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BIOC2301 > Membrane Transporters and Ion Channels > Flashcards

Membrane Transporters and Ion Channels Flashcards

0
Q

What are the four main classes of transporters?

A

ATP-powered pumps, ion channels, transporters and pores

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1
Q

What are the types of transport?

A

Simple diffusion, facilitated diffusion, active transport and co transport

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2
Q

What are beta-barrels?

A

Mostly all are pore forming complexes conditioning of mainly a beta structure. Not all are pores and not all are membrane proteins.

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3
Q

How many beta strands are in a barrel?

A

8-22

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4
Q

What is an aromatic belt or girdle?

A

A section at the interfaces of the the two bilayers where the residues are 40 % aromatic.

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5
Q

What are all transmembrane beta barrels?

A

Bacterial outer-membrane proteins and outer membranes of mitochondria and chloroplasts.

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6
Q

What are OmpF and OmpC?

A

The dominating OM porins in E.coli, passive diffusion channels.

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7
Q

When is a) OmpF and b) OmpC expressed?

A

a) OmpF is expressed at low ion osmolarity and has a bigger pore.
b) OmpC is expressed at high ion osmolarity and has a smaller pore.

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8
Q

Are beta barrels specific?

A

Most are not but some are. PhoE is specific for phosphate, LamB is specifIc for maltose and FepA and FhuA are specific for siderophores.

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9
Q

What is the opening and closing of a gap junction controlled by?

A

Phosphorylation

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10
Q

What do gap junction monomers consist of?

A

4 transmembrane alpha helices.

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11
Q

How is pore size of gap junctions regulated?

A

By different connexin mixtures.

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12
Q

How many membranes do gap junctions span?

A

2

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13
Q

What are the classes if ATP-powered pumps?

A

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

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14
Q

What do P-class pumps contain?

A

Two identical alpha subunits which have a transmembrane pump, phosphorylation site and ATPase domain.

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15
Q

How do V-class pumps work?

A

In reverse to F-class pumps. Hydrolyses ATP in the hydrophilic domain and a rotatory movement in the hydrophobic domain results in proton transport.

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16
Q

When are V-class pumps used?

A

To lower the pH in intracellular organelles and are also present in the plasma membrane of some animals gut cells.

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17
Q

What does ABC in ABC transporters stand for?

A

ATP-Binding Cassette

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18
Q

What can ABC transporters do?

A

Import and export and can be either promiscuous or specific.

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19
Q

How many domains do ABC transporters have?

A

4; 2 transmembrane (with 12 transmembrane helices) and 2 cytoplasmic domains (which bind ATP and are known as the nucleotide binding domain)

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20
Q

All ATP- powered pumps except for which one use energy generated by ATP hydrolysis to transport substrates uphill?

A

Except F-class, F-class synthesise ATP using a proton motive force in inner mitochondria membranes, thylakoid membranes in chloroplasts and plasma membranes of bacteria. They are ATP syntheses.

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21
Q

What is uni port transport?

A

Passive-mediated diffusion or facial ted transport which specifically transports one molecule from one side of a membrane to another from high to low concentration.

22
Q

What is symport?

A

Secondary active transport, can go from low concentration to high as two molecule move simultaneously.

23
Q

What is antiport?

A

Secondary active transport, can go from low to high concentrations as two molecules move; one in, one out.

24
Q

What are transporters also known as?

A

Carriers, permeases and channels.

25
Q

What can become uni porters by small single mutations?

A

Symporters

26
Q

What is the glucose uni porter GLUT?

A

Classic example of facilitated transport and has an alternating access mechanism.

27
Q

What is Mph1?

A

A hydantoin sodium coupled transporter, has an occluded state.

28
Q

What is an occluded state?

A

An intermediate state in which the binding pocket has no access from either side.

29
Q

What is BetP?

A

A betaine-sodium symporter, has an occluded state.

30
Q

What is Xy1E?

A

A bacterial homologue of GLUT, a D-xylose-proton symporter.

31
Q

What’s the difference between GLUT1 and GLUT4?

A

GLUT1 transports glucose into red blood cells and GLUT4 is found in muscles and is insulin-sensitive.

32
Q

What are the five families of multi drug resistant efflux pumps in bacteria?

A

ATP-binding cassette, major facilitator, multi drug and toxic-compound extrusion, small multi drug resistant and resistance nodulation division.

33
Q

What are ion channels (voltage-gated channels)?

A

All passive, specific with four subunits and many six transmembrane helices.

34
Q

How is KcsA different to many ion channels?

A

Only has two transmembrane helices.

35
Q

What does gating mean?

A

The opening or closing of an ion channel.

36
Q

Where and how does gating occur in ion channels?

A

In the bottom half of the protein using a glycine residue in the transmembrane (S6) helix as a hinge.

37
Q

What is NaVAb?

A

A voltage gated sodium ion channel.

38
Q

What is Kv1.2?

A

A eukaryotic channel functioning in action potentials and propagation.

39
Q

What is N-terminal inactivation in KV channels?

A

A second gate spontaneously closes after a FeS ms due to an N-terminal domain using a ball and chain mechanism. The positive charges of the N-terminal ball bring the domain to the pore, unfolds and 10 residues block the channel and 10 other interact with the T1 domain.

40
Q

What are TRP channels?

A

Transient receptor potential channels, have a role in all five senses, cation (positive) channels, many different types (27 in humans) with different specificities, typically have 6 transmembrane helices and are tetramers with a single central pore.

41
Q

How many TRP channel families are there?

A

7

C, V, M, A, N, ML, P

42
Q

Which TRP channel is involved in taste?

A

TRPM5

43
Q

How does TRPM5 work?

A

Present in taste cells, indirectly contributes to sense in bitter, sweet and umami. A calcium sensitive sodium channels which can also sense the depolarisation of other TRP channels, calcium and temperature.

44
Q

How does temperature effect taste?

A

Increased temperature makes us sense things to be sweeter.

45
Q

Which TRP channels are involved in nociception and where are they expressed?

A

TRPV1, TRPM8 and TRPA1.
V1 and M8 in nociceptors in dorsal root ganglion and trigeminal neurones and A1 in small-diameter nociceptors where it acts as a temperature sensor.

46
Q

What are all of the nociceptors TRP channels?

A

Promiscuous cation channels.

47
Q

What does TRPV1 respond to?

A

Noxious temperature, acidic pH, arachidonic acid metabolites and cannabis, capsaicin (chilli peppers).

48
Q

What does TRPM8 respond to?

A

Gentle cooling, menthol, icilin, eucalyptol, linalool, getanoil, hydroxycitronellal.

49
Q

What does TRPA1 respond to?

A

Mustard oil, allicin from garlic, tear gas, general anaesthetics, terpene alcohols like menthol and thymol, cinnamon.

50
Q

What does CFTR stand for?

A

Cystic fibrosis transmembrane conductance regulator.

51
Q

What is the structure of CFTR?

A

Contains two nucleotide binding domains, an R-domain and 12 transmembrane helices.
Looks a lot like an ABC transporter.

52
Q

How does CFTR work?

A

Channel opens by ATP hydrolysis in the two nucleotide binding domains and phosphorylation in the R-domain increases the affinity for ATP. Hydrolysis in nucleotide binding domain 2 closes the channel.

BIOC2301 (15 decks)

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