Tech Essay #1

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Lens of the Eye (Tech Essay #1)

Description

(1) one cell type

(1) no blood supply

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

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

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

(1) over 1k layers of cells

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

(1) uniform index of refraction

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

(1) colorless

Development & Growth

Cataracts

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

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

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

Crystallin Proteins

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

(1) form complexes in paracrystalline arrangements

paracrystalline?

Apoptosis

(1) STUDIES

(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) Dahm

other possibilities

Subtopic

(1) lens proteins are resistant to degrading enzymes

(1) braking mechanism

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

well, duh, the mitochondria and ribosomes are being destroyed

(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) van Leyen

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

(1) Wride and Saunders

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

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

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

(1) Bassnett

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

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

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