Carbohydrates and Glycoconjugates (5D) - Chem & Physics

What is mutarotation in aqueous solution?

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.
What are anomers, and which carbon is involved in their interconversion?

Stereoisomers differing at the anomeric carbon. Anomers arise from cyclization at the carbonyl carbon, creating a new stereocenter that allows interconversion through ring opening.
Which polymer is unbranched $\beta(1\rightarrow^4)$ glucose and forms structural fibers in plants?

Cellulose. Cellulose's linear $\beta$ -linkages form hydrogen-bonded fibers providing plant cell wall rigidity, indigestible to humans.
What is the definition of a carbohydrate in biochemical terms?

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.
What determines D versus L configuration for a monosaccharide in a Fischer projection?

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.
What is the difference between N-linked and O-linked glycosylation in proteins?

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.
Which polymer is primarily $\alpha(1\rightarrow^4)$ glucose with $\alpha(1\rightarrow^6)$ branches in animals?

Glycogen. Glycogen's branching structure facilitates rapid glucose release for energy in animals via enzymatic hydrolysis.
What is the functional group difference between an aldose and a ketose?

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.
Which statement is correct: humans can digest starch, cellulose, both, or neither?

Humans digest starch but not cellulose. Humans possess $\alpha$ -amylase for starch's $\alpha$ -linkages but lack cellulase for cellulose's $\beta$ -linkages.
What linkage connects monosaccharides in oligo- and polysaccharides?

Glycosidic bond (acetal/ketal linkage). Glycosidic bonds form via dehydration between an anomeric carbon and another sugar's hydroxyl, creating stable acetal linkages.
What is the anomeric carbon in an aldose versus a ketose (in cyclic 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.
What is the key chemical feature of glycosaminoglycans (GAGs) that drives water retention?

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.
What monosaccharides and linkage define sucrose?

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.
What is the definition of a reducing sugar?

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.
What distinguishes a proteoglycan from a glycoprotein?

Proteoglycan: mostly GAG carbohydrate; glycoprotein: mostly protein. Proteoglycans have extensive GAG chains dominating mass for structural roles, unlike glycoproteins with shorter oligosaccharides for signaling.
Identify whether sucrose is reducing or nonreducing.

Nonreducing. Sucrose lacks a free anomeric carbon due to its glycosidic bond involving both anomeric positions, preventing ring opening.
What is the relationship between D/L notation and optical rotation sign ( $+$ or $-$ )?

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.
What disaccharide is composed of glucose + glucose with an $\alpha(1\rightarrow^4)$ linkage?

Maltose. Maltose forms from starch breakdown, with its $\alpha(1\rightarrow^4)$ bond hydrolysable by human $\alpha$ -amylase and maltase.
What type of bond forms when a monosaccharide cyclizes to a ring?

Intramolecular hemiacetal (aldose) or hemiketal (ketose). Cyclization involves nucleophilic attack by a hydroxyl group on the carbonyl, forming a hemiacetal or hemiketal ring structure.
Which monosaccharide is an aldose and which is a ketose: glucose vs fructose?

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.
For a D-sugar in Haworth form, what defines the $b^1$ versus $b^2$ anomer?

$\alpha$ : 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.
What disaccharide is composed of galactose + glucose with a $\beta(1\rightarrow^4)$ linkage?

Lactose. Lactose's $\beta(1\rightarrow^4)$ linkage between galactose and glucose is cleaved by lactase in the human digestive system.
Which term describes two sugars that differ only at one stereocenter (not anomers)?

Epimers. Epimers are diastereomers differing at a single asymmetric carbon, excluding the anomeric one, which distinguishes them from anomers.
In a Haworth projection of a D-sugar, which direction does the $CH_2OH$ group point?

Up. Haworth projections represent the cyclic form where the $CH_2OH$ is above the plane for D-sugars to match Fischer orientation.
What disaccharide is composed of glucose + glucose with a $\beta(1\rightarrow^4)$ linkage?

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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