Proteoglycans, Glycosaminoglycans, and Glycoproteins

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Questions and Answers

What is the empiric formula for many simpler carbohydrates?

(CH2O)n, where n ≤ 3

(CH2O)n, where n = 1

(CH2O)n, where n ≥ 2

(CH2O)n, where n ≥ 3 (correct)

What is the primary function of carbohydrates in the body?

To regulate body temperature

To mediate intercellular communication

To provide a significant fraction of dietary calories (correct)

To synthesize proteins

What is the major metabolic fuel of mammals?

Sucrose

Galactose

Glucose (correct)

Fructose

Which of the following is NOT a disease associated with carbohydrate metabolism?

Hypertension Signup and view all the answers

What is the term for the entire complement of sugars produced by an organism?

Glycome Signup and view all the answers

What is the primary component of the exoskeleton of insects?

Chitin Signup and view all the answers

What is the function of glycogen in the body?

To provide a source of energy Signup and view all the answers

What is the precursor for the synthesis of all other carbohydrates in the body?

Glucose Signup and view all the answers

What type of bond is formed when the second group is an amine?

N-glycosidic bond Signup and view all the answers

Which of the following is NOT a type of carbohydrate polymer?

Amino acids Signup and view all the answers

What is the function of carbohydrate polymers in cell walls of bacteria, fungi, and plants?

Structural and protective elements Signup and view all the answers

Which antibiotic contains an amino sugar?

Erythromycine Signup and view all the answers

What type of sugar is deoxyribose?

Deoxy sugar Signup and view all the answers

Which of the following is a physiologically important disaccharide?

Maltose Signup and view all the answers

What is the function of carbohydrate polymers in lubricating skeletal joints?

Lubrication Signup and view all the answers

Which of the following is a constituent of hyaluronic acid?

D-glucosamine Signup and view all the answers

What is the primary reason for storing low molecular weight metabolites in polymeric form?

To avoid high osmolarity that would result from storing them as individual monomers Signup and view all the answers

What is the property of inulin that makes it useful for determining the glomerular filtration rate?

Its ready solubility in water Signup and view all the answers

What is the reason why mammals cannot digest cellulose?

Because mammals lack the enzyme to hydrolyze the β1 → 4 bonds Signup and view all the answers

What is the primary function of the carbohydrate layer on the surface of eukaryotic cells?

To serve as an information-rich surface that the cell shows to its surroundings Signup and view all the answers

What is the glycemic index a measure of?

The extent to which a starchy food raises the blood glucose concentration Signup and view all the answers

What type of polysaccharide is pectin?

A type of starch found in fruits Signup and view all the answers

Why does inulin have no nutritional value?

Because it is not hydrolyzed by intestinal enzymes Signup and view all the answers

In the α configuration of a monosaccharide, the –OH group on the anomeric carbon projects to the same side as the ring in which type of projection formula?

Modified Fischer projection formula Signup and view all the answers

What is the primary component of dietary fiber?

Cellulose Signup and view all the answers

Which of the following isomers differs from glucose due to variations in configuration of the -OH and -H on carbon atoms 2, 3, and 4?

Mannose Signup and view all the answers

Which type of sugars are reducing compounds and can be detected using a chemical test involving an alkaline copper solution?

Aldoses Signup and view all the answers

Which of the following metabolic pathways involves the formation of derivatives of trioses, tetroses, and pentoses?

Pentose phosphate pathway Signup and view all the answers

Which carboxylic acid derivative of glucose is involved in the uronic acid pathway?

L-gulonate Signup and view all the answers

Glycosides are formed by condensation between the hydroxyl group of the anomeric carbon of a monosaccharide and which of the following?

Another monosaccharide Signup and view all the answers

Which of the following is NOT a reducing 6C sugar?

Fructose Signup and view all the answers

Which of the following monosaccharides is epimerized at carbon 4?

Galactose Signup and view all the answers

Which of the following glycosaminoglycans is NOT typically found in humans?

Keratan sulfate III Signup and view all the answers

What is the primary function of glycosylation in proteins?

To enhance protein-ligand interactions Signup and view all the answers

Which of the following is NOT a type of glycoprotein?

Gangliosides Signup and view all the answers

What is the precursor molecule for the synthesis of neuraminic acid?

Mannosamine Signup and view all the answers

Which of the following glycoproteins is involved in the regulation of thyroid function?

Thyroid-stimulating hormone Signup and view all the answers

What is the term for the enzymic attachment of sugars to proteins?

Glycosylation Signup and view all the answers

Which of the following glycosaminoglycans is typically found in the skin?

Dermatan sulfate Signup and view all the answers

What is the general term for proteins that contain carbohydrate molecules?

Glycoproteins Signup and view all the answers

Study Notes

Glycosaminoglycans (GAGs)

There are at least seven GAGs:
- Hyaluronic acid (hyaluronan)
- Chondroitin sulfate
- Keratan sulfate I
- Keratan sulfate II
- Heparin
- Heparan sulfate
- Dermatan sulfate

Glycoproteins

Glycoproteins are proteins containing branched or unbranched oligosaccharide chains, including fucose.
Carbohydrate (oligosaccharide chains or glycans) is covalently bound to amino acids; glycosylation is the most frequent posttranslational modification of proteins.
They occur in cell membranes and many proteins are glycosylated.
Sialic acids are N- or O- acyl derivatives of neuraminic acid, a nine-carbon sugar derived from mannosamine and pyruvate.
Sialic acids are constituents of both glycoproteins and gangliosides.
Examples of glycoproteins include:
- Immunoglobulins (antibodies)
- Certain hormones, such as:
  - Follicle-stimulating hormone (FSH)
  - Luteinizing hormone (LH)
  - Thyroid-stimulating hormone (TSH)

Introduction to Carbohydrates

Carbohydrates (saccharides) are the most abundant organic molecules in nature and are widely distributed in plants and animals.
They have important structural and metabolic roles, providing a significant fraction of dietary calories for most organisms.
They act as a storage form of energy in the body and serve as cell membrane components that mediate some forms of intercellular communication.
They serve as a structural component of many organisms, including the cell walls of bacteria, the exoskeleton of insects, and the fibrous cellulose of plants.

Glucose

Glucose is the most important carbohydrate; most dietary carbohydrate is absorbed into the bloodstream as glucose.
Other sugars are converted to glucose in the liver.
Glucose is the major metabolic fuel of mammals and is a precursor for the synthesis of all other carbohydrates in the body, including:
- Glycogen for storage
- Ribose and deoxyribose in nucleic acids (DNA and RNA)
- Galactose for synthesis of lactose in milk, in glycolipids, and in combination with protein in glycoproteins and proteoglycans.

Diseases Associated with Carbohydrate Metabolism

Diabetes mellitus
Galactosemia
Glycogen storage diseases
Lactose intolerance

The Glycome

The glycome is the entire complement of sugars produced by an organism, whether free or in more complex molecules.

Classification of Carbohydrates

Monosaccharides
Epimers: isomers differing as a result of variations in configuration of the -OH and -H on carbon atoms 2, 3, and 4 of glucose.
Aldose-ketose isomerism: chemically, aldoses are reducing compounds, and are sometimes known as reducing sugars.

Physiological Importance of Monosaccharides

Derivatives of trioses, tetroses, and pentoses and of the seven-carbon sugar sedoheptulose are formed as metabolic intermediates in glycolysis and the pentose phosphate pathway.
Carboxylic acid derivatives of glucose are important, including:
- D-glucuronate (for glucuronide formation and in glycosaminoglycans)
- L-iduronate (in glycosaminoglycans)
- L-gulonate (an intermediate in the uronic acid pathway)

Glycosides

Glycosides are formed by condensation between the hydroxyl group of the anomeric carbon of a monosaccharide and a second compound that may be another monosaccharide or, in the case of an aglycone, not a sugar.
Examples of glycosides include:
- Digoxin, an inhibitor of the Na+–K+-ATPase of cell membranes
- Ouabain
- Other glycosides include antibiotics such as streptomycin.

Deoxy Sugars

Deoxy sugars are those in which one hydroxyl group has been replaced by hydrogen; an example is deoxyribose in DNA.

Amino Sugars (Hexosamines)

Amino sugars are components of glycoproteins, gangliosides, and glycosaminoglycans.
Examples of amino sugars include:
- D-glucosamine, a constituent of hyaluronic acid
- D-galactosamine (also known as chondrosamine), a constituent of chondroitin
- Erythromycin, an antibiotic containing amino sugars

Disaccharides

Disaccharides are sugars composed of two monosaccharide residues linked by a glycoside bond.
Physiologically important disaccharides include:
- Maltose
- Sucrose
- Lactose

Quick View of Carbohydrates

Carbohydrate polymers called glycans (polysaccharides) serve as structural and protective elements in the cell walls of bacteria, fungi, and plants, and in the connective tissues of animals.
Other carbohydrate polymers lubricate skeletal joints and participate in cell-cell recognition and adhesion.
Most hexoses of living organisms are D isomers.
Storage of low molecular weight metabolites in polymeric form avoids the very high osmolarity that would result from storing them as individual monomers.

Polysaccharides

Inulin is a polysaccharide of fructose (a fructosan) found in tubers and roots of dahlias, artichokes, and dandelions.
Cellulose is the chief constituent of plant cell walls, consisting of β-D-glucopyranose units linked by β1 → 4 bonds.
Chitin is a structural polysaccharide in the exoskeleton of crustaceans and insects, and also in mushrooms.
Pectin occurs in fruits.

Glycemic Index

The glycemic index of a starchy food is a measure of its digestibility, based on the extent to which it raises the blood glucose concentration compared with an equivalent amount of glucose or a reference food.

Glycoconjugates: Proteoglycans, Glycoproteins, and Glycolipids

On almost every eukaryotic cell, specific oligosaccharide chains attached to components of the plasma membrane form a carbohydrate layer (the glycocalyx), that serves as an information-rich surface that the cell shows to its surroundings.

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Description

This quiz covers the characteristics and types of proteoglycans, glycosaminoglycans, and glycoproteins. It includes information on the different types of glycosaminoglycans.