Amino Acids & Proteins

Question 1

α-AMINO ACID

Answer 1

Has general formula RCH(NH₂)COOH (with both a basic amine group and an acidic carboxyl group attached to the same α carbon atom).

Question 2

ISOELECTRIC POINT

Answer 2

The pH at which an amino acid exists as its zwitterion.

Question 3

ZWITTERION

Answer 3

Dipolar ion (consists of a +ve and a -ve charge) formed from an amino acid by the donation of H⁺ ion from a carboxyl group (-COOH) to amine (-NH₂).

Question 4

Effect of pH on amino acids

Answer 4

Low pH - positive charge (NH₃⁺)/NH₂ group accepts a H⁺

High pH - negative charge (COO⁻)/COOH group donates a H⁺

Question 5

Effect of -COOH and -NH₂ groups of isoelectric point

Answer 5

COOH - decreases isoelectric point

NH₂ - increases isoelectric point

Question 6

Amino Acids as ACIDS

Answer 6

• Amino acids act as acids when reacted with bases/alkalis
• They donate protons
RCH(NH₂)COOH + NaOH → RCH(NH₂)COONa + H₂O

Question 7

Amino Acids as BASES

Answer 7

• Amino acids act as bases when reacted with acids
• They accept protons
RCH(NH₂)COOH + HCl → RCH(NH₃⁺)COOH + Cl⁻

Question 8

Joining two amino acids together to form a dipeptide

Answer 8

OH from COOH group of one amino acid bonds with NH₂ group from another
RCOOH + RNH₂ → RCONHR + H₂O

Question 9

Acid Catalysed Hydrolysis of Polypeptides

Answer 9

Reagent: H₂SO₄(aq)
Conditions: Reflux/24 hours
RNH₃⁺ + RNH₃⁺

Question 10

Alkaline Catalysed Hydrolysis of Polypeptides

Answer 10

Reagent: NaOH(aq)
Conditions: Reflux
RCOO⁻Na⁺ + RCOO⁻Na⁺ + H₂O