CHAPTER 4: Movement of Water/Solutes

Question 1

simple diffusion

Answer 1

movement of molecules from one location to another (requires no energy other than heat)

Question 2

flux

Answer 2

amount of material crossing a surface in a unit of time

Question 3

diffusion equilibrium

Answer 3

when 2 one-way fluxes are now equal in magnitude but opposite in direction

Question 4

net flux always proceeds from _____ to _____ concentration

Answer 4

high to low (downhill)

Question 5

factors that magnitude of net flux depends on

Answer 5

temperature, mass of the molecule, surface area, medium through which the molecules are moving

Question 6

requirements for net flux to occur

Answer 6

1) concentration gradient of solute
2) surface must be permeable to solute

Question 7

how can diffusion rate across plasma membrane be measured?

Answer 7

by analyzing the rate at which its IC concentration approaches diffusion equilibrium with its EC concentration

Question 8

variables in fick’s law of diffusion

Answer 8

rate of diffusion, permeability constant, surface area, concentration in and out

Question 9

increases lipid solubility increases _____? why?

Answer 9

increases flux, because # of polar/ionized groups are decreased, so # of molecules dissolved in membrane lipids will increase

Question 10

how do ion channels show selectivity?

Answer 10

channel diameter, charged and polar surfaces of the subunits, and # of water molecules associated with the ions

Question 11

true or false: the excess negative charges inside of the cell attract the positive charges outside of it so they align on membrane’s surface

Answer 11

true

Question 12

electrochemical gradient

Answer 12

direction and magnitude of ion flux depends on concentration diff and mem potential

Question 13

channel gating

Answer 13

process of opening and closing ion channels = total # of ions that passes through the channel depends on how often channel opens & how long it stays open

Question 14

3 factors that alter channel protein conformations:

Answer 14

1) LIGAND GATED: binding of specific molecules to channel proteins may produce allosteric or covalent change in shape
2) VOLTAGE GATED: changes in potential can cause movement of certain charged regions on a channel protein
3) MECHANICALLY-GATED physically deforming (stretching) the membrane

Question 15

transporters

Answer 15

integral membrane proteins that mediate passage of molecules + non diffusional movements of ions

Question 16

true or false: transporters don’t have to change shape for each molecule transported across membrane

Answer 16

false

Question 17

as the concentration of solute to be transported increases…

Answer 17

of occupied sites increases until transporters become saturated (all sites are occupied)

Question 18

facilitated diffusion

Answer 18

net flux of a molecule across membrane always proceeds from higher to lower concentration

Question 19

how long does facilitated diffusion continue?

Answer 19

using a transporter to move solute, it continues until the concentrations of solute on both sides of membrane become equal

Question 20

active transport

Answer 20

energy is used to move a substance UPHILL across a membrane aka against its concentration gradient and requires a substance to bind to transporters in the membrane

Question 21

what is used in primary active transport?

Answer 21

phosphorylation of transporter by ATP

Question 22

what is used in secondary active transport?

Answer 22

use of electrochemical gradient via binding of ions

Question 23

how does Na move from?

Answer 23

from intracellular to extracellular

Question 24

how does K move from?

Answer 24

from extracellular to intracellular

Question 25

primary active transport

Answer 25

hydrolysis of AYP by a transporter provides energy --> ATPase

Question 26

secondary active transport

Answer 26

movement of an ion down its electrochemical gradient is coupled to transport of another molecule (ex: glucose, amino acid) ultimately, energy is required indirectly via primary Na+ pumps for maintaining the concentration gradient

Question 27

how is the electrochemical gradient for Na directed?

Answer 27

it is directed into the cell because of higher concentration of Na in the EC fluid + excess negative charges inside the cell

Question 28

binding of Na increases _____ for transported solute, then transporter changes conformation, which decreases _____

Answer 28

affinity, affinity

Question 29

what is the most important distinction between primary and secondary active transport?

Answer 29

secondary uses stored energy of an electrochemical gradient to move both an ion and second solute both use ATP because the energy in secondary is technically derived from ATP

Question 30

contransport

Answer 30

movement of actively transported solute in the cell (symport)

Question 31

countertransport

Answer 31

movement of actively transported solute out of the cell (antiport)

Question 32

how does water cross membranes?

Answer 32

1) diffusing through the lipid bilayer and 2) diffusing through protein channels in the membrane

Question 33

what is osmosis mediated by?

Answer 33

membrane proteins called aquaporins that form channels through which water can move

Question 34

describe movement of solute and water during osmosis

Answer 34

solute: low to high solute water: high to low water

Question 35

osmolarity

Answer 35

total solute concentration in the solution – determines the water concentration the higher the osmolarity of a solution, the lower the water concentration (and greater the osmotic pressure) mormal intracellular osmolarity is 300 mOsm

Question 36

tonicity

Answer 36

concentration of only the non-penetrating particles

Question 37

semi-permeable membrane

Answer 37

a membrane permeable to water but not to solutes

Question 38

what are substances that cannot cross the plasma membrane called?

Answer 38

non-penetrating solutes (ex: Na because it moves into cells and is also pumped back out)

Question 39

hypertonic solution

Answer 39

solution containing greater than 3 mOsm of non-penetrating solutes causing cells to SHRINK as water diffuses out

Question 40

isotonic solution

Answer 40

solution that doesn't cause a change in cell size

Question 41

endocytosis

Answer 41

when regions of the plasma membrane can often be seen to have folded into the cell, forming pockets that punch off to produce IC vesicles that enclose a small volume of EC fluid

Question 42

hypotonic solution

Answer 42

solutions have a non-penetrating solute concentration lower than that found in cells that causes them to SWELL as water goes in

Question 43

exocytosis

Answer 43

when membrane-bound vesicles in cytoplasm fuse w/ plasma membrane & release their contents to the outside of the cell

Question 44

pinocytosis

Answer 44

an endocytotic vesicle encloses a small volume of EC fluid (engulf water in EC fluid and solutes)

Question 45

phagocytosis

Answer 45

cells engulf bacteria or large particles like debris from damaged tissues, PM folds arounf surface to engulf entirely (psuedophobia --> phagosomes)

Question 46

receptor-mediated endocytosis

Answer 46

certain molecules in EC fluid bind to specific proteins called receptors, and each one recognizes a ligand w/ high affinity (ex: clathrin!)

Question 47

potocytosis

Answer 47

vesicles called caveolae pinch off and deliver their contents (vitamins, lipoproteins) directly into the cytosol

Question 48

active transport and facilitated diffusion within secondary active transport

Answer 48

AT: Na+ is then moved via active transport by the sodium pump to move uphill against the concentration gradient into the bloodstream FD: in organic solute, x, hitches a ride with the Na+ transporter via secondary active transport against the concentration gradient into the cell...it then uses facilitated diffusion to move down the concentration gradient into the bloodstream

Question 49

epithelial transport

Answer 49

epithelial cells line hollow organs or tubes & regulate absorption/secretion of substances across the surfaces

Question 50

apical membrane

Answer 50

PM on one surface of an e. cell that faces a hollow or fluid-filled tube or chamber

Question 51

basolateral membrane

Answer 51

PM on opposite surface that rests upon a basement membrane and is usually adjacent to a network blood vessels

Question 52

paracellular pathway

Answer 52

diffusion occurs in tight junctions BETWEEN adjacent cells which limits it

Question 53

transcellular pathway

Answer 53

substance moves into an e. cell via either membrane, diffuses through cytosol, and exits across the opp. mem

Question 54

movement of Na from lumen to e. cell occurs by diffusion vs Na channels in apical membrane and the concentration goes from _____ to _____

Answer 54

low to high