Carbohydrates and Glycoconjugates (5D) - MCAT Chemical and Physical Foundations of Biological Systems
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What is mutarotation in aqueous solution?
What is mutarotation in aqueous solution?
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Interconversion of $\alpha$ and $\beta$ anomers via the open-chain form. Mutarotation occurs as the ring opens to the linear form, allowing rotation at the anomeric carbon before re-closing.
Interconversion of $\alpha$ and $\beta$ anomers via the open-chain form. Mutarotation occurs as the ring opens to the linear form, allowing rotation at the anomeric carbon before re-closing.
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In a Haworth projection of a D-sugar, which direction does the $CH_2OH$ group point?
In a Haworth projection of a D-sugar, which direction does the $CH_2OH$ group point?
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Up. Haworth projections represent the cyclic form where the $CH_2OH$ is above the plane for D-sugars to match Fischer orientation.
Up. Haworth projections represent the cyclic form where the $CH_2OH$ is above the plane for D-sugars to match Fischer orientation.
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What determines D versus L configuration for a monosaccharide in a Fischer projection?
What determines D versus L configuration for a monosaccharide in a Fischer projection?
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The OH on the highest-numbered chiral carbon: right = D, left = L. In Fischer projections, the configuration at the penultimate carbon mirrors D/L-glyceraldehyde, determining the series for sugars.
The OH on the highest-numbered chiral carbon: right = D, left = L. In Fischer projections, the configuration at the penultimate carbon mirrors D/L-glyceraldehyde, determining the series for sugars.
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What is the difference between N-linked and O-linked glycosylation in proteins?
What is the difference between N-linked and O-linked glycosylation in proteins?
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N-linked: Asn amide N; O-linked: Ser/Thr hydroxyl O. N-linked glycosylation attaches via asparagine's nitrogen in the ER, while O-linked uses serine/threonine oxygens in the Golgi.
N-linked: Asn amide N; O-linked: Ser/Thr hydroxyl O. N-linked glycosylation attaches via asparagine's nitrogen in the ER, while O-linked uses serine/threonine oxygens in the Golgi.
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What are anomers, and which carbon is involved in their interconversion?
What are anomers, and which carbon is involved in their interconversion?
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Stereoisomers differing at the anomeric carbon. Anomers arise from cyclization at the carbonyl carbon, creating a new stereocenter that allows interconversion through ring opening.
Stereoisomers differing at the anomeric carbon. Anomers arise from cyclization at the carbonyl carbon, creating a new stereocenter that allows interconversion through ring opening.
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What is the anomeric carbon in an aldose versus a ketose (in cyclic form)?
What is the anomeric carbon in an aldose versus a ketose (in cyclic form)?
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Aldose: $C_1$; ketose: $C_2$. The anomeric carbon is the former carbonyl carbon that becomes chiral in the cyclic hemiacetal or hemiketal form.
Aldose: $C_1$; ketose: $C_2$. The anomeric carbon is the former carbonyl carbon that becomes chiral in the cyclic hemiacetal or hemiketal form.
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What is the definition of a reducing sugar?
What is the definition of a reducing sugar?
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A sugar with a free anomeric carbon (hemiacetal/hemiketal). Reducing sugars can open their ring to expose a free aldehyde or ketone group, enabling oxidation in reactions like Fehling's test.
A sugar with a free anomeric carbon (hemiacetal/hemiketal). Reducing sugars can open their ring to expose a free aldehyde or ketone group, enabling oxidation in reactions like Fehling's test.
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Identify whether sucrose is reducing or nonreducing.
Identify whether sucrose is reducing or nonreducing.
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Nonreducing. Sucrose lacks a free anomeric carbon due to its glycosidic bond involving both anomeric positions, preventing ring opening.
Nonreducing. Sucrose lacks a free anomeric carbon due to its glycosidic bond involving both anomeric positions, preventing ring opening.
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Which monosaccharide is an aldose and which is a ketose: glucose vs fructose?
Which monosaccharide is an aldose and which is a ketose: glucose vs fructose?
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Glucose is an aldose; fructose is a ketose. Glucose has an aldehyde group, classifying it as an aldose, while fructose's ketone group makes it a ketose.
Glucose is an aldose; fructose is a ketose. Glucose has an aldehyde group, classifying it as an aldose, while fructose's ketone group makes it a ketose.
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What is the relationship between D/L notation and optical rotation sign ($+$ or $-$)?
What is the relationship between D/L notation and optical rotation sign ($+$ or $-$)?
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No fixed relationship; D/L does not predict $+$ or $-$. D/L denotes relative configuration based on glyceraldehyde, independent of the direction of light rotation, which is an empirical property.
No fixed relationship; D/L does not predict $+$ or $-$. D/L denotes relative configuration based on glyceraldehyde, independent of the direction of light rotation, which is an empirical property.
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What is the definition of a carbohydrate in biochemical terms?
What is the definition of a carbohydrate in biochemical terms?
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Polyhydroxy aldehyde or ketone, or a compound yielding them. Carbohydrates are classified based on their polyhydroxylated carbonyl structure, which allows for hydration and energy storage functions in biology.
Polyhydroxy aldehyde or ketone, or a compound yielding them. Carbohydrates are classified based on their polyhydroxylated carbonyl structure, which allows for hydration and energy storage functions in biology.
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What is the functional group difference between an aldose and a ketose?
What is the functional group difference between an aldose and a ketose?
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Aldose: aldehyde at $C_1$; ketose: ketone (often at $C_2$). The carbonyl group's position and type define aldoses and ketoses, influencing their chemical reactivity and cyclic structures.
Aldose: aldehyde at $C_1$; ketose: ketone (often at $C_2$). The carbonyl group's position and type define aldoses and ketoses, influencing their chemical reactivity and cyclic structures.
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What distinguishes a proteoglycan from a glycoprotein?
What distinguishes a proteoglycan from a glycoprotein?
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Proteoglycan: mostly GAG carbohydrate; glycoprotein: mostly protein. Proteoglycans have extensive GAG chains dominating mass for structural roles, unlike glycoproteins with shorter oligosaccharides for signaling.
Proteoglycan: mostly GAG carbohydrate; glycoprotein: mostly protein. Proteoglycans have extensive GAG chains dominating mass for structural roles, unlike glycoproteins with shorter oligosaccharides for signaling.
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What is the key chemical feature of glycosaminoglycans (GAGs) that drives water retention?
What is the key chemical feature of glycosaminoglycans (GAGs) that drives water retention?
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High negative charge density (often sulfate and carboxylate groups). The anionic groups in GAGs attract cations and water via electrostatic interactions, enabling hydration in extracellular matrices.
High negative charge density (often sulfate and carboxylate groups). The anionic groups in GAGs attract cations and water via electrostatic interactions, enabling hydration in extracellular matrices.
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Which statement is correct: humans can digest starch, cellulose, both, or neither?
Which statement is correct: humans can digest starch, cellulose, both, or neither?
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Humans digest starch but not cellulose. Humans possess $\alpha$-amylase for starch's $\alpha$-linkages but lack cellulase for cellulose's $\beta$-linkages.
Humans digest starch but not cellulose. Humans possess $\alpha$-amylase for starch's $\alpha$-linkages but lack cellulase for cellulose's $\beta$-linkages.
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Which polymer is unbranched $\beta(1\rightarrow^4)$ glucose and forms structural fibers in plants?
Which polymer is unbranched $\beta(1\rightarrow^4)$ glucose and forms structural fibers in plants?
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Cellulose. Cellulose's linear $\beta$-linkages form hydrogen-bonded fibers providing plant cell wall rigidity, indigestible to humans.
Cellulose. Cellulose's linear $\beta$-linkages form hydrogen-bonded fibers providing plant cell wall rigidity, indigestible to humans.
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Which term describes two sugars that differ only at one stereocenter (not anomers)?
Which term describes two sugars that differ only at one stereocenter (not anomers)?
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Epimers. Epimers are diastereomers differing at a single asymmetric carbon, excluding the anomeric one, which distinguishes them from anomers.
Epimers. Epimers are diastereomers differing at a single asymmetric carbon, excluding the anomeric one, which distinguishes them from anomers.
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Which polymer is primarily $\alpha(1\rightarrow^4)$ glucose with $\alpha(1\rightarrow^6)$ branches in animals?
Which polymer is primarily $\alpha(1\rightarrow^4)$ glucose with $\alpha(1\rightarrow^6)$ branches in animals?
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Glycogen. Glycogen's branching structure facilitates rapid glucose release for energy in animals via enzymatic hydrolysis.
Glycogen. Glycogen's branching structure facilitates rapid glucose release for energy in animals via enzymatic hydrolysis.
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What monosaccharides and linkage define sucrose?
What monosaccharides and linkage define sucrose?
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Glucose + fructose with an $\alpha(1\rightarrow^2)\beta$ linkage. Sucrose's unique linkage joins glucose's anomeric carbon to fructose's, making it nonreducing and invert sugar upon hydrolysis.
Glucose + fructose with an $\alpha(1\rightarrow^2)\beta$ linkage. Sucrose's unique linkage joins glucose's anomeric carbon to fructose's, making it nonreducing and invert sugar upon hydrolysis.
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What disaccharide is composed of galactose + glucose with a $\beta(1\rightarrow^4)$ linkage?
What disaccharide is composed of galactose + glucose with a $\beta(1\rightarrow^4)$ linkage?
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Lactose. Lactose's $\beta(1\rightarrow^4)$ linkage between galactose and glucose is cleaved by lactase in the human digestive system.
Lactose. Lactose's $\beta(1\rightarrow^4)$ linkage between galactose and glucose is cleaved by lactase in the human digestive system.
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What disaccharide is composed of glucose + glucose with an $\alpha(1\rightarrow^4)$ linkage?
What disaccharide is composed of glucose + glucose with an $\alpha(1\rightarrow^4)$ linkage?
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Maltose. Maltose forms from starch breakdown, with its $\alpha(1\rightarrow^4)$ bond hydrolysable by human $\alpha$-amylase and maltase.
Maltose. Maltose forms from starch breakdown, with its $\alpha(1\rightarrow^4)$ bond hydrolysable by human $\alpha$-amylase and maltase.
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What disaccharide is composed of glucose + glucose with a $\beta(1\rightarrow^4)$ linkage?
What disaccharide is composed of glucose + glucose with a $\beta(1\rightarrow^4)$ linkage?
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Cellobiose (the repeating disaccharide unit of cellulose). Cellobiose's $\beta(1\rightarrow^4)$ linkage allows linear chaining in cellulose, which humans cannot hydrolyze due to lacking $\beta$-glucosidase.
Cellobiose (the repeating disaccharide unit of cellulose). Cellobiose's $\beta(1\rightarrow^4)$ linkage allows linear chaining in cellulose, which humans cannot hydrolyze due to lacking $\beta$-glucosidase.
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What linkage connects monosaccharides in oligo- and polysaccharides?
What linkage connects monosaccharides in oligo- and polysaccharides?
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Glycosidic bond (acetal/ketal linkage). Glycosidic bonds form via dehydration between an anomeric carbon and another sugar's hydroxyl, creating stable acetal linkages.
Glycosidic bond (acetal/ketal linkage). Glycosidic bonds form via dehydration between an anomeric carbon and another sugar's hydroxyl, creating stable acetal linkages.
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What type of bond forms when a monosaccharide cyclizes to a ring?
What type of bond forms when a monosaccharide cyclizes to a ring?
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Intramolecular hemiacetal (aldose) or hemiketal (ketose). Cyclization involves nucleophilic attack by a hydroxyl group on the carbonyl, forming a hemiacetal or hemiketal ring structure.
Intramolecular hemiacetal (aldose) or hemiketal (ketose). Cyclization involves nucleophilic attack by a hydroxyl group on the carbonyl, forming a hemiacetal or hemiketal ring structure.
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For a D-sugar in Haworth form, what defines the $b^1$ versus $b^2$ anomer?
For a D-sugar in Haworth form, what defines the $b^1$ versus $b^2$ anomer?
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$\alpha$: anomeric OH down; $\beta$: anomeric OH up. In D-sugars, the $\alpha$ anomer has the anomeric hydroxyl trans to the $CH_2OH$, pointing down, while $\beta$ is cis, pointing up.
$\alpha$: anomeric OH down; $\beta$: anomeric OH up. In D-sugars, the $\alpha$ anomer has the anomeric hydroxyl trans to the $CH_2OH$, pointing down, while $\beta$ is cis, pointing up.
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