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20 Amino Acids
學習目標 :•熟記胺基酸的基本結構 •熟記 20種標準胺基酸的物理、化學性質與分類。
Miss HuichunBiochemistry Dept.Tzu-Chi University
112/04/10
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Amino acid Protein
• Protein: – Building block (unit): amino acids– Polypeptide chain
a.a.1 a.a.3 a.a.4
a.a.5
a.a.6
a.a.2
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-Amino acid (residue)• Common structure
– -carbon– Acid group (Carboxyl
group)– Amino group – Functional group (Side chain) (R group)
Fig 3-2, p. 72
a.a.
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Common structures of a.a.
R R
• C– chiral center– Mirror images
• Stereoisoform (stereoisomer)– Enantiomers (Fig 1-19, p. 16)– Non-super-imposable mirror images of each other.
– L-amino acid and D-amino acid• Proteins are made exclusively from L-form a.a. !! (p.74)• D-form a.a. only in few small peptides
– Some peptides in bacterial cell walls– Certain peptide antibiotics
Fig 3-3a, p. 72
L-form D-form
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20 standard amino acids
• Chemical properties – by functional groupTable 3-1– Nonpolar, aliphatic (hydrophobic)– Aromatic– Polar, uncharged– Negatively charged– Positively charged
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Hydrophobic R groups
Fig 3-5
Secondary amino (imino) group
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BCAA• Branched-chain amino acid
– Valine– Leucine– Isoleucine
CarbonNitrogenOxygenHydrogen
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Aromatic R groups
Fig 3-5
Hydroxyl group
Polarity: Tyr ~ Trp >> Phe
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Spectroscopic Properties280 nm: Trp > Tyr >> Phe
Fig 3-6• Only Phe, Tyr, and Trp absorb
ultraviolet light– Absorbance at 280 nm is a good
diagnostic device for proteins
• The Lambert-Beer law– Box 3-1 (p. 76)
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Polar, uncharged R groups
Fig 3-5
Sulfhydryl group
Hydroxyl group
Amide group
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Disulfide bond
• Cys residues can form disulfide bondFig 3-7, p. 80
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Positively charged R groups
Fig 3-5
Imidazole group
At pH = 7.0
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Negatively charged R groups
Fig 3-5
At pH = 7.0
= Aspartic acid = Glutamic acid
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Leu L
-C-C-CONH2-C-CONH2
-C-COOH -C-C-COOH
-H -CH3
-C-OH -C-SH
-C-C-S-C PPro
-C-C C N N+
-C-C-C-C-NH3+ -C-
-C- -OH
-C-N
雙和線
環狀線
中央線
南港線
中山線
西北線
Aliphatic
Amide
Acidic
Imino,Circular
Basic
SulfurHydroxy
Aromatic-C-C-C-N-C-N
N+
=
C-C-C-C
C-C-C-C
C C-C
C C C HN C-COOH
-C-C OH
Gln QAsn N
Asp D Glu EPhe F
Arg R
Lys K
His H
Gly G AAAla VVal I Ile
YTyr
Ser S
Thr T Met M
Cys C
胺基酸地下鐵道圖 Trp W
Non-polar
Polar
Jua
ng
RH
(2
00
4)
BC
ba
sics
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If only one amino acid (a.a.) begins with a certain letter, that letter is used
Cysteine = Cys = CHistidine = His = HIsoleucine = Ile = IMethionine = Met = MSerine = Ser = SValine = Val = V
Key convention, p. 74
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If more than one a.a. begins with a certain letter, that letter is assigned to
the most commonly occurring one
Alanine = Ala = AGlycine = Gly = GLeucine = Leu = LProline = Pro = PThreonine = Thr = T
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Phonetically suggestive
Aspartic acid (“asparDic acid”) = Asp = DPhenylalanine (“Fenylalanine”) = Phe = F Arginine (“aRginine”) = Arg = R Tyrosine (“tYrosine”) = Tyr = YTryptophan (double ring in the molecule) = Trp = W
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A letter close to the initial is used
Asparagine (contains N) = Asn = NGlutamic acid (near D) = Glu = E Glutamine (“Q-tamine”) = Gln = QLysine (near L) = Lys = K
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THIS IS EASY …
GREAT
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Amino acids
• Alanine ( 丙胺酸 )• Arginine ( 精胺酸 )• Asparagine ( 天門冬醯胺 )• Aspartate ( 天門冬酸 )• Cysteine ( 半胱胺酸 )• Glutamate ( 麩胺酸 )• Glutamine ( 麩胺醯胺 )• Glycine ( 甘胺酸 )• Histidine ( 組織胺酸 )• Isoleucine ( 異白胺酸 )
• Leucine ( 白胺酸 )• Lysine ( 離胺酸 )• Methionine ( 甲硫胺酸 )• Phenylalanine ( 苯丙胺酸 )• Proline ( 脯胺酸 )• Serine ( 絲胺酸 )• Threonine ( 酥胺酸 )• Tryptophan ( 色胺酸 )• Tyrosine ( 酪胺酸 )• Valine ( 纈胺酸 )
Can you name these amino acids?
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Interesting websites
• Lehninger 4th ed. website: www.whfreeman.com/lehninger
• Chime plugin is required to run– Self-guided tour of the amino acids– Amino Acid Identification Quiz– Amino Acid Structure Quiz
• www.huichun.tcu.edu.tw• 台大莊榮輝老師教學網站
– http://juang.bst.ntu.edu.tw/JRH/lecture.htm
