Transcript 课件六

Amino acids
COOH3N+
C
H
R
Common structure of 19 AAs
Proline
1. a-carbon is chiral (asymmetric) except glycine
(R is H)
2. Only L-isomers are found in proteins
3. Amino acids are dipolar ions in aqueous
solution and are amphoteric
4. The side chains (R) differ in size, shape, charge
and chemical reactivity
5. Nonstandard amino acids (e.g. 4-OH proline and
5-OH lysine)
Amino acids-charged
(can form salt bridge, hydrophilic)
Acidic amino acids – containing additional carboxyl group
aspartic acid (Asp, D，天冬氨酸)
glutamic acid (Glu, E，谷氨酸)
Basic amino acids – containing positively charged group
Lysine (Lys, K, 赖氨酸)
Arginine (arg, R,精氨酸)
Histidine (His, H，组氨酸)
Amino acids-polar uncharged
(can form hydrogen bond with water, hydrophilic
Serine (Ser, S，丝氨酸)
Threonine (Thr, T，苏氨酸)
Asparagine (Asn, N，天冬酰氨)
Glutamine (Gln, Q，谷氨酰氨)
x-S-S-x
Cysteine (Cys, C，半胱氨酸) has a thiol group，
which is often oxidizes to cystine
Amino acids-nonpolar aliphatic
(hydrophobic)
Glycine (Gly, G，甘氨酸)
Proline (Pro, P，脯氨酸)
Methionine (Met, M，甲硫氨酸
Alanine (Ala, A，丙氨酸)
Valine (Val, V，缬氨酸)
Leucine (Leu, L，亮氨酸)
Isoleucine (Ile, I，异亮氨酸)
Amino acids-aromatic
(UV absorbance at 280 nm, hydrophobic)
Phenylalanine (Phe, F，苯丙氨酸)
Tyrosine (Tyr, Y，酪氨酸)
Tryptophan (Trp, W，色氨酸)
Protein-shape
Globular proteins: enzymes
Fibrous proteins
Polypeptides contain N- and C- termini and are
directional, usually ranging from 100-1500 aa
Formation of a peptide bond (shaded in gray) in a dipeptide.