PROTEIN
Characteristic of amino acid
Protein in our body
blood
hair and nails
brain and nerves
enzymes
muscles
cellular construction worker
antibodies
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cellular messenger
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Zwitterionic or dipolar ions
Can form isomers
chiral carbon
L enantiomer (clockwise) 
D enantiomer (anticlockwise) 
Protein Structure
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Function of amino acid
bulding lbocks of protein among the major function of amino acids
acting as chemical messenger
precursors of a variety of complex nitrogen
acting as metabolic intermediates
have two charge at pH 7 (amino group,+ve; carboxyl group, -ve)
secondary structure
tertiary structure
primary structure
quartenary structure
each amino acid is libked by peptide bond
exact and unique sequence of amino acid residue
the sequences of amino acids in the polypeptide
Classification of amino acid
cyclic amino acid
hydroxyl and sulfur containing amino acid
aromatic amino acid
basic amino acid
aliphatic amino acid
acidic amino acid and their amides
contains carcbons and hydrogens in R-group
unreactive; hydrophobic
5 proteinogenic
glycine(only achiral, smallest)
alanine
valine(branched amino acid)
leucine (branced amino acid)
isolucine (branched amino acid)
⬇
inreasing hydrophobicity
can absorbs UV light
amino acid
contains benzen-like ring structurte in R-group
phenylalanine
tyrosine, weak acid
tryptophan
an imino (2 degree amide) rather than amino acid
ring is not reactive
R group bonded to backbone nitrogen as well as to the alpha carbon
amino acid
non polar
proline
polar; positively charged
amino acid
arginine
histidine, pKa =6.5
lysine
both lys and Arg has pKa=10
positive charge at pH 6.0
more than 6.o, neutral
acidic;negatively charged; both Asp, Glu has pKa=4
amidic; cannot be ionised; uncharged
aspartate
glutamate
asparagine; amide of Asp
glutamine; Amide of Glu
characteristic depends on
chemical characteristic of amino acids
sequence of amino acid
number of amino acids
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general 3-diemensional form of local segments (or regular structure) in polypeptides chain stabilized by hygdrogen bonding
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alpha helix
beta pleated sheet
characteristic
rigid,rod-like shape
hydrogen bonding via H bond
a right handed helix
R-group of participating amino acids projected outward of helix
some amino acid cannot form alpha helix;eg: Gly, Pro, Glu,Asp, Trp
characteristics
peptide strands or sheets are arranged side by side, fully etended
each strand consist of amino acid residues arranged in zigzag fashion
H bond
parallel
anti-parallel (more stable)
group of alpha jhelices and beta sheets fold further and cross-link with one another to form a stable 3D shape
the function of protein depend on tertiery structure
forces that help to stabilize structure
hydrophobic interction
H bonding
ionic bonds
types of protein
fibrous
globular
hard; long and static;insoluble in water
eg: collagen, keratin, fibroin
compact;folded, containd groove, soluble in water
eg: haemoglobin, enzymes, antibody
the highest organizational level for some protein in which bonds are formed between different polypeptides chain
homo and hetero
stabilization forces similar to tertiary but between different polypeptides chains