Wednesday, October 20, 2010
Reminder: the midterm exam will take place tomorrow night starting at
in Baker 200, last names A – T
in Baker 219, last names U - Z
2. Re answer key to 2009 midterm exam on Blackboard: Windows users have
not been able to see the correctly formatted answer key graph for problem #13,
the Lineweaver-Burk question.
A new pdf version of the answer key solves this
problem, and is now up on Blackboard.
Carbohydrate roles in energy storage polymers and in structure
Glycosaminoglycans - The "proteoglycans" of the extracellular matrix are
made of proteins (the minor component) and heteropolysaccharide
glycosaminoglycans (major component).
The latter are polymers of repeating
Notice on page 165 that glycosaminoglycans (left side of page) are very
Thus, these molecules repel each other.
Being highly polar
and also charged, they bind lots of water.
They form a loose mesh.
immediately outside cells, this loose mesh allows all small molecules and even
many big molecules (proteins, hormones, for example) to penetrate to the cell
surface and bind to receptor proteins in the membrane.
In addition, glycosaminoglycans are “slippery,” since they bind a lot of water and
repel both each other and negatively-charged surfaces, and thus serve as
lubricating fluid in joints, and as mucous on other body surfaces.
Polysaccharides are not made from a template.
They are always linked
together by enzymes, with a different enzyme required for each different linkage.
Thus, size of polysaccharides is not strictly fixed.
Also, a given polysaccharide
does not have a complex sequence, like proteins, RNA, or DNA, since only a few
enzymes are involved in their synthesis.
We do not know the 3-d structure of polysaccharides very well.
Our methods for
characterizing the 3-d structure of polysaccharides, or even just the sequence,
are not as advanced as they are for proteins or nucleic acids.