Export your learner materials as an interactive game, a webpage, or FAQ style cheatsheet.
Unsaved Work Found!
It looks like you have unsaved work from a previous session. Would you like to restore it?
Total Categories: 6
A glycosidic bond exclusively links a carbohydrate molecule to another carbohydrate molecule.
Answer: False
Glycosidic bonds can connect a carbohydrate molecule to another carbohydrate molecule or to a non-carbohydrate molecule.
Glycosidic bonds are typically formed via the anomeric carbon of a saccharide and a hydroxyl group present on another molecule.
Answer: True
The formation of a glycosidic bond commonly involves the anomeric carbon of a saccharide and a hydroxyl group of another compound, such as an alcohol or another sugar.
A substance characterized by the presence of a glycosidic bond is termed an aglycone.
Answer: False
In naturally occurring glycosides, the term 'aglycone' refers to the non-carbohydrate portion of the molecule, while the carbohydrate portion is called the 'glycone'.
Within the structure of glycosides, the 'glycone' component represents the non-carbohydrate portion.
Answer: False
In glycosides, the 'glycone' refers to the carbohydrate residue itself, while the 'aglycone' is the non-carbohydrate moiety.
The anomeric carbon serves as the principal site involved in the formation of glycosidic bonds within saccharide molecules.
Answer: True
The anomeric carbon, derived from the carbonyl group of the open-chain monosaccharide, is the reactive center typically involved in the formation of glycosidic linkages.
What is the principal function of a glycosidic bond?
Answer: To connect a carbohydrate molecule to another group, which can be another sugar or a non-sugar molecule.
The primary role of a glycosidic bond is to link a carbohydrate moiety to another molecular entity, whether that entity is another carbohydrate or a non-carbohydrate compound.
Which chemical moieties are typically involved in the formation of a standard glycosidic bond?
Answer: The anomeric carbon's hemiacetal/hemiketal group and a hydroxyl group.
A standard glycosidic bond is typically formed through the reaction between the hemiacetal or hemiketal group of the anomeric carbon of a saccharide and a hydroxyl group present on another molecule.
Within the context of naturally occurring glycosides, what is designated as the 'aglycone'?
Answer: The non-carbohydrate portion of the molecule.
In a glycoside, the 'aglycone' refers specifically to the non-carbohydrate moiety that is attached to the carbohydrate part (the 'glycone') via the glycosidic bond.
What component of a glycoside molecule is designated as the 'glycone'?
Answer: The carbohydrate residue.
In the context of glycosides, the 'glycone' refers to the carbohydrate moiety itself, which is linked via the glycosidic bond to the 'aglycone' (the non-carbohydrate part).
What is the functional role of the anomeric carbon within a monosaccharide?
Answer: It is the carbon atom derived from the carbonyl group in the open-chain form, often participating in glycosidic bonds.
The anomeric carbon, originating from the carbonyl group of the open-chain form of a monosaccharide, is the key reactive site involved in the formation of glycosidic bonds.
The definition of a glycoside has been broadened to encompass linkages involving sulfur, nitrogen, and carbon atoms, extending beyond the traditional oxygen linkage.
Answer: True
The definition of glycosides has evolved to include linkages formed through heteroatoms like sulfur and nitrogen (thioglycosides, N-glycosides) and even direct carbon-carbon bonds (C-glycosides), not solely oxygen.
O-glycosidic bonds are characterized by a linkage established through a sulfur atom.
Answer: False
O-glycosidic bonds involve a linkage through an oxygen atom. Linkages through sulfur atoms are termed S-glycosidic bonds.
Thioglycosides are defined by the presence of an N-glycosidic bond.
Answer: False
Thioglycosides are characterized by an S-glycosidic bond, where a sulfur atom replaces the oxygen atom in the linkage. N-glycosidic bonds involve nitrogen.
According to IUPAC nomenclature, the term 'C-glycoside' is considered an accurate designation for compounds featuring a carbon-to-carbon linkage between the saccharide and the aglycone.
Answer: False
IUPAC discourages the term 'C-glycoside' as it implies a glycosidic linkage (typically involving a heteroatom) where there is instead a direct carbon-carbon bond.
Structures incorporating C-glycosyl linkages generally exhibit greater resistance to hydrolysis compared to O-, S-, or N-glycosidic bonds.
Answer: True
The direct carbon-carbon bond in C-glycosyl structures makes them significantly more stable and resistant to hydrolysis than glycosidic bonds involving oxygen, sulfur, or nitrogen.
C-glycosidic bonds are characterized by a direct carbon-to-carbon linkage, rendering them less stable than conventional O-glycosidic bonds.
Answer: False
C-glycosidic bonds, involving a direct carbon-to-carbon linkage, are generally more stable and resistant to hydrolysis than typical O-glycosidic bonds.
An S-glycosidic bond establishes a linkage for a carbohydrate through a sulfur atom, whereas an O-glycosidic bond utilizes an oxygen atom for this purpose.
Answer: True
S-glycosidic bonds involve a sulfur atom linking the carbohydrate moiety, contrasting with O-glycosidic bonds, which utilize an oxygen atom as the linking element.
A glycosylamine is characterized by an N-glycosidic bond, distinguishing it from a typical glycoside which commonly features an O-glycosidic bond.
Answer: True
A glycosylamine contains an N-glycosidic bond, where nitrogen serves as the linking atom, whereas a typical glycoside usually involves an O-glycosidic bond.
Which of the following is not enumerated as a type of linkage encompassed by the extended definition of glycosides?
Answer: P-glycosidic bonds (linking through phosphorus)
The extended definition of glycosides includes O-, S-, N-, and C-glycosidic linkages. P-glycosidic bonds are not typically included in this classification.
According to IUPAC, why is the designation 'C-glycoside' deemed problematic?
Answer: Because the linkage involves a direct carbon-to-carbon bond, not a heteroatom.
IUPAC discourages the term 'C-glycoside' because the term 'glycosidic' implies a linkage involving a heteroatom (like oxygen or nitrogen), whereas a C-glycosidic bond is a direct carbon-carbon linkage.
Which classification of glycosidic linkage generally exhibits the highest resistance to hydrolysis?
Answer: C-glycosidic bonds
C-glycosidic bonds, characterized by a direct carbon-carbon linkage between the sugar and the aglycone, are significantly more resistant to hydrolysis compared to O-, S-, or N-glycosidic bonds.
What characteristic differentiates a C-glycosidic bond from other prevalent glycosidic bond types, such as O- or N-glycosidic bonds?
Answer: It involves a direct carbon-to-carbon linkage.
C-glycosidic bonds are distinguished by a direct carbon-to-carbon linkage between the carbohydrate and the aglycone, unlike O-, S-, or N-glycosidic bonds which involve heteroatoms.
The differentiation between alpha (α) and beta (β) glycosidic bonds is fundamentally determined by the stereochemical configuration at the anomeric position of the saccharide.
Answer: True
The designation of alpha (α) or beta (β) for a glycosidic bond is based on the orientation of the substituent at the anomeric carbon relative to the ring structure, specifically its stereochemistry.
Attaining selectivity for specific glycosidic bond types, such as α versus β, is generally considered straightforward within glycosylation reactions.
Answer: False
Achieving high stereoselectivity for specific glycosidic bond types (α or β) is often challenging in glycosylation reactions due to factors like substrate specificity and reaction conditions.
Fluorine-directed glycosylations are predominantly employed to achieve alpha-selectivity.
Answer: False
Fluorine-directed glycosylations are typically utilized to achieve beta-selectivity, often by influencing the conformation of the transition state.
The anomeric effect generally promotes the formation of the beta (β) glycosidic bond.
Answer: False
The anomeric effect typically favors the formation of the alpha (α) anomer in glycosidic bonds, particularly in non-polar solvents or when the anomeric substituent is electronegative.
The Felkin-Ahn models are employed for the prediction of stereochemical outcomes in glycosylation reactions.
Answer: True
Models such as Felkin-Ahn (and related variants like Felkin-Ahn-Eisenstein) are utilized in the rational design of glycosylation reactions to predict and control stereochemical outcomes.
The anomeric effect typically favors the formation of the beta (β) isomer within glycosidic bonds, as exemplified by ethyl glucoside.
Answer: False
The anomeric effect generally favors the alpha (α) isomer in glycosidic bonds, such as in ethyl glucoside, due to stereoelectronic stabilization.
The gauche effect, influenced by the presence of fluorine, contributes to achieving alpha-selectivity in glycosylation reactions.
Answer: False
The gauche effect, particularly when influenced by fluorine substituents, is known to promote beta-selectivity in glycosylation reactions by stabilizing specific conformations.
By what criteria are alpha (α) and beta (β) glycosidic bonds differentiated?
Answer: By the stereochemistry at the anomeric position of the saccharide.
The distinction between alpha (α) and beta (β) glycosidic bonds is determined by the stereochemical orientation of the substituent at the anomeric carbon relative to the rest of the sugar ring.
What constitutes a principal challenge in achieving stereoselective glycosylation reactions (e.g., favoring α or β linkages)?
Answer: The high substrate specificity and activity of the pyranoside.
Achieving precise stereoselectivity in glycosylation reactions is challenging, partly due to the inherent substrate specificity and reactivity of the saccharide components, which can influence the reaction pathway.
By what mechanism do fluorine atoms contribute to achieving β-selectivity in glycosylations?
Answer: By influencing conformation through effects like the gauche effect.
Fluorine substituents can influence the conformational preferences of the sugar moiety, often through the gauche effect, which can stabilize transition states leading to beta-glycosidic bond formation.
In the context of glycosylation reactions, what is the significance attributed to the anomeric effect?
Answer: It influences the stereochemistry, often favoring the alpha (α) anomer.
The anomeric effect is a stereoelectronic phenomenon that influences the stability of different anomers, typically favoring the formation of the alpha (α) isomer in glycosidic bonds under certain conditions.
Nüchter et al. developed a microwave-assisted methodology for Fischer glycosidation, which yielded significant results.
Answer: True
Nüchter et al. introduced a microwave-assisted approach for Fischer glycosidation, achieving high yields and efficient synthesis.
The microwave-assisted Fischer glycosidation method developed by Nüchter et al. is limited to laboratory-scale synthesis.
Answer: False
The method developed by Nüchter et al. demonstrated scalability to multi-kilogram quantities, indicating its potential beyond laboratory-scale synthesis.
Vishal Y. Joshi et al. proposed the utilization of silver salts within a modified Koenigs-Knorr reaction.
Answer: False
Joshi et al. proposed using lithium carbonate as a promoter in the Koenigs-Knorr reaction, offering an alternative to the conventional use of silver or mercury salts.
The modified Koenigs-Knorr method proposed by Joshi et al. presents advantages, including the employment of less toxic reagents and the capability for reactions to proceed at ambient temperatures.
Answer: True
Joshi et al.'s modification of the Koenigs-Knorr reaction offers benefits such as reduced toxicity of reagents and the ability to conduct the synthesis at room temperature.
Sugar nucleotides function as activated intermediates for monosaccharides, preceding their integration into larger carbohydrate structures.
Answer: True
Monosaccharides are often activated by conversion into sugar nucleotides, which then serve as the donor substrates for glycosyltransferases in the synthesis of complex carbohydrates.
The application of glycosyltransferases for glycoside synthesis is frequently favored owing to their low cost and straightforward reaction conditions.
Answer: False
While glycosyltransferases are effective, they often require expensive starting materials and can be challenging to isolate, making cost and simplicity potential drawbacks rather than favored aspects.
De Winter et al. determined that ionic liquids were ineffective for the synthesis of alpha-glycosides catalyzed by cellobiose phosphorylase (CP).
Answer: False
De Winter et al. found that ionic liquids, particularly AMMOENG 101, were effective media for the cellobiose phosphorylase (CP) catalyzed synthesis of alpha-glycosides.
UDP and GDP exemplify nucleotide bases utilized in glycosylation processes.
Answer: False
UDP (uridine diphosphate) and GDP (guanosine diphosphate) are examples of sugar nucleotides, which act as activated sugar donors in glycosylation, not nucleotide bases themselves.
Protecting groups, such as peracetates, are applied to the hydroxyl groups of D-glucose to preclude side reactions prior to the formation of the glycosidic bond.
Answer: True
In synthetic strategies, hydroxyl groups on monosaccharides like D-glucose are often protected, for instance, by peracetylation, to prevent unwanted reactions and direct reactivity towards the anomeric center during glycosidic bond formation.
Nüchter et al.'s microwave-assisted Fischer glycosidation methodology was distinguished by its achievement of:
Answer: 100% yield and multi-kilogram scalability.
The microwave-assisted Fischer glycosidation developed by Nüchter et al. achieved complete yields (100%) and demonstrated scalability to multi-kilogram production levels.
What modification did Joshi et al. propose for the Koenigs-Knorr reaction in the synthesis of alkyl D-glucopyranosides?
Answer: Using lithium carbonate as a promoter.
Joshi et al. proposed using lithium carbonate as a promoter in the Koenigs-Knorr reaction for synthesizing alkyl D-glucopyranosides, offering an alternative to traditional heavy metal salts.
Which of the following constitutes an advantage of Joshi et al.'s modified Koenigs-Knorr methodology?
Answer: It uses less toxic reagents and can be done at room temperature.
The modified Koenigs-Knorr method by Joshi et al. offers advantages such as employing less toxic reagents (lithium carbonate) and enabling the reaction to proceed effectively at room temperature.
What role do sugar nucleotides fulfill in the biosynthesis of complex carbohydrates?
Answer: They serve as activated 'donor' forms of monosaccharides.
Sugar nucleotides function as activated precursors, providing monosaccharide units that are transferred by glycosyltransferases to acceptor molecules during the biosynthesis of complex carbohydrates.
What challenge is frequently encountered when employing glycosyltransferases for glycoside synthesis?
Answer: They require expensive starting materials.
A significant challenge in using glycosyltransferases for synthesis is the cost and availability of the activated sugar nucleotide donors, which are often expensive.
De Winter et al. employed cellobiose phosphorylase (CP) for alpha-glycoside synthesis predominantly within which medium?
Answer: Ionic liquids
De Winter et al. investigated and utilized ionic liquids as an effective medium for the synthesis of alpha-glycosides catalyzed by cellobiose phosphorylase (CP).
Glycoside hydrolases are enzymes primarily responsible for the formation of glycosidic bonds during biosynthetic processes.
Answer: False
Glycoside hydrolases (glycosidases) are enzymes that catalyze the hydrolysis, or breakdown, of glycosidic bonds, not their formation.
Glycoside hydrolases typically exhibit specificity, acting predominantly on either alpha- or beta-glycosidic bonds, rather than both.
Answer: True
The specificity of glycoside hydrolases, often targeting either alpha- or beta-linkages exclusively, is a key characteristic utilized in biochemical research and applications.
Glycosyltransferases facilitate the transfer of sugar units from acceptor molecules to activated sugar donors.
Answer: False
Glycosyltransferases transfer sugar units from activated sugar donors (e.g., sugar nucleotides) to acceptor molecules, not the other way around.
DNA glycosylases initiate the base excision repair (BER) pathway through the formation of N-glycosidic bonds.
Answer: False
DNA glycosylases initiate the base excision repair (BER) pathway by cleaving (hydrolyzing) the N-glycosidic bond of damaged bases, not by forming them.
Monofunctional glycosylases possess the capability to cleave N-glycosidic bonds through either a stepwise (S<sub>N</sub>1-like) mechanism or a concerted (S<sub>N</sub>2-like) mechanism.
Answer: True
Monofunctional glycosylases can employ two distinct mechanistic pathways for N-glycosidic bond cleavage: a stepwise S<sub>N</sub>1-like process or a concerted S<sub>N</sub>2-like process.
Ribonucleotides are typically subjected to hydrolysis via an S<sub>N</sub>1-like mechanism that involves an oxacarbenium ion intermediate.
Answer: False
Ribonucleotides are generally hydrolyzed via an S<sub>N</sub>2-like (concerted) mechanism, whereas deoxyribonucleotides often utilize an S<sub>N</sub>1-like mechanism involving an oxacarbenium ion.
The cleavage of N-glycosidic bonds mediated by DNA glycosylases constitutes a reversible reaction.
Answer: False
The cleavage of N-glycosidic bonds by DNA glycosylases is considered practically irreversible due to the potential for mutagenic and cytotoxic consequences if the process is not followed by repair.
Glycosyltransferases are indispensable for the synthesis of complex carbohydrates, achieved through the formation of glycosidic bonds.
Answer: True
Glycosyltransferases are the key enzymes responsible for catalyzing the formation of glycosidic bonds, thereby constructing complex carbohydrate structures.
The base excision repair (BER) pathway entails the action of DNA glycosylases, which cleave the N-glycosidic bond to facilitate the removal of damaged bases.
Answer: True
The base excision repair (BER) pathway is initiated by DNA glycosylases that specifically recognize and cleave the N-glycosidic bond of damaged or modified bases, thereby removing them from the DNA strand.
What is the principal function of glycoside hydrolases (glycosidases)?
Answer: To catalyze the breakdown (hydrolysis) of glycosidic bonds.
Glycoside hydrolases, also known as glycosidases, are enzymes whose primary function is to catalyze the hydrolysis (cleavage) of glycosidic bonds, playing a key role in carbohydrate metabolism.
Why is the specificity exhibited by glycoside hydrolases considered significant for researchers?
Answer: It enables the production of specific glycosides by targeting either α or β bonds.
The high specificity of glycoside hydrolases, often acting on either alpha- or beta-glycosidic bonds, is valuable for researchers aiming to selectively cleave or synthesize specific glycosidic linkages.
Which enzymes are accountable for the transfer of sugar units from activated donors to acceptor molecules?
Answer: Glycosyltransferases
Glycosyltransferases are the enzymes specifically responsible for catalyzing the transfer of sugar moieties from activated nucleotide-sugar donors to acceptor substrates, forming glycosidic bonds.
What function do DNA glycosylases fulfill in the repair of damaged DNA?
Answer: They catalyze the hydrolysis (cleavage) of the N-glycosidic bond in damaged bases.
DNA glycosylases are critical enzymes in DNA repair that initiate the base excision repair pathway by cleaving the N-glycosidic bond of damaged or modified nucleobases.
Why are the reactions catalyzed by DNA glycosylases regarded as practically irreversible?
Answer: Because the cleavage can lead to mutagenic and cytotoxic effects if not repaired.
The cleavage of the N-glycosidic bond by DNA glycosylases is considered practically irreversible because the resulting abasic site can lead to mutagenic or cytotoxic outcomes if not promptly repaired by cellular mechanisms.
Which statement most accurately delineates the role of glycosyltransferases?
Answer: They build complex carbohydrates by forming glycosidic bonds.
Glycosyltransferases are enzymes central to carbohydrate biosynthesis, responsible for catalyzing the formation of glycosidic bonds to construct complex oligosaccharides and polysaccharides.
Which represents a key distinction between the hydrolysis mechanisms employed for deoxyribonucleotides and ribonucleotides by glycosylases?
Answer: Deoxyribonucleotides typically use S<sub>N</sub>1 (stepwise), while ribonucleotides use S<sub>N</sub>2 (concerted).
A significant difference lies in their hydrolysis mechanisms: deoxyribonucleotides are often cleaved via an S<sub>N</sub>1-like pathway involving an oxacarbenium ion, whereas ribonucleotides typically undergo hydrolysis through an S<sub>N</sub>2-like concerted mechanism.
What is the principal function of enzymes such as glycosyltransferases and glycoside hydrolases in carbohydrate chemistry?
Answer: Glycosyltransferases form bonds, while hydrolases break them.
In carbohydrate chemistry, glycosyltransferases are responsible for the synthesis (formation) of glycosidic bonds, whereas glycoside hydrolases are responsible for their cleavage (breakdown).
Glucuronidation involves the conjugation of substances to glucuronic acid via glycosidic bonds, thereby enhancing water solubility.
Answer: True
Glucuronidation is a metabolic process where glucuronic acid is attached to various substances via a glycosidic bond, significantly increasing their hydrophilicity and facilitating excretion.
O-linked glycopeptides have demonstrated potential utility in enhancing peptide drug delivery across the blood-brain barrier.
Answer: True
Research indicates that O-linked glycopeptides possess favorable properties for crossing the blood-brain barrier, suggesting potential for improved drug delivery to the central nervous system.
The 'membrane hopping' mechanism elucidates the passive diffusion of O-linked glycopeptides, driven exclusively by Brownian motion.
Answer: False
The 'membrane hopping' mechanism proposes that O-linked glycopeptides cross membranes via discontinuities, not solely through passive diffusion driven by Brownian motion.
Within DNA, N-glycosidic bonds serve to link the nitrogen atoms of nucleobases to the anomeric carbon of the sugar moiety.
Answer: True
In nucleic acids like DNA, N-glycosidic bonds are formed by the covalent attachment of the nitrogen atom of a nucleobase to the anomeric carbon of the deoxyribose sugar.
Modifications occurring on nucleobases within DNA can serve to strengthen the N-glycosidic bond, thereby enhancing DNA stability.
Answer: False
Modifications to nucleobases often destabilize or damage the N-glycosidic bond, leading to lesions that threaten DNA integrity, rather than strengthening it.
The 'hop diffusion' process describes the movement of O-linked glycopeptides across membranes, attributed exclusively to random thermal motion.
Answer: False
The 'hop diffusion' model suggests movement facilitated by membrane discontinuities, not solely random thermal motion (Brownian motion).
Mammalian enzymes readily facilitate the degradation of O-glycosylated products, thereby diminishing the significance of O-glycosylation in metabolic pathways.
Answer: False
Mammalian enzymes do not readily degrade O-glycosylated products, which contributes to the significance of O-glycosylation in processes like Phase II metabolism and drug conjugation.
N-glycosidic bonds are integral to the structure of RNA and DNA, linking nucleobases to sugars, as observed in molecules like adenosine.
Answer: True
N-glycosidic bonds are fundamental in nucleic acids, connecting the nitrogen atom of a nucleobase to the anomeric carbon of the ribose or deoxyribose sugar, as seen in the formation of nucleosides like adenosine.
Unrepaired damage to N-glycosidic bonds within DNA can result in beneficial mutations.
Answer: False
Unrepaired damage to N-glycosidic bonds in DNA typically leads to detrimental mutagenic and cytotoxic effects, rather than beneficial mutations.
Glycosylation can enhance peptide drug properties by increasing clearance rates and reducing their half-life.
Answer: False
Glycosylation typically improves peptide drug properties by decreasing clearance rates and extending half-life, thereby prolonging their duration of action.
What is the pharmacological objective of glucuronidation?
Answer: To increase the water solubility of substances to aid administration or excretion.
Glucuronidation serves a crucial pharmacological purpose by increasing the hydrophilicity of various substances, thereby facilitating their excretion from the body or improving their administration characteristics.
What pharmaceutical advantage can O-glycosylation confer upon peptides?
Answer: Improved CNS permeability and extended half-life.
O-glycosylation of peptides can enhance their pharmaceutical profile by improving their ability to cross the blood-brain barrier and extending their biological half-life, leading to improved efficacy and dosing regimens.
The 'membrane hopping' mechanism, proposed for the central nervous system (CNS) penetration of glycopeptides, posits:
Answer: Movement facilitated by membrane discontinuities, not just Brownian motion.
The 'membrane hopping' mechanism suggests that glycopeptides penetrate membranes by exploiting transient discontinuities, combining free diffusion with movement between cellular compartments, rather than solely relying on random Brownian motion.
By what process are N-glycosidic bonds established within DNA molecules?
Answer: Through nitrogen atoms of nucleobases linking to the sugar's anomeric carbon.
In DNA, N-glycosidic bonds are formed when a nitrogen atom from a nucleobase covalently attaches to the anomeric carbon of the deoxyribose sugar.
What represents a significant consequence arising from nucleobase modifications associated with N-glycosidic bonds in DNA?
Answer: Formation of cytotoxic lesions threatening DNA cohesiveness.
Modifications to nucleobases can lead to the formation of cytotoxic lesions at the N-glycosidic bond, compromising DNA integrity and potentially leading to cellular dysfunction or disease.
The 'hop diffusion' model endeavors to elucidate how O-linked glycopeptides achieve:
Answer: Penetration across the blood-brain barrier.
The 'hop diffusion' model is proposed to explain the mechanism by which O-linked glycopeptides can effectively penetrate the blood-brain barrier, a critical step for CNS-acting therapeutics.
By what means can glycosylation enhance the pharmacokinetic properties of peptide-based pharmaceuticals?
Answer: By extending their duration of action and reducing clearance.
Glycosylation can improve the pharmacokinetic profile of peptide drugs by reducing their clearance rate and extending their biological half-life, thus prolonging their therapeutic effect.