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