Module 1 Section 3

Question 1

What is zwitterion

Answer 1

• neutral molecule with localized + and - charges
• amino acids predominantly zwitterions at neutral pH
• arise via intermolecular acid-base reaction, amine group deprotonates carboxylic acid

Question 2

What is mixture like when pH=pKa

Answer 2

-when pH=pKa, group exists as 50:50 mixture of acidic form and conjugate base

Question 3

pH equations

Answer 3

pH=-log[H+]

pH=pKa+log([A-]/[HA])

Question 4

Ka/pKa equations

Answer 4

Ka=([A-][H3O+]/[HA])

pKa=-log[Ka]

Question 5

Type I ionization

Answer 5

• neutral in acidic form (pH less than pKa)

- ie. carboxylic acid

Question 6

Type II ionization

Answer 6

• pos. charge in acidic form (pH less than pKa)

- ie. amino groups

Question 7

Isoelectric point

Answer 7

pI=(pK1+pK2)/2

• point where AA/polypeptide is ionized but has no net electric charge
• calculated by averaging pKa values that straddle the electrically neutral species
• make chart for polypeptide chains at different pH values

Question 8

Peptide bond formation

Answer 8

• dehydration reaction, H from amino and OH from carboxyl

- C-term and N-term groups join