Amino Acids — Structure, zwitter ion, essential
Biomolecules
8
JEE Qs
8%
Hard
60
min
Master the concept of zwitterions and understand how the charge of an amino acid varies with pH, along with the accurate calculation of its isoelectric point (pI) for different types of amino acids.
🧮 Key Formulas
✅ Key Points for JEE
- 1Amino acids are organic compounds containing both an amino group (-NH2) and a carboxyl group (-COOH). In alpha-amino acids, both groups are attached to the same carbon atom (alpha-carbon).
- 2Except for glycine, all alpha-amino acids are chiral at the alpha-carbon, and most naturally occurring amino acids found in proteins have an L-configuration.
- 3Amino acids exist predominantly as zwitterions (dipolar ions) in aqueous solutions at physiological pH. In this form, the amino group is protonated (-NH3+) and the carboxyl group is deprotonated (-COO-), resulting in an overall neutral molecule despite having charges.
- 4The isoelectric point (pI) is the specific pH at which an amino acid exists predominantly as a zwitterion and has no net electrical charge. Its calculation involves averaging relevant pKa values.
- 5Amino acids are classified as essential if the human body cannot synthesize them and they must be obtained from diet; non-essential amino acids can be synthesized by the body.
⚠️ Common Mistakes
- ✕Confusing the L- and D-configurations of amino acids; L-amino acids are typically found in proteins.
- ✕Incorrectly assigning the net charge to an amino acid at a given pH, especially when the pH is significantly different from its pI.
- ✕Miscalculating the isoelectric point (pI) for acidic or basic amino acids by incorrectly selecting the pKa values to average.
- ✕Memorizing essential amino acids without understanding the concept, leading to confusion during application.
📝 Practice Questions
See allQ51.Given below are two statements: Statement I: Fructose does not contain an aldehydic group but still reduces Tollen's reagent Statement II: In the presence of base, fructose undergoes rearrangement to give glucose. In the light of the above statements, choose the correct answer from the options given below (1) Both Statement I and Statement II are true (2) Both Statement I and Statement II are false (3) Statement I is true but Statement II is false (4) Statement I is true but Statement II is false
Q51.The carbohydrate "Ribose" present in DNA, is A. A pentose sugar B. present in pyranose from C. in "D" configuration D. a reducing sugar, when free E. in ∝-anomeric form Choose the correct answer from the 2025 (24 Jan Shift 1) JEE Main Previous Year Paper options given below: (1) A, D and E Only (2) A, C and D Only (3) A, B and E Only (4) B, D and E Only
Q60.Which of the following acids is a vitamin? (1) Adipic acid (2) Ascorbic acid (3) Saccharic acid (4) Aspartic acid
Q61.Identify the number of structure/s from the following which can be correlated to D-glyceraldehyde. (1) four (2) one (3) two (4) three
Q59.The α-Helix and β - Pleated sheet structures of protein are associated with its : (1) tertiary structure (2) quaternary structure (3) secondary structure (4) primary structure ∣∣∣ ∣∣∣ ∣∣∣ ∣∣ 2025 (23 Jan Shift 2) JEE Main Previous Year Paper
Q51.Given below are two statements: Statement I : D-glucose pentaacetate reacts with 2, 4-dinitrophenylhydrazine Statement II : Starch, on heating with concentrated sulfuric acid at 100∘C and 2-3 atmosphere pressure produces glucose. In the light of the above statements, choose the correct answer from the options given below 2025 (28 Jan Shift 1) JEE Main Previous Year Paper (1) Statement I is false but Statement II is true (2) Both Statement I and Statement II are false (3) Both Statement I and Statement II are true (4) Statement I is true but Statement II is false
NCERT Chapters
- Class 11 Chemistry Ch 7: Equilibrium
- Class 11 Chemistry Ch 12: Organic Chemistry - Some Basic Principles and Techniques
- Class 12 Chemistry Ch 13: Amines
- Class 12 Chemistry Ch 14: Biomolecules