Biochemistry: Concepts of Carbohydrates

Questions and Answers

What type of linkage is formed between monomeric sugars when they transform into glycosides?

Covalent linkage

Amino linkage

Glycosidic linkage (correct)

Peptide linkage

In the formation of a six-membered ring, which hydroxyl group participates in the reaction to the ketone group?

Hydroxyl of the 5th carbon

Hydroxyl of the 4th carbon

Hydroxyl of the 6th carbon (correct)

Hydroxyl of the 3rd carbon

Which of the following accurately describes the α anomer of D-glucose?

The OH group on the 1st carbon points in the same direction as the -CH2OH group

The OH group on the 5th carbon is involved in its formation

It does not form a cyclic structure

The OH group on the 1st carbon points in opposite direction to the -CH2OH group (correct)

What is the relationship between α and β anomers of D-glucose?

They differ in the orientation of the hydroxyl group at the 1st carbon Signup and view all the answers

What form do monomeric sugars predominantly exist in?

Cyclic hemicetal form Signup and view all the answers

What type of glycosidic bond links the glucose monomers in cellulose?

β-1,4-glycosidic bond Signup and view all the answers

Which of the following statements accurately describes amylopectin?

It is a branched polysaccharide with α-1,4 and α-1,6-glycosidic bonds. Signup and view all the answers

What characteristic of cellulose contributes to its structural role in plants?

The ability to form long linear fibers. Signup and view all the answers

Which statement about starch is correct?

It is the most common polysaccharide found in plants. Signup and view all the answers

What type of linkages allows cellulose to form strong fibers?

β-1,4-glycosidic linkages. Signup and view all the answers

How often do branches occur in the helical chain of amylopectin?

Every 10 units Signup and view all the answers

What is the primary role of cellulose in plants?

Providing structural support. Signup and view all the answers

Which of the following best differentiates amylose from amylopectin?

Amylose is unbranched while amylopectin is branched. Signup and view all the answers

What distinguishes epimers from other types of sugars?

They differ in stereochemistry at only one chiral carbon. Signup and view all the answers

Which of the following statements about aldoses is true?

They have an aldehyde group. Signup and view all the answers

In the Fischer projection, how are horizontal and vertical lines represented?

Horizontal lines come out of the plane, vertical lines go back into the plane. Signup and view all the answers

What is the empirical formula for monosaccharides?

C(H2O) Signup and view all the answers

Which type of glycosidic linkage involves a horizontal line representation in cyclic forms?

Beta-1,4-glycosidic linkage Signup and view all the answers

Which of the following descriptions is accurate for ketoses?

They are monosaccharides with an acetone group. Signup and view all the answers

What type of glycosidic bond connects the D-galactose and D-glucose in lactose?

Beta-1,4 glycosidic bond Signup and view all the answers

What does the symbol D or L indicate in relation to stereogenic carbons?

The orientation of the hydroxyl group closest to the aldehyde group. Signup and view all the answers

Which of the following is NOT a characteristic of lactose?

It is formed from D-fructose and D-glucose. Signup and view all the answers

Why is lactose classified as a reducing sugar?

It has a free hemiacetal portion. Signup and view all the answers

Which of the following is a characteristic of diastereomers?

They have different physical properties. Signup and view all the answers

Which monosaccharide contributes to lattice formation in lactose?

D-galactose Signup and view all the answers

What is the role of the glycosidic bond in disaccharides like maltose?

It connects individual sugar molecules in chains. Signup and view all the answers

What type of sugar structure is represented in the Haworth projection?

Cyclic structure of monosaccharides Signup and view all the answers

Which of the following disaccharides does NOT contain a reducing sugar?

Sucrose Signup and view all the answers

What is the specific structure of the glycosidic linkage in lactose?

Linkage between 1st carbon of galactose and 4th carbon of glucose Signup and view all the answers

What type of reaction occurs when an alcohol group attacks a carbonyl group in sugar chemistry?

Nucleophilic attack Signup and view all the answers

In D-isomers of sugars, which direction does the -OH group point?

Right Signup and view all the answers

Which type of sugar forms hemiketals through the binding of an alcohol to a ketone?

Ketohexoses Signup and view all the answers

What structural form do sugars predominantly adopt under normal physiological conditions?

Cyclized form Signup and view all the answers

What is produced when D-fructose undergoes cyclic formation?

Fructopyranose Signup and view all the answers

What is the relationship between enantiomers in terms of structural arrangement?

Mirror images of each other Signup and view all the answers

Which part of a sugar molecule typically acts as the nucleophile in the ring formation process?

Hydroxyl group Signup and view all the answers

Which of the following describes the carbonyl group in the context of nucleophilic attack?

Accepts electrons Signup and view all the answers

Study Notes

Carbohydrate Concepts

Monosaccharides: Simplest sugars, with empirical formula (C.H2O).
Aldoses vs. Ketoses: Aldoses contain an aldehyde group, while ketoses have a ketone group.
Epimers: Sugars differing in stereochemistry at one chiral carbon.
Fischer Projection: A method to represent sugar stereochemistry, indicating D/L configurations based on the position of -OH groups.

Cyclic Forms of Carbohydrates

Sugars can cyclize to form stable ring structures under physiological conditions, primarily due to lower energy states compared to open chains.
Aldoses: Cyclize to form six-membered rings (pyranoses).
Ketoses: Typically form five-membered rings (furanoses), such as D-fructose, which can also form six-membered rings in specific reactions.

Glycosidic Linkages

Glycosidic Bond: Link between monosaccharides in their cyclic form, resulting in disaccharides and polysaccharides.
Non-reducing Sugars: Certain sugars do not have a free hemiacetal form, making them unable to reduce other compounds.
Anomers: Isomers differing at the anomeric carbon; α-anomers with -OH in opposite direction to -CH2OH, β-anomers with -OH in the same direction.

Types of Polysaccharides

Lactose: A β-1,4 glycosidic link between D-galactose and D-glucose, classified as a reducing sugar due to its free hemiacetal.
Cellulose: Structural polysaccharide in plants made of glucose monomers linked by β-1,4 bonds, forming long, linear chains suitable for structure and support.
Starch: Primary plant polysaccharide with two forms:
- Amylose: Unbranched, α-1,4 linked glucose chains.
- Amylopectin: Branched structure featuring both α-1,4 and α-1,6 glycosidic bonds, resulting in a complex arrangement.

Key Functional Groups

Nucleophiles: Electron donors in bond formation, e.g., alcohol groups.
Electrophiles: Electron acceptors in reactions, like carbonyl carbons.
Hemiacetal Formation: Reaction between alcohol and aldehyde, crucial in cyclic formation of sugars.

Stability and Structure

Cyclic forms of sugars are favored due to their stability, which lowers energy levels compared to open-chain analogs.
Hydrogen bonding in structures like cellulose allows for stacking, contributing to the plant's structural integrity.

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Description

This quiz explores key concepts in carbohydrates, including aldolase, ketoses, and Fischer projection. It also covers the cyclic forms of carbohydrates and glycosidic linkages. Perfect for students wanting to deepen their understanding of carbohydrate chemistry.