Carbohydrates Quiz on Oligosaccharides and Polysaccharides

Carbohydrates - Structure and Function

• Carbohydrates are the most abundant class of bioorganic molecules on Earth, produced by photosynthesis in green plants.
• They are also known as saccharides due to the sweet taste of many.
• Carbohydrates store chemical energy (glucose, starch, glycogen)
• One gram of digested carbohydrate yields approximately 4 kcal of energy.
• Complex carbohydrates are beneficial for a diet.
• Carbohydrates are supportive structural components in plants and some animals (e.g., cellulose, chitin).
• Carbohydrates form part of the structural framework of DNA and RNA.
• Carbohydrate markers on cell surfaces are crucial for cell-cell recognition.

Classification of Carbohydrates

• Carbohydrates have the general formula (C_n(H_2O)_n).
• (n) varies from 3 to 8.
• They are classified based on the number of carbon atoms (triose, tetrose, pentose, hexose, heptose, octose).
• They can be further classified as aldoses (aldehyde group) or ketoses (ketone group)
• Monosaccharides are simple sugars, containing a single polyhydroxy aldehyde or ketone unit that can't be broken down further through hydrolysis.
• Disaccharides contain two monosaccharide units covalently bonded, crystallizing as water-soluble solids.
• Disaccharides produce monosaccharides upon hydrolysis.
• Oligosaccharides contain 3-10 monosaccharides units, and disaccharides are the common type.
• Polysaccharides contain tens of thousands of monosaccharides units.
• Homopolysaccharides are polymers of a single monosaccharide (e.g., glycogen, cellulose, starch).
• Heteropolysaccharides contain multiple different monosaccharides types (e.g., hyaluronic acid, heparin, chondroitin sulfate).
• Derived carbohydrates have gone through chemical reactions to form other products, such as sugar acids, sugar alcohols, deoxysugars, and sugar amines.

Carbonyl Group

• A carbonyl group is a chemically organic functional group, consisting of a carbon atom double-bonded to an oxygen atom.
• The two simplest examples of these are aldehydes and ketones.
• Aldehydes and ketones are usually attached to another carbon compound.

Monosaccharides

• These are simple sugars with the general formula (C_nH_{2n}O_n), where n can range from 3 to 8.
• Different numbers of carbons determine trioses, tetroses, pentoses, hexoses, heptoses, and octoses.
• An aldose has an aldehyde group, and a ketose has a ketone group.

Biochemically Important Monosaccharides

• Glucose, fructose, galactose, and ribose are crucial for various biological processes.
• Glucose is the most abundant monosaccharide found in nature and is also a key component of blood sugar.
• Fructose is the sweetest of common sugars, found in fruits and honey.
• Galactose is a component of milk sugar.
• Ribose is a part of RNA and DNA.
• D-Mannose is found in certain bacteria, fungi, and plants.
• D-glucose is used in hospitals as an intravenous source for nutrition.

Cyclic Forms of Monosaccharides

• Hemiacetals and hemiketals are formed from the reaction between aldehyde or ketone and alcohol.
• Cyclic hemiacetals/hemiketals exist widely in nature and are five-or six-membered rings.
• There is an a- and β-form for these.
• Mutarotation is the interconversion between the cyclic forms, (α-and β) of sugars, accompanied by a change in specific rotation. Only sugars that form hemiacetals or hemiketals exhibit this property.

Disaccharides

• Two monosaccharides are linked by an acetal formation reaction to form a disaccharide.
• The bond formed is called a glycosidic bond.
• Common examples of disaccharides include maltose, lactose, and sucrose.
• Maltose consists of two glucose units connected by an α(1 → 4) glycosidic linkage.
• Lactose consists of β-galactose and β-glucose linked by a β(1 → 4) glycosidic bond.
• Sucrose consists of an α-glucose and a β-fructose linked by an α(1 → 2) glycosidic linkage.

Oligosaccharides

• Oligosaccharides are carbohydrates containing between three and ten monosaccharides.
• Common examples include raffinose and stachyose, found in beans.

Polysaccharides

• Polysaccharides are macromolecules comprised of many monosaccharides joined by glycosidic linkages.
• Starch is a storage polysaccharide in plants, composed of amylose and amylopectin.
• Glycogen is an animal storage polysaccharide.
• Cellulose is a structural polysaccharide in plants, composed of linear chains of β-glucose units connected by β(1,4) glycosidic linkages.
• Chitin is a structural polysaccharide found in the exoskeletons of insects, crabs, and other arthropods.

Acidic Polysaccharides

• These have acidic groups and important biological functions.
• Hyaluronic acid is found in the vitreous humor, along joint fluid.
• Chondroitin sulfate plays a crucial structural role in cartilage, bone, and the cornea.
• Heparin is an anticoagulant, preventing blood clot formation.
• Alginic acid has a variety of applications, especially in food products.

Dietary Considerations

• The glycemic index (GI) measures how quickly dietary carbohydrates are digested and affect blood glucose levels.
• Low-GI foods are preferable for better blood sugar control.
• Unavailable carbohydrates, known as dietary fiber, are not digested by human enzymes.
• Fiber aids digestion and can ease bowel movements.
• Insufficient fiber consumption can affect digestive health.