Download aminoacids

Food
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Why food?
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Our body performs many processes and has
necessary infra-structure for this performance
Energy is needed to
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Perform these processes
Build necessary infra-structure
Sustain the molecular organization
Food provides this much needed energy
Aminoacids
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What is food
Food consists of six basic ingredients
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Carbohydrates
Lipids
Proteins
Vitamines
Minerals
Water
Aminoacids
Carbohydrates
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Include sugars and sugar polymers (starch
and glycogen) etc.
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Generally used for generation of energy
Some role in structure
Polymeric forms undergo digestion
Aminoacids
Lipids
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Include oils and fats etc
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Second most preferred source of energy after
carbohydrates
Some structural role e.g. biomembranes
Undergo digestion
Aminoacids
Proteins
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Undergo digestion to split into aminoacids
The least preferred role in energy generation
Perform a large number of roles, however,
major role in structure and catalysis
Aminoacids
Vitamins
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Cofactors for many enzymes
No role as energy substrate
No digestion (directly absorbed)
Aminoacids
Minerals
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Major role chemical reactions particularly
oxidation/reduction reactions
No digestion, directly absorbed
Aminoacids
Water
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Serve as solvent
No digestion, directly absorbed
Aminoacids
Proteins
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Proteins are made up of 20 different types of
aminoacids
Dietary proteins are digested to yield aminoacids
These aminoacids are absorbed by the intestine and
transferred to blood stream
Aminoacids enter into different body cells from blood
circulation
In cells, aminoacids are then bonded together to
from specific proteins (tissue /species specific)
These proteins then perform various but important
functions of the cell/body
Aminoacids
Aminoacids
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Aminoacids
Types of Aminoacids
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Protein & Non-protein aminoacids
(Standard & Non-standard aminoacids)
Protein Aminoacids are further classified on
the basis of
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The nature of their side chains
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Polar or non-polar
Aromatic or non-aromatic
Function groups (hydroxyl, thio, methyl-thio)
Capability of Synthesis (Essential or Non-essential)
Aminoacids
Definition
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Organic compounds containing an amino
and a carboxylic acid
Aminoacids
Building Blocks of Proteins
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Amino acids are the building blocks of
proteins
There are 20 different aminoacids used for
proteins synthesis in all living organisms
An α-amino acid consists of a
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central carbon atom, called the α carbon,
linked to
an amino group, the α amino group
a carboxylic acid group, the α carboxylic
group
a hydrogen atom, and
a distinctive R group called the side chain.
Aminoacids
Amino acid Isomers
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With four different groups α -amino acids are chiral
(except glycine)
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forms two mirror-image forms the L isomer and the D isomer
Aminoacids
Ionization of Amino Acids
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Only L amino acids are
used in proteins
Aminoacids are ionized
in solution
Aminoacids
Ionization of Amino Acids
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At acidic pH
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At neutral pH
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Amino group is protonated (NH3+)
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Carboxyl group is deprotonated (COO )
At basic pH
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Amino group is protonated (NH3+)
Carboxyl group is not deprotonated (COOH)
Amino group is not protonated (NH2)
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Carboxyl group is deprotonated (COO )
Aminoacids
General Formula of an Amino Acid
R= -H, -CH2, -CH2OH, C2H4OH etc
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Aminoacids
Side Chain Variations
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Size
Shape
Charge
hydrogen-bonding capacity
hydrophobic character
chemical reactivity
Aminoacids
Classification of Amino Acids
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Aminoacids
Uncharged (Non-Polar) Amino Acids
Uncharged (10)
Achiral (1)
G
Simple Chain(4)
AVLI
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Chiral (9)
Sulfur Cont. (2)
CM
Aromatic (2)
Phe T
Heterocyclic (1)
P
Aminoacids
Glycine
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Simplest amino acid
Side chain only a H atom
A chiral (optically inactive)
Aminoacids
Physiological Roles-Glycine
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Part of tripeptide coenzyme “Glutathione”, which protects –SH
group from oxidation
Takes part in synthesis of heme, purines and creatin
Detoxication of benzoic acid to make a soluble conjugate, the
hippuric acid
Formation of bile salts by conjugation to cholic acid (glyocholic
acid and glycochenodeoxycholic acid)
Can be converted to other aminoacids e.g. serine, which may be
converted to pyruvate (glucogenic aminoacid)
Glycine oxidase conver glycine into glyoxalic acid, which is
oxidized to form formic acid and oxalic acid
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Formic acid becomes a part of 1-carbon metabolism
Oxalic acid is excreted in urine
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Excess formation leads to “Hyperoxalurea” resulting in formation of Caoxalate which precipitates in urinary tract
Precipitation results in Urinary Calculi and Calcification of kidneys.
Aminoacids
Non-Polar Amino Acids
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Progressively larger side chains
Isoleucine contains an additional chiral center
Stabilize protein structure in aqueous solutions
Aminoacids
Physiological Roles-Valine
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Undergoes
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This results in the formation of
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transamination followed by
decarboxylation
isobytyryl-CoA ultimately converted into
Succenyl-Co-A, an intermediate of TCA
cycle
Aminoacids
Physiological Roles-Leucine
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Undergoes oxidative
transamination to ultimately form
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HMG-CoA may be converted into
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HMG-CoA
Cholysterol
Acetoacetate/Acetyl-CoA (so a
ketogenic aminoacid)
Aminoacids
Physiological Roles-Isoleucine
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Undergoes oxidative
transamination to form
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HMG-CoA may be converted into
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HMG-CoA
Cholysterol
Acetoacetate/Acetyl-CoA (so a
ketogenic aminoacid)
Aminoacids
Proline
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Imino acid
Heterocyclic: contains a pyrrole ring
(pyrrolidine derivative)
Side chain bonded to α amino group
Causes bends in protein structure
May form 4 hydroxyproline as a result
of post-transcriptional modification
perhaps only in collagen
A small proportion may also occur as
3-hydroxyproline too
Interchangeable with ornithine, thus it
can contribute to urea cycle
Can give rise to glutamate
Aminoacids
Sulfur Containing Amino Acids
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Met is always first amino acid of a nascent protein
Cys may be involved in forming disulfide bridges
Aminoacids
Sulfur Containing Amino Acids
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A disulfide bridges between to cysteines to form a
Cytine
Aminoacids
Aromatic Non-polar Amino Acids
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Phe is purely hydrophobic but Try is less so
Strongly absorb UV light (Amax 280λ)
Aminoacids
Phenylketonurea
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It is an autosomal recessive disorder
A disorder caused due to deficiency of phenylalanine
hydroxylase
Frequency 1 in 20,000
Blockage of conversion to tyrosine results in ~20 fold increase
in Phe.
Concentration of phenylpyruvate increases resulting in
excretion in urine
Addition of ferric chloride to urine turns it olive green
Phenylketonuric are severally mentally retarded, if not properly
treated
Low Phe diet is solution to the problem
Aminoacids
Classification of Polar Amino Acids
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Aminoacids
Charged Amino Acids
Charged (10)
Polar (5)
Hydroxyl group (3)
Basic (3)
Arg His Lys
Acidic (2)
Asp Glu
Amide group (2)
Asn Gln
Aliphatic (2)
Ser Thr
Aromatic (1)
Tyr
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Aminoacids
Polar aminoacids
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Aminoacids containing hydroxyl group
May be post-transcriptionally phosphorylated
Ser/Thr and Tyr phophorylation are very important in
Cellular
signaling
cell cycle regulation and tumor development
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Aminoacids
Serine
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Precursor for the synthesis of cysteine,
choline and cephalins
Takes part in the synthesis of nucleic acid
bases
Can be converted into glycine and pyruvic
acid
Serves as carrier of phosphorus in
phosphoproteins
Aminoacids
Threonine
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Can be converted into glycine
Can be converted in propionyl-CoA and then
to succinyl-CoA
Serves as carrier of phosphorus in
phosphoproteins
Aminoacids
Tyrosine
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Obtained from phenylalanine
Can be converted to dihydroxyphenylalanine
(DOPA) and Dopamine
Dopamine is precursor of catecholamines
(adrenaline and nor-adrenaline)
Tyrosine is also a precursor for T3 and T4
Skin pigment, melanin is also a produce to
tyrosine metabolism
Aminoacids
Basic Aminoacids
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Aminoacid group of these aminoacids gets
ionized in acidic pH range
They may make part of active site
Basic aminoacids include lysine, argenine
and histidine
Aminoacids
Lysine
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It is a basic aminoacid
It is among essential aminoacids
It does not allow α-helix to be
formed/continued
Aminoacids
Argenine
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Its hydrolysis yields urea
Takes part in urea cycle
Contributes in the formation of creatine
An essential aminoacid
Does not allow formation of α-helix
Aminoacids
Histidine
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Contains an imidazole ring
Near neutral pH the imidazole ring gets
charged
It is often found in the active site of enzymes
Imidazole ring can act as electron
acceptor/donor in an enzyme catalyzed
reactions
Aminoacids
Acidic aminoacids
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These aminoacids contain an additional
–COOH group
They get ionized in the basic pH range
Their side chains may act as proton acceptor
They may make part of active site of an enzyme
They may accept an amino group to become
amides i.e. asparagine and glutamine
Glutamine play important role in nitrogen
transport/urea cycle
Aminoacids
Essential Aminoacids
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Aminoacids
Aminoacids in special sources
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Non-protein aminoacids
May be a part of some molecules
Play important role in physiological functions
Aminoacids
1,2.
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Citruline and ornithine
Found in liver
Intermediates of urea cycle
Take part in conversion of NH3 to urea
NH2
H-N-(CH2)3-CH-COOH
C=O
NH2
H2N-(CH2)3-CH-COOH
Ornithine
NH2
Citrulline
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Aminoacids
3.
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β-alanine
Part of vitamin B (pantothenic acid)
H2N-CH2-CH2-COOH
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Aminoacids
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Pantothenic acid
A widely distributed vitamin
Make a part of co-enzyme A (Co-A)
Take part in a large number of metabolic reactions
CH3
O
CH2—C—CH—C—NH—CH2—CH2—COOH
OH
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CH3 OH
Aminoacids
5.
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γ-aminobutyric acid (GABA)
GABA is a neurotransmitter
Found in nervous tissue
H2N-CH2-CH2-CH2-COOH
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Aminoacids
6.
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Dihydroxyphenylalanine (DOPA)
A metabolite of phenylalanine and
tyrosine
L-DOPA is used in treatment of
Parkinsons Disease
OH
OH
Aminoacids
7.
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Homocystine
Formed by de-methylation of methionine
H
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Aminoacids
8.
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Iodinated aminoacids
Mono-iodotyrosine (MIT) and Di-iodotyrosine (DIT)
are intermediates in thyroxin synthesis
Tri-iodothyronine (T-3) and
Tetra-iodothyronine (T4) are thyroxins (thyroid
hormones)
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Aminoacids
The End
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Aminoacids