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Chapter 27 Amino Acids, Peptides, and Proteins. Nucleic Acids

Chapter 27 Amino Acids, Peptides, and Proteins. Nucleic Acids. 27.1 Classification of Amino Acids. Fundamentals. While their name implies that amino acids are compounds that contain an —NH 2 group and a —CO 2 H group, these groups are actually present as —NH 3 + and —CO 2 – respectively.

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Chapter 27 Amino Acids, Peptides, and Proteins. Nucleic Acids

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  1. Chapter 27Amino Acids, Peptides, and Proteins.Nucleic Acids

  2. 27.1Classification of Amino Acids

  3. Fundamentals • While their name implies that amino acids are compounds that contain an —NH2 group and a —CO2H group, these groups are actually present as —NH3+ and —CO2– respectively. • They are classified as a, b, g, etc. amino acids according the carbon that bears the nitrogen.

  4. + NH3 – CO2 + – H3NCH2CH2CO2 + – H3NCH2CH2CH2CO2 Amino Acids an a-amino acid that is anintermediate in the biosynthesisof ethylene a a b-amino acid that is one ofthe structural units present incoenzyme A b a g-amino acid involved inthe transmission of nerveimpulses g

  5. The 20 Key Amino Acids • More than 700 amino acids occur naturally, but 20 of them are especially important. • These 20 amino acids are the building blocks of proteins. All are a-amino acids. • They differ in respect to the group attached to the a carbon. • These 20 are listed in Table 27.1 (p 1054-1055).

  6. O H + – H3N O C C R Table 27.1 • The amino acids obtained by hydrolysis of proteins differ in respect to R (the side chain). • The properties of the amino acid vary as the structure of R varies.

  7. O H + – H3N O C C H Table 27.1 • Glycine is the simplest amino acid. It is the only one in the table that is achiral. • In all of the other amino acids in the table the a carbon is a stereogenic center. Glycine (Gly or G)

  8. Table 27.1 O H + – H3N O C C CH3 Alanine (Ala or A)

  9. Table 27.1 O H + – H3N O C C CH(CH3)2 Valine (Val or V)

  10. Table 27.1 O H + – H3N O C C CH2CH(CH3)2 Leucine (Leu or L)

  11. Table 27.1 O H + – H3N O C C CH3CHCH2CH3 Isoleucine (Ile or I)

  12. Table 27.1 O H + – H3N O C C CH3SCH2CH2 Methionine (Met or M)

  13. O H + – H2N O C C CH2 H2C CH2 Table 27.1 Proline (Pro or P)

  14. O H + – H3N O C C CH2 Table 27.1 Phenylalanine (Phe or F)

  15. O H + – H3N O C C CH2 N H Table 27.1 Tryptophan (Trp or W)

  16. O H + – H3N O C C H2NCCH2 O Table 27.1 Asparagine (Asn or N)

  17. O H + – H3N O C C H2NCCH2CH2 O Table 27.1 Glutamine (Gln or Q)

  18. Table 27.1 O H + – H3N O C C CH2OH Serine (Ser or S)

  19. Table 27.1 O H + – H3N O C C CH3CHOH Threonine (Thr or T)

  20. O H + – H3N O C C – OCCH2 O Table 27.1 Aspartic Acid (Asp or D)

  21. O H + – H3N O C C – OCCH2CH2 O Table 27.1 Glutamic Acid (Glu or E)

  22. O H + – H3N O C C CH2 OH Table 27.1 Tyrosine (Tyr or Y)

  23. Table 27.1 O H + – H3N O C C CH2SH Cysteine (Cys or C)

  24. Table 27.1 O H + – H3N O C C + CH2CH2CH2CH2NH3 Lysine (Lys or K)

  25. Table 27.1 O H + – H3N O C C CH2CH2CH2NHCNH2 + NH2 Arginine (Arg or R)

  26. CH2 N NH Table 27.1 O H + – H3N O C C Histidine (His or H)

  27. 27.2Stereochemistry of Amino Acids

  28. – CO2 + H3N H R Configuration of a-Amino Acids • Glycine is achiral. All of the other amino acids in proteins have the L-configuration at their a carbon.

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