67 Questions
What is the chemical formula for simple sugars?
(CH2O)n
Which sugars are important for mammalian cell surfaces among the D-aldohexoses?
Glucose, galactose, and mannose
What is the relationship between mannose and glucose in terms of epimerism?
Mannose is the C-2 epimer of glucose
How can you determine if a sugar is D- or L- in Fischer projections?
Sugars are D- if the bottom-most chiral OH is on the right, and L- if it is on the left.
What structural changes occur during sugar cyclization, converting from Fischer projections to Haworth perspectives?
Conversion from linear structures to rings, forming either hemiacetals or hemiketals.
For D-sugars, how does the terminal -CH2OH group project in the Haworth perspective?
Upward.
How is the anomeric OH positioned in the ring in relation to the CH2OH to distinguish β from α configurations?
Anomeric OH on the same side as CH2OH is β; on the opposite side from CH2OH is α.
What is the relationship between galactose and glucose in terms of epimerism?
galactose is C-4 epimer of glucose
What is the typical size of oligosaccharides, and what are their structural characteristics?
Oligosaccharides typically have less than 20 sugar groups (typically 14 unit), are non-repetitive, and branched. one of four sugars are use: glucose, galactose, mannose and Neu5Ac
How do glycosyltransferases facilitate the formation of glycosidic bonds?
They transfer carbohydrate monomers sugars from an activated donor to an acceptor molecule.
What are the common components of glycosaminoglycans, and how are they typically modified?
Glycosaminoglycans are linear polymers of repeating disaccharide units, consisting of a sugar (GlcNAc or GalNAc) and a uronic acid, often sulfated.
What are the structural differences between hyaluronate, chondroitin, and keratan?
Hyaluronate: GlcA(b1-3)-GlcNAc(b1-4) (unsulfated), chondroitin GlcA(b1-3)-GalNac4S (b1-4), Keratan Gal(b1-4)- GlcNac6S(b1-3) it has minimal -ve charge
What is the role of the extracellular matrix, and which components are involved?
It holds the cell together and provides porous pathway for diffusion, comprising fibrous proteins and glycosaminoglycans.
What is the characteristic feature of heparin that makes it an effective anticoagulant?
High charge density due to the presence of sulfate and carboxyl groups
What is the main difference between heparan sulfate and heparin?
Heparin is an intracellular form of heparan sulfate, mainly synthesized by mast cells
Why do glycosaminoglycans, such as heparan sulfate, adopt an extended conformation?
the negatively charged groups repel eachother, resulting in a rod-like helical conformation
What is the function of the glycocalyx on eukaryotic cells?
It's an information-rich carbohydrate layer extending from the cell surface
What type of molecules are glycoproteins, proteoglycans, and glycosphingolipids?
Glycoconjugates
What is unique about the structure of iduronic acid (IdoA) compared to other sugars?
It is an L-sugar, which is unusual
What are the main characteristics of NS domains in heparan sulfate?
NS domains are heavily sulfated, they are typically 3-8 disaccharides long, iduronate replacing glucuronate.
How do the binding pockets for heparan sulfate in thrombin and antithrombin facilitate their interaction?
The binding pockets are rich in positively charged Arg and Lys residues, which electrostatically attract the negatively charged regions of heparan sulfate.
What is the difference between NA and NS domains in heparan sulfate?
NA domains have little sulfation and contain glucuronate, whereas NS domains are highly sulfated and contain iduronate.
What is the function of proteoglycans in the extracellular matrix?
Act as tissue organizers, influence cellular processes such as attachment and growth factor activation
How do proteoglycans attach glycosaminoglycans to their structure?
Covalently, to a SGxG consensus motif within the protein
What is the mode of attachment for glypicans in membrane attached proteoglycans?
Via a GPI anchor
How is the globular domain of glypicans stabilized?
By 7 conserved disulfide bonds
What activates proteoglycan shedding, and what are some roles of this shedding?
activated in cancer cells; Involved in cell-cell recognition & adhesion, cell proliferation & differentiation
How can Syndecans and Glypicans be released from the membrane?
Syndecans by proteolytic cleavage; Glypicans by a phospholipase
how are polysaccarides different?
They are larger and can be found branched and unbranched. they can be made of a single or many sugars
what are sialic acids? What structure does it form?
they are N- or O- derivatives of Neuraminic acid. It forms Pyran rings (leaving a 3 Carbon hydroxylated tail)
what are the donors and the acceptors when GT transfers sugars
donors: a molecule w a phosphate on the anomeric C acceptors: saccharide, protein, small molecule
where can you find glycosaminoglycans
the extracellular matrix
where is hyaluronate important
synovial fluid in joints
where a keratan and chondroitin important
tendons and cartilage
Explain the structural differences between glycoproteins, proteoglycans, and glycosphingolipids
-Glycoproteins are proteins modified by oligosaccharides
- Proteoglycans have glycosaminoglycans attached to a “core protein” -Glycosphingolipids have oligosaccharides attached to sphingosine
what provides the attachment point for glycosaminoglycan
a tetrasaccharide linker
what are the 2 membrane families that attach proteoglycans
- syndecans. 2. glypicans
explain a characteristic of a syndican
it has a single TM domain and, 3-5 heparan sulfates and sometimes chondroitin sulfate
explain the characteristic of a glypican
they attach via a GPI anchor, 2-3 glycosaminoglycans attached near the membrane
What determines in part the human blood groups O, A, and B?
The oligosaccharide head groups of specific sphingolipids on the plasma membrane of red blood cells
Where are mucins commonly found in the body?
On epithelial surfaces of the body, e.g. the gastrointestinal, genitourinary, and respiratory tracts
What is the function of mucins in the body?
To shield the epithelial surfaces against physical and chemical damage and protect against infection by pathogens
What is the attachment site for N-linked oligosaccharides?
The amide N of asparagine in the consensus sequence Asn-X-Ser/Thr
What is the first sugar added to N-linked oligosaccharides?
N-acetyl-glucosamine
How can the sequence of monosaccharide residues in an oligosaccharide be determined?
Using exoglycosidases of known specificity to remove one sugar at a time, and based on the specificity, determining the terminal sugar and linkage of that sugar.
What is the purpose of exhaustive methylation in the characterization of oligosaccharides?
To convert all free OHs to acid-stable methyl ethers, allowing for the identification of glycosidic linkages.
How can mass spectrometry be used to identify oligosaccharides?
By differences in their mass,
What information does acid hydrolysis of a methylated oligosaccharide provide?
The location of glycosidic linkages, as any free OHs in the released sugars were involved in those linkages.
What is the limitation of mass spectrometry in the analysis of oligosaccharides?
Linkage sites and sugar chirality are not resolved.
What is the main determinant of immunological reactivity?
O-specific chain
What is the lipid A portion of some bacteria known as?
Endotoxin
What are some applications of lectins?
ELISA measurements, glycoconjugate purification, cell selection or sorting, cell agglutination, enzyme assays
What role do cell surface carbohydrates play in communication between cells and their surroundings?
communication between cell and surrounding, Label proteins for transport to specific cellular locations, label malformed proteins
What is the function of proteins called lectins?
Lectins are proteins that specifically recognize carbohydrates
What is the function of fibronectin in the ECM?
binds heparan sulfate, collagen and integrins, linking the ECM to the cytoskeleton of the cell
What is unique about the structure of glycoproteins compared to proteoglycans?
glycoproteins have smaller, branched, and structurally diverse glyans attached to the protein core
What is the function of integrins in the ECM?
integrins bind fibronectin and interact with the cytoskeleton, linking the ECM to the cell
What is the characteristic of O-linked oligosaccharides in glycoproteins?
O-linked saccharides connect the anomeric carbon to the –OH of Ser or Thr
What is the function of aggrecan core protein in the ECM?
aggrecan core protein is decorated with multiple chondroitin and keratan chains, contributing to tensile strength and resilience of connective tissue
How do lectins interact with sugars?
The polar side of sugars can hydrogen bond with lectins, while the less polar side interacts with non-polar amino acid residues.
What is the role of Mannose-6-PO4 binding in the cell?
Targets proteins for degradation in the lysosome.
How do lectin-ligand interactions benefit leucocytes?
Allow leucocytes to target inflammation.
Ricin, a potent toxin found in castor beans binds to GalNAc residues of cell surface oligosaccharides via a lectin to enter eukaryotic cells. A treatment for ricin poisoning is administration of GalNac itself or the oligosaccharide containing GalNac. Explain how this could be an effective treatment.
By flooding the system with free GalNAc or GalNAc-containing oligosaccharides, these molecules can competitively bind to the ricin's lectin domain instead of the cell surface oligosaccharides.
What are the neuraminidase inhibitors
oseltamivir and ZANAmivir
How does influenza target the cell
by binding to the Neu5Ac containing oligosaccharide on the cell surface
why is neuraminidase a useful drug?
it cleaves off sialic acids
mode of action of neuraminidase inhibitors
his274tyr mutation weakens oseltamivir binding site modifying the shape of the binding site
Test your knowledge on cell surface oligosaccharides, cell identity, and the extracellular matrix in the context of membrane biochemistry. Questions cover essential topics from Lehninger Chapter 7 and the Essentials of Glycobiology, including sugars, D-aldohexoses, and the importance of glucose, galactose, and mannose for mammalian cell surfaces.
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