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Amino acids chemistry
Dr. Almoeiz Yousif
MS.c.,Ph.D.,MEE
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Introduction:
• Amino acids are the building unit of proteins.
• There are than 300 amino acids found in nature.
• only 20 are usually found in proteins.
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Structure
• The general structure of amino acids includes an amino
group and a carboxyl group, both of which are bonded to
the α-carbon (the one next to the carboxyl group).
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• The α -carbon is also bonded to a hydrogen and to the side
chain group, which is represented by the letter R. The R
group determines the identity of the
• particular amino acid
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Physical and chemical properties
• 1- Most amino acids are soluble in water , have a sweet
taste and some are widely used in food industry .
• 2- they are optically active .
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• 3- Amino acids are considered as amphpolytes (bipolar), this
is due to presence of both amino and acidic groups
• 4- In aqueous or physiological conditions . Thy are found in the
form of zwitter ion (di polar).
• 5- they can act as buffers
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D& L amino acids:
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Classification of amino acid • We have four systemic classification of amino acid
according to:
• 1.Side chain.
• 2.solubilty .
• 3. Nutritional classification .
• 4. Metabolic classification.
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Amino Acids with Aliphatic R-Groups
Glycine Alanine Valine
Leucine Isoleucine Thursday, April 23, 2020 10
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Non-Aromatic Amino Acids with Hydroxyl R-Groups
Sulfur containing Amino acids
Serine Threonine
Cysteine Methionine Thursday, April 23, 2020 11
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Acidic Amino Acids and Their Amides
Aspartic Acid Asparagine
Glutamic Acid Glutamine Thursday, April 23, 2020 12
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Basic Amino Acids
Arginine Lysine
Histidine Thursday, April 23, 2020 13
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Aromatic Amino Acids
Phenylalanine Tyrosine
Tryptophan Thursday, April 23, 2020 14
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Proline
Imino Acid
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Classification by solubility
•There are two broad classes of amino acids
based upon whether the R-group is
1. Hydrophobic
2. Hydrophilic.
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The hydrophobic amino acids
The hydrophobic amino acids tend to repel the
aqueous environment and, therefore, reside
predominantly in the interior of proteins.
The side chain of this class of amino acids does not
ionize nor participate in the formation of H-bonds.
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The hydrophilic amino acids
The hydrophilic amino acids tend to interact with the
aqueous environment; polar or charged side chain.
They are often involved in the formation of H-bonds
They are predominantly found on the exterior surfaces of
proteins or in the reactive centers of enzymes
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Dietary Classification of Amino Acids
Some amino acids can be formed from metabolic
intermediates in the mammalian cells, thus are not
necessary taken in food (Dietary non-essential) .
Other amino acids must be obtained from diet, thus they
are termed (Dietary essential)
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peptide pond
• In proteins, amino acids are joined covalently by peptide
bonds, which are amide linkages between the α-carboxyl
group of one amino acid and the α-amino group of another.
For example, valine and alanine can form the dipeptide
valylalanine through the formation of a peptide bond
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• Peptide bonds are not broken by conditions that denature
proteins, such as heating or high concentrations of urea.
Prolonged exposure to a strong acid or base at elevated
temperatures is required to hydrolyze these bonds
nonenzymically.
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peptide pond
• Peptide bond formation is a condensation reaction leading
to the polymerization of amino acids into peptides and
proteins.
• Peptides are small consisting of few amino acids.
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Important of peptides
• Enzymes, many hormones, antibodies, antitumor agents
and neurotransmitters are peptides.
• Proteins are polypeptides of greatly divergent length and
amino acid composition.
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Formation of peptide bond
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Protein chemistry
• Definition
• Proteins are polymers of amino acids linked by peptide bond.
Proteins are formed of a set of 20 amino acids.
They are called standard amino acids.
There are more than 300 amino acid in nature, only these 20 amino acids
are found in protein from all living sources (bacteria, animal and plant).
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Importance of protein:
• 1- enzymes
• hormones
• 3- structural
• 4- transport
• 5- immunoglobulin's
• 6- clotting factors
• 7- complements
• 8- buffers
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Protein Structure
• Primary : linear sequence of amino acids
• Secondary: localized folding
• Tertiary: overall 3-D structure
• Quaternary: association of 2 or more protein subunits into a
protein
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Levels of structure in proteins
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1.Primary structure
no non-covalent bonds. Only peptide bonds
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2.Secondary Structures
• The two very important secondary structures of proteins
are:
• a-helix
• b-pleated sheet
• Both depend on hydrogen bonding between the amide H
and the carbonyl O further down the chain or on a parallel
chain.
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Secondary Structure – Alpha Helix
• Held by H bonds between the H of –N-H group and the –O of C=O of the fourth amino acid along the chain.
• Looks like a coiled “telephone cord”
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b-Pleated Sheet
• All of the carbonyl O and amide H are involved in the H bonds with the chain nearly completely extended.
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Two possible orientations
Parallel
Antiparallel
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3.Tertiary Structure
• • 3D folding of the protein
• Non-covalent bonds found
• • Non-polar residues are buried inside, polar
residues are exposed outwards to aqueous
environment
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Interactions Involved in Tertiary Structure
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4.Quaternary Structure
• • Association of more than
• one polypeptides
• • Each unit of this protein is called as a subunit
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Level of Proteins structure
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Protein Denaturation
• is the breakdown of all non-covalent bonds in a protein, causing loss of function.
• Disruption of secondary, tertiary and quaternary protein structure. Does not alter primary structure
-caused by changes in:
-pH
-temperature
-salt concentration
-heavy metal ions
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