Acid and Bases - Chemistry of Life
Why do biologists care about acid and bases
Amino acid and nucleic acids are the building blocks of proteins and DNA
Catalytic function is pH dependent
protein function may need certain pH to operate
What is an acid
This is a H+ donor
A strong acicf will fully dissociatre in water and a weak acid will partially dissociate in water
What is a base
These are H+ acceptors
When they are dissolved in water they form an OH-
What are conjugate pairs
Aciod and bases that operate at the same time so the acid will donate a hydrogen for the base to then accept and in the reverse the conjuate acid(base) will dontae a H+ to the conjugate base (acid)
What is the acid dissociation constant
Ka = [ H3O+][A-]/[HA]
If ka is large then the acid is strong due to mostly dissociated and if a small Ka then the acid is weak dude to limited dissociation
Kb= Base dissociation and is same equation
What are pKa and pKb used for
This is a logarithmic of the Ka in order to allow them to be easily compared
pKa= -log(Ka)
What is the ion product of water
KW= (H+)(OH-)
At 25 degress = 1x10^-14
Ka x Kb = KW
What is pH
The concentration of H+ ions that are generated from the acid
Due to potential large concentrations use a logartihmic
pH = -log(H+)
H+ = 10^pH
How to use Ka for weak acid to calculate pH
Use Ka to calculate the equilibrium concentrations of the H+
Do this by table to initial conc, chain in conc and equilibrium conc
The sub into pH equation
What is the Henderson Hasselbalch equation
pH = pKA + log ( Conjugate base concentration/ Weal aciod conc )
What are buffers
These are solutions that will resist pH change in cells and labs to maintain the optimal pH
How does water and Carboneric acid causde pH change
CO2 can make sea more acidic due to Co2 in the sea than form H2CO3 that can then split to HCo3- and H+ so more acidic sea, this will effect coral that need carbonatw to form and due to excess proton it will remove carbonate ions
In Blood: iF cO2 level increase then more H2CO3 formed sop then more H+ released so more acidic
This will effect O2 affinity for Hb so less binding
How is low affinity Hb stabilised
Salt bridge between Nh3 + of lycene and Coo- of Histine
Protontaed imidazole ring of Histine
How do proteins detect pH
Protonation will depend on pH and pKa of specific side chains
The net charge of a protein changes depending on number and titratability of side chains
Iso electric poinnt is thr pH when net chatge is 0
For pH above Pi then protein surgface is -
For pH below Pi then protein surface is +