Module 2.6 & 2.7: Membrane Transport & Vesicular Transport

Question 1

List some molecules that can readily permeate a plasma membrane

Answer 1

O2, CO2, urea, ethanol, and water. When it’s water it’s called osmosis

Question 2

List some examples of molecules that are not as able to permeate a plasma membrane and therefore rely on membrane transport proteins

Answer 2

Glucose, amino acids, ions like sodium and potassium and Ca2

Question 3

List the different types of unassisted membrane transport

Answer 3

Passive diffusion/simple diffusion which include particles/ions travelling down a concentration/chemical gradient, electrical gradient, or electro chemical gradient, and osmosis

Question 4

What is net diffusion

Answer 4

The difference between two opposing movements during diffusion. For example if 10 particles move from A to B and two particles move from B to A the net diffusion is eight moving from A to B. Also called net flux

Question 5

In regards to diffusion what is a steady state

Answer 5

Diffusional equilibrium, where movement is equal from a to B and B to a

Question 6

Under what conditions does a steady state of diffusion occur fastest

Answer 6

With a warm temperature and small molecules

Question 7

According to Fick’s law of diffusion, what circumstances increase the rate of net diffusion

Answer 7

An increase in the concentration gradient, an increase in the permeability of the membrane, and an increase in the surface area of the membrane

Question 8

According to Fick’s law of diffusion what circumstances lower the net rate of diffusion

Answer 8

An increase in molecular weight, and an increase in the distance or thickness

Question 9

Picture of the law of diffusion

Answer 9

Question 10

Explain how diffusion occurs via electrical gradient

Answer 10

A difference in charge between two adjacent areas promotes movement of ions toward area of opposite charge. Only ions that can permeate the plasma membrane can move along this

Question 11

Describe passive diffusion via electrochemical gradient

Answer 11

Both an electrical and concentration gradient act simultaneously on a specific ion

Question 12

Describe passive diffusion via osmosis

Answer 12

Diffusion of water from higher water concentration (lower solute concentration) to lower water concentration (higher solute concentration)

Question 13

Describe what happens when a membrane separating solutions is highly permeable

Answer 13

Both the water and the substance can move across, maintaining volume on each side and balancing concentration levels

Question 14

Describe what happens when a membrane is only permeable to the water and not the substance

Answer 14

The water will move to the area of lower concentration and the volumes will be uneequal, but solute concentrations and water concentrations will still be balanced on both sides.

Question 15

Describe what happens if pure water is on one side of the membrane and a solute and water are present on the other side, and the membrane is impermeable to the solute

Answer 15

The water will diffuse to the side with solute until hydrostatic fluid pressure builds to a level that it opposes further osmosis, pushing fluid back. Steady state occurs when hydrostatic pressure is equal to osmotic pressure

Question 16

What is tonicity

Answer 16

The effect a solution has on a cell

Question 17

What are the three types of tonicity

Answer 17

Isotonic, hypotonic, and hypertonic

Question 18

Of the three types of tonicity, which has the same concentration of non-penetrating solutes as normal body cells so no net movement of water across the membrane occurs

Answer 18

Isotonic

Question 19

Of the three types of tonicity, which has a below normal concentration of non-penetrating solutes there for a higher concentration of water, and the water enters the cell and it swells

Answer 19

Hypotonic solution

Question 20

Of the three types of tonicity solutions, which has above normal concentration of non-penetrating solutes and therefore a low concentration of water, so the cell loses water by osmosis and shrinks

Answer 20

Hypertonic solution

Question 21

One type of assisted membrane transport is carrier mediated transport, describe the carrier proteins for this, and how it works generally

Answer 21

The carrier proteins span the thickness of the membrane and has binding sites that can be exposed to either extracellular fluid or intracellular fluid. The protein flip-flops to deliver polar molecules from outside the cell to inside, and reverts to the original confirmation once the molecule has been delivered

Question 22

Carrier mediated transport proteins have the confirmation of X and why depending on which way they’re facing, in or out of the cell. What is the X confirmation and what is the Y confirmation

Answer 22

Y confirmation is inward and ex confirmation is outward

Question 23

What are the characteristics that determine the kind an amount of material that can be transferred across a membrane during carrier mediated transport

Answer 23

Specificity, saturation, and competition

Question 24

How does saturation affect the kind and amount of material that can be transferred across a membrane during carrier mediated transport

Answer 24

There are limited number of binding sites which determine the transport maximum (Tm) which is the amount of substance a carrier can transport across a membrane in a given time

Question 25

One form of assistive membrane transport is active or passive transport, what is the difference between these two

Answer 25

Active transport requires energy, whereas passive transport in the form of facilitated diffusion does not

Question 26

What is facilitated diffusion

Answer 26

A carrier protein facilitates the transfer of substance downhill from high concentration to low concentration. For example diffusing glucose into cells

Question 27

What is active transport

Answer 27

A carrier protein transfers a substance uphill and ATP is required to alter the affinity of binding site depending on which side of the membrane it’s on. An example is getting iodine into the thyroid

Question 28

Explain ATP’s role in active transport of specific ions and polar molecules

Answer 28

The carrier protein has a greater affinity for its passenger on the low concentration side due to the phosphorylation of the carrier. The carrier splits the phosphate from ATP and the inorganic phosphate is then attached to the carrier, which causes it to flip so the passenger is now exposed to the high concentrated side. With the change in shape the carrier molecule then experiences Dephosphorylation which reduces affinity for the passenger so it’s released, and the carrier then returns to original shape

Question 29

The process of active transport is often called what

Answer 29

A pump

Question 30

An important pump active transport pump in the body is the sodium potassium ATPase pump, in general what does this do

Answer 30

Pumps Na out of the cell and K into it, both against their concentration gradients. Moves three Na out and 2K in for each ATP split

Question 31

What important roles does the Na- K ATPase pump serve

Answer 31

Establishes sodium and potassium concentration gradients across plasma membrane of all cells which is critical for generating electrical signals. Regulate cell volume by control in concentration of solute inside cell, minimizing Osmetic effects. Energy used to run pump also indirect served as energy source for secondary active transport.

Question 32

What is secondary active transport, and give an example

Answer 32

Carrier molecule for glucose or anamino acid is driven by sodium concentration gradient established by the energy dependent sodium pump to transfer the glucose or amino acid uphill without directly expending energy to operate the carrier. An example of this would be carrying glucose and amino acids across intestinal and kidney cells from low to high concentration.

Question 33

Describe what a co-transport carrier or symport carrier is in secondary active transport

Answer 33

It has two binding sites with both permeants moving in the same direction

Question 34

Describe what counter transport is in secondary active transport

Answer 34

Also called anti-port, the two permeants are moving in the opposite directions

Question 35

Describe the rates of saturation during simple diffusion

Answer 35

An increase in the concentration gradient of a permeant that crosses the membrane equals a corresponding linear increase in net influx, as the concentration gradient increases so does the net flux

Question 36

Describe the rates of saturation with a Proteine mediated transport

Answer 36

An increase in the concentration gradient of a permeant that crosses the membrane equals an increase in the net flux only to the point at which the transport proteins are operating at maximum speed. At that point further increase in permanent concentration will not further increase the net flux. It is saturable

Question 37

Describe vesicular transport and state whether it is an active or passive process

Answer 37

Particles are transferred between intercellular fluid and extra cellular fluid by being wrapped in a membrane enclosed vessicle. It requires energy so it is active.

Question 38

What two processes are used in order to transport particle vesicles into and out of cells

Answer 38

Endocytosis and exocytosis

Question 39

Once endocytosis has occurred to create a vesicle inside of a cell, what happens to the vesicle

Answer 39

It will either fused with lysosomes to be degraded and have its contents released into the intracellular fluid, or it will travel to the opposite side of the cell where it releases its contents by exocytosis. Shuttles through the cell

Question 40

What are the three forms of endocytosis

Answer 40

Pinocytosis, receptor mediated endocytosis, and phagocytosis

Question 41

Describe pinocytosis and what cells are usually involved

Answer 41

Cell drinking, a drop of extra cellular fluid is internalized when membrane deforming coat proteins form a pouch into cell in membrane then seals. Dynamin severs vesicle from membrane and rings neck of pouch. This process also serves to retrieve extra plasma membrane that’s been added to the cell surface during exocytosis. Non-selective process. This process occurs in most body cells

Question 42

Describe what happens during receptor mediated endocytosis, and what type of cells it involves

Answer 42

This is a selective process in which specific large polar molecules are imported. It’s triggered by a specific molecule to its surface membrane receptor, the site then sinks in and seals at the surface. Happens with cholesterol, B12, insulin, iron, and some viruses also sneak in. This occurs in many body cells

Question 43

Describe the process of phagocytosis and what cells it affects

Answer 43

Phagocytosis affects only specialized cells. Multi molecular cells particles are internalized and only a few specialized cells are capable of this. Examples are white blood cells extending pseudopods that engulf and trap it within a vesicle. A lysosome fuses with this membrane releasing hydrolytic enzymes into the vesicle where they attack the bacteria or other trapped material without damaging the cell. Breaks engulfed material into reusable raw ingredients like amino acids, glucose, and fatty acids

Question 44

Describe the process of exocytosis

Answer 44

Membrane enclosed vessicle fuses with cell membrane, then opens up and out into the exterior.

Question 45

What type of products undergo exocytosis, and where are they packaged

Answer 45

Secretary product and large molecules that need to pass through the cell in tact, and they are packaged by the endoplasmic reticulum and the Golgi complex

Question 46

What does exocytosis serve to do

Answer 46

Secrete large polar molecules such as hormones and enzymes that are unable to cross the membrane,with the secular contents highly specific and released only if receiving appropriate signals. Also adds specific components to the cell membrane. The composition of the vesicle membrane is important

Question 47

Describe how secretory vesicles are dealt with in the Golgi complex

Answer 47

The golgi directs finished proteins to the dilated edges of its sacks, which then pinch off. Vesicles then take up a specific product and membrane has specific surface protein molecules which serve as docking markers

Question 48

What is transcytosis

Answer 48

Moving material across the cell by combining the events of endocytosis with those of exocytosis. Moves material across epithelial cell layers. Endocytosis at apical membrane than exocytosis at basolateral membrane