Lens of the Eye (Tech Essay #1)

(1) lens cells are clear because they destroy their organelles during development

(1) apoptosis is halted leaving just the outer membrane, cytoskeleton, and crystalline plams

(1) STUDIES

(1) Bassnett

(1)As lens grows, inner lens cells become oxygen deprived

(1) cells (spec. the mitochondria of the cells) sense the lack of oxygen and this triggers apoptotic factors

(1) mitochondria have been shown to initiate apoptosis in other cell types

(1) Bassnett

lactic acid is produced by the mitochondria during their breakdown of glucose

(1) increasing concn. of lactic acid could trigger apoptosis

(1) Wride and Saunders

(1) tumer necrosis factor, cytokine (messenger protein), induces apoptosis

(1) van Leyen

(1) enxyme 15-lipoxygenase enters cell membrane and makes holes, which allows proteases to enter and degrade the organelles

(1) Dahm

(1) braking mechanism

(1) lens cell produces galectin-3 while it still has its organelles

(1) galectin-3 in also involved in tissue growth, apoptosis, and differentation in other tissues

(1)synthesis is reduced once the organelles start to degrade

well, duh, the mitochondria and ribosomes are being destroyed

other possibilities

(1) lens proteins are resistant to degrading enzymes

Subtopic

(1) Nishimoto

(1) DNAase, enzyme that destroys the lens DNA

(1) when absent in mice, the mice are born with cataracts and the lens nuclei breakdown never occurs despite the fact that apoptosis happens normally in all other tissues/cells

(1) form complexes in paracrystalline arrangements

paracrystalline?

(1) these are responsible for making the cytoplasm of the lens cell optically homogenous

(1) long term dehydration, oxygen free radicals, UV radiation, elevated blood sugar lead to cataracts

(1) after-cataracts: result from undifferentiated stem cells growing (in a disorganized manner) onto the lens implant

(1) aging; lens turns yellow b/c proteins that absorb blue and green light accumulate

(1) colorless

(1) over 1k layers of cells

(1) layers are parallel so that light passes through at the same angle for all of them

(1) uniform index of refraction

(1)cells interlock tightly so that light is not scattered as it passes over the cell boundaries

(1) consist of a cell membrane , cytoskeleton, and crystalline plasma

(1) organelles present at development, but degrade as the lens matures

(1) no blood supply

(1) molecules and ions, nutrients, etc diffuse over the membranes

(1) one cell type