Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Bchem 471 > Electrophoresis > Flashcards

Electrophoresis Flashcards

1
Q

What are colloids

A

The are made of one phase dispersed into another phase (like liquid in liquid or solid in liquid)

We typically use liquid liquid, or solid in liquid (gel)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Explain colloid instability

A

Colloids in solution are not stable, they flocculate (clump together) then coagulate, then sediment out of solution

Or it can sediment (drop to bottom of container), flocculate, then coagulate

Not good

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Whag influence colloid stability

A

Concentration: if higher, they more likely to interact with each other

Do they like to stick together

What solution it’s in

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the two types of stabilization for colloids which are barriers to floculations

A

Steric stabilization (stick polymer chain on it that pushes away other molecule)

Electrostatic stabilization

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Explain why flocculation is favourable to happen

A

Using hard sphere model

Van der walls forces pulls the molecules together at the lowest energy

The model says that if we leave the molecules together, they will start to stick together due to these attractive forces

This is the precursor to flocculation thencoagulation and precipitate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the sources of charge on surfaces

A

Ph change: making a solution basic give a net negative charge on the surface groups

Silica: the silica changes charge depending on the pH of the solution (can go either way) , like running KOH in glass (basic) so net negative silica charge of the surface. Giving acid makes it acidic

Ionization of surface groups: ions like AgI, can solvate one ion and leave the other on the surface

Surfactants: can be cationic or anionic surfactants (like SDS), sick to the surface and carry a charge with it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the equation for van der waals attractive force

Repulsive force

A

-A/12pir^2

On sheet

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Explain the van der waal attractive force and repulsive force and the net energy in the one graph

A

attractive force which makes the line go down in energy as molecules get closer

Repulsive force which makes them go higher in energy as they get closer

Then net energy hump is in between them which shows how there is an energy hill the molecules need to climb so they can eventually attract and flocculate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Explain the flocculation curve

A

Particles far apart , no energy no interaction

Get close, start to have vander waals attractive forces, energy goes down

Then eventually you have repulsive force as they get too close, higher energy

If we get them close enough (for example higher concentration) Then they can cross over this high energy hump to follculate (crash out) and get closer together and to low energy

Eventually them stick together and turn into a clump that is incompressible

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Explain the double layer model

A

Surface: You have a negative charge particle in solution

Stern layer: Surrounding it is the tight bound positive charged counterions that move with the particle

Diffuse layer: has less tightly bound ions, can be postive or negative because now the particle looks postive, it’s all the ions outward of the stern layer

Inside diffuse layer the is the slipping plane

Slipping plane: the part where ions stop moving with the particle as it moves through the solution

this plane is the boundary between ions that are still moving with the particle and ions that are not and just stay in the solution (some point in the diffuse layer)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Explain the double layer plot

A

P vs r plot for a positively charged particle

Surface potential: surface layer of the particle (0 r), the potential would be positive because it’s postive ion (

Stern potential: As we move outward from the surface and go to stern layer, the negative counterions start to drop the potential

Diffuse Layer: the potential decreases more due to shielding of the ions in the diffuse layer

Zeta potential: At some point in the diffuse layer we reach the slipping plane, potential measures here is the zeta potential

Then furthest away from the ion is close to zero because looks neutral

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Why do we measure the zeta potential at ethe spliiping plane

A

If try to move particle through the fluid is act as if it has a size due to the ions surrounding it

Measuring the zeta potential at the slipping plane lets us measure the size of the particle because at this point you can see the end point of the ions that contribute to its size

40:04 idk

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why does the double layer plot go to zero at infinity

A

We’re so far away from the particle that there are a bunch of ions between where we measure and the particle

These in between ions position themselves around the particle based on what the charge on the particle looks like to them

This ultimately makes the potential neutralize and become zero

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Do the surface and the zeta potential have the same sign

A

No the sign of the zeta potential doesn’t tell you what the surface of the particle is

The zeta potential depends on the solution that the particle is in

If more polar, more ions, can change what the zeta potential looks like

There are ions close to the surface of the molecule that aren’t exactly associating with it but their charge affects what the zeta potential is

Just like how PAH and PSS affect what the charge looks like on the molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the compounds that let you change the charge on the surface

A

PAH (postive charge)

PSS (negative charge)

If postive surface, add PSS, Makes surface negative

Can keep going with PAH to make it back to postive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the purpose of reversing charges using PSS or PAH

A

If the surface was one third negatively charged and the rest neutral

You can still add PAH to make it look uniformly negative since it big and will cover regions that are neutral

Can turn something that is weakly charged into something that has a highly negative or postive charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

At was potential is a particle /colloid stable

What does this mean

A

+/- 30mV

This mean if we measure the zeta and that is it’s value, there is enough of an energetic hump that the particles won’t easily flocculate and crash out

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the effect of the pH on the zeta potential

A

low ph, zeta potential positive, stable

High pH, zeta potential negative, stable

At the isoelectric point, the zeta potential is zero and no net charge pushing the particles apart, unstable because now not +/- 30 mV

This means there will be flocculation since no charge repelling the ions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Can the isoelectric point of a particle be change and how

What could change shape of the zeta potential vs pH graph to start negative at low ph and get postive at high pH

A

Can be changed because of diff functional groups of the particle, can cause flocculation at lower ph or higher ph (so lower or higher isoelectric point)

Changing the sign at low ph would mean that having more h ions is causing the particle to be more negative , so not possible and weird

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is the Debye length

What does it mean

At what point does it end

A

Lambda D = 1/kappa

Describes the length of the diffuse layer and the amount shielding of the particle

How far you have to go before the potential of the particle is shielded by the many counter ions in the diffuse layer and the potential becomes zero

Since the diffuse layer has exponential decay (never goes to zero) we say that the diffuse layer ends at a potential 1/e of its original value

So 1/3 of the diffuse layers original potential value

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

If the diffuse layer drops has its exponential decay very quickly what does this mean

Very slow decay

A

Quick: say the diffuse layer is very thin, more ions, faster decrease because easier to drop the potential

Slow: diffuse layer very thick, less ions, , slower decrease because harder to drop the potential

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the effect of higher ionic strength of the diffuse layer

A

More ions in the diffuse layer, shielding is going to be very thin because that’s all you need to drop the potential to 1/e

If less ions (for example just water and not na+), the diffuse layer is bigger since you need more of them to shield and drop the potential to 1/e

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is meant by shielding and why does it happen

A

If the particle is postive, the stern is negative, but ions in the diffuse layer look at that and try to make it more postive

Then the negative ions out look at, see a general postive charge, and configure themselves to make it more negative

This accumulation of opp charged ions makes it so that shielding of the particle happens and the potential looks to be neutral/zero very far away

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

When do we say something is fully shielded

A

When the potential reaches 1/e or 1/3 of the original potential value (at the surface)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is the effect of higher valency ions on the Debye length

A

Ex. Fe3+ and fe2+

The higher valency ions is basically more charge meaning smaller Debye length since need less ion for shielding

Sheilds it faster, gets to 1/e faster

26
Q

Describe the Debye length in polar and non polar media

A

Polar more ions , smaller Debye length, need less to shield

Non polar less ions , larger Debye cause need more to shield

27
Q

Explain the implications of dilutions a sample and Whag you have to make sure

A

During dilution of something you want to preserve the pre-existing state of the surface of the particle

Need the same pH, ionic concentration, surfactant/polymer concentration

So you would centrifuge out the particles you want to dilute

Then use the resulting solvent (with all the same properties) to dilute the particles

28
Q

What is the equation for electric force

A

FE= q (V/d)

V is the potential difference across the electrodes

d is the distance between electrodes (how far apart they are)

q is the charge on the particle between the electrodes

29
Q

If F= ma what’s stopping something on a gel from just going really fast through the gel and flying off

A

There is resistance from the gel

So a force of drag

On sheet equation

30
Q

What is electrophoretic mobility

A

How fast a particle moves under a particular electric field

Equation on sheet

31
Q

In the electrophoretic mobility equation what does it mean if kappa a is&raquo_space;1 and «1

What are the names of the approximations

A

Smoluchowski:
ka&raquo_space; 1: the Henry function (f(kappa a) ) is 1.5

Huckel:
ka &laquo_space;1: Henry function is 1.0

32
Q

Which approximations are used for a non polar and polar media

A

Debye length = 1/kappa

So kappa= 1/ Debye length

Polar: need small Debye length, so kappa&raquo_space;1, smoluchowski

Non polar: need large Debye length, so kappa «1, huckel

33
Q

Explain the situations for the particle in each approximation

Explain what’s bad

A

For smoluchowski, polar media, you need to have a large particle and a small Debye length

Can get away with having a larger shielding layer as long as you have a larger particle

For huckle, non polar media, you need to have a small particle and large Debye length

If you have a small particle, to make this assumption hold you would need non polar solvent like benzene or hexene to get a larger Debye length

If you have a very tiny particle in a low ion concentration, this is bad because doesn’t fit the smoluchowski approximation

34
Q

Which approximation do we usually use and why

A

The schomulowski because using higher salt, not using non polar solvent

35
Q

What is the other way to write electrophoretic mobility

A

Velocity of the particle / electric field

v/E

36
Q

What affect would a greater charge of the particle have on the electrophoretic mobility

A

Using equation with zeta in it: The zeta value would increase because it’s related to the apparent charge on the particle

Using v/E: the higher charge on the particle causes more force of it moving in gel electrophoresis, so higher velocity

Each of these things causes higher electrophoretic mobility and the particle to move faster

37
Q

How would a higher gel concentration affect the electrophoretic mobility

A

Thicker gel, higher viscosity (denominator), decreases electrophoretic mobility , slower

Smaller velocity, smaller electrophoretic movility

38
Q

Electrophoretic mobility equating and browning motion equations

A

On sheet

39
Q

Explain the brownian motion equation

A

have a particle in solution colliding with particles from the solvent to knock it around

higher temp causes higher kinetic energy of solvent molecules, faster movement, high Vrms

If the mass of the particle being knocked around increases, have low Vrms, slower particle

40
Q

It’s the Brownian motion a distribution

A

Yes

41
Q

How does Brownian motion relate to chromatography and gel electrophoresis

A

Can affect the distribution of our protien molecules in the gel (due to interacting with the solvent particles)

This leads diffusion (causing band broadening)

42
Q

Explain the diffusion plot

A

There’s a greater probability of finding something further from where it started over time

the peaks broaden due to diffusions due to being at room temp

43
Q

How does the hydrodynamic radius relate to zeta potential

A

R

it’s related to the slipping plane

When the particle moves through solution it move not as if it has its own radius but as if it has a larger one that includes all the solvent molecules

44
Q

What is the stokes Einstein equation telling us

A

Another way to tell diffusion BUT FOR PARTICLES THAT ARE FREELY DIFFUSING

Fiset can Tell R (hydrodynamic radius)

Can rearrange to get diffusion coefficient (D) which is the rate of diffusion

Then if temp increases, D increases, so faster diffusion

If viscosity increases, D decreases, slower diffusion

If size increases, smaller D, slower diffusion (movement)

45
Q

What does stokes Einstein assume

A

Assume a spherical particle

But Not always spherical, sometimes unfold to look like they have a bigger radius sometimes and larger other times

46
Q

Why do we cut the band out of the gel right after finish with is

A

If leave it a lot room temp, higher diffusion, it’ll keep broadening

47
Q

Explain the stokes equation

A

The faster something moves through water the larger the drag is (Fd)

48
Q

What assumption do we make for each of the equations we’ve talked about

A

That the particle is free to move wherever it wants (not true)

Moves at the same speed everywhere (not true)

49
Q

Diff in laminate flow and turbulent flow

What do we assume for gels

A

Laminar flow all water is following the same uniform path

Turbulent flow the water is going in all different directions chaotic(like if filling water bottle)

Assume Laminar flow

50
Q

Explain the problem with the gels having laminar flow

A

The velocity of the flow is different at the edges of the lane than at the centre , not same speed all the way across it

This could lead to band broadening

Problem with this is that the particles pile up at the edges, usually backflow happens near the walls to stop this

51
Q

What is the advantage to gels being porous

A

It’s allows for slow flow

Suppress thermal convection: stops the solution from having motion due to heat transfer and things happening inside which cause it to move

52
Q

What is isoelectric focusing

A

Trying to separate the protiens by their isoelectric point

Cathode on one end anode on the other to make a pH gradient (high pH at cathode (-), low pH at anode (+))

Every time there is a peak , that is where the protien is at its isoelectric point

This tells us about the composition of the protien surface

Can do as a 2D gel to split according to mass and isoelectric point

53
Q

Using the FE (electrostatic force equation) and F drag equation explain what the electrostatic force is proportional to

What is the problem here

A

FE= qE

So the electrostatic force is proportional to the charge in the particle (q), more charge more force, faster

The drag is proportional to the size R, bigger size , more drag, slow

In a protien during gel electrophoresis, we have constant charge per unit mass, meaning the bigger the mass, the more charge

This is bad because if bigger mass it’s supposed to slow down (more drag) but also has more charge which is making it faster (more force)

Can’t be both fast and slow at the same time, get nothing

54
Q

What are balanced forces

A

fv=qE

Friction times velocity = charge times electric field

55
Q

Explain the free mobility of particles

A

The free mobility is independent of mass and charge

If log gel concentration increase, electrophoretic mobility decrease

If log zero percent gel, we only have the free mobility which is charge and mass independent

56
Q

Explain the free mobility of particles Ferguson plot

A

Log Ue (electrophoretic mobility) vs % gel

Increase gel, decreasing mobility

At 0% gel see the free mobility value

Small particle high charge
Small particle lowcharg
Big particle high charge
Big particle low charge

The small and big particle high charge have similar free mobilities, but the high mass electrophoretic mobility drops off a lot more than the small one (charge independent, size dependent)

This is because the gel introduced a new source of frictional force, making the movement size dependent

The small particle high charge and small particle low charge, should have no net force on it at gel concentration of zero

Big charge, big motion

IDK33.42

57
Q

Explain the free mobility of particles Ferguson plot when the charges are proportional to length

A

In the free mobility situation they all reach the same electrophoretic mobility value

Not getting good results from the electrophoresis

Based on the size effect from the gel, they split and have diff slopes (same starting point)

EMAIL AND ASK

60-65

58
Q

When doors diffusion happen

A

Always

59
Q

Explain ion exchange columns

A

The resin is a charged polycation or a charge poly anion

There’s is an interaction between the molecules and the resin

If negative resin, postive charge protiens move slowest and negative move fastest

Changing pH can make protien bind and release it the column by changing its charge

Higher Salt concentration also elutes , ions will compete with the particles on the column

60
Q

Explain sec columns

A

The smaller particles move slower because go into the resin cavities

Bigger particles move faster

61
Q

Explain affinity columns

A

Ligand protien interaction

Use salt or competing ligand to wash out

Bchem 471 (24 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions