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Karnataka Board PUCPUC Science 2nd PUC Class 12

Biomolecules in the Cell > Proteins - Amino Acids

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Estimated time: 4 minutes
CBSE: Class 12

Key Points: Amino Acids

α-Amino acids: Carboxylic acids where α-hydrogen is replaced by the –NH₂ group

General structure: \[ \mathrm{R} - \underset{\underset{\displaystyle \mathrm{NH}_2}{|}}{\overset{\overset{\displaystyle \alpha}{\displaystyle \mathrm{CH}}}{}} - \mathrm{COOH}\]
(where R = H or alkyl group at α-carbon)

Essential amino acids (not synthesised in the body; must be taken in food):

  1. Leucine
  2. Isoleucine
  3. Lysine
  4. Methionine
  5. Phenylalanine
  6. Threonine 
  7. Tryptophan
  8. Valine

Non-essential amino acids (synthesised in the body):

  1. Alanine
  2. Asparagine
  3. Aspartic acid
  4. Cysteine
  5. Glutamic acid
  6. Glutamine
  7. Glycine
  8. Proline
  9. Serine
  10. Tyrosine

Semi-essential (50% body + 50% food):

  1. Arginine
  2. Histidine

Glycine is the only optically inactive amino acid (no chiral centre; R = H)

Isoelectric Point (pI):

  • pH at which an amino acid does not migrate in an electric field → exists as a zwitterion (+NH₃–CH(R)–COO⁻)
  • At pI, the concentration of zwitterions is maximum; anionic and cationic forms are equal
  • At pI, an amino acid has the least solubility in water (used in separation by isoelectric precipitation)
  • For neutral amino acid: \[pI=\frac{1}{2}(pk_{a_1}+pk_{a_2})\]

Video Tutorials

We have provided more than 1 series of video tutorials for some topics to help you get a better understanding of the topic.

Series 1


Series 2


Shaalaa.com | Biomolecules part 15 (20 essential amino acids)

Shaalaa.com


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Biomolecules part 15 (20 essential amino acids) [00:21:35]
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