1. Amino Acids Proteins, and Enzymes
Types of Proteins
Amino Acids
The Peptide Bond

2. 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

3. Amino Acids Building blocks of proteins Carboxylic acid group
Amino group
Side group R gives unique characteristics
R side chain I
H2H—C —COOH H

4. Examples of Amino AcidsH I
H2N—C —COOH
H glycine
CH3
H alanine

5. Types of Amino Acids Nonpolar R = H, CH3, alkyl groups, aromatic O
Polar ll
R = –CH2OH, –CH2SH, –CH2C–NH2,
(polar groups with –O-, -SH, -N-)
Polar/Acidic
R = –CH2COOH, or -COOH
Polar/ Basic
R = –CH2CH2NH2

6. Learning Check AA1 A. NH2–CH2–COOH (Glycine) CH3 | CH–OH
Identify each as (1) polar or (2) nonpolar
A. NH2–CH2–COOH (Glycine)
CH3 |
CH–OH
B. NH2–CH–COOH (Serine)

7. Solution AA1 A.(2) NH2–CH2–COOH (Glycine) CH3 | CH–OH
Identify each as (1) polar or (2) nonpolar
A.(2) NH2–CH2–COOH (Glycine)
CH3 |
CH–OH
B. (1) NH2–CH–COOH (Serine)

8. 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

9. Amino Acids as Acids and Bases
Ionization of the –NH2 and the –COOH group
Zwitterion has both a + and – charge
Zwitterion is neutral overall +
NH2–CH2–COOH H3N–CH2–COO–
glycine Zwitterion of glycine

10. pH and ionization H+ OH– + + Positive ion zwitterion Negative ion
H3N–CH2–COOH H3N–CH2–COO– H2N–CH2–COO–
Positive ion zwitterion Negative ion
Low pH neutral pH High pH

11. Learning Check AA2 CH3 CH3 + H3N–CH–COOH H2N–CH2–COO– (1) (2)
(1) (2)
Select from the above structures
A. Alanine in base.
B. Alanine in acid.

12. Solution AA2 CH3 CH3 + H3N–CH–COOH H2N–CH2–COO– (1) (2)
(1) (2)
Select from the above structures
(2) Alanine in base.
(1) Alanine in acid.

13. The Peptide Bond
Amide bond formed by the –COOH of an amino acid and the –NH2 of the next amino acid
O CH3
| | |
NH3–CH2–COH H3N–CH–COO–
O CH3
| | |
NH3–CH2–C – N–CH–COO–
| peptide bond H

14. Peptides Amino acids linked by amide (peptide) bonds
Gly Lys Phe Arg Ser
H2N COOH
end Peptide bonds end
Glycyllysylphenylalanylarginylserine

15. Learning Check AA3
What are the possible tripeptides formed from one each of leucine, glycine, and alanine?

16. 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

17. Learning Check AA4
Write the three-letter abbreviations for the following tetrapeptide:

18. Solution AA4
Ala-Leu-Cys-Met