Proteoglycans and glycoproteins Flashcards
What are glycoconjugates?
conjugate molecules of carbs + other molecules such as proteins and lipids
Glycoconjugate Classes
proteoglycans
glycoproteins
glycolipids
Functions of glycoconjugates
communication between cells and their extracellular surroundings
Name the 6 specific functions of glycoconjugates
- mediators of specific cell-cell interaction
- mediators of interaction between cell and ECM
- cell-cell recognition
- adhesion
- immune response
- wound healing
What are proteoglycans?
macromolecules of the cell surface of ECM
- 1 or more sulfated glycoaminoglycan chains are joined covalently to a membrane protein or a secreted protein
Glycosaminoglycans are ____________ of the extracellular matrix
heteropolysaccharides
How does the glycosaminoglycan chain bind to extracellular proteins?
through electrostatic interactions between the protein and the negatively charged sugar moieties on the proteoglycan
Proteoglycans are major components of
all extracellular matrices
Mammalian cells can produce at least
40 types of proteoglycans
Proteoclycans act as ______ ________, and they influence various cellular activities, such as ________ _______ ______ and ________.
tissue organizers, growth factor activation, adhesion
Most proteoglycans are secreted into the ____.
However, some are ____ _____ ______.
ECM
integral membrane proteins
Proteoglycans are major components of ______ ______ such as ________.
connective tissues
cartilage
What does the basic proteoglycan unit consist of?
a ‘core protein’ with covalently attached glycosaminoglycans
The point of attachment is a ___ _______, to which the glycosaminoglycan is joined through a __________ ______.
ser residue
tetrasaccharide bridge
What are smaller oligsaccharides usually attached to?
the core protein near its site of attachment to hyaluronate
Some proteoglycans can form
proteoglycan aggregates
What are proteoglycan aggregates?
enormous supramolecular assemblies of many glycosaminoglycan-decorated core proteins all bound to a single molecule of hyaluronan
What core protein is usually involved?
aggrecan
What does aggrecan do?
it binds multiple chains of chondroitin sulfate and keratin sulfate via covalent linkages to serine residues
Aggrecan interacts with ______ in the ECM of ______, contributing to the development, _____ strength, and resilience of this connective tissue.
collagen, cartilage, fensile
What is the ECM?
a strong and resilient meshwork containing proteoglycans in association with collagen, elastin, and fibronectin
What are glycoproteins?
Glycoproteins have 1 or several oligosaccharides of varying joined covalently to a protein
Where are glycoproteins?
usually found on the outer face of the plasma membrane
- ECM
- in the blood
Where are glycoproteins found inside cells?
they are found in specific organelles such as golgi complexes, secretory granules, and lysosomes
Glycoproteins are
carb-protein conjugates in which the glycans are branched +smaller + more structurally diverse than the huge glycosaminoglycans of proteoglycans
What are 2 classes of glycoproteins that occur in nature?
O-linked and N-linked glycoproteins
O-linked glycoproteins
the carb is attached at its anomeric carbon through a glycosidic linkage to the -OH group of a ser or Thr residue
N-linked glycoproteins
the carb is attached via an N-glycosyl linkage to the amide nitrogen of an Asn residue of the protein
About half of all proteins of mammals are
gllycosylated
What are examples of glycosylated secretory proteins?
immunoglobulins (antibodies) certain hormones (follicle-stimulating hormones and luteinizing hormone)
What are biological advantages of protein glycosylation?
improving the solubility of proteins
providing address labels directing targeting in cells and between tissues
protein folding
stabilization
In glycolipids and lipopolysaccharides, complex oligosaccharide chains are
attached to membrane-anchored lipid moieties
Plants and animals contain many types of
glycolipids and glycosphingolipids
What are gangliosides?
glycosphingolipids w/ complex oligosaccharide chains w/ sialic acid residues
What are gangliosides important for?
cell-cell recognition
some serve as receptors for the entry of bacterial toxins such as cholera toxin into mammalian cells
Other glycosphingolipds, the _______, contain oligosaccharide chains that serve as the ______ _______ ________.
globosides, blood group antigens
