Transport across membranes I, II: Ion Gradients, Electrochemical Driving Forces, Membrane Potential

Question 1

molecules/ions can only cross via

Answer 1

Transporters or channels that act as gates

Question 2

where are transport systems located?

Answer 2

both the cell membrane and on the membrane of intracellular organelles

Question 3

what electrically active cells depends on constant changes in ion fluxes? (action potential)

Answer 3

neurons, cardiomyocytes, and muscle cells

Question 4

simple diffusion occurs through the ____________

Answer 4

lipid bilayer

Question 5

describe diffusion through a Semi-Permeable Barrier

Question 6

transport can be classified into which two categories?

Answer 6

active transport or passive transport (diffusion)

Question 7

active transport can be classified into which two categories?

Answer 7

primary and secondary

Question 8

secondary active transport happens via which two methods?

Answer 8

symports (same direction) and antiports (opposite directions)

Question 9

diffusion can be classified into which two categories?

Answer 9

simple and facilitated

Question 10

what type of transport does bulk flow derive from?

Answer 10

diffusion

Question 11

simple diffusion happens via which two methods?

Answer 11

via bilayer and via ion channels

Question 12

bulk flow is driven via which two methods?

Answer 12

hydrostatic pressure (force exerted by a fluid) and osmotic pressure (pressure required to prevent the flow)

Question 13

What are the 3 modes of passive through the plasma membrane according to Fick’s First Law

Answer 13

1. simple diffusion via lipid bilayer
2. simple diffusion via ion channels
3. facilitated diffusion with aid of carrier proteins

Question 14

Is energy required for passive transport through the cell membrane?

Answer 14

No energy is required for passive transport.

Question 15

what mode of transport does the cell invest energy to force ions/molecules to cross the membrane?

Answer 15

active transport

Question 16

describe Brownian movement in diffusion via lipid bilayer

Answer 16

dictates chance spread from high concentration to the low concentration area, creating a homogenized, equalized average concentration & driven by thermal energy

Question 17

what does a semi-permeable barrier consider changes in?

Answer 17

net flux of molecules across membrane as the concentration gradient changes

Question 18

True or False: The two sides of the
membrane are parts of one continuous compartment

Answer 18

True

Question 19

True of False: The compound randomly diffuses down its concentration gradient from low concentration to high concentration.

Answer 19

False.

from high concentration to low concentration

Question 20

what is the driving force in diffusion through a semi-permeable barrier?

Answer 20

the concentration gradient

Question 21

What happens to the net flux of molecules when there is a large initial concentration gradient?

Answer 21

A large initial concentration gradient creates a significant net flux of molecules from the side with higher concentration to the side with lower concentration.

Question 22

How does the net flux change as the concentration gradient decreases?

Answer 22

As the concentration gradient decreases, the net flux of molecules also decreases.

Question 23

What is the concentration on side 1 and side 2 during the intermediate stage of diffusion?

Answer 23

During the intermediate stage, the concentration on side 1 has decreased to 0.75 M, while the concentration on side 2 has increased to 0.25 M.

Question 24

What happens to the net flux during the intermediate stage of diffusion?

Answer 24

The net flux decreases as the concentration gradient between the two sides decreases

Question 25

What is the final state of concentrations on both sides of the membrane?

Answer 25

In the final state, the concentrations on both sides of the membrane become equal and the net flux becomes 0. This ensures a dynamic steady state

Question 26

what determines how permeable the membrane is for a solute and how readily it diffuses across the bilayer?

Answer 26

the solubility of the solute in lipid

Question 27

if the solute can cross, where does it go down?

Answer 27

its concentration gradient

Question 28

define concentration gradient?

Answer 28

A concentration gradient is the difference in the concentration of a substance between two regions. It represents the gradual change in the concentration of solutes in a solution as a function of distance through a solution.

Question 29

what does the permeability of the bilayer to different molecules depend on?

Answer 29

hydrophilic/hydrophobic nature

Question 30

True or False: the hydrophobic molecule penetrates easily

Answer 30

True

Question 31

How are hydration shells created?

Answer 31

Polar molecules associate with water molecules

Question 32

The smaller the molecules the _____ polar it is and the more rapidly it diffuses across the bilayer.

Answer 32

the smaller the molecule, the LESS polar

Question 33

lipids without proteins are....

Answer 33

highly impermeable to ions, no matter how small they are

Question 34

Give examples of Hydrophobic molecules

Answer 34

O2, CO2, N2, steroid hormones (testosterone, progesterone, estrogen)

Question 35

Give example of small uncharged polar molecules

Answer 35

H20, urea, glycerol, NH3

Question 36

Give examples of large uncharged polar molecules

Answer 36

glucose, sucrose

Question 37

give examples of Ions

Answer 37

H+, Na+, HCO3-, K+, Ca2+, CI-, Mg2+

Question 38

if lipid solubility is high, does it create a strong or weak concentration gradient across the membrane?

Answer 38

strong concentration

Question 39

If the lipid solubility is high, does the molecule's transfer accelerate or decelerate?

Answer 39

If lipid solubility is high, the membrane, accelerating the molecule’s transfer.

Question 40

what does Fick's Law describe?

Answer 40

passive movement molecules down its concentration gradient

Question 41

Fick's Law Equation

Answer 41

Flux (J) (molecules per unit time) = (C2 – C1) · (Area · Permeability coefficient) / Thickness

Question 42

what is the permeability coefficient ?

Answer 42

the mobility of the solute in the diffusion path

Question 43

What are the C2 and C1 in Fick's Law ?

Answer 43

C2 is the higher concentration and C1 is the lower concentration * C2 - C1 = Concentration difference.

Question 44

what is the thickness in Fick's Law?

Answer 44

the length of the diffusion path

Question 45

Simple diffusion through ion channels as well as facilitated diffusion with the aid of carrier proteins are mediated by what? *Hint: the answer in in the question

Answer 45

proteins that function as gates

Question 46

True or False: All modes of transport follow Fick's Law of Diffusion.

Answer 46

False. Not all modes of transport follow Fick's Law of Diffusion. Fick's Law specifically applies to passive diffusion, where the movement of molecules is driven by a concentration gradient and does not require energy input.

Question 47

is diffusion via carrier proteins passive?

Answer 47

Yes, but solute transport is accelerated/ facilitated by the presence of the carrier protein (compared to unaided diffusion through the membrane).

Question 48

What does the protein provide in both channels and carriers?

Answer 48

a permeation path

Question 49

How does diffusion through a channel/transporter facilitate the transport?

Answer 49

by making it less difficult energetically

Question 50

in simple diffusion, is peeling off the hydration shell lowly or highly energetic?

Answer 50

peeling off the hydration shell is highly energetic

Question 51

is the activation energy for delta G in diffusion through the bilayer low or high?

Answer 51

the activation energy ΔG for diffusion through the bilayer is high

Question 52

True or False: A transporter protein reduces the delta G for transmembrane diffusion of the solute

Answer 52

True.

Question 53

How does a transporter protein reduce the delta G for transmembrane diffusion of the solute ?

Answer 53

by making the peel-off easier - forming non-covalent interactions with the dehydrated solute to temporarily replace the hydrogen bonding with water - providing a hydrophilic transmembrane passageway.

Question 54

describe facilitative transport

Answer 54

molecule binds to protein transporter and the mechanism/driving force is passive diffusion - momentary binding to protein transporter that makes transport saturable

Question 55

the molecule (substrate) is released to the other side due to ______ concentration

Answer 55

lower

Question 56

define carrier

Answer 56

a transmembrane protein that binds substrates on one side of a membrane and transports them to the other side - spontaneous conformational change

Question 57

define spontaneous conformational change

Answer 57

natural change in 3D shape of substrate/molecule - possesses 1+ binding sites specific for molecules of certain substances

Question 58

what happens when velocity of transport reaches maximum rate transport

Answer 58

it gets saturated

Question 59

how does simple diffusion differ from Facilitative transport

Answer 59

- it does not require binding to a protein - the graph remains linear - no saturation

Question 60

in facilitated diffusion, saturation kinetics is due to .....

Answer 60

a finite # of carriers & the conformation changes

Question 60

in terms or kinetics, channels are ________, while carriers are ________.

Answer 60

channels are linear where carriers are saturable

Question 61

what causes saturation?

Answer 61

more solutes being transported than the transporters can handle - maxing-out of the increasing rate to a steady state rate (Vmax)

Question 61

do channels have a weak or strong interaction with the permeating compound? and is the permeation slow or fast?

Answer 61

weak interaction with permeating compound/molecule/substrate - very rapid permeation - no conformational changes - no saturation (simple diffusion)

Question 62

what are ionophores used for?

Answer 62

increasing permeability of membrane to specific ion

Question 63

what are ionophores?

Answer 63

small hydrophobic molecules

Question 64

what classes can ionophores be divided into?

Answer 64

1. mobile ion carriers - Valinomycin --> K+ - FCCP --> H+ - A23187 --> Ca2+/Mg2 2. synthetic channel formers - Gramicidin A)

Question 65

Sometimes a "cracked" transporter in facilitated diffusion can be used as a _______ in simple diffusion.

Answer 65

channel

Question 66

how do transporters get "cracked" in the first place?

Answer 66

they get stuck in a confirmation where a crack opens in the protein complex allowing selected ions to flow through - so it works more as a channel

Question 67

give examples of "cracked" transporters

Answer 67

some glutamate transporters - CFTR

Question 68

in terms of simple diffusion, it is driven by a _______ gradient

Answer 68

concentration

Question 69

in terms of Facilitated Diffusion and Ion Transport, they are driven by an ___________ gradient

Answer 69

electrochemical

Question 70

diffusion can ________ electrical gradient

Answer 70

generate

Question 71

What is a difference in electrical charge between 2 spots called?

Answer 71

Electrical Potential/ Voltage

Question 72

How do we measure electrical gradients?

Answer 72

in Volts

Question 73

What is Ohm's Law?

Answer 73

Speed of flow (current) of electrical charge depends on the electrical concentration gradient (electrical potential) & properties of the flow path (resistance).

Question 74

What is Ohm's Law?

Answer 74

I = V/R V = I x R I = current (amp) V = electrical potential (volt) R = resistance (R, Ohm , horse shoe looking ahh symbol)

Question 75

define membrane potential

Answer 75

net charge inside the cell - net charge outside the cell

Question 76

in most cases, the inside of the cell is slightly more ________.

Answer 76

negative

Question 77

The difference in charges establishes an _________________________.

Answer 77

electrical gradient

Question 78

When the chemical concentration is higher inside than outside, the direction of the chemical driving force is ____________.

Answer 78

outward

Question 79

when the chemical concentration is higher outside than inside, the chemical driving force is ____________.

Answer 79

inward

Question 80

in both cases, if permeable the molecules will move passively in the direction of the direction of the driving or.....

Answer 80

down the concentration gradient

Question 81

charged ions have what kind of force

Answer 81

electrical driving force

Question 82

on a positively charged ion, the direction of the electrical driving force is

Answer 82

inward

Question 83

the positive ion will go in,

Answer 83

down its electrical gradient

Question 84

the direction of the electrical driving force on a negatively charged ion is the _________ that of the positive ion.

Answer 84

opposite

Question 85

The direction of the electrical gradient depends both on

Answer 85

concentration and on the charge

Question 86

Do the two driving forces, chemical and electrical gradients, work dependently or independently?

Answer 86

independently