Biochemistry: Carbohydrates Overview

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Questions and Answers

Which type of carbohydrate consists of a single sugar unit?

Monosaccharides (correct)

Oligosaccharides

Disaccharides

Polysaccharides

What is the general formula for many simple carbohydrates?

[C6H12O6]n

[C2H2O]n

[CH2O]n (correct)

[C5H10O5]n

What type of carbohydrate serves as a storage form of energy in plants?

Glycogen

Cellulose

Ribose

Starch (correct)

Which of the following carbohydrates cannot be digested by humans?

Cellulose Signup and view all the answers

Which category of carbohydrates provides a rapid rise in blood sugar levels?

Simple carbohydrates Signup and view all the answers

What is the primary biochemical role of carbohydrates?

Source of energy Signup and view all the answers

Which monosaccharide has six carbon atoms?

Hexose Signup and view all the answers

Which of the following is not a category of carbohydrate classification based on the number of sugar units?

Triglycerides Signup and view all the answers

What type of sugar is glucose primarily classified as?

Aldose Signup and view all the answers

What is the main sugar found in fruits?

Fructose Signup and view all the answers

Which monosaccharide has no asymmetric carbon atom?

Dihydroxyacetone Signup and view all the answers

Which of the following correctly describes the number of optical isomers for a pentose aldose?

4 Signup and view all the answers

What kind of isomers are glucose and fructose categorized as?

Constitutional isomers Signup and view all the answers

Which structural feature does fructose possess in its stable form?

Five membered ring Signup and view all the answers

How does the number of asymmetric carbon atoms in ketoses compare to aldoses of the same carbon length?

Ketoses have one less asymmetric carbon than aldoses. Signup and view all the answers

What is the role of galactose in biological systems?

Component of milk sugar (lactose) Signup and view all the answers

Which characteristic distinguishes D and L isomers?

The position of the OH group on the reference carbon Signup and view all the answers

What is an example of an epimer of glucose?

Mannose Signup and view all the answers

What does optical activity in monosaccharides depend on?

The presence of an asymmetric carbon atom Signup and view all the answers

What happens during mutarotation of glucose?

The specific rotation changes due to interconversion of anomers Signup and view all the answers

Which statement about a racemic mixture is true?

It contains equal amounts of two enantiomers. Signup and view all the answers

Which type of isomerism is characterized by non-superimposible mirror images?

Optical isomerism Signup and view all the answers

What defines an anomer in carbohydrate chemistry?

Forms that differ in configuration around the carbonyl carbon Signup and view all the answers

Which of the following compounds is not a monosaccharide?

Sucrose Signup and view all the answers

What is produced during alcoholic fermentation?

Ethyl alcohol and carbon dioxide Signup and view all the answers

Which of the following describes the oxidation of a primary alcoholic group?

Produces glucuronic acid Signup and view all the answers

Which type of sugar is formed from the reduction of sugars?

Sugar alcohols Signup and view all the answers

Disaccharides are formed by the condensation of what?

Two monosaccharides Signup and view all the answers

Which of the following disaccharides is reducing?

Maltose Signup and view all the answers

What type of glycosidic linkage is present in sucrose?

α-1,2 linkage Signup and view all the answers

What do reducing sugars contain that non-reducing sugars do not?

Free aldehyde or ketone groups Signup and view all the answers

Which of the following is not an example of a derived sugar?

Glucose Signup and view all the answers

What are the hydrolytic products formed when sucrose is hydrolyzed?

Glucose and fructose Signup and view all the answers

Why is lactose considered to be a perfect sugar for babies?

It does not produce gases during fermentation. Signup and view all the answers

What is the linkage type between the glucose molecules in maltose?

Alpha-1,4 glucosidic linkage Signup and view all the answers

What property distinguishes lactose from yeast fermentation?

Absence of lactase enzyme in yeast Signup and view all the answers

Which enzyme is responsible for hydrolyzing maltose to glucose?

Maltase Signup and view all the answers

Study Notes

Carbohydrates: Polyhydroxy Aldehydes or Ketones

Carbohydrates are polyhydroxy aldehydes or ketones containing carbon, hydrogen, and oxygen.
Many simple carbohydrates follow the general formula (CH2O)n, where n represents the number of carbon atoms (ranging from 3 to 8).
The ratio of hydrogen to oxygen is 2:1.
They are a primary source of energy, providing 4 kcal/g.
Carbohydrates serve as a storage form of energy: glycogen in animals and starch in plants.
They are structural components, such as glycosaminoglycans in humans and cellulose in plants.
Non-digestible carbohydrates, like cellulose, act as dietary fibers.
Carbohydrates are constituents of nucleic acids (RNA and DNA), including ribose and deoxyribose sugars.
They play a role in cellular communication, immunity, and detoxification.
Examples of food sources include grains, vegetables, fruits, milk, and dairy products.

Carbohydrate Classification

Carbohydrates are classified into four major groups based on the number of sugar units:
- Monosaccharides (one sugar unit)
- Disaccharides (two sugar units)
- Oligosaccharides (3-10 sugar units)
- Polysaccharides (more than 10 sugar units)

Nutritional Classification of Carbohydrates

Complex Carbohydrates (polysaccharides): Digested and converted slowly, found in lentils, beans, peanuts, potatoes, peas, corn, whole-grain bread, and cereals..
Simple Carbohydrates (rapid rise in blood sugar levels): Include monosaccharides, disaccharides, and oligosaccharides.

Monosaccharides: The Building Blocks

Monosaccharides are sugars that cannot be further hydrolyzed.
They are the building blocks of all carbohydrates.

Monosaccharide Classification

1. Based on the Number of Carbon Atoms

Number of carbon atoms	Generic name
3	Trioses
4	Tetroses
5	Pentoses
6	Hexoses
7	Heptoses
9	Nanoses

2. Based on the Functional Group

Generic name	Aldoses	Ketoses
Triose	Glyceraldehyde	Dihydroxyacetone
Tetrose	Erythrose	Erythrulose
Pentose	Ribose, Xylose (Epimer of Ribose), Arabinose	Ribulose, Xylulose (Epimer of Ribulose)
Hexose	Glucose, Galactose, Mannose	Fructose
Heptose		Sedoheptulose

Biochemical and Biological Importance of Some Hexoses

1. Glucose

Sugar of grape
Main blood sugar
The principle sugar utilized by tissues.

2. Fructose

Found in fruits, honey
Sugar of fetal blood and is the principle sugar of semen.

3. Galactose:

Present in combination with glucose in milk sugar (lactose).
Found in tissues as galactolipids and glycoproteins.
All Hexoses have a free functional group, making them reducing sugars.

Asymmetric Carbon Atom

A carbon atom attached to four different atoms or groups.
Number of isomers = 2^n (where n is the number of asymmetric carbon atoms).
Ketoses have fewer asymmetric carbon atoms than aldoses (2^n-1).
Dihydroxyacetone is a monosaccharide without any asymmetric carbon atoms.

Optical Activity

Optical activity refers to the ability of a substance to rotate the plane of polarized light.
Dextrorotatory (+, d): Rotates light to the right.
Levorotatory (-, 1): Rotates light to the left.
Racemic mixture (dl, ±): Equal mixture of optical isomers with no optical activity.

Mutarotation

Spontaneous change in the angle of rotation of a freshly prepared sugar solution due to the interconversion of alpha and beta anomers.

Some Chemical Properties of Monosaccharides

1. Reactions with Concentrated Acids (e.g., H2SO4)

Basis of the Molish test, a general test for all carbohydrates.

2. Alcoholic Fermentation

Microorganisms convert monosaccharides into ethyl alcohol and carbon dioxide.

3. Properties of -OH Groups

Esterification: Formation of esters, particularly with phosphoric acid (e.g., glucose 6-phosphate).
Oxidation of Primary Alcoholic Group: Produces uronic acids (e.g., glucose to glucuronic acid, involved in detoxification).
Formation of Glycosides: Compounds formed by linking a carbohydrate to another carbohydrate or a non-carbohydrate.

4. Properties of the Carbonyl Group (aldehyde or ketone)

Reduction: Conversion to their corresponding alcohols.
Reducing Properties: Ability to reduce Fehling's and Benedict's reagents, used for detecting glucose in urine.
Oxidation: Formation of carboxylic acids (aldonic or aldaric acids) depending on the oxidizing agent.

Derived Sugars

Monosaccharides with unusual structures or properties.
Examples:
- Acid Sugars
- Sugar Alcohols
- Deoxy Sugars (e.g., deoxyribose in DNA)
- Amino Sugars (e.g., glucosamine, galactosamine)
- Glycosides

Disaccharides: Two Sugar Units Linked Together

Formed by condensation of two monosaccharides.
Crystalline, water-soluble, and sweet to taste.
Classified based on the presence or absence of a free reducing group:
- Reducing (with a free aldehyde or ketone group)
- Non-reducing (without a free aldehyde or ketone group)

Disaccharide Classification

Reducing	Non-reducing
Example	Constituent
Maltose	Glucose + Glucose
Lactose	Galactose + Glucose
Isomaltose	Glucose + Glucose

1. Sucrose

Cane sugar, beet sugar, or table sugar.
Produced by plants but not by humans.
Composed of alpha-D-glucose and beta-D-fructose linked by an alpha-1-2 glycosidic linkage.
No free aldehyde or ketone groups, making it:
- Non-reducing - Does not reduce Fehling or Benedict's solutions.
- Does not show mutarotation.
Hydrolyzed by dilute acids or sucrase (invertase) into glucose and fructose.
"Invert sugar" in honey is mostly fructose, contributing to its sweetness.

2. Lactose

Milk sugar, composed of beta-D-galactose and alpha-D-glucose linked by a beta-1,4 glycosidic linkage.
Contains a free aldehyde group (from glucose), making it:
- Reducing - Reduces Fehling's and Benedict's solutions.
Considered a perfect sugar for babies because:
- Not fermented, reducing disturbances.
- Not overly sweet.
- The only natural source of galactose.
- Mild laxative effects.

3. Maltose

Two molecules of alpha-D-glucose linked by an alpha-1-4 glycosidic linkage.
Found during starch digestion by salivary amylase.
Has optical activity and can show mutarotation.
Hydrolyzed by maltase enzyme to glucose.
Has a free carbonyl group, enabling it to reduce Fehling's or Benedict's solutions..
Isomaltose: similar to maltose, but with an alpha-1-6 glycosidic linkage. Found from hydrolysis of starch and glycogen.

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Description

This quiz covers the fundamentals of carbohydrates, including their structure, classification, and functions in the body. It examines their roles as energy sources and structural components, as well as their significance in human health and nutrition. Test your knowledge on types, examples, and properties of carbohydrates.