Glycosaminoglycans, Proteoglycans, and Glycoproteins Flashcards
What are glycosaminoglycans (GAGs)?
Large complexes of negatively charged heteropolysaccharide chain
-Generally associated with a small amount of protein (core protein), forming proteoglycans (which are 95% carbohydrate)
What special ability to GAGs have?
Bind large amounts of water, producing gel-like matrix basis of body’s ground substance
- Along with fibrous structural proteins and adhesive proteins -> make up the extracellular matrix (ECM)
- Viscous, lubricating properties of mucous secretions also result from presence of GAGs
Hydrated GAGs serve as ______ _______ for the ECM.
flexible support
Describe the structure of glycosaminoglycans.
Long, unbranched, heteropolysaccharide chains of a repeating disaccharide unit [acidic sugar-amino sugar]n
What is the amino sugar of a glycosaminoglycan?
D-glucosamine or D-galactosamine
-Acetylated -> eliminating positive charge
What is the acidic sugar of a glycosaminoglycan?
D-glucoronic acid or L-iduronic acid
-Carboxyl groups negatively charged -> strong negative nature
What produces the slippery consistency of mucous secretions and synovial fluid?
High concentration of negative charges -> chains extended in solution -> repel each other and are surrounded by a shell of water molecules
-When brought together, they slide past each other, much as 2 magnets
What contributes to the resilience of synovial fluid and the vitreous humor of the eye?
When a solution of GAG is compressed, the water is squeezed out and the GAG are forced to occupy a smaller volume
-When the compression is released, the GAG spring back to their original, hydrated volume because of the repulsion of their negative charges
How is hylauronic acid different from the 5 other major types of GAG?
All GAG, except for hylauronic acid, are sulfated and are found covalently attached to protein, forming proteoglycan monomers
Where are proteoglycans found?
In the ECM and on the outer surface of cells
What is the structure of a proteoglycan?
A monomer structures
- In cartilage consists of core protein + about 100 linear chains of GAGs
- Up to 200 disaccharide units
- Separated by charge repulsion
- Resemble a “bottle brush”
What are proteoglycan aggregates?
Many proteoglycan monomers can associate with one molecule of hyaluronic acid to form proteoglycan aggregates through ionic interactions (non-covalent)
-Stabilized by additional small proteins: “link proteins”
What are GAGs degraded by?
In lysosomes degraded by acid hydrolases
-Require a large number of acid hydrolases for complete digestion
What must first happen to GAGs to be degraded?
Must be engulfed by invagination of cell membrane because GAGs are part of ECM
What are mucopolysaccharidoses?
Hereditary diseases (1:25,000 live births) caused by deficiency of any one of the lysosomal hydrolases characterized by lysosomal accumulation of GAGs in various tissues -range of symptoms: skeletal and extracellular matrix deformities, and intellectual disability; severe cases, death in childhood
