Membrane Transport

Question 1

the interior of the cell is ? and why?

Answer 1

electronegative

Due to the presence of nucleic acids (lots of negatively charged phosphate molecules) and intracellular proteins that cannot cross the cell membrane, the inside of most cells is “electronegative” with respect to the extracellular space.

Question 2

ways molecules can go in / out of the cell

Answer 2

diffusion
vesicular transport
solute carries

Question 3

Permeability refers to

Answer 3

the ease with which molecules cross biological membranes. Due to the chemical and structural nature of the phospholipid bilayer (hydrophobic core), only lipid-soluble molecules and some small molecules are able to freely pass through the lipid bilayer. Ions and large polar molecules cannot pass through the lipid bilayer. Yet, each cell has metabolic needs that need to be fulfilled by delivery of nutrients to the cell. In addition, ions and other signaling molecules may need to enter the cell for the cell to fulfill its physiological duties. Finally, waste products and/or signaling molecules generated from within the cell need to be moved out of the cell. All of these processes need the regulated import/export of materials across the cell membrane. This necessitates the use of specialized mechanisms, such as diffusion, transmembrane carriers, and vesicular transport to effect transmembrane transport of substances.

Question 4

what has led to the evolution of, in many cases, specialized transport mechanisms.

Answer 4

Different cells throughout the body have differing needs and differing functions.

Examples include exchange of oxygen/carbon dioxide between blood and cells, nerve impulse conduction, absorption of nutrients from food that we eat, urine formation, and release of hormones.

Question 5

what type of diffusion does not require a channel

Answer 5

simple diffusion

Question 6

With time, if a substance is lipid soluble (which is a property of gases, some hormones, and cholesterol), it will

Answer 6

move down its concentration gradient through the cell membrane by simple diffusion

Question 7

the transfer of oxygen between the alveoli and the pulmonary capillaries is an example of ?

explain

Answer 7

An example of diffusion across membranes.

In this example, the concentration of oxygen (solute) is initially high in the alveoli but low in the capillaries. Given that the membrane being permeable to oxygen diffusion, the concentration in the capillary increases as the concentration in the alveoli decreases until a steady state between the two is achieved.

Question 8

Explain how changes in the concentration gradient, surface area, time, and distance
influence diffusional movement of a compound (Fick’s Law of Diffusion)*****

Answer 8

J = ( DA (C1-C2))/h

Question 9

the Na-K pump is found almost exclusively on the _____ surface of the epithelial cells

Answer 9

basolateral

Question 10

T/F Many substances traverse the lipid bilayer

Answer 10

False

Very few substances/solutes can traverse the semi-permeable lipid bilayer. Most substances require the use of some form of transmembrane facilitation to enter/exit the cells. These transmembrane processes may not require energy (passive) for transport or may need energy indirectly or directly (secondary or primary active transport, respectively).

Question 11

T/F gap junctions can help with communication between two different cells

Answer 11

true - Intercellular Transport

Question 12

Cotransport (Symport) and Countertransport (Antiport) are an example of ______

Answer 12

secondary active transport

Question 13

example of Countertransport (Antiport)

Answer 13

Sodium‐calcium exchanger

Question 14

types of ATPases (Pumps)

Answer 14

P‐type, V‐type, F‐type (E‐type, A‐type)

Question 15

simple diffusion is dependent on

Answer 15

Permeability of substance being transported

Question 16

T/F ABC ion carriers only carry in one direction

Answer 16

FALSE

ABC ion carriers are bidirectional

Question 17

1. Describe features of solute diffusion across cell membranes

Answer 17

1. Describe features of solute diffusion across cell membranes
   a. Across a semipermeable membrane
   b. There is a net flux down a gradient (from high conc. to low conc.)
   c. Eventually reaches a diffusion equilibrium

Question 18

2. Write Fick’s Law of diffusion, and explain how changes in the concentration gradient, surface area, time, and distance influence diffusional movement of a compound

our learning objective : Explain how changes in the concentration gradient, surface area, time, and distance influence
diffusional movement of a compound (Fick’s Law of Diffusion)

Answer 18

2. Write Fick’s Law of diffusion, and explain how changes in the concentration gradient, surface area, time, and distance influence diffusional movement of a compound
   a. J = (D*A(C1-C2))/h
   i. (C1-C2) - stronger gradient increases rate of diffusion
   ii. A - higher surface area increases rate of diffusion
   iii. D - diffusion coefficient that factors in Temp and molecular mass
   iv. h - the greater the diffusion distance (thickness), the lower the rate of diffusion

Question 19

3. Define gating, activation, and inactivation of ion channels
   a. Ion channels work as gate. When activated but closed, the top (closest to exterior) gate is closed while bottom is open. Top opens when activated to let ions in (such as Na). the bottom closes when inactivated.

Answer 19

3. Define gating, activation, and inactivation of ion channels
   a. Ion channels work as gate. When activated but closed, the top (closest to exterior) gate is closed while bottom is open. Top opens when activated to let ions in (such as Na). the bottom closes when inactivated.

Question 20

4. Describe features of the different types of carrier-mediated solute transport

Answer 20

4. Describe features of the different types of carrier-mediated solute transport
   a. Passive transport
   i. Can work through a pore(such as aquaporins) or a gate
   ii. Facilitated diffusion - carrier protein is open to outside → X enters and binds binding site → outer gate closes while X still bound → inner gate opens → X released into interior → gate closes
5. Can work in reverse
6. Two gates never open at same time
   b. Active transport
   i. Secondary active transport - uses energy from another molecule to allow a different molecule to enter or exit against its gradient
7. Symport (co-transport) - both solutes go in same direction
   a. Na-Glc symport
8. Antiport (counter-transport) - the solutes move in opposite directions
   a. Na-Ca exchanger
   ii. Primary active transport - use of pumps and ABC transporters
9. Require energy from ATP
10. Have not found ABC importers in humans, only exporters

Question 21

5. Describe transport rates of certain molecules and ions through specific membrane transport proteins
   * **

Answer 21

5. Describe transport rates of certain molecules and ions through specific membrane transport proteins
   a. Na-K pump - pump has ATP bound → Na inside cell bind → ATP is hydrolyzed → conformation change opens outside of protein → 3 Na out → K binds → conformation change → ATP binds returning to original conformation → 2 K in

Question 22

6. Describe how energy from downhill transport of one ion is used to transport other ions or substances across the cell membrane (co-transport/counter-transport)
   a. One solute is moving down its gradient though a transporter and brings another molecule against it gradient with it

Answer 22

6. Describe how energy from downhill transport of one ion is used to transport other ions or substances across the cell membrane (co-transport/counter-transport)
   a. One solute is moving down its gradient though a transporter and brings another molecule against it gradient with it
7. Describe how energy from ATP hydrolysis is used to transport ions such as Na, K, Ca, and H+ against their electrochemical gradients
   a. ATP hydrolysis causes conformation changes in transport proteins that open, occlude, and allow ions to move against their gradient across the membrane

Question 23

7. Describe how energy from ATP hydrolysis is used to transport ions such as Na, K, Ca, and H+ against their electrochemical gradients
   a. ATP hydrolysis causes conformation changes in transport proteins that open, occlude, and allow ions to move against their gradient across the membrane

Answer 23

7. Describe how energy from ATP hydrolysis is used to transport ions such as Na, K, Ca, and H+ against their electrochemical gradients
   a. ATP hydrolysis causes conformation changes in transport proteins that open, occlude, and allow ions to move against their gradient across the membrane

Question 24

8. Define functioning of the Na-K pump (ATPase)
   a. Na-K pump - pump has ATP bound → Na inside cell bind → ATP is hydrolyzed → conformation change opens outside of protein → 3 Na out → K binds → conformation change → ATP binds returning to original conformation → 2 K in

Answer 24

8. Define functioning of the Na-K pump (ATPase)
   a. Na-K pump - pump has ATP bound → Na inside cell bind → ATP is hydrolyzed → conformation change opens outside of protein → 3 Na out → K binds → conformation change → ATP binds returning to original conformation → 2 K in

Question 25

9. Define functioning of ATP-binding cassette transporters and describe examples of the role of these transporters in physiology and disease

Answer 25

9. Define functioning of ATP-binding cassette transporters and describe examples of the role of these transporters in physiology and disease
   a. ABC transporters use ATP hydrolysis to transport varying molecules such as vitamins, minerals, and ions. They are integral membrane proteins.
   i. Dimer open to inside → ligand binds → ATP binds → dimer closed inside, open outside → ligand released → ATP hydrolyzed → back to original conformation
   ii. Cystic Fibrosis caused by delF508 of ABCC7 gene.
10. Normally allows water and anions out of epithelial cells. Mutation renders this nonfunctional and traps it in the epithelial cells

Question 26

10. Describe epithelial/vectorial transport and discuss the importance of its selective nature in normal physiology of the kidney and GI system

((note - not one of our objectives?) )

Answer 26

10. Describe epithelial/vectorial transport and discuss the importance of its selective nature in normal physiology of the kidney and GI system
    a. Cells are asymmetrical (having apical and basolateral surfaces). SLCs and ABC transporters move solutes across cell membranes directly through tight junctions. This is used for moving solutes across tightly packed cells, drug administration, and maintaining pH
    b. Can involve endo/exocytosis as well as transcytosis^

Question 27

11. Understand how various transporters (Na/H+ exchange, Cl/HCO3 exchange, Na-HCO3 co-transport, etc.) contribute to the control of cytosolic pH

(note - not one of our objectives?)

Answer 27

11. Understand how various transporters (Na/H+ exchange, Cl/HCO3 exchange, Na-HCO3 co-transport, etc.) contribute to the control of cytosolic pH
    a. Sodium comes in to allow H+ out (increase pH)
    b. Cl comes in while HCO3(buffer) goes out (decrease pH)
    c. Na enters, allowing Cl out and HCO3 in (increase pH)

Question 28

13. Define and describe vesicular transport

* **

Answer 28

13. Define and describe vesicular transport
    a. Transport of molecules in bulk by trapping in vesicle to move across membrane and merge with membrane to enter or exit or cross cell.

Question 29

Differentiate between passive and active transport *****

Answer 29

lo

Question 30

Describe how energy from ATP hydrolysis is used to transport ions in primary active transport
systems*****

Answer 30

lo

Question 31

Vectorial Transport: Role in maintaining pH

Answer 31

Vectorial Transport: Role in maintaining pH

Question 32

Vesicular transport important for bulk movement and/or processing of large amounts of particles into or out of cells
Exocytosis: secretion, replacement of portions of membrane
Endocytosis: pinocytosis, phagocytosis, receptor‐mediated endocytosis Transcytosis: from one side of the cell to the other (epithelial cells of capillaries)

Answer 32

• • •
Vesicular transport important for bulk movement and/or processing of large amounts of particles into or out of cells
Exocytosis: secretion, replacement of portions of membrane
Endocytosis: pinocytosis, phagocytosis, receptor‐mediated endocytosis Transcytosis: from one side of the cell to the other (epithelial cells of capillaries)