Download Chapter 24 Amino Acids and Proteins

Chapter 24 Amino Acids
and Proteins
ORGANIC CHEMISTRY
Chapter 24
24.1 Introduction
Department of Chemistry, Xiamen University
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Chapter 24
Proteins are large biomolecules that occur in
every living organism.
They’re of many different types,and they have
many different biological functions.
All protein are made up of many amino acid
units linked together by amide bonds in a long
chain.
Amino acids can link together by forming
amide, or peptide, bonds.
Chains with fewer than 50 amino acids are
called polypeptides.
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Chapter 24
24.2 Amino Acids
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24.2A Structures and Names
Most of the important natural amino acids are
α-amino acids.
22 α-amino acids can be obtained from proteins.
With the exception of glycine, the alpha
carbons of amino acids are chiral.
The naturally occurring α-amino acids are often
referred to as L-amino acids.
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24.2B Essential Amino Acids
The 20 common amino acids can be further
classified as either neutral, acidic, or basic,
depending on the nature of their side chains.
All 20 of the amino acids are necessary for
protein synthesis, but humans are thought to be
able to synthesize only 10 of 20.
The remaining 10 are called essential amino
acids because they must be obtained from
dietary sources.
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Chapter 24
Valine 缬氨酸
O
H2N CH C OH
CH CH3
CH3
Valine Val
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Leucine 亮氨酸
O
H2N CH C OH
CH2
CH CH3
CH3
Leucine Leu
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Isoleucine 异亮酸
O
H2N CH C OH
CH CH3
CH2
CH3
Isoleucine Ile
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Tryptophan 色氨酸
O
H2N CH C OH
CH2
HN
Tryptophan Try
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Methionine 蛋氨酸
O
H2N CHC OH
CH2
CH2
S
CH3
Methionine Met
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Lysine 赖氨酸
O
H2N CH C OH
CH2
CH2
CH2
CH2
NH2
Lysine Lys
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Phenylalanine 苯丙氨酸
O
H2N CH C OH
CH2
Phenylalanine Phe
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Threonine 苏氨酸
O
H2N CH C OH
CH OH
CH3
Threonine Thr
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Arginine 精氨酸
O
H2N CH C OH
CH2
CH2
CH2
NH
C NH
NH2
Arginine Arg
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Chapter 24
Histidine 组氨酸
O
H2N CH C OH
CH2
N
NH
Histidine His
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Chapter 24
Amino Acids as Dipolar Ions
H
O
O
H2N CH C O
H2N CH C OH
R
R
H
O
In acid
+
+
H
O
H
N
CH
C
O
solution 2
3
R
H
A zwitterion
两性离子
H
O
H2N CH C OH + H2O
R
O
In base
solution H2N CH C O
R
O
+ OH
H2N CH C O
+ H2 O
R
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Isoelectric Point
In acid solution at low pH, an amino acid exists
primarily as a cation.
In basic solution at high pH, an amino acid
exists primarily as an anion.
At some intermediate point, the amino acid
must be exactly balanced between anionic and
cationic forms and exist primarily as the neutral,
dipolar zwitterion.
—— pH ——isoelectric point.
Department of Chemistry, Xiamen University