Membrane Transporters and Ion Channels

Question 0

What are the four main classes of transporters?

Answer 0

ATP-powered pumps, ion channels, transporters and pores

Question 1

What are the types of transport?

Answer 1

Simple diffusion, facilitated diffusion, active transport and co transport

Question 2

What are beta-barrels?

Answer 2

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

Question 3

How many beta strands are in a barrel?

Answer 3

8-22

Question 4

What is an aromatic belt or girdle?

Answer 4

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

Question 5

What are all transmembrane beta barrels?

Answer 5

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

Question 6

What are OmpF and OmpC?

Answer 6

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

Question 7

When is a) OmpF and b) OmpC expressed?

Answer 7

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.

Question 8

Are beta barrels specific?

Answer 8

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

Question 9

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

Answer 9

Phosphorylation

Question 10

What do gap junction monomers consist of?

Answer 10

4 transmembrane alpha helices.

Question 11

How is pore size of gap junctions regulated?

Answer 11

By different connexin mixtures.

Question 12

How many membranes do gap junctions span?

Answer 12

2

Question 13

What are the classes if ATP-powered pumps?

Answer 13

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

Question 14

What do P-class pumps contain?

Answer 14

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

Question 15

How do V-class pumps work?

Answer 15

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

Question 16

When are V-class pumps used?

Answer 16

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

Question 17

What does ABC in ABC transporters stand for?

Answer 17

ATP-Binding Cassette

Question 18

What can ABC transporters do?

Answer 18

Import and export and can be either promiscuous or specific.

Question 19

How many domains do ABC transporters have?

Answer 19

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

Question 20

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

Answer 20

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.

Question 21

What is uni port transport?

Answer 21

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.

Question 22

What is symport?

Answer 22

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

Question 23

What is antiport?

Answer 23

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

Question 24

What are transporters also known as?

Answer 24

Carriers, permeases and channels.

Question 25

What can become uni porters by small single mutations?

Answer 25

Symporters

Question 26

What is the glucose uni porter GLUT?

Answer 26

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

Question 27

What is Mph1?

Answer 27

A hydantoin sodium coupled transporter, has an occluded state.

Question 28

What is an occluded state?

Answer 28

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

Question 29

What is BetP?

Answer 29

A betaine-sodium symporter, has an occluded state.

Question 30

What is Xy1E?

Answer 30

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

Question 31

What's the difference between GLUT1 and GLUT4?

Answer 31

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

Question 32

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

Answer 32

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

Question 33

What are ion channels (voltage-gated channels)?

Answer 33

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

Question 34

How is KcsA different to many ion channels?

Answer 34

Only has two transmembrane helices.

Question 35

What does gating mean?

Answer 35

The opening or closing of an ion channel.

Question 36

Where and how does gating occur in ion channels?

Answer 36

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

Question 37

What is NaVAb?

Answer 37

A voltage gated sodium ion channel.

Question 38

What is Kv1.2?

Answer 38

A eukaryotic channel functioning in action potentials and propagation.

Question 39

What is N-terminal inactivation in KV channels?

Answer 39

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.

Question 40

What are TRP channels?

Answer 40

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.

Question 41

How many TRP channel families are there?

Answer 41

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

Question 42

Which TRP channel is involved in taste?

Answer 42

TRPM5

Question 43

How does TRPM5 work?

Answer 43

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.

Question 44

How does temperature effect taste?

Answer 44

Increased temperature makes us sense things to be sweeter.

Question 45

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

Answer 45

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.

Question 46

What are all of the nociceptors TRP channels?

Answer 46

Promiscuous cation channels.

Question 47

What does TRPV1 respond to?

Answer 47

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

Question 48

What does TRPM8 respond to?

Answer 48

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

Question 49

What does TRPA1 respond to?

Answer 49

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

Question 50

What does CFTR stand for?

Answer 50

Cystic fibrosis transmembrane conductance regulator.

Question 51

What is the structure of CFTR?

Answer 51

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

Question 52

How does CFTR work?

Answer 52

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.