+-ATPases in the plasma membrane and ER (SR)membranes (gets pumped into SR)

53
Q

Types ATPases

A
  1. P-type ATPases (phosphorylatoin dependent)
  2. F-type ATPases
  3. V-type ATPases
54
Q

F-type ATPases

A
  • structurally unrelated to P-type ATPase
  • located in bacteria, mitochondria, chloroplasts
  • usually run in reverse (ATP production); ATP synthase
  • transmembrane units cross protein across gradient passively powering ATP synthase (turns basically a cytosolic turbine which rotates as protons move through channels)
55
Q

V-type ATPases

A
  • structurally related to F-type ATPases
  • located in lysosomes, synaptic vesicles, plant vacuoles
  • acidification of organelle interior
56
Q

How does ATP synthase work

A

proton driven conformational change in membrane -> rotate stalk -> protons released on other side membrane by exit channel -> rotation -> enzymatic units binding phosphate and ADP -> ATP

57
Q

ABC transporters

A
  • characterized by two highly conserved ATP-binding cassettes
  • constitute largest family of membrane transport proteins
  • in bacteria use energy stored in ATP or proton gradient to import nutrients or small molecules
  • in eukaryotes medically relevant ABC transporters = multi drug resistant proteins found over expressed in tumors (can pump hydrophobic drugs out cytosol making tumor cells resistant to cytotoxic drugs ie chemo)
  • chloroquine transporter in Plasmodium falciparum responsible for resistance against antimalarial drugs
  • cystic fibrosis transmembrane conductance regulator found mutated in CF (looks like a transporter but functions like a channel)

Block Two Cell Signaling (12 decks)

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