Classification and Structure of Standard Amino Acids

Basic learning of amino acids for beginners.

1. INSTITUTE OF BIOMEDICAL SCIENCES, BUNDELKHAND UNIVERSITY, JHANSI CLASSIFICATION AND STRUCTURE OF STANDARD AMINO ACIDS PRESENTED BY – Ms. PALAK AGRAWAL

2. INTRODUCTION HISTORY STRUCTURE CLASSIFICATION 21 st AND 22 nd AMINO ACIDS CONCLUSIONS REFERENCES CONTENTS

3. What are ‘PROTEINS’? Proteins are the most abundant organic molecules of the living system which occur in every part of the cell and constitute about 50% of the cellular dry weight.

4. INTRODUCTION As many of 300 amino acids occur in nature. Of these, only 20 , known as standard amino acids are repeatedly found in the structure of proteins , isolated from different forms of life – animal, plant and microbial. This is because of the universal nature of the genetic code available for the incorporation of only 20 amino acids when the proteins are synthesised in the cells. This process is controlled by DNA. After the synthesis of proteins, some of the incorporated amino acids undergo modifications to form their derivatives.

5. HISTORY The first few amino acids were discovered in the early 19th century. In 1806, French chemists   Louis-Nicolas Vauquelin   and  Pierre Jean Robiquet   isolated a compound in   asparagus   that was subsequently named   asparagine , the first amino acid to be discovered. Cystine  was discovered in 1810,   although its monomer,   cysteine , remained undiscovered until 1884. Glycine   and   leucine   were discovered in 1820.   The last of the 20 common amino acids to be discovered was   threonine   in 1935 by   William Cumming Rose , who also determined the   essential amino acids   and established the minimum daily requirements of all amino acids for optimal growth. The unity of the chemical category was recognized by   Wurtz   in 1865, but he gave no particular name to it. Usage of the term "amino acid" in the English language is from 1898, while the German term,  Aminosäure , was used earlier. Proteins were found to yield amino acids after enzymatic digestion or acid   hydrolysis . In 1902,  Emil Fischer   and  Franz Hofmeister   independently proposed that proteins are formed from many amino acids, whereby bonds are formed between the amino group of one amino acid with the carboxyl group of another, resulting in a linear structure that Fischer termed " peptide ".

6. GENERAL STRUCTURE OF AMINO ACIDS

7. CLASSIFICATION OF AMINO ACIDS Amino acids are classified on the basis of : Structure and Chemical Nature Polarity Nutritional Requirements Metabolic Fate

8. Amino acid classification based on structure and chemical nature : A comprehensive classification of amino acids is based on their structure and chemical nature. Each amino acid is assigned a 3 letter or 1 letter symbol. These symbols are commonly used to represent the amino acids in protein structure. The 20 amino acids found in proteins are divided into 7 distinct groups.

9. Amino Acids

10. ( Phe , F) (Tyr, Y) ( Trp , W)

11. Imino Acid : Proline Proline (Pro, P) is unique in that its R group is attached to the amino nitrogen as well as to the alpha carbon. This bond means that proline necessarily introduces a kink in the polypeptide backbone. The lack of an H attached to the N means that proline can’t form hydrogen bonds. All other amino acids can atleast form hydrogen bonds with the N-H in the backbone. Proline is hydrophobic and hence, an imino acid . (Pro, P)

12. (II) Amino acid classification based on polarity : Amino acids are classified into 4 groups based on their polarity. Polarity is important for protein structure. (1) Non-polar amino acids : Also referred to as ‘hydrophobic’ amino acids. They have no charge on the ‘R’ group.

13. (2) Polar amino acids with no charge on ‘R’ group : These amino acids carry no charge on the ‘R’ group. They however possess groups such as hydroxyl, sulfhydryl and amide, and participate in hydrogen bonding of protein structure.

14. (3) Polar amino acids with positive ‘R’ group :

15. (4) Polar amino acids with negative ‘R’ group : It includes the dicarboxylic monoamino acids.

16. (III) Amino acid classification based on nutritional requirements : All the 20 amino acids need not be taken in the diet. Based on the nutritional requirements, amino acids are grouped into two classes - essential and non-essential amino acids. (1) Essential/ Indespensible amino acids : The amino acids which cannot be synthesized by the body and, therefore, need to be supplied through the diet are called essential amino acids. They are required for proper growth and maintenance of the individual.

17. Sources of Essential Amino Acids Cheese ( Leucine ) Eggs ( Isoleucine ) Almonds (Lysine) Legumes ( Methionine ) Milk (Phenylalanine) Cashewnuts ( Arginine ) Leafy Greens ( Threonine ) Dark Chocolate (Tryptophan) Apricots ( Valine ) Soybeans ( Histidine )

18. (2) Non-essential/Dispensable amino acids : The body can synthesize about 10 amino acids to meet the biological needs, hence they need not be consumed in the diet. These are— glycine , alanine , serine, cysteine , aspartate , asparagine , glutamate, glutamine, tyrosine and proline . Serine

19. (IV) Amino acid classification based on their metabolic fate : The carbon skeleton of amino acids can serve as a precursor for the synthesis of glucose (glycogenic) or fat ( ketogenic ) or both. From metabolic view point, amino acids are divided into three groups: Glycogenic amino acids : These amino acids can serve as precursors for the formation of glucose or glycogen. Ketogenic amino acids : Fats can be synthesized from these amino acids. Glycogenic and ketogenic amino acids : Four amino acids are precursors for synthesis of glucose as well as fat.

20. Amino acid classification based on their metabolic fate Glycogenic Both Ketogenic

21. Selenocysteine –the 21st amino acid In recent years, a 21st amino acid namely selenocysteine has been added. It is found at the active sites of certain enzymes/proteins ( selenoproteins ). e.g ) glutathione peroxidase , glycine reductase , 5c-deiodinase, thioredoxin reductase . Selenocysteine is an unusual amino acid containing the trace element selenium in place of the sulfur atom of cysteine . Incorporation of selenocysteine into the proteins during translation is carried out by the codon namely UGA . It is interesting to note that UGA is normally a stop codon that terminates protein biosynthesis . Another unique feature is that selenocysteine is enzymatically generated from serine directly on the tRNA ( selenocysteine-tRNA ), and then incorporated into proteins.

22. Pyrrolysine – the 22nd amino acid? In the year 2002, some researchers have described yet another amino acid namely pyrrolysine as the 22nd amino acid present in protein. The stop codon UAG can code for pyrrolysine . ------------------------------------------------------------------------------------------- Conclusion : Amino acids are basis of all life processes as they are absolutely essential for every metabolic process. Among their most important tasks are the optimal transport and storage of nutrients. Diseases such as obesity, high cholestrol levels, diabetes, insomnia, arthritis, etc. , can essntially be traced back from metabolic disturbances. Amino acids also have positive effects on osteoporosis, cholestrol , hair loss, sleeplessness and mood swings.

23. REFERENCES Biochemistry : Dr. U. Satyanarayana Dr. U. Chakrapani Fourth Edition, Reprint 2013, ISBN : 978-81-312-3601-7 https://en.wikipedia.org/wiki/Amino_acid

24. THANK YOU!