Chapter 9

Question 1

Porins: Structure and Location of channel (and number)

Answer 1

Trimer,
16-18 strand BETA sheets
beta barrel: water core, hydrophobic side chains

Center of barrel, 3 channels

Question 2

Porins: Specificity/Selectivity, Regulation,

Answer 2

small cations

1. loop restricts pore size
2. Carboxylate side chains (CO2-), selections for + charge

Open, solute can travel in either direction depending on concentration

Question 3

Ion Channels: Structure and location of channel (and number)

Answer 3

Multimer, alpha helical
(in the example, tetramer: 3x helices per subunit, 2 were transmembrane, 1 was extracellular)

Where subunits meet, 1 channel

Question 4

Ion channels: Specificity/selectivity, regulation

Answer 4

Small Cations; Open

Question 5

Gated channels: Structure and location of channel (and number)

Answer 5

6x α helices/subunits
S6- moves inward (linear?) when closed, out when opened

Where subunits meet, but can be 1+ due to complexity

Question 6

Gated Channels: Specificity/selectivity, regulation

Answer 6

Small Cations, Open/Close due to 4 types of stimulus:

pH, phosphorylation (covalent), ligand, voltage

Question 7

Aquaporins: Structure and location of channel (and number)

Answer 7

Tetrameter, alpha helices

Ex: APQ1- 6x membrane span alpha helices and 2x shorter ones in bilayer

4 channels through helices centers

Question 8

Aquaporins: Specificity/selectivity, regulation

Answer 8

Water, but not H+, open

Asparagine (Asn)

Question 9

Glucose Transporters: Structure and location of channel (and number)

Answer 9

12x membrane spanning alpha helices in 2 domains

1 channel

Question 10

Glucose Transporters: Specificity/selectivity, regulation

Answer 10

More solute-selective than porins or ion channels. Why? → Vulnerable to competitive/other types of inhibition
Side chains/protein structure accounts for selectivity

Ligand bind changes conformation (rocks back and forth between open/closed state)

Question 11

Killer pore

Answer 11

Disrupt gradient/membrane integrity

introduce leak channels

Question 12

What does killer pore’s complement do?

Answer 12

set of circulating proteins that sequentially activate each other and lead to formation of doughnut shaped structure (aka membrane attack complex) that creates pore in target’s membrane.

Question 13

Structure of Na+/K+ ATPase pump

Answer 13

Large alpha subunit with 10 transmembrane spanning helices
beta and gamma subunits have 1 transmembrane helix

ATP binding site and Asp on cytoplasmic side

Question 14

ABC transporter

Answer 14

2 parts that reorient to expose ligand sight on either side
ATP binding Cassette
Overexpression: resistance to antibiotics/anticancer drugs

Question 15

ABC transporter structure

Answer 15

Each half has bundle of membrane-spanning α helices linked to globular nucleotide-binding domain, where ATP binding takes place.

Question 16

ABC specificity/selectivity

Answer 16

Some specific for ions, sugars, amino acids, or other polar substances
P-glycoprotein/other drug resistance prefer non-polar substrates
Transmembrane domain allows entry of substances from within the lipid bilayer

Question 17

ABC examples

Answer 17

lipid flippases
P-glycoprotein
multidrug resistance transporter

Question 18

ABC most important/popular function

Answer 18

Get lipid soluble molecules out of the membrane

Question 19

Secondary active transport

Answer 19

high Na+ by Na/K pump outside intestinal cells, brings glucose in from digested food

Question 20

In acetylcholine release, what happens to Ca2+ once in cells?

Answer 20

Vesicle binds to calmodulin, kinase activates protease which releases vesicle into cleft

Question 21

What do SSRIs block?

Answer 21

Na+ symporter

Thus, inhibit serotonin reuptake