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BHS 150.2 – Biochemistry II
Notetaker: Elisabeth Anderson
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Date: 1/14/2013, 1st hour
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Clicker Questions
o Q: Melanin functions in the RPE to
 A: Absorb extra light that is coming in to the retina
o Q: The apical infoldings increase surface area to provide more
 A: Area for transferring 11-cis-retinal to the rods and cones
o Q: In the retina, protection against lipid peroxidation is provided by
 A: Glutathione, Vitamin A, Vitamin E with Vitamin C
Metabolism of retina
o Shedding is a process where we have a turnover in the rods and cones
 Important because without this turnover rods and cones will not be able to respond
 Process measures how long a rod or cone keeps its disks
 Disks are where rhodopsin is and this detects light
 If those proteins gets damaged the only way to get rid of them is the shedding
process
 Studies done where a pulse of radioactive amino acids is given and collect data to see
how long it takes for radioactivity to travel to different locations
 Day 1: Radioactivity is in inner segments
o Amino acids are incorporated into opsin proteins
 Being made the most
o Incorporated into all proteins that are being made during that time
period
 As time moves on they are found in connecting cilium
o Radioactivity is being put into opsin by rER
o rER is pinching it off to the golgi
o Gogli is making any modifications and adding it in at the cilium
 Later in time it is found in the outer segment
 Being pushed closer and closer to RPE over time
 10-15 days after pulse a group of disks will be broken off and taken up by the
RPE and recycled
 When the rod makes opsin protein it is taking in radioactivity so it can be
recycled and reused to have active opsin protein again
 Heavy turnover in rods and cones that need to be supplied
 To make opsin protein you need lots of amino acids in retina
 To make more disks you need lots of lipids and energy
o Retina has very high energy demand for production and phototransduction
 It is important that the retina has a good supply of oxygen and mechanisms that it is able
to make ATP
 Aerobic glycolysis is high in retina
 Lots of krebs cycle and mitochondria
 Oxygen is usually available from choriocapillaris
 LDHK is regulated primarily by oxygen availability
 Makes sure aerobic glycolysis is moving forward as quickly as possible
 Finely tuned by oxygen levels
 Similar LDH to ones found in cancer cells
o Retina takes advantage of it
 Regardless of what oxygen levels are pyruvate is switched to lactate and back
and forth very quickly
 Uses combination of oxygen with pyruvate concentrations to keep process
moving very quickly
 Pentose phosphate pathway is also highly active in retina
 Need NADPH for lipids
 Need for ribose 5 phosphate productions
 Need NADPH for glutathione recycling
 Need for membrane production
BHS 150.2 – Biochemistry II
Notetaker: Elisabeth Anderson
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Date: 1/14/2013, 1st hour
Page2
Diabetes
 Why do diabetics have neovascularization?
 Increased chance of new blood vessels growing in retina
o are very leaky and weak
 Blood vessels in retina are very tortuous looking
o Not solid nice blood vessels
 Apparent problem is glycation of collagen
o High blood sugar
 Collagen is exposed to a lot of glucose leading to glycation of
collagen framework
 Covalent linking of collagen makes extracellular matrix of
basement membrane thicker
 Thick basement membranes lead to decreased oxygen
diffusion
 Regions of oxygen deprivation
 Cells of retina really don’t like this because of their high
energy demand
 RPE releases HIF (Hypoxia Inducible Factor)
 Stimulates neovascularization
 Stimulates the release of vascular endothelial growth
factor (VEGF) from capillary endothelium
 VEGF is a substance that says “I need more
endothelial cells because the cells I have are not
getting enough oxygen. I need more blood vessels in
this area”
 VEGF works with a tyrosine kinase
 Tyrosine kinase phosphorylates cells so they start to
divide very rapidly
 Getting new endothelial cells and new blood vessels
 The endothelial cells don’t have the time to make
thick solid extracellular matrix to support blood
vessels because they are differentiating so quickly
 Takes longer than it takes for endothelial cells to
divide
 Without the support of extracellular matrix the
vessels leak in an area where there should be a lot of
tightness
 The leaking leads to edema which can alter vision
 Leads to blood being released out to the vitreous
which can alter vision
 Vessels aren’t providing the oxygen that we need still
so more HIF and VEGF are continually released and
more cell division and neovascularization occurs
 This is not helping oxygen demands
 Not a big problem when neovascularization is in
periphery but becomes more of a problem when in
macula where central vision is affected
 Treatment is to close off these new vessels before
they can leak
 Lasers will hit all cells in the area that may be
providing a lot of visual information as well as the
leaky cells
 Need better technique that won’t do as much damage
with the lasers
BHS 150.2 – Biochemistry II
Notetaker: Elisabeth Anderson
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
Date: 1/14/2013, 1st hour
Page3
Age related macular degeneration
o A misbalance between supply and demand
o The supply through the RPE gets downgraded
 Drusen are areas in the RPE where you get extracellular deposits
 Deposits of lipids, proteins, calcium
 Separate RPE from rods and cones so you can’t get nutrients to and from rods and cones
 Loss of supply but demand hasn’t changed
 Not sure what causes Drusen
 Decrease of metabolism ability
 Could be genetic
 Could be a buildup of aging cells
 Do know it leads to cell death of RPE and rods and cones
 Macular pigment may slow it down
 Vitamins may slow it down
 Not sure who is susceptible to it or not
 Tends to run in some families but not always
 There is a push that as you reach a certain age you might want to take more
antioxidants
 Not sure that it will help slow down onset
 Can slow down progression of it from stage 2 to 3 or 3 to 4
 Can slow moderate impairment from becoming severe impairment
 There is a lot of research going on about it
Phototransduction
o In the diagrams solid grey=inactive, gray with white shading=active
o For example Rhodopsin is inactive at this point
o Transducin is G protein
 Has GDP on it when it is inactive
o Phosphodiesterase
 Breaks down cyclic GMP compound to 5’ GMP
 4 subunits
 Gamma subunits are regulatory subunits
o When they are away from alpha and beta it is active
o When they are attached to alpha and beta it is inactive
o Guanylate cyclase
 Uses GTP to make cyclic GMP
 Rods and cones use a lot of GMP
 Cyclic GMP binds to cyclic GMP sensitive channel that allows sodium and calcium into
the cell the cell
o Cation exchanger is always active
 Moves sodium and calcium out of the cell and potassium into the cell
 Keeps sodium and calcium concentrations from getting too high
o In the dark:
 We have what is known as a dark current
 Cyclic GMP channel is open/active creating dark current
 It is called a current because sodium is moving in and depolarizing the cell
 Calcium moving in permits the release of neurotransmitters
 When we have current we are releasing glutamate
 What causes the channel to be opened?
 Guanylate cyclase is active which is making cyclic GMP which is making these
channels open
 Phosphodiesterase that breaks down cyclic GMP is inactive
 Transducin is inactive
 Rhodopsin is inactive sitting there with 11-cis retinal on it
 Because rhodopsin is inactive transducin is inactive
BHS 150.2 – Biochemistry II
Notetaker: Elisabeth Anderson
Date: 1/14/2013, 1st hour
Page4
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Because trandsucin is inactive phosphodiesterase is inactive
Because phosphodiesterase is inactive cyclic GMP is being made keeping the
channels open
o Sodium and calcium are coming in
o Releasing glutamate at synaptic terminal
o Cation exchanger is working to make sure there isn’t too much sodium
and calcium inside the cell keeping the current going