Amino Acids Proteins, and Enzymes

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Amino Acids Proteins, and Enzymes

• Types of Proteins
• Amino Acids
• The Peptide Bond

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Types of Proteins

• Type Examples
• Structural tendons, cartilage, hair, nails
• Contractile muscles
• Transport hemoglobin
• Storage milk
• Hormonal insulin, growth hormone
• Enzyme catalyzes reactions in cells
• Protection immune response

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Amino Acids

• Building blocks of proteins
• Carboxylic acid group
• Amino group
• Side group R gives unique characteristics
• R side chain
• I
• H2HC COOH
• I
• H

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Examples of Amino Acids

• H
• I
• H2NC COOH
• I
• H glycine
• CH3
• I
• H2NC COOH
• I
• H alanine

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Types of Amino Acids

• Nonpolar R H, CH3, alkyl groups, aromatic
• O
• Polar ll
• R CH2OH, CH2SH, CH2CNH2,
• (polar groups with O-, -SH, -N-)
• Polar/Acidic
• R CH2COOH, or -COOH
• Polar/ Basic
• R CH2CH2NH2

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Learning Check AA1

• Identify each as (1) polar or (2) nonpolar
• A. NH2CH2COOH (Glycine)
• CH3
• CHOH
• B. NH2CHCOOH (Serine)

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Solution AA1

• Identify each as (1) polar or (2) nonpolar
• A.(2) NH2CH2COOH (Glycine)
• CH3
• CHOH
• B. (1) NH2CHCOOH (Serine)

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Essential Amino Acids

• 10 amino acids not synthesized by the body
• arg, his, ile, leu, lys, met, phe, thr, trp, val
• Must obtain from the diet
• All in diary products
• 1 or more missing in grains
• and vegetables

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Amino Acids as Acids and Bases

• Ionization of the NH2 and the COOH group
• Zwitterion has both a and charge
• Zwitterion is neutral overall
• NH2CH2COOH H3NCH2COO
• glycine Zwitterion of glycine

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pH and ionization

• H OH
• H3NCH2COOH H3NCH2COO H2NCH2COO
• Positive ion zwitterion Negative ion
• Low pH neutral pH High pH

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Learning Check AA2

• CH3 CH3
• H3NCHCOOH H2NCH2COO
• (1) (2)
• Select from the above structures
• A. Alanine in base.
• B. Alanine in acid.

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Solution AA2

• CH3 CH3
• H3NCHCOOH H2NCH2COO
• (1) (2)
• Select from the above structures
• (2) Alanine in base.
• (1) Alanine in acid.

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The Peptide Bond

• Amide bond formed by the COOH of an amino acid
  and the NH2 of the next amino acid
• O CH3
• 
  
• NH3CH2COH H3NCHCOO
• O CH3
• NH3CH2C NCHCOO
• peptide bond
• H

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Peptides

• Amino acids linked by amide (peptide) bonds
• Gly Lys Phe Arg
  Ser
• H2N- -COOH
• end Peptide bonds end
• Glycyllysylphenylalanylarginylserine

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Learning Check AA3

• What are the possible tripeptides formed from
  one each of leucine, glycine, and alanine?

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Solution AA3

• Tripeptides possible from one each of leucine,
  glycine, and alanine
• Leu-Gly-Ala
• Leu-Ala-Gly
• Ala-Leu-Gly
• Ala-Gly-Leu
• Gly-Ala-Leu
• Gly-Leu-Ala

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Learning Check AA4

• Write the three-letter abbreviations for the
  following tetrapeptide

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Solution AA4

• Ala-Leu-Cys-Met