Carbohydrates Overview

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Questions and Answers

What type of bond is formed when two monosaccharides join together?

Peptide bond

Ionic bond

Disulfide bond

O-glycosidic bond (correct)

Which of the following disaccharides is classified as a reducing sugar?

Lactose

Sucrose

Maltose (correct)

Trehalose

What is the primary function of sucrose in plants?

The principal form of sugar transported from leaves (correct)

Building structural components in cell walls

Energy storage in roots

Enhancing water absorption

Which of the following sugars results from the hydrolysis of lactose?

D-galactose and D-glucose Signup and view all the answers

What is a characteristic of the configuration of the anomeric carbon atom in maltose?

It is in its alpha configuration Signup and view all the answers

What configuration indicates that a sugar is a D isomer?

The hydroxyl group is on the right in the projection formula. Signup and view all the answers

Which of the following pairs of sugars are considered epimers?

D-glucose and D-mannose Signup and view all the answers

What type of bond is formed during the reaction of monosaccharides to create disaccharides?

Glycosidic bond Signup and view all the answers

In the context of cyclic monosaccharides, what does the term 'anomeric carbon' refer to?

The carbon that is derived from the carbonyl carbon. Signup and view all the answers

What is mutarotation in relation to monosaccharides?

The reversible change in the configuration of the anomeric carbon. Signup and view all the answers

What are the primary functions of carbohydrates in the body?

Storage form of energy and cell membrane components Signup and view all the answers

Which of the following correctly describes monosaccharides?

Single polyhydroxy aldehyde or ketone units Signup and view all the answers

What type of bond connects monosaccharide units in oligosaccharides?

Glycosidic bonds Signup and view all the answers

Which of the following polysaccharides is known for having a branched structure?

Glycogen Signup and view all the answers

What is the significance of the empirical formula (CH2O)n for carbohydrates?

It shows the ratio of hydrogen to oxygen in carbohydrates. Signup and view all the answers

What property is NOT commonly associated with carbohydrates?

Freely soluble in nonpolar solvents Signup and view all the answers

How many stereoisomers can a sugar molecule with 4 chiral centers have?

16 stereoisomers Signup and view all the answers

Which of the following statements about disaccharides is true?

They are composed of monosaccharides connected by glycosidic bonds. Signup and view all the answers

Study Notes

Carbohydrates

Abundant organic molecules in nature
Serve many functions, including energy storage, acting as components of cell membranes, and structural components such as cell walls of bacteria, insect exoskeletons, and plant cellulose.
They are polyhydroxy aldehydes or ketones, or substances that yield such compounds on hydrolysis.
Empirical formula (CH₂O)ₙ; some also contain N, P, or S.

Classes of Carbohydrates

Monosaccharides (simple sugars)
Oligosaccharides (short chains)
Polysaccharides (sugar polymers)
Sakcharon—> saccharides

Monosaccharides

Consist of a single polyhydroxy aldehyde or ketone unit
Glucose (sometimes called dextrose).
Four or more carbons tend to have cyclic structures.
Two Families:
- Aldoses (backbone)
- Ketoses (three-carbon trioses)
Monosaccharides with four, five, six, and seven carbon atoms
Colorless, crystalline solids that are freely soluble in water and insoluble in nonpolar solvents.
- Most have a sweet taste.
Asymmetric carbon atoms (except dihydroxyacetone).
- Glyceraldehyde has two different optical isomers
- Aldohexoses, with 4 chiral centers have 2⁴ = 16 stereoisomers
D and L forms: Hydroxyl group configuration on the reference carbon in Fischer projection
Epimers: Two sugars that differ only in their configuration around one carbon atom;
- Examples:
  - D-glucose and D-mannose(differs only at C-2)
  - D-glucose and D-galactose (differs at C-4)

Formation of Cyclic Structures

Five or more carbon atoms in the back bone are predominantly cyclic structures
Carbonyl group forms a covalent bond with a hydroxyl group along the chain.
Formation of cyclic structures results from a general reaction between alcohols and aldehydes or ketones to form hemiacetals or hemiketals.

Reactions of Monosaccharides

Two molecules of an alcohol can add to a carbonyl carbon producing a hemiacetal (aldose) or hemiketal (ketose).
If the hydroxyl and carbonyl groups are on the same molecule a five or six-membered ring forms.
The addition of a second alcohol molecule produces an acetal or ketal.
The resultant linkage is a glycosidic bond.
If the two molecules reacting together are monosaccharides, the acetal or ketal formed is a disaccharide.

Anomers

Isomeric forms of monosaccharides that differ in their configuration about the hemiacetal or hemiketal carbon atom (anomeric carbon).
α- and β-D-glucopyranose are examples.

Mutarotation

The process of conversion of a- to b- or vice-versa with changing the optical rotation.

Reducing Sugars

Monosaccharides can be oxidized by relatively mild oxidizing agents
Carbonyl carbon is oxidized into a carboxyl group
Glucose and other sugars can reduce cupric ions

Oligosaccharides

Short chains of monosaccharide units, joined by glycosidic bonds
Sucrose (table sugar)
Glycoconjugates.

Polysaccharides

Sugar polymers containing 20+ units
Some are linear chains(e.g., Cellulose)
Some are branched chains(e.g., Glycogen)
Both glycogen and cellulose are formed by recurring units of D-glucose.

Disaccharides

Consist of two monosaccharides covalently joined by an O-glycosidic bond
The hydroxyl group on one sugar molecule reacts with the anomeric carbon of another sugar molecule
Hydrolyzed easily by acid and readily
Examples:
- Maltose (two D-glucose residues)
  - alpha-glycosidic linkage
- Lactose (D-galactose and D-glucose residues)
- Sucrose (glucose and fructose residues)
  - Nonreducing sugar
N-glycosyl bonds join the anomeric carbon of a sugar to a nitrogen atom in glycoproteins and nucleotides.
- Formation of a glycosidic bond renders a sugar nonreducing

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Description

Explore the fundamental aspects of carbohydrates, including their structure, functions, and classifications. This quiz covers monosaccharides, oligosaccharides, and polysaccharides, as well as their roles in energy storage and cell structure. Test your knowledge on these essential organic molecules!