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CSMLS > CHEM Electrophoresis > Flashcards

CHEM Electrophoresis Flashcards

1
Q

Define electrophoresis

A

Movement of charged particles by an external electrical field
- rate of migration is dependent on properties of support media, the electric field strength, and temperature

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2
Q

Explain the principle of gel electrophoresis

A
  • agarose gels have pores through which the analyte will migrate; determined by agarose concentration; separation by size is called molecular sieving
  • DNA migration is generally by size since all DNA molecules have the same mass:charge ratio
  • in protein electrophoresis, proteins separate into bands based on mass:charge ratios
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3
Q

List 4 characteristics of capillary electrophoresis

A
  • silica capillary tubes with exterior coating of polyimide
  • high voltage (~25 to 30 kV)
  • narrow tube efficiently dissipates heat
  • uses electrokinetic or hydrodynamic injection
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4
Q

Describe capillary Serum Protein Electrophoresis (SPE)

A
  • no supporting medium (capillary zone electrophoresis)
  • negatively charged silanol groups of silica capillary induces electroendosmosis force, moving sample in the opposite direction to the electrical field
  • samples injected at anode (+); despite negative charge, proteins migrate towards cathode (-)
  • proteins separate based on electrophoretic mobility and endosmosis
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5
Q

Why is agarose gel more advantageous than starch or cellulose acetate ?

A
  • no charge; minimal Electroendosmosis
  • low affinity for proteins
  • relatively clear when dried
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6
Q

What is Electroendosmosis ?

A
  • charged components of agarose gel (typically negative) attract counterions (cations) from buffer
  • when the electric field is applied, cations will move towards the cathode, taking water with it (as well as all negative ions trapped within)
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7
Q

Both protein and DNA are carried out at an __ pH

A

Both protein and DNA are carried out at an alkaline pH

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8
Q

Under fixed current conditions, the rate of migration in a system __ as the ionic strength of the buffer increases

A

Under fixed current conditions, the rate of migration in a system DECREASES as the ionic strength of the buffer increases

NOTE: a buffer with a higher ionic strength will conduct the current more than the sample

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9
Q

How does pH affect electrophoresis ?

A

Determines charge of analyte, and therefore its mobility

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10
Q

How does ionic strength affect electrophoresis ?

A
  • lower ionic strength allows for higher voltage without overheating
  • increased ionic strength = increased heat
  • increased ionic strength reduces rate of migration
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11
Q

How might current negatively affect electrophoresis ?

A

too much current = excessive heat

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12
Q

How does voltage affect electrophoresis ?

A

migration rate is proportional to voltage

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13
Q

What is the difference between voltage and current ?

A

Voltage is the potential difference between two points in an electric field, which causes current/ electrons to flow in the circuit

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14
Q

How does temperature affect electrophoresis ?

A
  • unstable temperatures cause curved bands
  • excess heat denatures proteins
  • lower temperatures decrease migration rate
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15
Q

How does time affect electrophoresis ?

A

Resolution of bands increases with time

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16
Q

How does the support media affect electrophoresis ?

A

Electroendosmosis and pore size affect migration rate

17
Q

The rate of migration of an analyte in agarose gel electrophoresis is based on its __, __, and __.

A

The rate of migration of an analyte in agarose gel electrophoresis is based on its CHARGE, MOLECULAR WEIGHT, and SHAPE.

NOTE: if pore size of agarose is not sufficient for molecular sieving, proteins and nucleic acids will migrate based on mass:charge ratio

18
Q

What is an ampholyte ? Give an example.

A

A species that has both positive and negative charges ie. proteins

19
Q

DNA has a __ charge due to its __.

A

DNA has a NEGATIVE charge due to its PHOSPHATE backbone.

20
Q

DNA migrates through an electric field from the __ (-/+) to the __ (-/+) at pH 8.

A

DNA migrates through an electric field from the CATHODE (-) to the ANODE (+) at pH 8.

21
Q

At the isoelectric point (pI), protein has __ net charge.
At pH > pI, protein has __ net charge.
At pH < pI, protein has __ net charge.

What pH is SPE done on ?

A

At pI = no net charge
pH > pI; negative charge
pH < pI; positive charge

SPE is done at pH 8; proteins are negatively charged

22
Q

Although all proteins are __ charged in SPE, their __ varies.

A

Although all proteins are NEGATIVELY charged in SPE, their MASS:CHARGE ratio varies.

23
Q

List 3 dyes used for SPE

A
  1. Coomassie Brilliant Blue
  2. Amino Black
  3. Ponceau
24
Q

Causes of migration across the well

A
  • dirty electrodes
  • uneven wetting of gel
25
Q

Causes of distorted protein zones

A
  • bent applicator
  • bubble introduced during sample application
  • too much sample added
26
Q

Causes of unusual bands

A

Interferences:
- hemolyzed sample
- plasma sample
- medication

27
Q

Describe capillary DNA electrophoresis

A
  • DNA must be FLUORESCENTLY LABELLED before separation
  • sample is injected by electrokinetic injection at the cathode (-) and MIGRATE TO ANODE (+)
  • fragments migrate through polymer of polyacrylamide at alkaline pH
  • coated capillary (supporting medium) ELIMINATES ELECTROENDOSMOSIS and enhances separation efficiency
  • DNA migrates based on nucleic-acid length/ size
28
Q

Since all nucleic acids have the same __, the flowable polymer acts as a __ to separate the nucleic acids based on __.

A

Since all nucleic acids have the same MASS:CHARGE ratio, the flowable polymer acts as a molecular sieve to separate the nucleic acids based on MOLECULAR WEIGHT/LENGTH/SIZE.

29
Q

Which of the following stains is suitable for CSF protein electrophoresis?

a.
Coomaisse brillant blue

b.
Silver nitrate

c.
Ethidium bromide

d.
Oil red O

A

b.
Silver nitrate

29
Q

Which technique separates proteins by ELECTROPHORESIS and identifies the presence of a target protein with a LABELLED ANTIBODY ?

A

Western blotting

30
Q

Which of the following support media provides the best resolution for nucleic acids?

a.
agar

b.
polyacrylamide

c.
agarose

d.
cellulose

A

b.
polyacrylamide

31
Q

Which of the following describes conditioning of an electrophoresis capillary?

a.
flushing the capillary with dilute NaOH

b.
flushing the capillary with silyalation reagent

c.
flushing the capillary with separation buffer

d.
flushing the capillary with dilute HCl

A

c.
flushing the capillary with SEPARATION BUFFER

32
Q

T or F: In electrophoresis, as the temperature decreases so does the resistance.

A

FALSE; In electrophoresis, temperature and resistance are INVERSELY PROPRTIONAL.
- as temp increases, resistance decreases = hot things move faster

33
Q

T or F: In gel electrophoresis, resolution of molecules depends on the pore size of the media.

A

TRUE; In gel electrophoresis, resolution of molecules depends on the pore size of the media.

  • When pore size of gel matrix ≈ diameter of macromolecule, molecular sieving is possible and can enhance resolution
34
Q

Which of the following is an advantage of capillary columns?

a.
decreased back pressure

b.
increased sample capacity

c.
increased number of theoretical plates per column length

d.
decreased need for derivatization

A

c.
increased number of theoretical plates per column length

  • Column efficiency = increased number of theoretical plates (N) per column length

CSMLS (46 decks)

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