Ocular Biochemistry - Lens Flashcards
What is the lens made up of
Crystallins - alpha and beta/gamma
What are alpha crystallins?
Heat shock proteins - prevent aggregation of unfolded proteins
- prevents cataract formation
How can light travel through the lens without distortion?
Regular lens fibre structures
Absence of membrane bound organelles
Uniform extracellular space between fibre cells
What is the function of microtubules in the lens
Stabilising fibre cell membrane
Transporting vesicles to apical and basal ends of elongating fibre cells
What allows the lens membranes to be rigid?
High level of cholesterol and sphingomyelin in plasma membranes of fibre cells
What is the most common membrane protein in lens fibre
MIP
What connects lens fibres cells
N-cadherin
This is linked to actin cytoskeleton by alpha an dbeta catenin
Tight adhesions holds fibres together reducing light scatter
Lens fibres jointed at apical and basal ends - by N-cadherin and vinculin
What protects lens from oxidative damage
Low oxygen tension around the lens
Glycolysis is main source of energy
Transferrin in aqueous humour binds iron and prevents it from reacting with H2O2 and releasing free radicals
Glutathione production by lens fibres (and imported from aq)
Ascorbix acid from aq
Catalase present
What is the result of solar radiation on lens fibre cells
UV light causes damage to lens fibres
Most absorbed by cornea
Free radical production
What does glutathione do?
Sulfhydryl group taht is readily oxidized
Diffuses to deeper lens fibres
How does ascorbic acid prevent oxidative damage
Oxidation of ascorbate by free radical prevents molecules causing damage elsewhere
What is the function of catalse
H2O2 –> H2O + O2
What is the function of glutathione peroxidase
Reudction of H2O2 and oxidation of glutathione
Which has more mitochondria superficial or deep lens fibres
Superficial
Deep uses glycolysis
Increased protein in deep
What happens to alpha crystallin with age
Alpha crystallin becomes less soluble towards the centre of the lens and functioning alpha crystallins binds to hydrophobic regions of ptoeins that are found in gigher molecular aggregates with age.
LEss alpha crystallin for chaperone duties - cataract formation
