Amino Acids

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

1

Types of Proteins • • • • • • •

Type Structural Contractile Transport Storage Hormonal Enzyme Protection

Examples tendons, cartilage, hair, nails muscles hemoglobin milk insulin, growth hormone catalyzes reactions in cells immune response 2

Amino Acids • • • •

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

3

Examples of Amino Acids H I H2N—C —COOH I H glycine CH3 I H2N—C —COOH I H alanine

4

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

5

Learning Check AA1 Identify each as (1) polar or (2) nonpolar A. NH2–CH2–COOH

(Glycine)

CH3 | CH–OH | B. NH2–CH–COOH

(Serine) 6

Solution AA1 Identify each as (1) polar or (2) nonpolar A.(2) NH2–CH2–COOH

(Glycine)

CH3 | CH–OH | B. (1) NH2–CH–COOH

(Serine)

7

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 8

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 glycine

H3N–CH2–COO– Zwitterion of glycine 9

pH and ionization H+ +

OH– +

H3N–CH2–COOH

H3N–CH2–COO–

H2N–CH2–COO–

Positive ion

zwitterion

Negative ion

Low pH

neutral pH

High pH 10

Learning Check AA2 CH3

CH3

+ H3N–CH–COOH (1)

H2N–CH2–COO– (2)

Select from the above structures A. Alanine in base. B. Alanine in acid. 11

Solution AA2 CH3

CH3

+ H3N–CH–COOH (1)

H2N–CH2–COO– (2)

Select from the above structures •

(2) Alanine in base.

•

(1) Alanine in acid. 12

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– | H

peptide bond 13

Peptides • Amino acids linked by amide (peptide) bonds Gly

Lys

Phe

H2Nend

Arg

Ser -COOH

Peptide bonds

end

Glycyllysylphenylalanylarginylserine 14

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

15

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 16

Learning Check AA4 Write the three-letter abbreviations for the following tetrapeptide: CH3 CH3 CH3 O

S

CH CH3

SH

CH2

CH O

CH2 O

CH2 O -

H3N CH C N CH C N CH C N CH C O H

H

H

17

Solution AA4 CH3 CH 3 CH 3 O

S

CH CH 3

SH

CH2

CH O

CH 2 O

CH2 O

H 3N CH C N CH C N CH C N CH C O

H

H

H

Ala-Leu-Cys-Met 18