Membrane Transport Mechanisms Syed

Question 1

The sodium potassium pump is an example of which of the following kinds of transport?
A. Diffusion
B. Primary active transport
C. Secondary active transport
D. Facilitated diffusion

Answer 1

Primary active transport - ATP is directly involved in providing energy for the transport

Question 2

The sodium-glucose pump is an example of which of the following kinds of transport?
A. Diffusion
B. Primary active transport
C. Secondary active transport
D. Facilitated diffusion

Answer 2

Secondary active transport

Question 3

The sodium-calcium pump is an example of which of the following kinds of transport?
A. Diffusion
B. Primary active transport
C. Secondary active transport
D. Facilitated diffusion

Answer 3

Secondary active transport

Question 4

Glucose transporters (GLUT transporters) employ kind of transport?

Answer 4

Facilitated Diffusion

Question 5

What’s the difference between Diffusion and Osmosis?

Answer 5

Diffusion is the movement of particles from an area of high concentration to low concentration
While Osmosis is the movement of a solvent across a semi-permeable membrane from high to low concentration
**Semi-permeable membrane is required for osmosis, but not for diffusion

Question 6

What does it mean when equilibrium is met across a membrane?

Answer 6

It does not mean that water or something isn’t moving anymore. It moves left and right, but the net movement is equal

Question 7

What is osmotic pressure?

Answer 7

The pressure that has to be applied to a solvent to stop it from passing into a solution by osmosis. It depends on the concentration of the osmotically active particles aka solution (Van’t Hoff’s Law)

Question 8

What is the osmotic pressure equation?

Answer 8

Pi = g * C * RT

Osmotic Pressure = (Number of particles in solution ism/mol) * Concentration mol/L * gas constant * Absolute temperature

Question 9

How do you calculate Effective osmotic pressure?

Answer 9

Osmotic pressure * Reflection coefficient (Rho)

Question 10

What is the reflection coefficient?

Answer 10

It is the ease with which a solute permeates a membrane

1 = impermeable; 0 = completely permeable.

Question 11

What does a reflection coefficient closer to 1 represent?

Answer 11

It means that that membrane is a major contributor to osmotic pressure and letting things through. It is responsible for controlling the environment

Question 12

What are the pressure differences between A and B?

ADD PICTURE

Answer 12

Column A has a lot of pressure because it is higher and with gravity, it is pushing on the membrane

Question 13

What are the two types of non-gated channels?

Answer 13

• Aquaporins - channels that are permeable to water

- Ion channels

Question 14

What are the two type of gated channels and what do they do?

Answer 14

• Ligand Gated - They open and close and respond to a kind of signal channel (such as a hormone)
• Voltage Gated - They open and close based on a voltage channel

Question 15

What is the difference between Primary and Secondary Active Transport?

Answer 15

Primary active transport - Energy is derived from breakdown of ATP
Secondary active transport - Energy is derived from energy that has been stored in the form of ionic concentration differences of secondary molecular or ionic substances. Secondary active transport also requires multiporters

Question 16

What are multiporters and what are the two kinds?

Answer 16

Symporters (cotransporters) and antiporters (countertransporters or exchangers)
They transport two or more substances across the membrane in either direction.

Question 17

What are some molecules that can diffuse across the biphospholipid layer?

Answer 17

Oxygen, CO2, Nitrogen, alcohols diffuse readily because they are soluble

Question 18

What factors affect the RATE of diffusion?

Answer 18

• Proportional to concentration difference across membrane (hyper vs hypo)
• Membrane electric potential (Nernst potential) - if one side is positive, etc
• Pressure difference - Piston example

Question 19

What factors increase permeability for diffusion?

Answer 19

• Increase in oil/water partition coefficient
• Decrease in size of solute
• Decrease in membrane thickness

Question 20

What is special about simple diffusion?

Answer 20

Simple diffusion (including osmosis) is the only form of transport that is not carrier mediated

Question 21

Equation for measuring diffusion

Answer 21

J = - P*A(C1 - C2)
J = flow(flux) in mmol/sec
P = permeability in cm/sec
A = area in cm2
C1 = [ ]1 in mmol/L
C2 = [ ]2 in mmol/L

Question 22

Describe facilitated diffusion in relation to carrier proteins

Answer 22

• Have binding sites on both sides of membrane
• Very stereospecific to what they transport
• It changes states to get it in. But, the rate at which molecules can be transported by this mechanism can never be greater than the rate at which the carrier protein molecule can under change back and forth between its two states. Remember that it’s still diffusion

Question 23

What is an example of facilitated diffusion?

Answer 23

Glucose. Its transport can be activated by insulin. All cells have members of the GLUT (glucose transporter) family of proteins

Question 24

How does the rate of facilitated diffusion change compared to simple diffusion?

Answer 24

The rate of facilitated diffusion can never be higher than Vmax, while the rate of simple diffusion increases proportionally as concentration increases. (See graph)

Question 25

How does the selective filter of the potassium channel work to stop sodium from entering the channel?

Answer 25

The problem with this channel is that it is always on. But sodium ions are smaller than K ions. So why doesn’t Na always go through? Sometimes it does, but what happens is that it has a selectivity filter. One a hydrated K comes through the filter in front of the channel, it is big enough to bind with the edges in the selective filter, to become dehydrated. But the hydrated Na is too small and can’t bind. Hydrated BUT, the hydrated Na ions are actually bigger than the dehydrated K ions. So that is where the selectivity comes from

Question 26

What is the patch-clamp method?

Answer 26

They take a patch from the cell and test for it inside a free solution. It can measure current flow to learn about transport characteristics of the channel (pic)

Question 27

How does secondary transport get its energy from sodium?

Answer 27

The movement of Na out of the cell releases energy. This can then be used to either pump something else in or out.

Question 28

If sodium moves down its electrochemical gradient, why is this referred to as secondary active transport?

Answer 28

It requires ATP to set up the gradient in the first place.

We always have to keep moving the Na out of the cell so we keep the gradient so that we can move it back down the cell.

Question 29

Sodium/calcium antiporters move three sodium ions per calcium ion. Why does it take three sodium ions to move one calcium ion?

Answer 29

Calcium is a larger ion, so it has a larger electrochemical gradient. So it needs more energy to move the calcium ion.

Question 30

Why do we pump out 3Na for only 2K?

Answer 30

It helps maintain the negative environment inside the cell, which is extremely important for many biological processes

Question 31

Explain the secondary active transport for Na/Glucose co-transport.

Answer 31

A sodium gradient is created by primary active transport, with sodium more concentrated outside the cell. It then moves to secondary active to move the glucose in. As Na diffuses in, it uses that energy to move the glucose in.

Question 32

Explain the active transport of Na across a layer of cells

Answer 32

Once there is a lot of Na in the cell (through diffusion), the gradient is no longer there. So then we actively transport it out of the cell and water will follow too through osmosis because it follows concentration gradients.