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UNIT 8
THE AMINO ACIDS
LEARNING OBJECTIVES
State the composition and
describe the structure of
amino acids.
Classify amino acids.
List essential, semi-essential and non-
essential amino acids.
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AMINO ACID
Principal source:
hydrolysis of
protein
 Proteins: high
molecular weight
substances (found
in all living tissues)
 attached to the
same α-carbon

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AMINO ACID STRUCTURE
OH
+H N
3

C
R
O
R
BUILDING AN R GROUP
Glycine Alanine Phenylalanine Tyrosine
H
CH3
CH2
CH2
OH
• With an H, glycine is the simplest amino acid
• Alanine with a methyl group is the next simplest.
• Phenylalanine arises when a phenyl group replaces an H on alanine’s
methyl group
• Tyrosine evolves by adding an –OH group to the para position on the
phenyl ring of phenylalanine
Substances (found in all living
tissues)
Upon Acid, base or enzymes
catalyzed hydrolysis:
 Broken into thousands
of amino acids molecules
 Most proteins produce approximately 20 different αamino acids
 Amino Acids - have both an amino & a carboxylic acid
group attached to the same α-carbon
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FUNCTIONS OF AMINO
ACIDS
1. Building blocks of
proteins
2. Specific amino acids give
rise to specialized products:
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FUNCTIONS OF AMINO ACIDS
2. Specific amino acids give rise to
specialized products:
• TYROSINE forms thyroid hormones T3 T4 and
melanin
• TRYPTOPHAN can synthesize a vitamin called niacin
• GLYCINE, ARGININE AND METHIONINE synthesize
creatinine.
• GLYCINE and CYSTEINE helps in the synthesis of bile
salts.
• CYSTEINE and METHIONINE are sources of sulphur.
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LEARNING OBJECTIVES
State the composition and describe the
structure of amino acids.
Classify amino acids.
List essential, semi-essential and non-
essential amino acids.
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Classification and Structure
of Amino Acids
Neutral
Acidic
Basic
•Alipathic
•Aromatic
•Heterocyclic
•Sulphur containing amino acids
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LEARNING OBJECTIVES
State the composition and describe the
structure of amino acids.
Classify amino acids.
List essential, semi-essential
and non-essential amino acids.
11
ESSENTIAL AMINO ACIDS
8 Amino Acids not Synthesized by
the body & Therefore Must Be
Taken in the Diet
1.
Leucine
2.
Isoleucine
3.
Threonine
4.
Tryptophan
5.
Phenylalanine
6.
Valine
7.
Metheonine
8.
Lysine
Mnemonic
Pvt. Tim Hall
563 427 18
H – Histidine
A – Arginine
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ESSENTIAL AMINO ACIDS

Leucine

Isoleucine

Threonine

Tryptophan

Phenylalanine

Valine

Metheonine

Lysine
To Maintain The Proper
Nitrogen Balance In
The Body
DEFICIENCY
(1 or more)
CHILD: Growth failure
ADULT: decrease plasma
protein and hemoglobin
levels
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SEMI-ESSENTIAL AMINO
ACIDS

Histidine

Arginine
Synthesized
partially by the
body
But not at the rate
to meet the
requirement in
growing children,
pregnant and
lactating women
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NON-ESSENTIAL AMINO
ACIDS

Alanine

Aspartic acid

Serine

Proline
•Can be
synthesized by the
body
•May not be
required in the
diet
•Derived from carbon skeletons of
lipids and carbohydrates during
metabolism or from the transamination
of essential amino acids
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•
Complete or Adequate Proteins:
Animal Proteins- Supply all of the essential amino acids.
•
Incomplete Proteins:
Vegetable Proteins- Low in one or more of the essential amino acids
ANIMAL PROTEINS
SOURCE
TYPE OF CHON
MISSING AA
Egg
Complete
None
Milk (Dairy)
Complete
None
Meat, Fish
Complete
None
VEGETABLE PROTEINS
SOURCE
TYPE OF CHON
MISSING AA
Wheat
Incomplete
Lysine
Corn
Incomplete
Lysine &Tryptophan
Rice
Incomplete
Lysine
Beans
Incomplete
Methionine
&Tryptophan
Peas
Incomplete
Methionine
•The two vegetable proteins are called complementary proteins.
–Ex. Rice and Beans
-C-C-C-N-C-N
=
N+
Basic
Arg
R
N
-OH
Tyr
K
-C-C-C-C-NH3+
His
Phe
H
-C-C-CONH2
Asn
N
Gln
Q
Amide
F
Asp
D
Glu
E
Acidic
-C-COOH
Central line Gly G
Ala
-H
AA
Val
-C-C-COOH
V
C C
-C
-CH3
Ser
S
Cys
-C-C Thr
OH
T
Met M -C-C-S-C
-C-OH
Polar
Y
-C-CONH2
-C-
-C-C C
N N+
Non-polar
This is NOT a metabolic pathway
Trp W -C-C-
Lys
Amino Acid Subway Map
Aromatic
Hydroxy
Sulfur
Ile
Aliphatic
I
Leu
C
-C-C-C
C -C-SH
L
C
-C-C-C
C
C
C
HN C-COOH

Pro
P
Imino,
Circular
Classification of Amino Acids by Polarity
NONPOLAR
POLAR
Acidic
Asp
Neutral
Basic
Asn Ser
Arg
Cys
Tyr
His
Gln
Thr
Lys
Glu
Gly
Ala Ile
Phe Trp
Val Leu Met Pro
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