Membrane Biochemistry: Cell Surface Oligosaccharides Quiz

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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. Signup and view all the answers

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. Signup and view all the answers

For D-sugars, how does the terminal -CH2OH group project in the Haworth perspective?

Upward. Signup and view all the answers

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. Signup and view all the answers

What is the relationship between galactose and glucose in terms of epimerism?

galactose is C-4 epimer of glucose Signup and view all the answers

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 Signup and view all the answers

How do glycosyltransferases facilitate the formation of glycosidic bonds?

They transfer carbohydrate monomers sugars from an activated donor to an acceptor molecule. Signup and view all the answers

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. Signup and view all the answers

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 Signup and view all the answers

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. Signup and view all the answers

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 Signup and view all the answers

What is the main difference between heparan sulfate and heparin?

Heparin is an intracellular form of heparan sulfate, mainly synthesized by mast cells Signup and view all the answers

Why do glycosaminoglycans, such as heparan sulfate, adopt an extended conformation?

the negatively charged groups repel eachother, resulting in a rod-like helical conformation Signup and view all the answers

What is the function of the glycocalyx on eukaryotic cells?

It's an information-rich carbohydrate layer extending from the cell surface Signup and view all the answers

What type of molecules are glycoproteins, proteoglycans, and glycosphingolipids?

Glycoconjugates Signup and view all the answers

What is unique about the structure of iduronic acid (IdoA) compared to other sugars?

It is an L-sugar, which is unusual Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

What is the function of proteoglycans in the extracellular matrix?

Act as tissue organizers, influence cellular processes such as attachment and growth factor activation Signup and view all the answers

How do proteoglycans attach glycosaminoglycans to their structure?

Covalently, to a SGxG consensus motif within the protein Signup and view all the answers

What is the mode of attachment for glypicans in membrane attached proteoglycans?

Via a GPI anchor Signup and view all the answers

How is the globular domain of glypicans stabilized?

By 7 conserved disulfide bonds Signup and view all the answers

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 Signup and view all the answers

How can Syndecans and Glypicans be released from the membrane?

Syndecans by proteolytic cleavage; Glypicans by a phospholipase Signup and view all the answers

how are polysaccarides different?

They are larger and can be found branched and unbranched. they can be made of a single or many sugars Signup and view all the answers

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) Signup and view all the answers

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 Signup and view all the answers

where can you find glycosaminoglycans

the extracellular matrix Signup and view all the answers

where is hyaluronate important

synovial fluid in joints Signup and view all the answers

where a keratan and chondroitin important

tendons and cartilage Signup and view all the answers

Explain the structural differences between glycoproteins, proteoglycans, and glycosphingolipids

-Glycoproteins are proteins modified by oligosaccharides <ul> <li>Proteoglycans have glycosaminoglycans attached to a “core protein” -Glycosphingolipids have oligosaccharides attached to sphingosine</li> </ul> Signup and view all the answers

what provides the attachment point for glycosaminoglycan

a tetrasaccharide linker Signup and view all the answers

what are the 2 membrane families that attach proteoglycans

<ol> <li>syndecans. 2. glypicans</li> </ol> Signup and view all the answers

explain a characteristic of a syndican

it has a single TM domain and, 3-5 heparan sulfates and sometimes chondroitin sulfate Signup and view all the answers

explain the characteristic of a glypican

they attach via a GPI anchor, 2-3 glycosaminoglycans attached near the membrane Signup and view all the answers

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 Signup and view all the answers

Where are mucins commonly found in the body?

On epithelial surfaces of the body, e.g. the gastrointestinal, genitourinary, and respiratory tracts Signup and view all the answers

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 Signup and view all the answers

What is the attachment site for N-linked oligosaccharides?

The amide N of asparagine in the consensus sequence Asn-X-Ser/Thr Signup and view all the answers

What is the first sugar added to N-linked oligosaccharides?

N-acetyl-glucosamine Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

How can mass spectrometry be used to identify oligosaccharides?

By differences in their mass, Signup and view all the answers

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. Signup and view all the answers

What is the limitation of mass spectrometry in the analysis of oligosaccharides?

Linkage sites and sugar chirality are not resolved. Signup and view all the answers

What is the main determinant of immunological reactivity?

O-specific chain Signup and view all the answers

What is the lipid A portion of some bacteria known as?

Endotoxin Signup and view all the answers

What are some applications of lectins?

ELISA measurements, glycoconjugate purification, cell selection or sorting, cell agglutination, enzyme assays Signup and view all the answers

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 Signup and view all the answers

What is the function of proteins called lectins?

Lectins are proteins that specifically recognize carbohydrates Signup and view all the answers

What is the function of fibronectin in the ECM?

binds heparan sulfate, collagen and integrins, linking the ECM to the cytoskeleton of the cell Signup and view all the answers

What is unique about the structure of glycoproteins compared to proteoglycans?

glycoproteins have smaller, branched, and structurally diverse glyans attached to the protein core Signup and view all the answers

What is the function of integrins in the ECM?

integrins bind fibronectin and interact with the cytoskeleton, linking the ECM to the cell Signup and view all the answers

What is the characteristic of O-linked oligosaccharides in glycoproteins?

O-linked saccharides connect the anomeric carbon to the –OH of Ser or Thr Signup and view all the answers

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 Signup and view all the answers

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. Signup and view all the answers

What is the role of Mannose-6-PO4 binding in the cell?

Targets proteins for degradation in the lysosome. Signup and view all the answers

How do lectin-ligand interactions benefit leucocytes?

Allow leucocytes to target inflammation. Signup and view all the answers

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. Signup and view all the answers

What are the neuraminidase inhibitors

oseltamivir and ZANAmivir Signup and view all the answers

How does influenza target the cell

by binding to the Neu5Ac containing oligosaccharide on the cell surface Signup and view all the answers

why is neuraminidase a useful drug?

it cleaves off sialic acids Signup and view all the answers

mode of action of neuraminidase inhibitors

his274tyr mutation weakens oseltamivir binding site modifying the shape of the binding site Signup and view all the answers