Module 01 - Section 03

Question 1

What are Zwitterions?

Answer 1

Neutral molecule with both positive and negative charges

Question 2

What determines the charge (ionization state) on the amino, carboxyl and some R groups?

Answer 2

The pH of their surroundings

Question 3

What form of amino acids can act as both acid and base?

Answer 3

Zwitterions

Question 4

What is the relationship pKa value and the strength of base/acid (2)

Answer 4

(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

Question 5

Which amino acids have low pKa values?

Answer 5

Aspartate and Glutamate

Question 6

Which amino acids have high pKa values?

Answer 6

Arginine and Lysine

Question 7

What is pH?

Answer 7

Power of hydrogen, it is a measure of hydrogen ion concentration, from 0 to 14

Question 8

What is the normal pH of human blood?

Answer 8

7.4

Question 9

Why is pH important?

Answer 9

It influences the structure and function of many enzymes in living systems

Question 10

Describe the regulation of Cellular pH

Answer 10

The body use buffer systems like our lungs and our blood.

Question 11

How does the lung function as a buffer system

Answer 11

It moves carbon dioxide out of the body

Question 12

Explain the mechanism of the blood buffer system

Answer 12

CO2 combines with water to make carbonic acid which partially dissociates into hydronium and bicarbonate, reducing H+ concentration

Question 13

Explain the mechanism of ionization of amino acids

Answer 13

(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

Question 14

What is the pH equation?

Answer 14

pH= -log(H+)

Question 15

What is the pOH equation?

Answer 15

pOH= -log(OH-)

Question 16

How do you find H+ concentration from pH?

Answer 16

10^(H+)

Question 17

How do conjugate acid-base pairs differ from each other?

Answer 17

Presence or absence of a single hydrogen ion (proton)

Question 18

What does the pKa value describe?

Answer 18

the ratio of charged (A-) to neutral (HA) acid molecules at equilibrium in aqueous solution

Question 19

What is the relationship between pKa and dissociation

Answer 19

the larger the value of pKa the smaller the extent of dissociation.
weak acid: 2

Question 20

what is the Henderson-Hasselbalch equation?

Answer 20

pH=pKa+log(A-/HA)

Question 21

What are the 2 conditions implied by the pKa with respect to the pH of the environment?

Answer 21

pH>pKa -> ratio of (A-) to (HA) is greater than 1
pHratio of (A-) to (HA) is less than 1

Question 22

What does it mean when the pH equals pKa?

Answer 22

The group exist as a 50:50 mixture of the its acidic form and the conjugate base

Question 23

What is the pKa of the carboxyl groups on amino acids?

Answer 23

2

Question 24

What is the pKa of the amino groups on amino acids?

Answer 24

9.5

Question 25

What is Type I ionization?

Answer 25

Neutral in their acidic form (pHpKa

Question 26

What is Type II ionization?

Answer 26

Positively charged in Acidic form (pHpKa

Question 27

What is the isoelectric point?

Answer 27

pH at which an amino acid or polypeptide is ionized and yet has no net electric charge

Question 28

How is the isoelectric (pI) point calculating?

Answer 28

Averaging the pKa values for the ionization states that straddle the electrically neutral species