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Cell Physiology - Exam 2 > 2.1 - Membrane Transport > Flashcards

2.1 - Membrane Transport Flashcards

1
Q

components permeable to the cell membrane

A

CO2, N2, O2, ethanol

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2
Q

Types of Molecules Crossing Plasma Membrane

Most Permeable → Least Permeable

A

gases (nonpolar molecules)

small uncharged polar molecules

large uncharged polar molecules

ions

charged polar molecules

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3
Q

water flow in hypotonic and hypertonic solutions

A

hypotonic: water flows into cell

hypertonic: water flows out of cell into solution

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4
Q

contractile vacuole

A
  • evoluationary adaptation in paramecium for osmoregulation
  • can expell fluid from the cell when the vacuole fills up
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5
Q

aquaporin

A
  • a “water channel”
  • alpha-helices form central pore
  • channel diameter just large enough for water molecule
  • hydrophlic amino acids in channel to help attract water molecules through
  • no conformation change or energy used
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6
Q

aquaporin frog egg experiment

A

control:

  • natural frog eggs – frog eggs do not normally contain aquaporins and are impermeable to water

experiment:

  • mRNA encoding aquaporin protein injected into frog eggs
  • frog eggs expressing aquaporin protein placed into water
  • frog eggs burst within minutes

conclusion

  • aquaporin = water channel protein
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7
Q

selective transport / facilitated transport

A
  • a specific protein embedded in the membrane is the transporter
  • solute moves down gradient
  • no ATP needed
  • example: channel
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8
Q

cotransport proteins

A

symporters and antiporters

involve the movement of two molecules across the membrane simultaneously

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9
Q

transport rates of transporters: fastest to slowest

A

Fastest

  • channels
  • transporters
  • ATP-powered pumps

Slowest

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10
Q

uniport transporter protein kinetics

A
  • kinetics of uniporter similar to that of enzyme kinetics demonstrating Michaelis-Menten kinetics
  • can use Michaelis-Menten model to describe transporter activity
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11
Q

Michaelis-Menten Constant

A

Km = conc. of substance at 1/2 Vmax

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12
Q

Types of GLUT transporters

A

GLUT 1 = erythrocytes

GLUT 2 = liver cells

GLUT 4 = adipose / muscle cells

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13
Q

process of removing integral membrane protein for study

A
  • disrupt membrane
  • add detergen to solubilize protein
  • mix detergent-covered proteins with phospholipids
  • dialyze or dilute to remove detergent molecules
  • result: liposome with transport protein in membrane
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14
Q

non-gated potasium channels

A
  • specific to K+
  • always open
  • channel environment similar in nature and size to when an K+ is surrounded by water molecules
  • water molecules stripped from K+ when K+ passes through the channel
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15
Q

membrane electric potential with the membrane is impermeable

A

generation of a transmembrane electric potential (voltage) depends on the selective movement of ions across a semipermeable membrane – if the membrane is impermeable then there will be no generation of membrane potential

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16
Q

Process of Gate Ion Channel Opening/Closing

A
  1. resting state – positively charged alpha-helices atttracted to the negative charges on the cytosolic side of the resting membrane, which keeps gate closed
  2. depolarization – voltage-sensing helices move through the phospholipid bilayer toward the outer membrane surface ⇒ conformational change and gate opens
  3. short after depolarization – ball and chain (inactivating segment) moves into open channel and prevents further flow
  4. repolarization – voltage-sensing helices return to the resting position, channel inactivating segment replaced, and gate closes
17
Q

Structure of Voltage Gated K+ Ion Channel

A
  • N-terminus is globular domain
    • ball of the ball and chain inactivating segment
    • cytosolic face
  • 6 membrane-spanning alpha helices
18
Q

Types of ATPases

A

P-class, V-class, F-class, and ABC

19
Q

P-class Pump

A
  • has two identical alpha subunits, each with an ATP-binding site
  • during transport, at least one of the subunits becomes phosphorylated; transported ions move through
20
Q

P-Class Pump Examples

A
  • Na+/K+ pump
  • H+/K+ pump of apical membrane of stomach
  • Ca2+ pumps (i.e. ER, SR)
21
Q

Sodium-Potassium Pump Process

A
  1. 3 Na+ and 1 ATP attach (cyt. side)
  2. phosphorylation of aspartate
  3. conformational change
  4. 2 K+ attach, 3 Na+ release (extra. side)
  5. dephosphorylation and conformational change
  6. 2 K+ release (cyt. side)
22
Q

Typical Intracellular and Extracellular Ion concentrations (high/low)

A

Intracellular: K+

Extracellular: Na+, Ca2+, Cl-

23
Q

Calcium ATPase Structure

A

Cytosolic face has:

  • actuator domain
  • phosphorylation domain
  • nucleotide-binding domain
24
Q

Ca2+ ATPase in SR: Process

A
  1. calcium and ATP-binding on cytosolic side (E1)
  2. phosphorylation of aspartate (E1)
  3. conformational change (E1)
  4. calcium release (E2)
  5. dephosphorylation (E2)
  6. conformational change (E2)
25
Q

V-Class Proton Pumps

A
  • transport only protons (H+) and does so in a process that doesn’t require phosphoprotein intermediate
  • often used to lower pH of an environment
26
Q

Examples of V-Class Proton Pumps

A
  • endosomal and lysosomal membranes in animal cells
  • plasma membrane of osteoclasts
27
Q

getting an acidic environment with V-class pumps

A

V-class pumps pump H+ into the cell, but this generates an electric potential –> need to pair with import of a (-1) molecule like Cl- to keep the charge neutral so that more protons can get into the cell

28
Q

F-class proton pumps

A
  • H+ flow through to lead down concentration gradient in order to produce
  • ATP synthases
29
Q

ABC Superfamily

A
  • “ATP-binding casette”
  • two transmembrane domains
  • two nucleotide binding domains
  • can act as a flippase
  • known as multi-drug resistant transporter
30
Q

glucose transporters in hepatocytes

A
  1. the sodium-potassion pump in the basolateral surface membrane generates Na+ and K+ concentration gradients
  2. the outward movement of K+ ions through non gated K+ channels generates an inside-negative membrane potential across the entire plasma membrane. both the Na+ conc. gradient and the membrane potential are used to drive uptake of glucose from the intestinal lumen by the two-Na+/one-glucose symporter located in the apical surface membrane
  3. glucose leaves the cell via facilitated diffusion catalyzed by GLUT 2, a glucose uniporter located in the basolateral membrane
31
Q

calcium transport out of a myocardial cell

A

To relax muscle → get calcium out of the myocardial cell
Calcium Antiporter; gets energy from Na+ gradient which was created by the Sodium Potassium pump (one Ca++ pumped out for every 2 Na+ pumped in)

32
Q

acidification of the stomach lumen by parietal cells in the gastric lining

A

Function → Acidifying the Stomach (pH=1) → High H+ Concentration

apical membrane has H+/K+ ATPase (P-class pump); K+ and Cl- channels leading from cytosol to stomach lumen, H+ from H20 — OH- combines with Co2 to give HCO3- that is transported to blood through HCO3-/Cl- antiporter

33
Q

ways to inhibit calcium antiporter

A

digoxin and oubin

Cell Physiology - Exam 2 (5 decks)

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