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BS1060: Physiology, Pharmacology & Neuroscience > VS2: Cellular homeostasis (1) > Flashcards

VS2: Cellular homeostasis (1) Flashcards

1
Q

What are the two types of proteins that mediate transmembrane transport?

A

Channel protiens

Carrier protiens

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2
Q

What is the main difference in how channel and carrier proteins work?

A

Channel proteins form a hole in the membrane, allowing molecules to move through

Carrier proteins undergo a transformational change to allow molecules across

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3
Q

What are the similarities and differences between facilitated and simple diffusion?

A

Similarities

  • Both are passive (i.e. move solutes down an electrochemical gradient from high concentration to low concentration)

Differences

  • Facilitated diffusion can be saturated, whereas simple diffusion depends linearly on solute concentration
  • Facilitated diffusion is more temperature-dependent because it is protein-dependent
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4
Q

What is the permeability coefficient?

A

The rate of transport of water

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5
Q

Is water generally considered to be membrane-permeable or -impermeable?

A

Generally membrane-permeable

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6
Q

Where in the body is there low H2O permeability?

A

Ascending loop of Henle (especially the thick limb)

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7
Q

Where in the body is there a high H2O permeability?

A

Red blood cells, renal proximal-tubule cells

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8
Q

On what does the water permeability of membranes depend?

A
  • Lipid composition
    • Unsaturated phospholipids increase membrane fluidity ∴ more permeable to water
    • Sterol content (e.g. cholesterol) decreases membrane fluidity ∴ less permeable to water
    • This explains why artificial lipid bilayers have varying permeabilities
  • Water pores (aquaporins)
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9
Q

What are aquaporins?

A

Transmembrane proteins that allow water to pass through their pore

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10
Q

What is the structure of an aquaporin?

A
  • Transmembrane protein
  • Consists of four subunits ∴ tetrameric protein
  • Each subunit has six α-helical transmembrane regions arranged in a ring, forming a transmembrane pore
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11
Q

What is the transport rate of an aquaporin?

A

Up to 109 molecules/sec

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12
Q

How many pores does each aquaporin have, and what is the diameter of these pores?

A

4 pores per aquaporin

2.8 Å

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13
Q

What is the diameter of a water molecule? How is this relevant?

A

Approx. 2.75Å

The diameter of a pore in an aquaporin is 2.8Å so a water molecule fits perfectly through the pore

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14
Q

How many subtypes of aquaporin are there? Are they all only permeable to water?

A

12

No – others can be permeable to small molecules such as glycerol (aquaglyceroporins)

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15
Q

How can pH modulate the permeability of an aquaporin?

A

A change in pH alters the ionic states of amino acids in an aquaporin, causing a small conformational change

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16
Q

How is the direction of movement of ions through ion channels determined?

A

By the electrochemical gradient

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17
Q

By what can ion channels be gated? What is the name for these types of ion channels?

A
  • Membrane voltage – voltage-gated channels
  • Extracellular/intracellular messengers – ligand-gated channels
  • Mechanical stress – sensory channels/mechanosensitive channels
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18
Q

How do solute carriers work?

A
  1. A solute binds to the solute carrier on one side of the membrane
  2. The protein undergoes a conformational change
  3. The solute is released on the other side of the membrane
  4. The protein undergoes another conformational change and returns to its original shape
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19
Q

What are the names for solute carriers that transport glucose?

A

GLUT1 – GLUT4

20
Q

What are the similarities and differences between channels and carriers?

A

Similarities

  • Both are passive (do not require ATP)

Differences

  • Carriers undergo a conformational change for each molecule they transport, whereas channels only change conformation when opening/closing
21
Q

What drives passive transport?

A

The concentration gradient

22
Q

What is active transport and what drives it?

A

The movement of a solute against a concentration gradient, driven by energy (ATP)

23
Q

What are the two forms of active transport?

A

Primary and secondary

24
Q

What is primary active transport?

A

Active transport using hydrolysis of ATP to generate energy for transport, e.g. ATP-dependent transporters (pumps)

25
Q

What are the three subtypes of ATPase ion transporters?

A
  • P-type (pump)
    • e.g. Na+/K+-ATPase
  • V-type (vesicular)
  • F-type
26
Q

How do P-type ATPase ion transporters work?

A

ATP hydrolysis leads to phosphorylation causing a conformational change

27
Q

Where are V-type ATPase ion transporters found?

A

Synaptic vesicles and cytoplasm

28
Q

How do F-type ATPSase ion transporters work?

A

They use proton gradients for ATP synthesis in mitochondria

29
Q

How many domains are there in Na+/K+-ATPase and what are they?

A

Four:

  • N – nucleotide-binding (ATP-binding) domain
  • P – phosphorylation domain
  • A – actuator domain
  • M – transmembrane domain
30
Q

How does Na+/K+-ATPase work?

A
  1. Resting state: 3 Na+ ions bind from the intracellular space
  2. ATP binds, causing a conformational change
  3. 3 Na+ ions are released into the extracellular space
  4. 2 K+ ions bind from the extracellular space
  5. Na+/K+-ATPase returns to the resting state, releasing 2 K+ ions into the intracellular space
31
Q

What are the common features of ABC transporters?

A
  • ATP-binding cassette
  • Usually homodimer (2 identical subunits)
  • Each subunit consists of:
    • transmembrane domain
    • nucleotide-binding domain
32
Q

What is the mode of action of ABC transporters?

A
  1. Open dimer has high ligand affinity so ligand binds
  2. Ligand binding increases ATP affinity so ATP binds to two subunits
  3. Conformational change reduces ligand affinity so ligand released
  4. ATP is hydrolysed and released, so transporter returns to open configuration
33
Q

What is co-transport? Give an example.

A

The movement of two or more solutes in one transport cycle of the same carrier

e.g. Na+/K+-ATPase

34
Q

What are the two types of co-transport? Define them and give an example of each.

A
  • Symport
    • Both solutes are transported in the same direction
    • e.g. Na+ and glucose
  • Antiport
    • Solutes are transported in opposite directions
    • e.g. Na+/K+-ATPase
35
Q

What is secondary active transport?

A

The energy from the movement of solute A down its electrochemical gradient drives the co-transport of solute B against its electrochemical gradient

36
Q

Is this symport or antiport? What is the energy source?

A

Symport

Energy source = Na+ gradient

37
Q

Is this symport or antiport? What is the energy source?

A

Symport

Energy source = Na+ gradient

38
Q

Is this symport or antiport? What is the energy source?

A

Symport

Energy souce = Na+ gradient

39
Q

Is this symport or antiport? What is the energy source?

A

Symport

Energy source = K+ gradient

40
Q

Is this symport or antiport? What is the energy source?

A

Antiport

Energy source = Na+ gradient

41
Q

Is this symport or antiport? What is the energy source?

A

Antiport

Energy source = Na+ gradient

42
Q

Is this symport or antiport? What is the energy source?

A

Antiport

Energy source = Cl– gradient

43
Q

What is the transport mode and rate of a water channel?

A

Pore (gated)

Up to 109 molecules per second

44
Q

What is the transport mode and rate of an ion channel?

A

Gated

106 – 108 molecules per second

45
Q

What is the transport mode and rate of a solute carrier?

A

Cycle

102 – 104 molecules per second

46
Q

What is the transport mode and rate of an ATP-dependent channel?

A

Cycle

102–104 molecules per second

BS1060: Physiology, Pharmacology & Neuroscience (27 decks)

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