Week 2 Review

Question 1

Describe the concentration of ions in the intracellular and extracellular compartments of our bodies. What permits these differences in ionic concentration to exist?

Answer 1

• intracellular = negative
• extracellular = positive
• selective permeability of the cell membrane permits the differences in ionic concentration to exist
• cell membrane is impermeable to K+ but it’s leaky, not perfect at keeping K+ in
• Every time a + charged potassium makes its way out, it leaves a net negative charge behind

Question 2

Explain the phrase “materials move from areas of high concentrations to areas of low concentrations unless somehow prevented from doing so”

Answer 2

• nature of molecules is to be at equilibrium, but a mechanism such as the cell membrane has the ability to regulate molecules in/out of the cell, causing the concentrations to be unequal
• molecules will always move from high to low concentration because of thermal energy unless there is something in their way

Question 3

What is a major function of the cell membrane?

Answer 3

• protection

- regulation of substances going in/out of the cell

Question 4

What molecules easily pass through the cell membrane? What molecules do not?

Answer 4

• non-polar molecules (uncharged, lipid soluble, hydrophobic) move through rapidly
• polar molecules (charged, water soluble, hydrophilic) are largely refused entry

Question 5

How does the anatomy of the cell membrane help this structure function in regulating the movement of solutes across it?

Answer 5

• ion channels on the membrane allow for and regulate movement of ions
• phospholipid bilayer allows lipid soluble molecules through
• other channels on the membrane allow movement of other substances

Question 6

How might changing the properties of the cell membrane change the function of the cell?

Answer 6

the cell no longer has a protective layer that regulates substances going in/out

Question 7

selectively permeable

Answer 7

allows some molecules to cross the membrane but not others

Question 8

non-carrier mediated transport

Answer 8

molecules move through a semipermeable membrane from high concentration to low concentration

Question 9

mediated transport

Answer 9

transporters (membrane proteins) move molecules through the membrane to the other side either up or down the concentration gradient

Question 10

simple diffusion

Answer 10

• spontaneous net movement of particles down a concentration gradient resulting in equal distribution of the particles
• driven by thermal energy

Question 11

facilitated diffusion

Answer 11

• passive process
• random movement of molecules, no ATP, high to low conc, and transporters can help
• Ex: glucose will move down its conc gradient without help but glucose transporters (Glut4) can pick up glucose to move them into the cell quicker

Question 12

active transport

Answer 12

• energy requiring
• molecules can move from low to high concentration or high to low concentration
• involves ATP and specific carrier molecules

Question 13

membrane channels and pores

Answer 13

“holes” in the membrane that can open and close to regulate movement of molecules

Question 14

osmosis

Answer 14

movement of water molecules from areas of high water concentration to areas of low water concentration

Question 15

Explain why a solute concentration gradient between 2 compartments can also influence water concentrations.

Answer 15

Addition of a solute to water decreases the concentration of water in that solution (water and sweet tea example).

Question 16

What physical factors influence the rate of simple diffusion?

Answer 16

• membrane permeability
• solute concentration
• size of the molecule
• electrochemical gradient

Question 17

Explain the role distance plays in the diffusion of solutes

Answer 17

• shorter distance = less travel for the molecule; higher saturation of molecules
• longer distance = more travel for the molecule; takes longer to diffuse; lower saturation

Question 18

hydrophilic

Answer 18

• water loving
• heads of phospholipids that form the external and internal layers of the bilayer
• interact with charged water molecules and with proteins

Question 19

hydrophobic

Answer 19

• water hating
• tails of phospholipids
• interact with nonpolar/uncharged molecules

Question 20

In order for a drug to cross a cell membrane by simple diffusion, would it have to be a polar or non-polar molecule?

Answer 20

• non-polar
• the tails of the phospholipid are hydrophobic, so they like uncharged, non-polar molecules
• non-polar molecules move easier across the membrane

Question 21

What is an ion channel or pore and what is its function?

Answer 21

• part of cell membrane that is selectively permeable to certain ions
• regulates movement of ions
• difference in charges creates an electrical gradient

Question 22

What is an electrochemical gradient? What is its role in ion movement?

Answer 22

• used for an ion that can move across the membrane (pulls + ions in, pushes - ions out)
• chemical gradient = difference in solute conc across the membrane
• electrical gradient = difference in charges across the membrane

Question 23

What is a resting membrane potential (RMP) and what causes it?

Answer 23

• when cell is at rest and there is no net movement (-60-75 mV)
• generated by the “leaking” of K from inside to outside, creating a - charge in the intracellular
• no net movement = no conc is changing even though there is slight movement of a few ions (leakiness)

Question 24

Explain the general purpose and mechanisms of mediated transport.

Answer 24

• occurs when more of a molecule is needed faster than normal (i.e. cannot just rely on simple diffusion)
• passage of molecules through a membrane is mediated by a transporter
• can move from low to high conc OR high to low conc
• Ex: Glut4 transporter with glucose

Question 25

What happens when a transporter moves a molecule from low to high concentration?

Answer 25

• Requires expenditure of energy
• Solute binds to a specific site on the transporter
• Conformational change occurs in transporter
• Transporter & solute move through the membrane
• Dissociation of solute from the transporter then occurs, depositing solute either inside or outside the cell
• Transporter can then pick up a molecule and move it to another compartment or go back to its starting point

Question 26

What factors determine the magnitude of solute movement that can occur by mediated transport?

Answer 26

• Number of transporters available
• Speed at which transporter undergoes conformational change to move the molecule
• Extent to which binding sites are saturated

Question 27

What is a limitation of facilitated diffusion?

Answer 27

movement is still driven by concentration gradients, so can’t go from low to high

Question 28

What are the characteristics of active transport?

Answer 28

• requires energy in the form of ATP
• can move up or down conc gradient
• specific carrier molecules and/or biological pumps
• have to bind, better bind = more effective carrier molecule
• using energy to move molecules down the conc gradient speeds up the facilitated diffusion process

Question 29

endocytosis

Answer 29

• process by which a piece of the cell membrane engulfs an organism, molecule, etc.
• The resulting vesicle then enters the cell and is degraded
• Ex: WBCs protecting our body from invasions

Question 30

exocytosis

Answer 30

• vesicle is formed inside the cell and fuses with the membrane, releasing the contents into the extracellular space
• Ex: insulin; excretion of proteins into the extracellular matrix

Question 31

epithelial transport

Answer 31

• movement of substances across the apical (luminal) and basolateral (serosal) membranes via the paracellular or transcellular pathway of epithelium
• Ex: absorption of material in the GI tract into the blood, movement of substances between the kidney tubules

Question 32

paracellular pathway of epithelial transport

Answer 32

substance diffuses between the adjacent cells of the epithelium

Question 33

transcellular pathway of epithelial transport

Answer 33

substance moves into the epithelial cell across the apical or basolateral membrane, diffuses through the cytosol and exits across the opposite membrane

Question 34

osmosis

Answer 34

the movement of water across a concentration gradient

Question 35

osmotically active

Answer 35

• solutes that cannot cross a membrane and promote osmosis
• play important role in movement of water in capillaries
• role in edema formation

Question 36

hypotonic

Answer 36

higher water concentration outside the cell, so the water moves into the cell and causes it to swell

Question 37

isotonic

Answer 37

solute concentrations are equal, cell will not change shape

Question 38

hypertonic

Answer 38

lower water concentration outside the cell, so water moves out of the cell and causes it to shrink

Question 39

osmotic pressure

Answer 39

amount of pressure required to stop the movement of water

Question 40

Explain the role that non-diffusible large molecules (proteins) play in defining the tonicity of a cell in driving osmosis

Answer 40

• larger molecules determine flow of osmosis
• the side with more large molecules (less water) will require more water coming into the cell, making it a hypotonic solution

Question 41

Explain why active transport but not an ion channel is needed to facilitate the movement of potassium into a cell.

Answer 41

• Because the movement of K and Na is forced, it requires ATP
• Ion channels do not require energy
• High concentration of K inside cell, so it has to go against concentration gradient to get into the cell

Question 42

Explain why an ion channel is sufficient to facilitate the inward movement of Cl ion into a neuron.

Answer 42

[Cl] is higher outside the cell, lower inside. Since ions move from high to low conc, energy isn’t required for Cl to move in. Since energy isn’t required, ion channel can move it.

Question 43

What barriers to movement are created by an epithelial layer?

Answer 43

it is harder for molecules to move through since the epithelial layer can be thick
vs. a simple squamous epithelium layer which is just one layer of cells and thinner