Flashcards in Schegg: Carb Metabolism III Deck (74)
What are complex polysaccharides?
an oligosaccharide with more than one type of sugar residue
Types of complex polysaccharides
Formation of complex polysaccharides dependent on two important classes of enzymes
These transfer a saccharide from a donor to an acceptor
donor-glycose + acceptor --> glycose-acceptor + donor
Glycosyltransferases are very specific for these four things:
1. sugar transferred
3. the site
4. anomeric linkage formed
These remove specific sugar residues
Also very specific for the bond hydrolyzed
Proteins which contain one or more saccharide bound covalently to protein
About what percent of all eukaryotic proteins are glycosylated?
Glycoproteins are all synthesized on the rER via the (blank) pathway
How much of a glycoprotein is sugar?
What do the carbohydrate (sugar) portions of glycoproteins look like?
Usually less than 12-15 residues
What is the distribution of carbohydrates on glycoproteins?
Sometimes evenly distributed across the protein, sometimes in a defined area
Glycoproteins are important for four things
1. cell membranes
2. mucus constituents
3. secreted hormones
4. plasma proteins
T/F: Cell surface glycans are the first molecules encountered by anything that approaches the cell
Two basic types of glycoproteins
1. N-linked to Asn
2. O linked to Ser or Thr
N-linked glycoproteins have complex structures, but all have (blank) as first sugar residue
The final structure of N-linked glycoproteins can be one of three types
The common core from N-linked oligosaccharides is assembled on (blank) as a lipid-linked polysaccharide
N-linked glycoproteins begin on the cytoplasmic side of the ER, accept GlcNAc, get glycosylated, and then are flipped into the (blank), where they are then transferred to a (blank) on a protein being synthesized.
ER lumen; Asparagine
After glucoses are removed in the ER, N-linked glycoproteins are moved in vesicles to the (blank) and then one of two things happens. They are either (blank) or sent to (blank).
golgi; secreted or in membranes; lysosomes
In (blank) glycoproteins, the protein is synthesized, folded, and moved to the golgi before saccharide units are added.
Product formed in O-linked glycosylation depends on what?
number and type of glycosyltransferases in a cell
In (blank), saccharides are also O-linked to 5-OH Lys
O-linked highly glycosylated glycoproteins that are secreted or membrane-bound
They can form gels that lubricate, provide chemical barriers and hold water
The oligosaccharide chains of mucin are often sulfated and contain (blank)
Disorders of N-linked glycosylation
Type 1: most common, involves early steps in the synthesis of N-linked glycoproteins
Type 2: enzymatic defects in N-glycan processing
Most common disorder of N-linked glycosylation
-involves early steps in the synthesis of N-linked glycoproteins
enzymatic defects in N-glycan processing enzymes
The most common defect in N-linked glycoprotein synthesis is a deficit in (blank)