Biochemistry of Carbohydrates Quiz

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Questions and Answers

Which of the following is NOT a characteristic of monosaccharides?

They are the simplest form of sugar.

They are crystalline solids.

They are colorless and water-soluble.

They can be further hydrolyzed to simpler compounds. (correct)

What is the defining characteristic of a ketose?

The presence of an aldehyde group.

The presence of a ketone group. (correct)

The presence of a hydroxyl group.

The presence of at least five carbon atoms.

Which of the following is an example of a disaccharide?

Fructose

Ribose

Lactose (correct)

Glucose

What is the general formula for monosaccharides?

CnH2nOn (B) Signup and view all the answers

Which type of carbohydrate is formed by the linkage of 3-10 monosaccharide units?

Oligosaccharide (A) Signup and view all the answers

The type of covalent bond joining two monosaccharides in a disaccharide is called a(n):

Glycosidic bond (C) Signup and view all the answers

Which of the following carbohydrates is composed of glucose and fructose?

Sucrose (C) Signup and view all the answers

Which of the following describes the relationship between glucose and fructose?

They are structural isomers. (A) Signup and view all the answers

Which of the following is a characteristic of heparin?

It is an anticoagulant that prevents blood clotting. (D) Signup and view all the answers

What is the primary function of keratan sulfate?

To provide structural support in connective tissues. (A) Signup and view all the answers

Which of the following correctly describes an epimer?

Two stereoisomers that differ in the position of a hydroxyl group at only one asymmetric carbon. (C) Signup and view all the answers

Which of the following are examples of epimers?

Glucose and mannose. (A), Glucose and galactose. (B) Signup and view all the answers

Which of the following is NOT a type of glycosaminoglycan (GAG)?

Butene (C) Signup and view all the answers

What is the main structural difference between cis and trans isomers?

The arrangement of atoms in space. (A) Signup and view all the answers

Which of the following best describes the structure of chondroitin sulfate?

A linear chain of alternating sugars. (C) Signup and view all the answers

Where is chondroitin sulfate primarily found in the body?

Cartilage, bone, tendons, cornea, skin. (D) Signup and view all the answers

What is the general formula for carbohydrates?

Cn(H2O)n (C) Signup and view all the answers

Which of the following is NOT a function of carbohydrates?

Genetic information storage (D) Signup and view all the answers

What is the primary difference between aldoses and ketoses?

The presence of a keto group (A) Signup and view all the answers

Which of these is NOT a correct pairing of a carbohydrate and its function?

Fructose - structural component of cell walls (A) Signup and view all the answers

What is the primary type of carbohydrate breakdown occurring during digestion?

Hydrolysis to simpler sugars (A) Signup and view all the answers

What type of isomerism is common in carbohydrates?

Optical isomerism (A) Signup and view all the answers

What is the main reason for the large abundance of carbohydrates in nature?

Their high energy content (C) Signup and view all the answers

Study Notes

Carbohydrate Introduction

Carbohydrates are broadly defined as polyhydroxy aldehydes or ketones and their derivatives.
They are composed of carbon, hydrogen, and oxygen (Cn(H₂O)n).
Functional groups include hydroxyl groups.
The suffix "-ose" indicates a sugar.
Carbohydrates are one of the three major classes of biological molecules.
They are the most abundant biological molecules.

Carbohydrate Definition

Carbohydrates are defined as polyhydroxyaldehydes or ketones or compounds that produce them on hydrolysis.
Alternatively, carbohydrates are carbon compounds with large quantities of hydroxyl groups.
Carbohydrates are chemically characterized as polyhydroxy aldehydes or polyhydroxy ketones.

Aldoses and Ketoses

Sugars containing an aldehyde group are called aldoses.
Sugars containing a ketone group are called ketoses.

Functions of Carbohydrates

About 65% of the food consumed consists of carbohydrates.
Disaccharides like sucrose (table sugar) and lactose (milk sugar) are examples of other carbohydrates.
During digestion and metabolism, carbohydrates are converted to glucose.
They are a major source of energy for cells.
Carbohydrates are major structural components of plant cells.
Carbohydrates provide immediate energy in the form of glucose.
They store energy as glycogen in animals and starch in plants.

Additional Functions of Carbohydrates

Carbohydrates are involved in nutritional processes, energy storage, and metabolic intermediates.
They contribute to structural components of nucleotides, plant cell walls, arthropods' exoskeletons, and animal connective tissues.
They play a role in cellular communication and molecular recognition within eukaryotes.
Carbohydrates are critical for osmotic pressure regulation in bacteria.
Red blood cells (RBCs) and brain cells have an absolute requirement for carbohydrates.
Excess carbohydrates are converted to fat and participate in the formation of glycoproteins and glycolipids, which are components of cell membranes and receptors.
Further oxidation in cells provides energy and carbon atoms for building proteins, lipids, and nucleic acids.

Aldoses

Aldoses are monosaccharides with an aldehyde group and multiple hydroxyl (-OH) groups.
The number of carbon atoms determines the classification (triose, tetrose, pentose, hexose).
Erythrose is an aldotetrose.

Ketoses

Ketoses are monosaccharides with a ketone group and multiple hydroxyl (-OH) groups.
Fructose is an example of a ketohexose.

Carbohydrate Classification

Carbohydrates are classified into monosaccharides, disaccharides, oligosaccharides, and polysaccharides.

Monosaccharides

Monosaccharides are simple sugars (the most basic units of carbohydrates).
They are the fundamental units of carbohydrates and cannot be further hydrolyzed.
The general formula for monosaccharides is CnH₂nOn.
Some have a sweet taste and are usually colorless, water-soluble, and crystalline solids.
They are classified as aldoses or ketoses based on their functional groups.
Important examples include glucose, fructose, and galactose.

Disaccharides

Disaccharides are formed by the condensation of two monosaccharides.
Examples include sucrose (glucose + fructose), lactose (galactose + glucose), and maltose (glucose + glucose).
They are soluble in water.
A glycosidic bond links the monosaccharide units.

Oligosaccharides

Oligosaccharides consist of 3 to 10 monosaccharide units.
They have diverse functions, including cell recognition and binding (e.g., in glycolipids).

Polysaccharides

Polysaccharides are polymers of more than ten monosaccharide units.
They are often referred to as glycans and are composed of repeating units of monosaccharides linked by glycosidic bonds.
Polysaccharides can be either linear or branched.
They serve primarily in structural roles and as energy storage molecules.
Examples include starch, glycogen, cellulose, dextran, inulin, chitin, proteoglycans, and glycosaminoglycans.

Homopolysaccharides

Homopolysaccharides are composed of one type of monosaccharide.
Examples include starch, glycogen, cellulose, dextran, inulin, and chitin.

Heteropolysaccharides

Heteropolysaccharides are composed of more than one type of monosaccharide.
Examples include proteoglycans and glycosaminoglycans (GAGs).

Starch

Starch is a polymer consisting of two polysaccharide units: amylose and amylopectin.
Amylose consists of long unbranched chains of glucose.
Amylopectin consists of long chains of glucose with branches.
Starch is a storage polysaccharide in plants.

Glycogen

Glycogen is a storage polysaccharide in animals.
It contains both linear α(1-4) and branched α(1-6) linkages among glucose units.

Cellulose

Cellulose is a structural polysaccharide in plants containing long, linear chains of glucose with β(1-4) linkages between glucose units.

Chitin

Chitin is a structural polysaccharide found in the exoskeletons of insects and crustaceans.
It consists of N-acetyl-D-glucosamine units.

Inulin

Inulin is a storage polysaccharide in plants consisting of ẞ(1-2) linked fructofuranoses.
It is used as a diagnostic agent for glomerular function.

Heteropolysaccharides: Neutral Sugars

This group includes hemicellulose, gums, mucilages, and pectic substances.
They have more than one type of sugar unit.
Sometimes, they include non-sugar components.

Heteropolysaccharides: Mucopolysaccharides

Mucopolysaccharides are also known as Glycosaminoglycans (GAGs)
These are heteroglycans consisting of repeating units of sugar derivatives.
They include amino sugars and uronic acid.
They are components of tissue structure and found in combination with proteins to form mucoproteins, mucoids, and proteoglycans.
Examples of GAGs include hyaluronic acid, heparin, dermatan sulfate, and keratan sulfate.

Hyaluronic Acid (Hyaluronate)

This is a GAG with ẞ(1-3) and ẞ(1-4) linkages among repeating disaccharide units of glucuronic acid and N-acetyl-glucosamine.
It acts in lubrication and shock absorption within connective tissues, including the skin.

Keratan Sulfate.

This GAG consists of alternating units of D-galactosamine and N-acetylglucosamine, with various sulfate content.
It is found in cartilage, bone, cornea, hooves, and claws.

Heparin

Heparin is an anticoagulant found in blood, lung, liver, kidneys, and spleen.
It is made in mast cells and released into the blood.
The structure consists of alternating units of N-sulfo D-glucosamine 6-sulfate and glucoronate 2-sulfate.

Chondroitin Sulfate

Chondroitin sulfate is a sulfated GAG.
It consists of a chain of alternating sugar units, predominantly found attached to proteins within proteoglycans.
It is abundant in cartilage, bone, tendons, cornea, and skin.

Isomers and Stereoisomers

Isomers are compounds with the same molecular formula but different arrangements of atoms.
Stereoisomers are isomers that differ in the spatial arrangement of atoms.
Glucose, fructose, galactose, and mannose are examples of stereoisomers with the formula C₆H₁₂O₆.

Epimers

Epimers are stereoisomers that differ in the configuration at only one asymmetric carbon.
Examples of epimeric pairs include glucose and galactose; glucose and mannose.

Asymmetric Carbon

An asymmetric carbon (or chiral carbon) is a carbon atom bonded to four different atoms or groups.
The number of asymmetric carbons in a molecule determines the number of possible stereoisomers (2ⁿ, where n is the number of asymmetric carbons).

Enantiomers

Enantiomers are stereoisomers that are mirror images of each other and are non-superimposable.

Mutarotation

α and β anomers of sugars spontaneously interconvert in solution.
This process is called mutarotation.

Cyclization

Most carbohydrates exist primarily in cyclic forms, rather than linear chain forms.
The reaction involves the carbonyl group reacting with a hydroxyl group.
Sugars form either five-membered (furanose) or six-membered (pyranose) rings.

Fischer Projections

Fischer projections are two-dimensional representations of three-dimensional molecules that are used to represent carbohydrates.

D and L Notations

The configuration of chiral centers in sugars determines if the molecule is D or L, based on the position of the hydroxyl group on the chiral carbon farthest from the carbonyl group.

Optical Activity

Monosaccharides exhibit optical activity.
Plane-polarized light passing through a solution of a chiral carbohydrate will be rotated, either to the right (dextrorotatory) or to the left (levorotatory).

Glycolysis

Glycolysis is a sequence of reactions that converts glucose to lactate/pyruvate.
It produces ATP and is a cytosolic process.

Glycogenesis

Glycogenesis involves the synthesis of glycogen from glucose.
It is an anabolic process requiring ATP and UTP, primarily in the cytosol of liver and muscle cells.

Gluconeogenesis

Gluconeogenesis is a metabolic pathway that generates glucose from non-carbohydrate precursors like lactate, glycerol, and glucogenic amino acids.
This occurs mainly in the liver and kidney.

Glycogenolysis

Glycogenolysis is the breakdown of glycogen into glucose.
It is the opposite process to glycogenesis and occurs in muscle and liver cells in response to hormonal and neural signals.

Clinical Concepts

Dextrose (glucose) is used in medical practice.
Fructose is found in semen.
Disorders related to carbohydrates include diabetes mellitus, glycogen storage diseases, and galactosemia.
Accumulation of sorbitol and dulcitol can lead to certain pathological conditions.
Other concepts and applications include the role of cellulose in nutrition, hyaluronic acid's properties in joints, heparin's role as an anticoagulant, antifreeze proteins in certain fish species, and Streptomycin's use in tuberculosis treatment.

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Description

Test your knowledge on the fundamental characteristics of carbohydrates, including monosaccharides, disaccharides, and glycosaminoglycans. This quiz covers key definitions, structures, and functions related to carbohydrates. Ideal for students studying biochemistry or related fields.