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BC3003: Introduction to Cell Biology & Biomembranes > Transport of Molecules Across Membranes > Flashcards

Transport of Molecules Across Membranes Flashcards

1
Q

What types of molecules are able to cross a pure lipid bilayer? By what mechanism do they cross?

A
  • Gases & small polar / uncharged molecules
  • Passive diffusion
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2
Q

What types of molecules are NOT able to cross a pure lipid bilayer?

A
  • Ions
  • Charged molecules
  • Large uncharged / polar molecules
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3
Q

What TWO factors influence the movement of charged molecules across a membrane?

A
  1. Concentration gradient (chemical)
  2. Electrical Potential (voltage)
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4
Q

What does the Electrochemical gradient determine?

A

The energetically favourable direction of movement of a molecule

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5
Q

What equation gives the equilibrium potential for two solutions separated by a membrane that is permeable only for a given ion (X+/-)?

A

Nernst Equation

(don’t need to know the equation)

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6
Q

TRUE OR FALSE:
When ΔG is negative, there is net movement of a molecule INTO the cell?

A

True

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7
Q

What are the THREE broad classes of transport proteins?

A
  1. ATP-powered Pumps
  2. Transporters /Carriers
  3. Ion Channels
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8
Q

What type of transport do ATP-powered Pumps facilitate?

A

Active Transport

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9
Q

What type of transport do Transporters / Carriers facilitate?

A
  • Facilitated Diffusion
    OR
  • Coupled Transport / Secondary Active Transport
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10
Q

What type of transport do Ion Channels facilitate?

A

Facilitated Diffusion

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11
Q

What are the THREE classes of ATP-powered Pumps?

A
  1. P class
  2. V class
  3. ABC superfamily
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12
Q

What are the THREE classes of Ion Channels?

A
  1. Voltage gated
  2. Ligand gated
  3. Non-gated (resting)
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13
Q

What are the THREE classes of Transporters / Carriers?

A
  1. Uniporters
  2. Symporters
  3. Antiporters
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14
Q

What reaction powers ATP-powered Pumps?

A

ATP hydrolysis
* ATP –> ADP + Pi

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15
Q

TRUE OR FALSE:
ATP-powered Pumps transport molecules WITH their electrochemical gradient?

A

False.
They transport AGAINST the gradient

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16
Q

What is Active Transport?

A

Coupling of ATP hydrolysis and “uphill” transport of ions or small molecules

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17
Q

Does Active Transport provide high or low rates of transport?

A

Low

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18
Q

What type of molecule do P-Class ATP-powered Pumps transport?

A

Ions

19
Q

What type of molecule do V-Class ATP-powered Pumps transport?

A

Protons

20
Q

Where in the cell are V-class pumps found?

A

Lysosomes and Vacuoles
* generate acidic compartments

21
Q

What type of molecules do ABC superfamily pumps transport?

A
  • Ions
  • Sugars
  • Amino acids
  • Phospholipids
  • Peptides
22
Q

What are the domains of an ABC superfamily pump?

A

Two transmembrane and two ATP binding ‘core’ domains

23
Q

What does ‘ABC’ stand for in ABC superfamily pumps?

A

ATP Binding Cassette

24
Q

What is the structure of the P-class pump?

A

2x α and 2x β subunits

25
Q

What happens to the Ion during transport through a P-class pump?

A

Phosphorylated on a conserved Aspartate in α subunits

P for Phosphorylated and P-class

26
Q

What are TWO examples of P-class pumps?

A
  1. Na+ / K+ ATPase - pumps K+ IN and Na+ OUT of cell
  2. Ca++ ATPases in PM and ER - pump Ca++ OUT of cytosol
27
Q

What is the mechanism of action for Na+ / K+ ATPase?

A

Hydrolyis of 1 ATP per cycle coupled to transport of 3 Na+ OUT of cell and 2 K+ INTO cell

28
Q

How many conformational states does Na+ / K+ ATPase have?

A

2
E1 & E2
* unidirectional transport

29
Q

What are the affinities for Na+ and K+ in the E1 state?

A

3 HIGH affinity Na+
and
2 LOW affinity K+
sites on Cytosolic side

30
Q

What are the affinities for Na+ and K+ in the E2 state?

A

3 LOW affinity Na+
and
2 HIGH affinity K+
sites on Extracellular side

31
Q

TRUE OR FALSE:
V-class proton pumps run the in SAME direction as ATP Synthase?

A

False.
They run in the OPPOSITE direction

32
Q

Where are the V0 and V1 components of a V-class proton pump located respectively?

A
  • V0 located in MEMBRANE
  • V1 located in CYTOSOL
33
Q

Which subunits hydrolyse ATP to provide energy to pump protons across the membrane in V-class proton pumps?

A

β subunits of V1

34
Q

What is the pH of a Lysosome?

A

4.5 - 5

35
Q

What is the mechanism of action for V-class proton pumps to acidify intracellular compartments?

A
  • Protons are charged (cations) so pumping protons in is electrogenic
  • Charge builds up across membrane to prevent acidification of compartment
  • Anions are transported in the same direction to counteract
36
Q

What are the domains of ABC superfamily pumps?

A

2x Transmembrane domains
and
2x Cytosolic ATP-binding domains

37
Q

What protein is an example of an ABC superfamily pump?

A

Multi-drug resistance transport proteins (MDR1 & 2)

38
Q
A
38
Q

Are MDR1 & 2 over or under expressed in tumours?

A

Overexpressed
* higher concentration of drug required to kill tumour cells

39
Q

What mechanism does MDR1 & 2 use to transport molecules across the membrane?

A

Flippase

40
Q

What molecule does the Cystic Fibrosis Transmembrane Regulator (CFTR) transport?

A

Cl- ions

41
Q

Mutation of which ABC gene causes a rare disorder called Tangiers Disease?

A

ABC A1

42
Q

Mutation of which ABC gene causes X-linked Adrenoleukodystrophy (ALD)?

A

ABC D1

BC3003: Introduction to Cell Biology & Biomembranes (15 decks)

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