Electrophoresis And Electric Charge Flashcards
What are the positive charged amino acids?
Lysine (K)
Arginine (R)
Histidine (H)
What are the negatively charged amino acids?
Aspartic acid (D)
Glutamic acid (E)
What does pKa value represent?
The pH value at which half the molecules are protonated and half are deprotonated
If the pH is lower than the pKa, what does this mean?
Proton acceptor
If the pH is higher than the pKa, what does this mean?
Proton donor
Are aspartic acid and glutamic acid proton donors or acceptors and why?
D and E are lower than physiological pH values
Always proton donors and negatively charged
Always deprotonaated -1
Are lysine and arginine proton donors or acceptors and why?
K and R are higher than physiological pH value
Always proton acceptors and positively charged
Always protonated +1
What is the isoelectric point?
pH value at which the net charge is 0
What do the pI and pKa each refer to?
pI - proteins
pKa - specific chemical bond
What is the overall charge is the pH is lower than the isoelectric point?
Positive
What is the overall charge is the pH is higher than the isoelectric point?
Negative
Where are proteins most stable and why?
Near their pI
There is a perfect mix of positively and negatively charged amino acids which stabilise it
Where are proteins least soluble?
At their pI
What does the velocity of a charged protein moving through an electric gel depend on?
Charge density
Size
Shape
What does SDS do in a PAGE?
SDS binds to amino acid residues in proteins
Proteins acquire a high negative charge which masks their net charge, causing unfolding
Proteins will have an equal charge density
