Polymers are not very soluble in water, but their solubility...

Polymers are not very soluble in water, but their solubility increases if they have charged groups. (a) Casein, a milk protein, contains many $-\mathrm{COO}^{-}$ groups on its side chains. How does the solubility of casein vary with pH? (b) Histones are proteins essential to the function of DNA. They are weakly basic due to the presence of side chains with $-\mathrm{NH}_{2}$ and $=\mathrm{NH}$ groups. How does the solubility of a histone vary with pH?

Key Concepts

pH and Protein Solubility

This concept explains how a protein's solubility is influenced by the pH of the surrounding solution. Changes in pH alter the ionization state of the protein's functional groups, which can either increase or decrease the net charge and thus affect how well the protein interacts with water molecules.

Ionization of Functional Groups

Proteins contain various functional groups, such as carboxyl (–COOH) and amino (–NH2) groups, that can gain or lose protons depending on the pH. The degree of ionization influences the molecular charge and, consequently, the solubility and stability of the protein in aqueous environments.

Isoelectric Point

The isoelectric point is the pH at which a protein has no net charge because the positive and negative charges balance each other. At this pH, proteins typically exhibit minimal solubility as reduced electrostatic repulsion leads to aggregation. Adjusting the pH away from this point increases the net charge, enhancing solubility.

Transcript

00:01 So we are looking at two different proteins.

00:03 The first one, the castlene, the second one will be hit stone.

00:06 So first of all, for a priority for cassidy, contain a lot of different carbociculate groups.

00:11 So we'll be looking at c .o.

00:14 Minus.

00:15 And how ph will affect the soil base here, cassin? so first of all, when we have a protein, contain a lot of polar group, so the more the polar group, or a charge group.

00:29 So also we have charged.

00:32 The solubility will increase.

00:35 The reason is that it is able to inter have with water strongly.

00:42 So therefore, if we have more hapocle, so you can increase the solubility of the molecule of the protein of castin.

00:53 So we have our caposate acid group.

00:55 Essentially, under different ph value, so it will exceed it will two different forms.

01:02 The first one will be carposylate.

01:04 The set one will be carposulate caposolate on the left.

01:09 The second one will be carposulate acid on the right.

01:12 Okay, so we can see that the...

01:15 Actually there's an equilibrium.

01:16 So on the left, it will be level charge, so circle the lateral charge.

01:20 On the way, it will be neutral.

01:21 We've got the coh, it will be neutral, but still polar.

01:25 But in terms of solubility, if the molecule is containing more charge group, then it's much more soluble than the molecule only contain a neutral, group.

01:33 Okay, so in other words, if we have more carposlate group on the left, the solubility will increase.

01:41 But if you have more carboslidate group on the right, the solability will decrease.

01:46 Okay, so how ph come into play? you know, when at different ph, if we affect whether the equilibrium lie on the left or on the right.

01:58 Okay, so when ph decrease.

02:01 Ph decrease means we have a lot of hydrogenium concentration.

02:07 So where we have a lot of hydrogening concentration, our carboscelates group are going to shift to the right to form more...

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