9. Wrist short notes on: a. crystallins and b. laminin.
Crystallins are the most abundant lens proteins, constituting 80 to 90% of the soluble protein of the eye lens.
The abundance and close packing of the crystallins allow the lens to focus an image onto the retina with minimal distortion and also explain the transparency of the lens. 
Three types of crystallins are identified in mammals, a, b and g but recently b and g have been grouped together as bg crystallins.
The different cystallins differ in their molecular weights and their ability to aggregates.
The ratio of different crystallins changes with age.

Laminin is a adhesion glycoprotein than forms an integral part of basement membrane.
It is prominent in basal lamina and underlies epithelium and endothelium.
It is a cross-shaped trimer in which the B1, B2 and A chains form a triple helix in the stem of the cross. 
It is bound tightly to nidogen, a protein that mediates the binding of laminin to heparin containing proteoglycans.

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