Lecture 3: Transporters and Pumps

Question 1

What is selective permeability?

Answer 1

It is the ability of the membrane to differentiate between different types of molecules, allowing some molecules while blocking others

Question 2

List the types of molecules & if they are able to pass through the membrane

Answer 2

Pass: Hydrophobic molecules, small uncharged polar molecules
May pass or not: Large uncharged polar molecules
Will not pass: Ions

Question 3

What is GDS?

Answer 3

GLUT1 Deficiency Syndrome

Question 4

Name the mechanism of GDS

Answer 4

it is a genetic disorder that impairs brain metabolism. specifically, the brain is not supplied with sufficient glucose

Question 5

Name symptoms of GDS

Answer 5

symptoms include: seizures, developmental delay, motor disorders

Question 6

What is treatment of GDS?

Answer 6

ketogenic (high fat) diet

Question 7

What does GLUT1 facilitate?

Answer 7

Facilitates the transport of glucose across the membranes of mammalian cells

Question 8

T/F: GLUT1 is a uniporter

Answer 8

True

Question 9

What does a uniporter do?

Answer 9

It has one or more specific binding sites for a solute (substrate), and will transport it across the membrane in a clothes pin fashion (if that makes sense)

Question 10

The binding of solute induces a irreversible conformational
change in the transporter, GLUT1

(this is also specific to uniporters)

Answer 10

False, induces a reversible change

Question 11

For a uniport, how is the direction of transport inversed?

Answer 11

Direction of transport is inversed if the direction of the

concentration gradient is changed

Question 12

What is protein conformation determined by?

2 things

Answer 12

1. Amino acid sequence of the protein

2. Interactions between individual amino acids

Question 13

What bonds are involved in protein conformational change?

Answer 13

Via hydrogen bonds, salt bridges, disulfide bonds,

hydrophobic interactions

Question 14

Name three ways that conformational changes are induced?

3 things

Answer 14

1. binding of a ligand
2. posttranslational modification of the protein
3. change in the pH, voltage or temperature

Question 15

Transporter-mediated transport reaches

a maximal transport rate known as ____.

Answer 15

Vmax

Question 16

What does Vmax indicate?

Answer 16

each transporter in a cell is working at its maximal rate, ie. all binding sites are filled (which requires a steep concentration/electrochemical gradient)

Question 17

What does Km measure?

Answer 17

measures the affinity of the transporter for the solute

Question 18

Name the 3 distinct transport systems in a biological membrane

Answer 18

1. Transporters (uniporter)
2. ATP - powered pumps
3. Ion channels

Question 19

Name an example of each of the three transport systems

Answer 19

1. transporters-GLUT1, Na+/Glc
2. ATP powered pumps- Na+/K+
3. Ion Channels- SCN1A - Nav1.1

Question 20

How can we experimentally test if a mutation in GLUT1 affects glucose transport?

Problem: GLUT1 is a transmembrane protein - how can it be removed from the membrane?

Answer 20

We need to isolate wt. and mutant GLUT1 and examine ability to transport glucose into a liposome

1. Extract protein from membrane
2. Reconstitute into liposomes
3. Perform functional activity assays

Question 21

T/F: Passive transport does not require direct energy input

Answer 21

True

Question 22

Define the energy standpoint of active transport

Answer 22

AT is an energy-dependent transport against an electrochemical gradient

Question 23

How exactly does energy input assist with transport?

Answer 23

Electrochemical gradient for one molecule drives transport of the other

eg, ATP

Question 24

Name the 3 types of ATP Driven Pumps

Answer 24

1. P-type pump
2. ABC transporter
3. V-type proton pump

Question 25

What types of molecules does P-type pump move?

Answer 25

ions; H+, K+, Na+, Ca2+

Question 26

What types of molecules does ABC transporter move across?

Answer 26

small molecules

Question 27

What does V-type proton pumps move across?

Answer 27

H+

Question 28

P-type pumps transport molecules ____ their electrochemical gradient

Answer 28

against

Question 29

Name the most famous type of Ptype pumps?

Answer 29

Na+/K+ pump
Na+: low inside, high outside
K+: high inside, low outside

Question 30

What is the result of the Na+/K+ pump?

Answer 30

Transport of 3 Na+ out of the cell, and 2 K+ into the cell/ATP

Question 31

T/F: Transporters (carriers such as GLUT1) are highly specific for molecule to be transported, and are insaturable

Answer 31

False; they are saturable

Question 32

Active (____ or___) and passive (______) transport is possible

Answer 32

1. sym
2. or anti-porter
3. uniporter

Question 33

With regards to pumps/ATPases, energy from ATP hydrolysis is converted into ___________ ______ , such as ion transport against their electrochemical gradient

Answer 33

mechanical work

Question 34

T/F: Transport down the electrochemical gradient is passive and does not require energy

Answer 34

True

Question 35

Transport against the electrochemical gradient requires energy
• _____ ________ (Na+/K+ pump), light-driven)
• “_____ ______” (sym- and antiport) taking advantage of the steep electrochemical gradient of other molecules

Answer 35

1. ATP Hydrolysis

2. Ride Along

Question 36

1. Which of the following statements is most correct for an ion transporter?
   A. It contains a selectivity filter
   B. It transports ions only down their electrochemical gradient
   C. It contains specific binding sites for the ion to be transported
   D. It transports ions faster than ion channels
   E. It contains 3 transmembrane domains

Answer 36

C?

Question 37

What do you conclude from this experiment?
You are measuring Glc uptake into liposomes into which you have reconstituted wt or mutant forms of GLUT1
a.) The mutation increases the number of Glc binding sites
b.) the mutation increases the affinity of the Glc binding sites
c.) The mutation decreases the affinity of the Glc binding sites
c.) The mutation has no effect on Glc transport
d.) The mutation blocks Glc transport

Answer 37

C

Question 38

CFTR is a protein with 12 transmembrane domains that is mutated in many cystic fibrosis patients. Its molecular analysis led
to some surprises. CFTR is homologous to a transporter of the family of ABC transporters, which use ATP hydrolysis to pump
solutes in or out of the cell. However, CFTR shows an unusual behavior. Which of the following statements would suggest that
CFTR functions differently from the ABC transporter family?
A: CFTR binds to Cl- to move the ions across membranes
B: CFTR can move Cl- against a concentration gradient
C: CFTR produces a robust Cl- current across membranes
D: CFTR requires ATP to move Cl- across membranes

Answer 38

A?