Amino Acids with ionizable side chains

[growingpains]

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Why isn't serine's side chain ionizable if it's more basic than cysteine's side chain (which is ionizable)?

 

[MedPR]

Why isn't serine's side chain ionizable if it's more basic than cysteine's side chain (which is ionizable)?

Where did you read that serine isn't ionizable?

 

[growingpains]

"Another subgroup of the amino acids are those with ionizable side chains. These include: aspartate, glutamate, histidine, cysteine, lysine, tyrosine and arginine." (http://webhost.bridgew.edu/fgorga/proteins/aminoacids.htm)

"There are only 7 amino acids with ionizable side chains" -BR

 

[MedPR]

"Another subgroup of the amino acids are those with ionizable side chains. These include: aspartate, glutamate, histidine, cysteine, lysine, tyrosine and arginine." (http://webhost.bridgew.edu/fgorga/proteins/aminoacids.htm)

"There are only 7 amino acids with ionizable side chains" -BR

Well I don't know, but apparently threonine isn't ionizable either and threonine has a hydroxyl group on the sidechain just like serine does.

 

[theseeker4]

Why isn't serine's side chain ionizable if it's more basic than cysteine's side chain (which is ionizable)?

Serine's chain is more BASIC than cysteine's, meaning it is less acidic, and therefore less likely to lose its proton.

 

[MedPR]

Serine's chain is more BASIC than cysteine's, meaning it is less acidic, and therefore less likely to lose its proton.

But aren't alcohols pretty ionizable in water?

 

[pfaction]

I've read that no, they're not. Not even NaOH will tear apart ROH's, according to TPR Organic Chemistry.

 

[theseeker4]

But aren't alcohols pretty ionizable in water?

They are quite tightly bound, actually. Very difficult to de-protonate an alcohol.

 

[chiddler]

They are quite tightly bound, actually. Very difficult to de-protonate an alcohol.

Do you know the threshold pKa that hydroxide will deprotonate?

 

[pfaction]

TPR:

An alkoxide ion is a poor leaving group. Conjbase of alcohol, a fairly weak acid pKa 15-19