19 Amino acids.ppt

Chapter 19
Biomolecules: Amino Acids, Peptides,
and Proteins
Structures of Amino Acids
Isoelectric Points
Peptides and Proteins
Peptide Synthesis
Classification of Proteins
Protein Structure
Amino acids(氨基酸):
Alanine
(丙氨酸)
Peptides(肽):
Many
Chains with fewer than 50
amino acids
Amide bonds
Protein:
(蛋白质)
For larger chains
Structures of Amino Acids
Dipolar ion
Zwitterion
(偶极分子)
Amino acids are amphoteric(两性离子):
In base solution:
In acid solution:
20α- amino cids found in protein.
19 of the 20amino acids are primary amines;
Proline(脯氨酸) is a secondary
amine.
P476,Table
Differ only in the nature of side chain.
Glycine(甘氨酸)
(S)-Alanine
L- Alanine
(S)-Phenylalanine
L-Phenylalanine
(s)-Serine
L-Serine
L-Glycer-
aldehyde
Aspatic acid
(天冬氨酸)
Glutamic acid
(谷氨酸)
Acidic
Lysine
(赖氨酸)
arginine
(精氨酸)
Histidine
(组氨酸)
basic
The others are neutral amino acids.
Isoelectric Points(等电点)
pH
Low pH
(protonated)
High pH
(deprotonated)
Isoelectric Points (pI):
At some intermediate pH, the concentration
of the dipolar ion is maximal, the concen-
trations of the anions and cations are equal.
pI pH=~
Neutral amino acid:
acidic amino acid:
pI at lower pH
basic amino acid:
pI at higher pH
Separation of a mixture of amino acids by
Electrophoresis(电泳).
-
+
Lysine
pI=
Glycine
pI=
Aspartic acid
pI=
Paper strip at pH=
C-terminal
Amino acids polymers linked together by
amide bonds.
Peptide bond
Peptides and Proteins
Alainine(Ala)
Serine(Ser)
Alanylserine(Ala-Ser)
(丙氨酰-丝氨酸)(丙-丝二肽)
Dipeptide(二肽)
Tripeptide(三肽)
Proteins:
MW: >10000
N-terminal
Peptide Synthesis
Protection of the amino group by BOC
group:
Ex.: Synthesis of Alanine-Leucine:
Alanine
Di-tert-butyldicarbonate
Boc-Ala
2. Protection of the carboxyl group by
treatment with methanol or benzyl alcohol:
BOC group can be removed by CF3COOH
The groups
can easily be
removed
by NaOH(aq).
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