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Amino Acids & Proteins (Biomedical Importance (Receptors: proteins in…
Amino Acids & Proteins
Biomedical Importance
Receptors
: proteins in cell membrane.
Transport
.
•
Mechanical support
: Structural proteins. •
Contracting muscles
:
Actin & myosin
.
Storage
:
ferritin
.
Hormones
are proteins in nature:
Respiratory
:
cytochromes, heamoglobin, & myoglobin
.
Defense
:
Immunoglobulin
.
Supply energy
: Catabolism.
Enzymes
are proteins.
Electrolyte & water balance
.
•
N Source
. • Main components in the
cytoskeleton
.
Functions of A.As
Detoxicants
:
glycine & cysteine
Transmethylation
:
Methionine
.
Source of S
:
Methionine & Cystine
.
Specific A.As give rise to specialized products.
Tyrosine >> thyroid hormones
Tryptophan >> niacin vitamin
Glycine, Arginine, & Methionine >> creatine.
Glycine & Cysteine >> bile salts.
Glycine, Cysteine, & Glutamate >> glutathione.
Glycine >> heme
Aspartic acid & Glutamine >> pyrimidines
Aspartic acid, Glutamine, Glycine, & Serine >> purine
some are converted to carbohydrates:
Glucogenic A.As
Monomeric constituents of proteins
Classification
Classification of A.As
Nutritional Classification of A.As
:
Essential
Trp
Val
Thr
Leu
Phe
Lie
Met
Lys
Semi-essential
Arg
Cys
Tyr
His
Non-essential
Ser
Ala
Pro
Asp
Gly
Asn (Asparagine)
Gln
Glu
Classification of A.As according to their reaction in solutions
:
Acidic:
Glu
Gln
Asp
Basic:
Hyl
Arg
Lys
Neutral:
Heterocyclic:
His
Trp
IminoAcids:
Pro
Hyp
Aromatic:
Phe
Tyr
Sulfur containing
Cys
Met
Aliphatic:
Leu
Lie
Val
Ser
Ala
Thr
Gly
Classification of Proteins
On the
shape & Size
:
Fibrous
: Length:width
>
10
α-keratin, collagen
Globular
: Length:width
<
10
myoglobin, heamoglobin, & ribonuclease
On
Functional
properties:
contractile
Respiratory
:
heamoglobin, myoglobin, & cytochromes
Defense
:
Immunoglobulins
Structural
Enzymes
Hormones
On
Solubility
and Physical properties:
Conjugated
contain prosthetic group
Muco-proteins/ Mucoids
simple protein + MPS (mucopolysaccharides). •contain (>4%) N-acetylated hexasamine.
#
Glycoproteins
simple protein + Carbohydrate moiety. •CHO bound +firmly than in Mucoproteins.
Nucleo-proteins
simple basic protein + nucleic acid.
Chromoproteins
simple protein + colored substance. •Haemoproteins: Heam: red.
ceamoglobin & cytochromes.
•Flavoproteins: Riboflavin: Yellow •Visual Purple: caroteinoid pigment: purple! (protein of the retina).
Phosphoproteins
simple protein + Phosphoric acids.
Lipooproteins
simple protein + Lipids.
Metalloproteins
simple protein + Metal ions.
Derived
formed from a native protein
1ry
denatured or coagulated.
2ry
formed by progressive hydrolysis at the peptide linkage.
Simple
yield only A.As on hydrolysis
Globulinss
•INsol. in: water. but sol. in dil. neutral salt soln. •Coagulate on heating.
Gliadins (prolamines)
•:check: Proline. •:red_cross: lysine. •INsol. in: water, salt soln, & absolute alcohol. But sol. in 50-80% ethanol.
Albumins
• :green_cross: deficient in glycine. • sol. in: water, dil. salt soln. • Coagulate on heating. >> become INsol. in water and salt slon.
Glutelins
plant proteins
•:check: rich in glutamic acid. •large molecules •INsol. in water & neutral salt soln. but sol. in: dil. (acids, alkalies) •Coagulate on heating.
Histones
• :check: Histidine & arginine. • sol. in: water, dil. (acids & salt soln). but INsol. in ammonia. alkaline isoelectric pH >> Basic proteins. • Coagulate on heating.
Scleroproteins/ Albuminoids
•fibrous •very stable. •low sol. •form animals supporting structures.
Keratins, Collagen, &Elastins.
Protainines
•:check: rich in arginine. •:red_cross: cysteine, tryptophan, & tyrosine. •small molecules •sol. in: water, dil. (acids, alkalies or ammonia) •isoelectric pH = 7.4 >> Basic proteins. •Non-coagulable by heat.
General Properties of Proteins
Tasteless.
Odorless
Large M.wt.
Visvosity vaies w/ kind &conc.
Fibrous (long) are +viscous than Glbular.
#
several proteins
Coagulate at high temp.
undergoes
Denaturation
during the coagulation.
max.coagulation & precipitation at the isoelectric pH.
Ampholytes
at isoelectric pH, protein exists as Zwitter ion.
General Properties of Peptides
Water soluble.
Un-coagulated by heat.
Not salted out of solutions
Can be precipitated by phosphotungstic acid.