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Chemical and physical features of proteins
3
+
2
Important terms
•ISOELECTRIC POINT (pI)
•ISOIONIC point
Protein classification according to the size
Classification of protein according to the size
Fewer than 50 aa called peptideMore than 50 is called protein
Insulin is 53 aa long Is it a peptide or protein hormone?
Protein sequence and structure
The protein seq can be directly retrieved from the corresponding gene sequence ?
True False
Protein primary structure
Amino acids are attached by .………………………These bonds are both planner and rigid
Can they rotate about their axis?
Protein secondary structure
Stabilized by hydrogen bonding and depends on the sequence of aa in the chain
Protein secondary structure
Some amino acids disrupt the secondary alpha helix structure :
Proline, isoleucin, tryptophan, asparagine
Do all proteins have secondary structures?
Yes
No
Tertiary structure
Stabilized by many types of bonds
-electrostatic bonds (-ve & +ve)
-Van der waals forces
-hydrophobic or hydrophillic attractions
Hbonds
Disulfide bridges
Quaternary structure
All proteins do posses quaternary structure ?
True
False
Quaternary structure
More than one polypeptide chains come together to form quaternary
structure
)we call the protein oligomeric(
Quaternary structure
Stabilized by the same types of bonds found in the tertiary structure
Disulfide bridges can be of two types :
Intrachain
Interchains
The one polypeptide chain in oligomeric protein is called..……… :
Oligomeric protiens
All subunits should be different
True
False
Oligomeric protiens
4 chains Heamoglobin
2 alpha and 2 beta
chians
Oligomeric protiens
On the otherhand, some proteins such as LDH enzyme is
composed of 4 identical subunits.
The final folded protein shapeDetermines the final function
of this protien
Protein folding
There are 2 main final shapes of folded proteins :
Globular proteins
fibrous proteins
Globular proteins
Spherical in their final shapeWater solubleContains mixture of α β and other random structuresEnzymes, transport proteins, hormones and antibodies
fibrous proteins
Are structural protiensWater insolubleBuilt of either α or β
Include cellulose fiber in the cell wall of plant cellsCollagen and elastin in humanKeratin in the hair and nailsChitin in the cuticle of some organisms
What you need to know to investigate the protein structure
I- Molecular mass determination:
1 -SDS-PAGE
2 -Exclusion chromatography
Size exclusion chromatography