Write the general structure of an $\alpha$-amino acid, and explain what is meant by saying it exists as a zwitterion.

Write the general structure of an α-amino acid, and explain what is meant by saying it exists as a zwitterion.

Example · Example 9

\alpha

West Bengal WbchseTextbookSubjectiveImportance★★★★★

18% · 9/49 Questions

🔒 Locked · start free trial →

You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.

Start your 14-day free trial to unlock the full solution →

An $\alpha$ -amino acid's general structure is $\text{R}{-}\text{CH}(\text{NH}_2){-}\text{COOH}$ : a central alpha carbon bonded to an amino group ( $-\text{NH}_2$ ), a carboxyl group ( $-\text{COOH}$ ), a hydrogen atom, and a variable side chain R that determines the identity of the specific amino acid.

Because the acidic $-\text{COOH}$ group and the basic $-\text{NH}_2$ group are both present on the same molecule (and close together, both on the alpha carbon), an internal proton transfer occurs spontaneously: the $-\text{COOH}$ group donates its acidic proton directly to the neighbouring $-\text{NH}_2$ group. This converts the carboxyl group into a negatively charged carboxylate ion, $-\text{COO}^-$ , and the amino group into a positively charged ammonium ion, $-\text{NH}_3^+$ -- giving the structure $\text{R}{-}\text{CH}(\text{NH}_3^+){-}\text{COO}^-$ . Although this molecule now carries both a positive and a negative charge simultaneously, the two charges cancel and the molecule as a whole is electrically neutral. A molecule carrying separated positive and negative charges like …

Start your 14-day free trial to unlock the full solution →

Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2026Set SEM31 markMCQ
$Q. At isoelectric point structure of glycine is$
(a) H2N-CH2-COOH
(b) H2N-CH2-COO(-)
(c) H3N(+)-CH2-COOH
(d) H3N(+)-CH2-COO(-)
›Reveal solutionSolution

At the isoelectric point an amino acid carries no net charge and exists as a zwitterion, with -COOH deprotonated and -NH2 protonated. Correct option (d).

In an amino acid the -COOH group loses a proton and the -NH2 group gains it, giving an internal salt (zwitterion). At the isoelectric point the positive and negative charges balance so the net charge is zero and the molecule does not migrate in an electric field.

…

Start your 14-day free trial to see the full solution →
CBSE 2022Set ANNUAL1 markMCQ
$Q. Insulin is$
(a) an amino acid
(b) a protein
(c) a carbohydrate
(d) a lipid OR Hydrolysis of protein produces .......... number of amino acids.
(a) 15
(b) 20
(c) 25
(d) 35
›Reveal solutionSolution

Insulin is a peptide hormone made of two polypeptide chains linked by disulfide bonds, making it a protein.

Reasoning: Insulin is a hormone secreted by the beta-cells of the pancreas that regulates blood glucose levels. Structurally, it consists of two polypeptide chains (the A-chain and B-chain, made of amino acids joined by peptide bonds) held together by disulfide (-S-S-) bridges. Since it is built from amino acids linked by peptide bonds, insulin is classified biochemically as a prote …

Start your 14-day free trial to see the full solution →
CBSE 2022Set ANNUAL1 markMCQ
$Q. Optically inactive compound is$
(a) Aspartic acid
(b) Lysine
(c) Cystine
(d) Glycine
›Reveal solutionSolution
Optical activity requires a chiral (asymmetric) carbon; glycine's alpha-carbon carries two identical hydrogen substituents, so it has no chiral centre and is optically inactive.

Reasoning: An amino acid's alpha-carbon is chiral (and hence the amino acid is optically active) only if it bears four different groups: -NH2, -COOH, -H, and a side chain (R group) that is different from H.

Aspartic acid, Lysine, and Cystine all have side chains different from hydrogen (a -CH2COOH, a -(CH2)4NH2, and a -CH2SSCH2- linked side chain respectively), so their alpha-carbons are genuinely chiral centres — these are optically active. …
Start your 14-day free trial to see the full solution →

←Previous questionExample 8 — Sucrose does not reduce Fehling's solution or Tollens' reagent, i.e. i…→Next questionExample 10 — Glycine and alanine combine to form a dipeptide. Show how the peptide …

Q.Write the general structure of an $\alpha$ -amino acid, and explain what is meant by saying it exists as a zwitterion.

Concept understanding — Amino Acids and the Peptide Bond

Q.Write the general structure of an α\alphaα-amino acid, and explain what is meant by saying it exists as a zwitterion.

🎓Unlock everything free for 14 days

Q.Write the general structure of an $\alpha$ -amino acid, and explain what is meant by saying it exists as a zwitterion.

Unlock everything free for 14 days