Module 01 - Section 03 Flashcards
pH and Ionization (28 cards)
What are Zwitterions?
Neutral molecule with both positive and negative charges
What determines the charge (ionization state) on the amino, carboxyl and some R groups?
The pH of their surroundings
What form of amino acids can act as both acid and base?
Zwitterions
What is the relationship pKa value and the strength of base/acid (2)
(1) The lower the pKa, the stronger the acid - higher tendency to give up its proton
(2) The higher the pKa, the stronger the base - higher tendency to accept protons
Which amino acids have low pKa values?
Aspartate and Glutamate
Which amino acids have high pKa values?
Arginine and Lysine
What is pH?
Power of hydrogen, it is a measure of hydrogen ion concentration, from 0 to 14
What is the normal pH of human blood?
7.4
Why is pH important?
It influences the structure and function of many enzymes in living systems
Describe the regulation of Cellular pH
The body use buffer systems like our lungs and our blood.
How does the lung function as a buffer system
It moves carbon dioxide out of the body
Explain the mechanism of the blood buffer system
CO2 combines with water to make carbonic acid which partially dissociates into hydronium and bicarbonate, reducing H+ concentration
Explain the mechanism of ionization of amino acids
(1) At low pH carboxyl and amino groups are protonated
(2) when pH=pKa carboxyl, 50% of the molecules have a deprotonated carboxyl group
(3) when pH>pKa carboxyl, amino acid could be in zwitterionic form (if non ionizable R-group), carboxyl group fully deprotonated
(4) when pH=pKa amino group, 50% of molecules have a deprotonated amino group
(5) at high pH, fully deprotonated
What is the pH equation?
pH= -log(H+)
What is the pOH equation?
pOH= -log(OH-)
How do you find H+ concentration from pH?
10^(H+)
How do conjugate acid-base pairs differ from each other?
Presence or absence of a single hydrogen ion (proton)
What does the pKa value describe?
the ratio of charged (A-) to neutral (HA) acid molecules at equilibrium in aqueous solution
What is the relationship between pKa and dissociation
the larger the value of pKa the smaller the extent of dissociation.
weak acid: 2
what is the Henderson-Hasselbalch equation?
pH=pKa+log(A-/HA)
What are the 2 conditions implied by the pKa with respect to the pH of the environment?
pH>pKa -> ratio of (A-) to (HA) is greater than 1 pHratio of (A-) to (HA) is less than 1
What does it mean when the pH equals pKa?
The group exist as a 50:50 mixture of the its acidic form and the conjugate base
What is the pKa of the carboxyl groups on amino acids?
2
What is the pKa of the amino groups on amino acids?
9.5
