Lecture 11 Part 2 - Composition Flashcards
When does viscosity increase?
When proteoglcyans are linked onto the hyaluronic acid, but the complex is not stable you can dissociate it
How could there be a drop in viscosity?
If the proteoglcyans join the short chain of hyaluronic acid instead of the long chain, short chain is the same as free protein
How can proteoglycan aggregates be investigated?
Using gel filtration
What is gel filtration?
A whole series of beads in a column, the beads have holes in them. If you have a small molecule and put it on the top of the column the beads will fit through the hole. If you out something big it can’t go through the beads so will flow around the outside
Where would the proteoglycan come out in gel filtration?
It would come out the VO - volume void as it is too big
Can you make the proteoglycans smaller?
Can chop the top off, still has G1 and a little bit of glycosylation
How much HA (hyaluronan) is present in cartilage?
1% in vivo concentration
What is an example for the mechanism of aggregation?
Pulse chase
What is the pulse?
The radioactive sulphur (35S)
At the end of the pulse mechanism what should you end up with?
Sulphating proteoglycan culture chondrocytes
What do chondrocytes contain?
A lot of core protein
How can you inhibit protein synthesis?
By cycloheximide by interfering with the translocation step
How can you interfere with aggregation?
If you add 10-20 HA - not stable aggregate
How many sugars do you need to be able to bind both a proteoglycan and a link protein?
More than 20 sugars, you need 26-30 sugars to form a stable molecular aggregate
What is the major function of aggregation?
When the proteoglycans are immobilised in the collagen matrix as aggregates
What needs to happen if you want to take the proteoglycans out?
Need to deaggregate them
How much in ml will a proteoglycan occult in solution?
30-50ml
What can disrupt aggregation?
A high ionic solvent will disrupt the interaction
What is an example for a high ionic solvent?
You can use calcium chloride
How are proteoglycans restrained from swelling by?
By the collagen meshwork ‘a swelling pressure’
What happens if collagen was removed from the matrix?
The proteoglcyans would expand and form a gel
What happens in oesteroarthitis to the collagen network?
The collagen network relaxes which enables the proteoglycans to expand more
What can the hydrated proteoglycan be?
They can be reversible compressed by displacement of some of the water from their hydration shells
What is an Intramolecular force?
When the proteoglcyans are too close together - the hydration cells overlap
What happens when you apply a load to the intermolecular force?
You will squash the proteoglycans even closer together and will push the hydration spheres even closer together
What happens when you remove the load?
The proteoglycans will spring back up and take the water back up - reversible compressibility
What happens to the fluid in cartilage when load is applied?
The fluid will be displaced from the domains of the proteoglycans at that point
What is the redistribution of fluid like when pressure is applied?
Is slow because the proteoglycans are trapped in the collagen meshwork
What type of effect is caused when cartilage is under pressure?
Cartilage only deforms gradually under pressure is it is a damping effect
What happens in SOKKOLOFF’S experiment with the addition of Lanthanium chloride?
It causes precipitation of proteoglycans
What destroys proteoglycans in Thomas experiment?
Papain - causes loss in cartilage support function
What is versican?
It is a chondroitin sulphate proteoglycan that is helpful in the brain to prevent damage by compressive forces
What happens in the receptive stage? Embryo implantation?
You lose mUC1 expression - means that heparin sulphate binding sites at the apical surface of the uterine become accessible
