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23 Cards in this Set
- Front
- Back
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What is pH? |
Measure of proton concentration. |
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What is Keq? |
Equilibrium Constant; governed by concentration of each species in a reaction |
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What is Kw, and how does it differ from Keq? |
Ionic product of water; product of Keq and [H2O], = 10^-14. H2O is treated as a constant since dissociation changes concentration very little. |
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Name the non-covalent interactions. |
Van der Waals forces; Hydrophobic Forces; Hydrogen Bonds; Ionic Bonds. |
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Define ionisable group. |
A species that can reversibly bind protons, changing it charge state. |
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What is the mass action law for the reverse binding of protons? |
pKa = -log[Ka] |
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What is Ka? What values define a strong or weak acid? |
Acid Dissociation Constant. ~1 = Weak acid, >>1 = Strong acid |
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What is the Henderson-Hasslebalch Equation? |
pKa = pH + log ([A-]/[HA]); Valid for WEAK acids only. |
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What affect does the pH have on an ionisable group? |
Determines whether it's charge increases or decreases by 1; charged or neutral. |
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What is pKa? |
pH at which an ionisable group is half dissociated |
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How do you know pH = pKa at half dissociation of an ionisable group? |
For pKa = pH + log ([A-]/[HA]); At half dissociation A- and HA will be equal. Therefore, log(x/x) = 1, therefore pKa = pH + log(1). log(1) = 0 |
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What happens if pKa > pH? |
Undissociated form favoured; Group retains H+ so charge remains same. |
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What happens if pH > pKa? |
Dissociated form favoured; group loses H+, charge decreases by 1. |
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What do you need to calculate degree of dissociation a? |
INITIAL concentration of acid ([HA] + [A-]) and Ka. Solve quadratic: Ka = (ca^2)/(1-a) |
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How do you determine overall charge of a protein? |
Determined by balance of ALL +ve / -ve charges of ionisable groups in the protein. These charges will change as buffer pH changes, depending on Ka. |
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What is the Isoelectric Point (pI)? |
pH at which the overall charge of a protein is 0. |
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How can structures affect isoelectric point? |
Certain ionisable groups may be buried within the structure, unable to dissociate, which will affect isoelectric point. |
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How do you measure isoelectric point? |
Proteins placed on isoelectric focusing gel with a pH gradient. +ve/-ve pole on either side of gel. Proteins will attract to oppositely charged pole. As pH of gel approaches isoelectric point, movement will stop as protein no longer has charge for attraction. |
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At the pKa value, a species is best able to... |
... buffer against small changes in pH. |
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What is the size of a hydrogen bond? |
0.28nm, from nucleus to nucleus. |
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Why is is important to use the hydrogen bond size as a marker for other bonds? |
If nearby bonds are much longer than the 0.28nm length, then it is unlikely a hydrogen bond will form nearby. |
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How does water act as a solvent? |
Water has a overall positive (H) and negative (O) dipole. Negative oxygen dipole will face and surround positive ions, and Positive hydrogen dipole will face and surround negative ions. |
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Why do H+/OH- not exist in aqueous solvents? |
Will bond to undissociated water molecules. |
