Tutorial - Week 3 - pH, acid-base, charge of amino acids & peptides Flashcards
Key concept: Describe pH, acid, and base
- The pH of a soluWon indicates its acidity or basicity
- Acid is a molecule (or group) that donates H +
- Base is a molecule (or group) that accepts H +
Key concept: Describe pKa and isoelectric point (pl)
- pKa is the pH at which the H + dissociates
- Acids have a low pKa
- Bases have a high pKa
- pI, isolectric point: pH at which the net charge is zero
Key concept: Describe acid-base properties of amino acids
- Amino acids have at least 1 acid group (COOH)
& 1 base group (NH 2 ) - The side chain of polar charged amino acids
has one ionisable group
Key concept: Describe how to calculate the charge of individual amino acids
- Charge of amino acid depends on the pH and pKa of
ionisable groups - pKa differ for each amino acids
- pKa (COOH) is < 7.4, negative at pH 7.4
- pKa (NH 3+ ) is >7.4, positive at pH 7.4
- pKa of the side chain of polar charged amino acids
Key concept: Describe how to calculate the charge of a peptide/protein
- Charge of peptide/protein depends on the pH
and pKa of the residue side chains, N-terminus
and C-terminus - N-terminus group (NH 3+ ) is positive at pH 7.4
- C-terminus (COO - ) is negative at pH 7.4
Label each category
T/F: Biomolecules can be very sensitive to pH
True
As the pH of a solution changes, what may also vary?
The charge
What does the charge of molecules, such as in proteins, have a profound effect on?
How they work or if they are going to function
The pH of a solution indicates the…
Acidity or the basicity
What does pH correlate with in a solution?
the H+ (hydrogen ions)
ph = ? (equation)
-log [H+]
[H+] = ? (equation)
10^-pH M
pOH = ? (equation)
-log [-OH]
pOH = ? (equation)
-log [OH-]
pH + pOH = ?
14 - The sum of pH and pOH is always 14. This is because the product of proton concentration and hydroxide concentration must always equal the equilibrium constant for the ionization of water
What does a low pH indicate in terms of how acidic or basic a solution is and which ion is most prominent?
High H+ ions and acidic (pH < 7)
What does a high pH indicate in terms of how acidic or basic a solution is and which ion is most prominent?
Basic (pH > 7) and high OH- ions
What is the neutral pH? What are the values for OH- and H+?
pH = 7 and OH- = H+
What is the value for physiological pH?
7.4 (close to neutral)
Inside cells how low do some compartments get in pH?
4.5-6
Do strong acids dissociate in water? Why?
Yes
1 mol of HCl in water will dissociate and add 1mol of H+ and 1 mol of Cl- to the water
Do strong bases dissociate in water? Why? What gets added to the water?
What will happen to 1 mol of NaCl?
Yes
Dissociates due to unstableness of the molecules due to the strong charges pulling the molecules apart.
1 mol of NaCl will dissociate into 1 mol of OH- and 1 mol of Na+ in the solution
Do weak acids and bases dissociate in water?
Why are they important?
No
Important as they help to keep the concentration of H+ stable and therefore help to keep the pH of the solution relatively constant