Lecture 17-18 Membrane Transport Proteins

Question 1

Describe active versus passive transport

Answer 1

passive transport does not require energy as it is able to travel down the concentration gradient

active transport is coupled to ATP hydrolysis and travels against the concentration gradient

Question 2

What are the three general modes of transport?

Answer 2

antiporter
symporter
uniporter

Question 3

What are the three categories of transporters?

Answer 3

PUMPS- primary active transport
CARRIERS-traverse the membrane without extra energy
CHANELS- used in passive transport and allow things to pass through as needed

Question 4

Describe the structure of the P-type ATPases

Answer 4

They have 4 domains

1. transmembrane domain that spans the bilayer
2. A- actuator, links the cytosolic domain to the transmembrane domain
3. N-nucleotide binding, domain binds ATP
4. P-phosphorylation, domain accepts the phosphate from ATP

Question 5

Describe ATP-driven active transport with a specific focus on….
P type ATPases

Answer 5

P type ATPases couple phosphorylation and conformational changes to pump Ca2+
The P domain accepts the ATP and is then able to cause a conformational change that traps the ions. The ATP is hydrolyzed and the molecule is allowed to undergo self phosphorylation which releases shit to go into the cell

Question 6

Describe ATP-driven active transport with a specific focus on…. ABC transporters

Answer 6

ABC transporters use 2 ATPs to cause the eversion of the transporter which allows the molecule to be released

Question 7

Distinguish between primary and secondary transporters

Answer 7

Primary transporters create a concentration gradient and lets things pass

secondary transporter: uses the gradient that is created by the primary transporter and then allows the ions to fall back down the gradient with the use of energy

Question 8

Describe the sodium glucose transporter and how is relates to secondary active transport

Answer 8

2 sodium ions are transporter DOWN their gradient and act as the primary transporters that create the gradient

The energy that is collected from this allows for the transport of 1 glucose molecule to occur, against its gradient

Question 9

Describe the process of the lactose permease

Answer 9

1. H+ binds to an empty carrier that increases the affinity for lactose
2. lactose binds to the complex which causes eversion
3. lactose is released
4. Complex is deprotonated
5. eversion happens again so everything can start over

Question 10

Describe in detail how SERCA works

Answer 10

1. Calcium ions bind to the unphosphorylated E1
2. ATP binds to the complex and causes a conformational change that traps calcium in the complex
3. ATP hydrolysis and self phosphorylation occurs
4. Eversion
5. Ca2+ is released
6. Pi is released
7. eversion back to E1

Question 11

Describe how the Na/K pump works in detail

Answer 11

1. The molecule is in the E1 state and the sodium ions bind along with ATP
2. The Na ions get trapped from the inside
3. ATP hydrolysis and self phosphorylation happens
4. Eversion to E2, Na2+ ions are released
5. K+ binds
6. K+ ions get trapped and Pi is released, ATP rebinds
7. Eversion to E1
8. Release K+

Question 12

In the sodium potassium pump, which state is open to the INSIDE?

Answer 12

E1

Question 13

In the sodium potassium pump, which state is open to the OUTSIDE?

Answer 13

E2

Question 14

If the magnitude of the concentration gradient is larger, what will be true of the rate of the diffusion?

Answer 14

It will be faster

Question 15

If the size of the molecule is smaller, what will be true of the rate of the diffusion?

Answer 15

Faster for smaller molecules

Question 16

If the surface area:volume ratio is low, what will be true of the rate of the diffusion?

Answer 16

It will be faster

Question 17

What effect does density of the solvent have on the rate of diffusion?

Answer 17

The higher the density, the slower everything goes

Question 18

What are the two important pieces of the ion channels?

Answer 18

1. selectivity filter

2. Gate

Question 19

Describe facilitated diffusion via ion channels

Answer 19

ion channels have a selectivity filter and a gate that responds to voltage, ligands, or stress

gap junctions allow for communication between the cytoplasms which allows small hydrophobic ions to pass

aquaporins- lets water in via hydrophilic

Question 20

Describe the role of transport mechanisms in neurotransmission

Answer 20

There are 5 mechanisms that work together

1. depolarization occurs, which allows the voltage gated calcium channels to open
2. ACH is released from the cells and opens the ligand gated Na+ channels
3. Local depolarization opens Na+ channels
4. Ca2+ voltage channels keep opening
5. Ca2+ channels in the SR open

Question 21

Describe the transport through gap junctions and water channels

Answer 21

gap junctions traverse two membranes and the aquaporins just traverse one

Aquaporins just allow water to get through, and the gap junctions allow for small hydrophilic ions to pass

Gap junctions do not have a specificity filter

Question 22

Describe the bacterial K+ channel

Answer 22

The channel has HIGH selectivity and rapid flow

Hydrated K+ ions enter the sites and lose the hydration shells

When two ions occupy adjacent sites, electrostatic repulsion pushes them apart, and forces them out of the channel

Question 23

BTLO: Describe the distinguishing features that allow you to discern If a channel is more like and ion channel or an aquaporin?

Answer 23

If the protein traverses two membranes, then it will be a gap junctions, if it is just one membrane that is crossed, then it will be an ion channel

Question 24

BTLO: Describe the distinguishing features that allow you to determine if an ATPase is a P-type ATPase versus and ABC?

Answer 24

A P-type ATPase will self-phosphorylate and are multi-pass transporters

ABC transporters have multiple domains that bind two ATP molecules and does NOT phosphorylate itself

Question 25

BTLO: Predict which of each pair would be slower or faster to move through a membrane via simple diffusion.
CO2 or CH4

Answer 25

CH4 because it is small and non polar, which are two of the things that classify if something is able to pass through a membrane

Question 26

BTLO: Predict which of each pair would be slower or faster to move through a membrane via simple diffusion.
Urea/CO(NH)2)2 or NH2

Answer 26

NH2 because smaller?

Question 27

BTLO: Describe the different ways that a membrane transport proteins can control the open-closed transition (include examples from both active and passive transport)

Answer 27

1. The membrane proteins are able to control what goes in and out of the cell; can respond to the voltage, mechanical stress, ligands. The pore can also be occluded by the ball and the chain portion of the voltage gated (idk look at the picture)
2. selectivity filter is a way of passive transport opening and closing

Question 28

BTLO: Describe the different mechanisms we discussed in lecture for a membrane transport protein to be selective about what it transports

Answer 28

1. selectivity filter
2. depends on the transporter: SERCA is specific for Calcium, Na/K obviously is selective to the Na/K, Bacterial K+ Is selective to K+
3. based on what the body needs and how quickly it needs it
4. Structure of the ions