Download Amino Acids

Protein Chemistry
Ass.Prof./Naglaa Fathy Alhusseini
4/30/2017
Naglaa Alhusseini
1
Proteins chemistry
 Definition:
Proteins are organic nitrogenous compound of high molecular
weight, consisting largely or entirely of α-amino acids
united together by peptide linkages.
They are composed of carbon, hydrogen, oxygen and nitrogen,
many types of proteins may contain sulfur.
Nitrogen is a characteristic component of proteins, forming
about 16% of their weight.
4/30/2017
Naglaa Alhusseini
2
Functions of proteins:
 Synthesis of tissue proteins e.g., contractile
protein of muscles, collagen …etc...
 Synthesis of cell organelles as cell membrane
,receptors…….etc
 Synthesis of enzymes
 Synthesis of milk proteins.
 Synthesis of plasma proteins.
 Synthesis of protein hormones.
 Synthesis of nucleoproteins.
4/30/2017
Naglaa Alhusseini
3
Biological importance of proteins:













Fibrous or structural protein
Keratin- elastin
Collagen- reticulin
Muscle protein (Myocin and Actin)
Protein of cell membrane
Protein of cytoplasm
Functional protein
Enzyme
Hormones
Receptors
Igs
Plasma protein
Hemoglobin
4/30/2017
Naglaa Alhusseini
4
Questions
 1- What are the biological importance
of proteins?
 All the following are functional protein
EXCEPT
A.
B.
C.
D.
4/30/2017
Igs
enzyme
Collagen
Hemoglobin
Naglaa Alhusseini
5
Amino Acids
 Amino acid is an organic acid
containing one or more amino group
and carboxylic group (COOH)
 carboxylic group (COOH) and amino
group (NH2) are both attached to the
α-carbon
 They are the building units of protein.
4/30/2017
Naglaa Alhusseini
6
Hydrogen atom
H
carboxylic
group
side chain
radicle
R
a- carbon
atom
C
COOH
NH2
amino group
Representation of a Amino Acid
4/30/2017
Naglaa Alhusseini
7
 Amino acids found in proteins are of L-configuration, this
means that the amino group to the left and the hydrogen
to the right of the a-carbon
 D-amino acid
 L-amino acid
Isomerism of amino acids
4/30/2017
Naglaa Alhusseini
8
Functions of amino acids: Question
 Synthesis of structural and functional proteins.
 L-amino acid and their derivatives play a role
in intracellular functions as nerve impulse
transmission and regulation of cell growth.
 Biosynthesis of purines, pyrimidines, urea and
porphyrins.
 L-and D-amino acids are present in polypeptide
antibiotics secreted by microorganisms.
True or false ??
4/30/2017
Naglaa Alhusseini
9
Classifications:
Amino acids can be classified by
different classification:




Chemical classification.
Nutritional classification.
Metabolic classification.
Reaction classification (Charge
properties).
4/30/2017
Naglaa Alhusseini
10
1. Chemical classification:
A) Aliphatic amino acids: have no ring;
These amino acids may be subclassified
into:
 Branched chain amino acids: as valine,
leucine, and isoleucine.
 Hydroxy amino acids: as serine and threonine.
 Sulphur containing amino acids: as cysteine
and methionine.
 Amino acids with amide group: as
asparagine and glutamine.
4/30/2017
Naglaa Alhusseini
11
4/30/2017
Naglaa Alhusseini
12
Glycine
Gly - G
Alanine
Ala - A
Val - V
Valine
Leu – L
Leucine
Isoleucine
Ile - I
13
Serine
Ser - S
Threonine
Thr - T
Cysteine
Cys - C
Methionine
Met - M
Cystine
4/30/2017
Naglaa Alhusseini
14
Aromatic amino acids
Phenylalanine
Phe - F
Tyrosine
Tyr - Y
Tryptophan
Trp - W
4/30/2017
Naglaa Alhusseini
15
Heterocyclic amino acids: They have heterocyclic ring as
histidine, tryptophan, proline and hydroxyproline.
Proline
Hydroxy
proline
4/30/2017
Pro – P
Hyp
Naglaa Alhusseini
16
Reaction classification ( charge properties):
Non polar (Neutral): having equal number of amino
and carboxyl groups
e.g. alanine, serine, valine …etc
 Polar Basic AA: having more than one amino group
and one carboxyl
e.g. arginine, lysine, histidine …etc
 Polar (Acidic): having one amino group and two
carboxyl
e.g. glutamic acid and aspartic acid

4/30/2017
Naglaa Alhusseini
17
Polar Basic AA: having more than one amino group
and one carboxyl e.g. arginine, lysine, histidine
Arginine
Arg - R
Lysine
Lys - K
Histidine
His - H
4/30/2017
Naglaa Alhusseini
18
Acidic Amino Acids and their Amides
Aspartic Acid
Asp - D
Asparagine
Asn - N
Glutamic Acid
Glu - E
Glutamine
Gln - Q
4/30/2017
Naglaa Alhusseini
19
B) Aromatic amino acids: They have benzene
ring in their side chains like



Phenylalanine
Tyrosine
Tryptophan
C) Heterocyclic amino acids: They have
heterocyclic ring as



Histidine,
Tryptophan,
Proline and hydroxyproline.
4/30/2017
Naglaa Alhusseini
20
2. Nutritional classification:
They are classified into three groups:
 Essential amino acids: They are amino acids which
cannot be synthesized in the body and must be taken
in diet; phenylalanine, methionine, isoleucine, leucine,
lysine, valine, threonine and tryptophan.
 Semi essential amino acids: They are amino acids
required in the food of growing children not in the
food of adult as histidine and arginine.
 Non essential amino acids: can be synthesized
inside the body as glycine, alanine, serine, cysteine,
cystine, aspartic, tyrosine, glutamic, proline and
hydroxyproline
4/30/2017
Naglaa Alhusseini
21
Memory Aid for Essential Amino
Acids
Any Help In Learning These Little
Molecules Proves Truly
Valuable
Arginine –Histedine – Isoleosine
– Leosine – Threonine- LysineMethionine –PhyenylalanineTryptophan –Valine
4/30/2017
Naglaa Alhusseini
22
3. Metabolic classification:
According to their fate in the body they are
classified into three groups:
 Glucogenic amino acids: give glucose
inside the body as glycine, alanine, aspartic
and glutamic.
 Ketogenic amino acid: gives ketone
bodies as leucine.
 Glucogenic and ketogenic amino acids:
They give both glucose and ketone bodies
as lysine, tryptophan, tyrosine,
phenylalanine and isoleucine.
4/30/2017
Naglaa Alhusseini
23
Clinical importance of amino
acids and their derivatives









L-tyrosine is sometimes recommended by practitioners as
helpful for weight loss, clinical depression.
Dopamine derived from tyrosine is a neurotransmitter.
Thyroxine is an important thyroid hormone from tyrosine.
Gamma aminobutyric acid (GABA) derived from glutamic
acid; which is a neurotransmitter.
Cycloserine derived from serine is an anti-tuberculous drug.
Arginine stimulates the healing of burning wound and other
wounds.
Arginine together with lysine can limit herpes attacks
(bladders in the mouth) for people that carry this virus.
Cysteine can help to recover the damage by smoking and
alcohol.
Glutamine can give the mind new energy and can help to
prevent and treat inflammations of the large intestine.
4/30/2017
Naglaa Alhusseini
24
 Which of the following amino acid
is an acidic amino acid.




4/30/2017
Arginine
Aspartic acid
Lysine
Leucine
Naglaa Alhusseini
25
 Which of the following amino
acid is both neutral and aromatic
in nature?




4/30/2017
Alanine
Histidine
Plyenylalanine
Proline
Naglaa Alhusseini
26
 All amino acids which both
glucogenic and ketogenic are
essential amino acids EXCEPT




4/30/2017
Phenylalanine
Tyrosine
Glycine
Alanine
Naglaa Alhusseini
27
4/30/2017
Naglaa Alhusseini
28
4/30/2017
Naglaa Alhusseini
29
4/30/2017
Naglaa Alhusseini
30
4/30/2017
Naglaa Alhusseini
31
4/30/2017
Naglaa Alhusseini
32
4/30/2017
Naglaa Alhusseini
33
4/30/2017
Naglaa Alhusseini
34
4/30/2017
Naglaa Alhusseini
35
4/30/2017
Naglaa Alhusseini
36
Amino acid not found in
proteins:
Few amino acids are not found in proteins (non-protein amino acids)
 L-Ornithine is an intermediate of urea cycle . It is formed from
arginine
 L- citrulline is intermediate of urea cycle . It is formed from
ornithine
 Homoserine is an intermediate in methionine metabolism. It is
formed from serine.
 GABA: γ amino butyric acid :is an inhibitor neurotransmitter
 DOPA: Dihydroxyphenylalanine : Is formed from tyrosine and
precursor for biosynthesis of epinephrine and norepinephrine
 β alanine : occurs in coenzyme A , Pantothenic acid and it is also
formed during degeneration pyrimidine nucleotides
Selenocysteine is an amino acid containing selenium ( trace element). It
is considered as the 21st amino acid since it is coded by the stop
codon UGA. Examples of proteins containing selenocysteine are
glutathione peroxidase enzyme and 5'deiodinase .
4/30/2017
Naglaa Alhusseini
37
4/30/2017
Naglaa Alhusseini
38