Harper's Biochemistry Chapter 15 - Saccharides (ie, Carbohydrates) of Physiological Significance

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Questions and Answers

What distinguishes the β-l-iduronate from α-d-glucuronate?

The position of the hydroxyl group on the anomeric carbon (correct)

The number of glucose residues

The presence of an amino group

The type of glycosidic linkages

Which statement about starch is correct?

Starch contains no branched chains.

Starch is composed of only α1 → 6 linkages.

Starch's hydrolysis is influenced by its degree of crystallization. (correct)

Starch consists solely of β-glucose residues.

Which structural form does 2-deoxy-d-ribofuranose primarily adopt?

Cyclic form

β-form (correct)

Linear form

α-form

What is the primary glycosidic linkage found in the linear chains of starch?

α1 → 4 Signup and view all the answers

What is the significance of the degree of hydration in starch digestion?

It influences the hydrolysis rate by amylase. Signup and view all the answers

What characteristic of galactosamine distinguishes it from glucose?

Presence of an amino group at C2 Signup and view all the answers

In polysaccharides, what type of residue is primarily found at the branching points?

α-glucose Signup and view all the answers

What type of carbohydrate is glucosamine classified as?

Monosaccharide Signup and view all the answers

Which disaccharide is not hydrolyzed by intestinal enzymes, but is fermented by intestinal bacteria?

Lactulose Signup and view all the answers

What type of bond links the monosaccharides in cellulose?

β1 → 4 bonds Signup and view all the answers

Which disaccharide is primarily derived from the enzymic hydrolysis of starch?

Isomaltose Signup and view all the answers

What clinical condition is associated with a rare genetic lack of sucrase?

Diarrhea and flatulence Signup and view all the answers

What is the primary sugar found in insect hemolymph?

Trehalose Signup and view all the answers

What term describes a carbohydrate composed of two monosaccharides?

Disaccharide Signup and view all the answers

Which of the following is an example of a polysaccharide?

Glycogen Signup and view all the answers

What is the primary role of glucose in the body?

Serving as a metabolic fuel Signup and view all the answers

Which of the following correctly describes an oligosaccharide?

Composed of three to ten monosaccharide units Signup and view all the answers

Which of these glucose configurations represents a six-membered ring structure?

Pyranose Signup and view all the answers

Which carbohydrate is a key precursor for synthesizing nucleic acids?

Ribose Signup and view all the answers

Which of the following properties characterizes saccharides?

Highly polar molecules Signup and view all the answers

What defines the glycemic index of a carbohydrate?

The rate at which a carbohydrate raises blood glucose levels Signup and view all the answers

Which statement about disaccharides is true?

They are formed via condensation reactions. Signup and view all the answers

What distinguishes a monosaccharide from other types of saccharides?

It is the simplest form of sugar. Signup and view all the answers

Which of the following best defines monosaccharides?

Simple sugars that cannot be hydrolyzed into smaller carbohydrate units Signup and view all the answers

What is the primary function of disaccharides in the body?

To provide immediate energy after digestion Signup and view all the answers

Which carbohydrate is primarily utilized by the body's tissues for energy?

Glucose Signup and view all the answers

What does the term polysaccharide commonly refer to?

A compound consisting of multiple simple sugars linked together Signup and view all the answers

Which metabolic disorder is associated with carbohydrate metabolism?

Diabetes mellitus Signup and view all the answers

What role do glycosidic bonds play in carbohydrates?

They connect monosaccharides to form di- and polysaccharides Signup and view all the answers

What are glycomes?

The entire complement of saccharides of an organism Signup and view all the answers

Which statement about saccharides is FALSE?

All saccharides have the same level of sweetness as sucrose Signup and view all the answers

What process enables the synthesis of glucose in plants?

Photosynthesis Signup and view all the answers

Which carbohydrate is not typically classified as a polysaccharide?

Sucrose Signup and view all the answers

Which pentose sugar is a structural component of nucleic acids and coenzymes, including ATP?

d-Ribose Signup and view all the answers

What is the primary source of d-Glucose?

Fruit juices Signup and view all the answers

What condition is associated with the accumulation of fructose metabolites due to hereditary fructose intolerance?

Hypoglycemia Signup and view all the answers

Which sugar is readily metabolized to glucose and is synthesized in the mammary gland for lactose production?

d-Galactose Signup and view all the answers

What is the significance of d-Ribulose in metabolism?

It is an intermediate in the pentose phosphate pathway. Signup and view all the answers

Which sugar can be a constituent of glycoproteins and is sourced mainly from plant gums?

d-Arabinose Signup and view all the answers

What is the clinical significance of d-Glucose in poorly controlled diabetes mellitus?

It is excreted in urine as glucosuria. Signup and view all the answers

What intermediate is produced during the metabolism of d-Xylose?

Ribulose Signup and view all the answers

Which hexose sugar is known as 'blood sugar' and serves as the main metabolic fuel for tissues?

d-Glucose Signup and view all the answers

Which sugar is particularly important in the context of essential pentosuria?

l-Xylulose Signup and view all the answers

What is the result of the nonenzymatic addition of a saccharide to a protein?

Glycation Signup and view all the answers

Which sugar is used as a marker for diagnosing diabetes?

Hemoglobin A1c Signup and view all the answers

Glycomics primarily studies what aspect of biological organisms?

Glycomes Signup and view all the answers

What role do sialic acids play in biological systems?

Binding to specific glycosyl residues Signup and view all the answers

Why are individuals with blood type O considered universal donors?

They lack all antigens Signup and view all the answers

What is the primary structural feature of hemiacetals formed from sugar alcohols?

They have both a hydroxy group and a hydrogen. Signup and view all the answers

Which of the following statements accurately describes the energy yield of sugar alcohols?

They yield about half the energy of sugars. Signup and view all the answers

What characteristic of oligosaccharides distinguishes them from monosaccharides?

They consist of 3 to 10 sugar units. Signup and view all the answers

What happens to unabsorbed sugar alcohols in the human intestine?

They undergo fermentation by bacteria. Signup and view all the answers

What is the composition of a disaccharide?

It is a condensation product of two monosaccharide units. Signup and view all the answers

Why are sugar alcohols considered poor in absorption?

They are not digested by human enzymes. Signup and view all the answers

Which of the following correctly represents the primary view of cyclic sugar structures?

The Haworth projection illustrates their cyclic form. Signup and view all the answers

What is a common characteristic of most oligosaccharides regarding digestion?

They are typically not digested by human enzymes. Signup and view all the answers

Which monosaccharides are physiologically significant hexoses?

Glucose, Galactose, Fructose, Mannose Signup and view all the answers

What type of glycosidic bond is formed between a monosaccharide and a nonsaccharide group?

N-glycosidic bond Signup and view all the answers

What is formed when galactose is involved in a glycosidic bond?

Galactoside Signup and view all the answers

What is the structural form of glycosides when the anomeric hydroxy group is involved?

Acetal Signup and view all the answers

Which of these components can be an aglycone in a glycosidic bond formation?

Steroid Signup and view all the answers

Which derivative of glucose is significant for glycosaminoglycan formation?

D-Glucuronate Signup and view all the answers

How do pentoses contribute to nucleotide structure?

As the backbone component Signup and view all the answers

What type of compound results from the condensation between monosaccharides?

All of the above Signup and view all the answers

Which of these sugar formations plays a crucial role in metabolic pathways?

Trioses, tetroses, and pentoses as intermediates Signup and view all the answers

What results from the combination of an anomeric carbon of a monosaccharide with another monosaccharide?

A disaccharide Signup and view all the answers

What determines the extent of starch hydrolysis by amylase?

The degree of crystallization and hydration Signup and view all the answers

What type of linkages primarily comprise the branched chains of starch?

α1 → 4 and α1 → 6 linkages Signup and view all the answers

Which structural characteristic is true of 2-deoxy-d-ribofuranose?

It contains a hydroxyl group at the 2' position Signup and view all the answers

What feature distinguishes glucosamine from galactosamine?

Position of the nitrogen in the structure Signup and view all the answers

In what form are glucose residues primarily linked within starch?

Linear chains with α1 → 4 linkages Signup and view all the answers

What is the main effect of cooking on starch?

It breaks down amylopectin into simpler sugars Signup and view all the answers

What structural aspect of plant cell walls influences starch digestibility?

The degree of crystallization of starch Signup and view all the answers

Which statement about the configuration of glucosamine is accurate?

It can exist in both α and β forms Signup and view all the answers

What defines the structure of α-d-glucuronate?

It has a distinct stereochemistry at the anomeric carbon Signup and view all the answers

What differentiates the polysaccharide composition within different plant sources?

The types of glycosidic bonds formed Signup and view all the answers

What is one of the primary functions of glycosaminoglycans in biological systems?

To cushion and lubricate other structures Signup and view all the answers

Which of the following is NOT considered a glycosaminoglycan?

Sialic acid Signup and view all the answers

What is the main component that allows carbohydrate chains to repel each other in glycosaminoglycans?

The large number of negative charges and —OH groups Signup and view all the answers

Which type of proteins contain branched or unbranched oligosaccharide chains?

Glycoproteins Signup and view all the answers

Which carbohydrate is recognized as an important anticoagulant?

Heparin Signup and view all the answers

What type of sugar is fucose classified as?

Hexose Signup and view all the answers

Which of the following oligosaccharides is primarily found in glycoproteins?

Mannose Signup and view all the answers

What predominant sialic acid is derived from neuraminic acid?

N-Acetylneuraminic acid Signup and view all the answers

What role do —OH groups play in the structure of glycosaminoglycans?

They assist in water retention and solubility Signup and view all the answers

What type of carbohydrate chains do glycoproteins contain?

Branched or unbranched oligosaccharide chains Signup and view all the answers

Match the following terms related to carbohydrates with their correct descriptions:

Monosaccharides = Simple sugars absorbed directly into the bloodstream Polysaccharides = Complex carbohydrates formed from numerous sugar units Glycolysis = The metabolic pathway that converts glucose into pyruvate Glycogen = A stored form of glucose in animals, primarily found in the liver and muscles Signup and view all the answers

Match the following metabolic disorders with their corresponding characteristics:

Diabetes mellitus = Characterized by high blood sugar resulting from insulin issues Galactosemia = A genetic disorder affecting the metabolism of galactose Fructose intolerance = Inability to break down fructose, leading to gastrointestinal symptoms Lactose intolerance = Deficiency of lactase resulting in digestive issues after consuming lactose Signup and view all the answers

Match the following saccharides with their typical roles:

Glucose = Primary energy source for cells Sucrose = Common table sugar composed of glucose and fructose Starch = Energy storage polysaccharide in plants Cellulose = Structural polysaccharide found in plant cell walls Signup and view all the answers

Match the following carbohydrate-related terms with their definitions:

Hydrolysis = The chemical process that breaks down sugars by adding water Photosynthesis = The process by which plants convert carbon dioxide and water into glucose Glycome = The complete set of saccharides within an organism Glycomics = The study of glycomes and their functions in biological processes Signup and view all the answers

Match the following types of sugars with their examples:

Hexoses = Glucose, fructose, and galactose Pentoses = Ribose and deoxyribose Disaccharides = Sucrose and lactose Oligosaccharides = Raffinose and stachyose Signup and view all the answers

Match the following sugars with their sources and clinical significance:

d-Ribose = Nucleic acids and metabolic intermediate d-Glucose = Fruit juices, hydrolysis of starch d-Fructose = Fruit juices, honey, hydrolysis of cane or beet sugar d-Galactose = Hydrolysis of lactose Signup and view all the answers

Match the following pentoses with their importance:

d-Ribulose = Intermediate in the pentose phosphate pathway d-Arabinose = Constituent of glycoproteins d-Xylose = Constituent of glycoproteins l-Xylulose = Excreted in the urine in essential pentosuria Signup and view all the answers

Match the following hexoses with their metabolic roles:

d-Glucose = Main metabolic fuel for tissues d-Fructose = Rapidly metabolized by the liver d-Galactose = Readily metabolized to glucose d-Ribose = Structural component of nucleic acids Signup and view all the answers

Match the following sugars with their clinical significance:

d-Glucose = Excreted in the urine in poorly controlled diabetes mellitus d-Fructose = Hereditary fructose intolerance d-Galactose = Hereditary galactosemia d-Ribose = Component of ATP and coenzymes Signup and view all the answers

Match the following sugars with their biochemical importance:

d-Ribose = Structural component of nucleic acids d-Fructose = Impaired glucose production and induces hypoglycemia d-Galactose = Synthesized in the mammary gland for lactose d-Glucose = Known as 'blood sugar' Signup and view all the answers

Study Notes

Saccharide Nomenclature

Saccharides are preferred over carbohydrates when speaking about biomolecules
Saccharides are polar
Saccharides have structural and metabolic roles

The Glycome and Glycobiology

The glycome refers to all saccharides in an organism, whether free or part of complex molecules
Glycobiology is the study of the roles of saccharides in health and disease
Glycomics is the comprehensive study of the glycome, including genetic, physiological, and pathological aspects

Types of Saccharides

Monosaccharides are the simplest sugars
Disaccharides are made up of two monosaccharides
Oligosaccharides are made up of 3 to 10 monosaccharides
Polysaccharides are made up of many monosaccharides

Important Monosaccharides

Glucose is a major metabolic fuel in mammals
Glucose is the precursor for other carbohydrates such as glycogen, ribose, deoxyribose, and galactose
Fructose is rapidly metabolized by the liver
Galactose is readily metabolized to glucose

Important Disaccharides

Sucrose is comprised of glucose and fructose
Lactose is comprised of galactose and glucose
Maltose is comprised of two glucose molecules
Isomaltose is comprised of two glucose molecules, but with a 1→6 bond

Important Polysaccharides

Starch is a storage form of glucose in plants
Starch is comprised of amylose and amylopectin
Cellulose is a structural component of plant cell walls
Cellulose is comprised of glucose molecules that are linked by β1→4 bonds
Humans cannot digest cellulose due to a lack of enzymes to break the β1→4 bonds

Sugar Alcohols

Sugar alcohols are formed when the aldehyde or ketone group of a polyol (e.g., sugar alcohol) is reduced to an alcohol.
Sugar alcohols are naturally present in foods. - They are also synthesized by reducing monosaccharides for use in the manufacture of foods for weight reduction and diabetics. - They are poorly absorbed and provide about half the energy yield of sugars. - The main side effect is flatulence, due to bacterial fermentation of unabsorbed sugar alcohol in the intestine.

Disaccharides

Disaccharides are condensation products of two monosaccharide units. - Examples include lactose, maltose, isomaltose, sucrose, and trehalose.

Oligosaccharides

Oligosaccharides are condensation products of 3 to 10 monosaccharides.
Most are not digested by human enzymes.

### Carbohydrates in Diabetes

Poorly controlled diabetes mellitus can be treated by reducing an alkaline copper solution.

Physiologically Important Monosaccharides

Derivatives of trioses, tetroses, pentoses, and the seven-carbon sugar sedoheptulose are formed as metabolic intermediates in glycolysis and the pentose phosphate pathway. - Pentoses are important in nucleotides, nucleic acids, and several coenzymes. - Glucose, galactose, fructose, and mannose are the physiologically important hexoses.

### Saccharides Form Glycosides

Glycosides are formed by condensation between the hydroxyl group of the anomeric carbon of a monosaccharide and a second compound, which can be another monosaccharide (glycone) or a non-saccharide group (aglycone). - The bond is an acetal link if the second group is also a hydroxyl, resulting from a reaction between a hemiacetal group (formed from an aldehyde and an -OH) and another -OH. - If the hemiacetal portion is glucose, the resulting compound is a glucoside; If galactose, a galactoside; and so on. - If the second group is an amine, an N-glycosidic bond is formed, for example, between adenine and ribose in nucleotides. - Glycosides are widely distributed in nature. - The aglycone can be methanol, glycerol, a steroid, a phenol, or a base such as adenine.

### Glycosaminoglycans (GAGs)

GAGs are negatively charged polysaccharides containing repeating disaccharide units.
They hold large quantities of water and occupy space due to the numerous -OH groups and negative charges, which repel each other.
They cushion and lubricate structures such as connective tissue and cartilage.
Examples include hyaluronic acid and chondroitin sulfate.
Heparin is another important glycosaminoglycan, acting as an anticoagulant.

### Glycoproteins

Glycoproteins are proteins containing branched or unbranched oligosaccharide chains.
They occur on cell surfaces and in many secretions.
Fucose is a component of glycoproteins.
Sialic acids are N-acyl derivatives of neuraminic acid, with the predominant sialic acid being N-acetylneuraminic acid. - Sialic acids are found in both glycoproteins and gangliosides.

### Gylcation

Gylcation is the nonenzymatic addition of a saccharide (e.g., glucose) to a protein. - It increases as glucose levels rise. - A glycated form of hemoglobin (hemoglobin A1c) increases in individuals with diabetes. - HbA1c is useful for both diagnosing and monitoring the management of diabetes.

The Gylcome

The glycome is the sum of all carbohydrates found in an organism, free or present in complex molecules.
Glycomics is the study of glycomes, including their genetic, physiological, and pathological aspects.

### Carbohydrates as Essential Nutrients

Carbohydrates are major constituents of animal food and animal tissues. - The type and number of monosaccharide residues differentiate carbohydrate moieties. - Glucose is the most important carbohydrate in mammalian biochemistry as nearly all dietary carbohydrate is converted to glucose for metabolism.

### Properties of Saccharides

Saccharides contain many asymmetric carbon atoms, leading to a vast number of possible stereoisomers. - Physiologically significant monosaccharides include glucose (blood sugar) and ribose (an important constituent of nucleotides).

### Cell Membranes and Lipoproteins

Approximately 5% of the weight of cell membranes is composed of carbohydrates, primarily as part of glycoproteins and glycolipids. - The glycocalyx on the outer surface of the plasma membrane interacts with plant lectins, proteins that bind specific glycosyl residues. - For example, concanavalin A binds α-glucosyl and α-mannosyl residues.

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Description

Explore the fascinating world of saccharides and their roles in biology. This quiz covers key concepts, including saccharide nomenclature, types of saccharides, and the significance of the glycome in health and disease. Test your understanding of how these biomolecules function in various biological contexts.