Week 3 Flashcards
(145 cards)
What is a complex polysaccharide?
- Any oligosaccharide with more than one type of sugar residue
- usually attached to proteins, protein anchors or lipids
What does a glycotransferases do?
- Transfers a monosaccaride from a donor to an acceptor
- Donor - UDP, GDP, CMP, Dolichol
- Acceptor - protein, lipid, non-reducing end of another sugar
- glycotransferases are VERY specific for every aspect of the binding
What does glycosidases do?
- Removes a specific sugar reisdues with the help of H20
- Specific for the bond hydrolyzed
- Important for
- Producing final carbohydrate struture
- degrading carb structures in lysosome
Describe a N-Linked glycoprotein
- GlcNAc attached to a Asn
- specific site: Asn-X-Thr/Ser
- Common core: GlcNAc-GlcNAc-(mannose in triangle)
What is a dolichol and how is it used in glycoportein synthesis?
- an isoprenoid compound with 16-20 isoprene units embedded in ER membrane
- during the synthesis of N-linked glycoproteins it is attached to dolichol
How is a N-linked glycoprotein synthesized?
- GlcNAc is attached to dolichol on cytoplasmic side of ER
- Addictional glycosylation occurs then flipped to lumen of ER
- 4 mannose and 3 glucoses added
- Entire carbohydrate structure is transferred to Asn on a nascent protein
- glucoses removed then put in vesicles to golgi
What is the final processing of a N-linked glycoprotein?
- GlcNAc phosphate added
- packaged in vesicles and merge with lysosomes
- Trimming and addition of other sugars may occur goes through Golgi
- Diverse final products
- secreted or incorporated into membranes
Describe a O-linked Glycoprotein
- GalNAc attached to either Ser/Thr
- protein has to be assembled before it can be added
- other types
- O-mannosylation
- O-fucosylation
- Collagen: O-lined to 5-OH Lys
What is Type 1 Congenital Disorders of Glycosylation?
- Most common
- Problem occurs in the early steps in the synthesis of N-linked glycoproteins
What is type II congenital disorders of glycosylation?
- Enzymatic defects in N-glycan processing enzymes
What is Walker-Warburg syndrome? and type of glycosylation disorder is it?
- Walker is deficit in O-mannosyltransferase I
- caueses alpha-dystroglycanopathies (congential muscular dystrophy)
- example of O-linked glycosylation
What is the deficiency in a combined N- and O- glycosylation defect?
- CMP-sialic acid transporter deficiency
What is lysosomal storage disease?
- lysosomes contain exoglycosidases and endoglycosidases needed to break down glycoproteins and glycolipids
- if the lysomes are not working correctly, incomplete degraded compounds accumulate in tissues and urine
- results in hepatosplenomegaly, cataracts, and mental retardation
- very rare usually autosomally recessive
What is I-cell disease (mucolipidosis II)?
- defiency in GlcNAc-P glycosyltransferase
- enzyme marks lysosomal proteins for their destination
- lysosomal enzymes are instead secreted from cell and found in either the plasma or other body fluids
- glycoproteins are not degraded and accumulate in enlarged lysosomes
- severe psychomotor retardation, skeletal abnormalities, restricted joint movement, death by age 8
What are glycolipids built on mainly?
- build on sphingosine

What is ceramide?
- X is a H

What is a cerebroside?
If X is
- a single monosaccharide (glucose or galactose)
- most prevalent in neuronal cell membranes of brin
- esstenial to myelin structure and function
- occur in membranes of other tissues and is the precursor for most complex glycospingolipids

What is globoside?
If X
- has multiple monosaccharides that are neurtal
- Found in membranes of kidneys, RBCs, liver and spleen

What is a ganglioside?
If X is
- sialic acid (NANA) is present
- Most important Gm1, Gm2, Gm3
- Act as
- receptors for hormones and bacterial protein toxins
- determinants for cell-cell recognition

What is a sulfatide?
If x
- contains monosaccharidesulfates
- important Myelin constituent, white matter
- synthesized primary in oligodendrocytes
- found in the membranes of kidney, spleen and retina

How is cerebroside synthesized?
- made from ceramide
- synthesized on luminal surface of the ER and then switched to cytosolic side of Golgi apparatus and reach plasma membrane through vesicle flow
How are globosides and gangliosides synthesized?
- Synthesized by a series of specifc glycosyltransferases
- UDP-Gal + glucocerebroside -> lactosyl ceramide
- lactosyl ceramide is the precursor to both globosides and gangliosides
- Glycosyltransferases add remaining hexoses
What is Tay-Sachs Disease?
- Autosomal recessive defiency in hexoaminidase A
- Ganglioside GM2 accumulates as shell-like inclusions in lysosomes. Looks like a milky halo occurs around the fovea of eye due to a build up ganglioside
- red dot that develops in fovea is the result of the ganglion nerve death
What does glycocaylax with the microvilli?
- glycocaylax provide the final stages of protein and carbohydrate breakdown for absorption
- enzymes at the microvilli surface make sure the nutrients get absorbed immediately