Amino Acids and the Amino Acids and the Primary Structure of Primary Structure of Proteins Proteins Important biological functions of proteins 1. Enzymes, the biochemical catalysts 2. Storage and transport of biochemical molecules 3. Physical cell support and shape (tubulin, actin, collagen) 4. Mechanical movement (flagella, mitosis, muscles) (continued)
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Amino Acids and the Primary Structure of Proteins Important biological functions of proteins 1. Enzymes, the biochemical catalysts 2. Storage and transport.
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Amino Acids and the Amino Acids and the Primary Structure of ProteinsPrimary Structure of Proteins
Important biological functions of proteins
1. Enzymes, the biochemical catalysts
2. Storage and transport of biochemical molecules
3. Physical cell support and shape (tubulin, actin, collagen)
4. Mechanical movement (flagella, mitosis, muscles)
(continued)
Amino Acids and the Amino Acids and the Primary Structure of ProteinsPrimary Structure of Proteins
5. Decoding cell information (translation, regulation of gene expression)
6. Hormones or hormone receptors (regulation of cellular processes)
7. Other specialized functions (antibodies, toxins etc)
Zwitterionic form of amino Zwitterionic form of amino acidsacids
• Under normal cellular conditions amino acids are zwitterions (dipolar ions):
Amino group = -NH3+
Carboxyl group = -COO-
Two representations of an amino Two representations of an amino acid at neutral pHacid at neutral pH
Titration Curve for Titration Curve for AlanineAlanine
• Titration curves are used to determine pKa values
• pK1 = 2.4
• pK2 = 9.9
• pIAla = isoelectric point
Aliphatic R Groups
• Glycine (Gly, G) - the -carbon is not chiral since there are two H’s attached (R=H)
• Four amino acids have saturated side chains:
Alanine (Ala, A) Valine (Val, V)
Leucine (Leu, L) Isoleucine (Ile, I)
• Proline (Pro, P) 3-carbon chain connects -C and N
Stereoisomers of IsoleucineStereoisomers of Isoleucine
• Ile has 2 chiral carbons, 4 possible stereoisomers
Aromatic Amino AcidsAromatic Amino Acids
Methionine and CysteineMethionine and Cysteine
Formation of CystineFormation of Cystine
Histidine, Lysine, and ArginineHistidine, Lysine, and Arginine