Mammalian Diet and Fiber Quiz

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Questions and Answers

What is the role of insoluble fibers in the mammalian diet?

They slow down the movement of food through the gastrointestinal tract.

They facilitate nutrient absorption from the diet.

They soften stools and make them easier to pass. (correct)

They increase the rate at which digestion products pass through the small intestine.

Which statement regarding chitin is true?

Chitin is composed of β-1,4 linked N-acetylglucosamine. (correct)

Chitin is primarily found in mammalian tissues.

Chitin can be synthesized from plant fibers.

Chitin is a homopolymer of glucose linked by α-1,4 bonds.

What is a characteristic of chitosan derived from chitin?

It can only be used in pharmaceutical applications.

It is insoluble in water and used mainly as a dietary fiber.

It serves as a carrier for drug delivery and is versatile in various products. (correct)

It cannot be used in cosmetic formulations.

Why can mammals digest some plant fibers but not cellulose?

Mammals do not possess cellulases necessary for digesting cellulose. Signup and view all the answers

What role does soluble fiber play in digestion?

It slows the movement of food through the gastrointestinal tract. Signup and view all the answers

What is a defining characteristic of glycoproteins?

They have a carbohydrate group covalently attached to a protein. Signup and view all the answers

What distinguishes epimers from other sugars?

They differ in configuration only at a single asymmetric center. Signup and view all the answers

In the context of glycoproteins, what is the role of glycosylation?

Increases the complexity of the proteome. Signup and view all the answers

Which statement is true regarding the formation of a hemiacetal?

An aldehyde reacts with an alcohol to form it. Signup and view all the answers

Which of the following correctly describes proteoglycans?

They have a protein core conjugated to a glycosaminoglycan. Signup and view all the answers

What characteristic defines the anomeric carbon in glucose?

It creates an additional asymmetric center upon cyclization. Signup and view all the answers

What sequence must Asn be part of for N-linkage in glycoproteins?

Asn-X-Ser or Asn-X-Thr Signup and view all the answers

Which form of D-Fructose predominates in solution due to reduced steric hindrance?

Furanose form Signup and view all the answers

What is true about the core structure of N-linked oligosaccharides?

It contains three mannoses and two N-acetylglucosamine residues. Signup and view all the answers

What is the prevalent conformation of β-D-Glucose and why?

The chair form, because it minimizes steric hindrance. Signup and view all the answers

Which type of conformation do furanose rings typically adopt?

Envelope form Signup and view all the answers

What feature of pyranose rings contributes to their non-planarity?

The tetrahedral geometry of saturated carbon atoms. Signup and view all the answers

How do axial substituents in a chair conformation of pyranose rings interact?

They sterically hinder each other. Signup and view all the answers

What role do glycosaminoglycans play in the function of aggrecan?

They allow aggrecan to resist compressive forces by binding water. Signup and view all the answers

Which statement accurately describes the structure of aggrecan?

Aggrecan features a central polymer of hyaluronate with noncovalent G1 binding. Signup and view all the answers

In which cellular location does N-linked glycosylation primarily occur?

In the endoplasmic reticulum (ER) and continues in the Golgi complex. Signup and view all the answers

What is a primary function of mucins?

To hydrate and protect underlying epithelial cells. Signup and view all the answers

What effect does aging have on proteoglycans in relation to osteoarthritis?

It leads to the loss of water from proteoglycans. Signup and view all the answers

Which of the following is true about the tandem repeats region in mucins?

It is characterized by O-glycosylated Ser and Thr residues. Signup and view all the answers

What type of glycosylation is limited to the Golgi complex?

O-linked glycosylation. Signup and view all the answers

Which component does cartilage primarily contain for structure and function?

Aggrecan that provides structure and tensile strength. Signup and view all the answers

What is I-cell disease primarily characterized by?

Severe psychomotor impairment and skeletal deformities Signup and view all the answers

Which enzyme deficiency is associated with the glycosylation issue in I-cell disease?

N-acetylglucosamine phosphotransferase Signup and view all the answers

What is the resultant effect of glycosylation errors on lysosomal enzymes in I-cell disease?

Enzymes are synthesized but not sequestered in lysosomes Signup and view all the answers

What role does the mannose 6-phosphate residue play in lysosomal targeting?

It directs enzymes to the lysosomes Signup and view all the answers

Which technique is NOT typically used for analyzing oligosaccharides?

Gel electrophoresis Signup and view all the answers

Why do certain types of muscular dystrophy relate to errors in glycosylation?

They affect the structure and function of proteins Signup and view all the answers

What is a characteristic feature of lysosomes affected in I-cell disease?

Accumulation of undigested glycosaminoglycans and glycolipids Signup and view all the answers

How can points of attachment of oligosaccharides on glycoproteins be determined?

Through chromatography following protease treatment Signup and view all the answers

What role do Ca2+ ions play in the binding mechanism of C-type lectins?

They act as a bridge between lectin and sugar during the binding process. Signup and view all the answers

Which type of lectins is primarily involved in receptor-mediated endocytosis in animals?

C-type lectins Signup and view all the answers

Which statement accurately describes the function of selectins?

They recruit leukocytes specifically to sites of inflammation. Signup and view all the answers

What is a distinguishing feature of L-type lectins compared to C-type lectins?

L-type lectins are rich in legumes and can act as chaperones. Signup and view all the answers

What mechanism does hemagglutinin utilize to facilitate viral entry into host cells?

It binds specifically to sialic acid residues on cell-surface glycoproteins. Signup and view all the answers

How do lectins usually interact with carbohydrates?

Using a variety of weak, noncovalent interactions. Signup and view all the answers

How does neuraminidase function in the context of influenza virus pathology?

It cleaves oligosaccharide chains to release viral particles. Signup and view all the answers

Which form of selectin is involved in binding carbohydrates on lymph-node vessels?

L-selectin Signup and view all the answers

Study Notes

Carbohydrates and Glycoproteins

Carbohydrates are carbon-based molecules high in hydroxyl groups.
Their empirical formula is (CH₂O)ₙ.
They can have additional groups or modifications.
Monosaccharides are aldehydes or ketones with two or more hydroxyl groups.
The smallest are composed of three carbons.
Monosaccharides exist in isomeric forms.

Monosaccharides

Monosaccharides are carbohydrates with three to seven carbons.
Also called simple sugars.
Nomenclature is based on carbon chain length (trioses, tetroses, pentoses, hexoses, heptoses).
Also based on the most oxidized group (ketose or aldose).

Isomers

Constitutional isomers have identical molecular formulas but different atom order.
Stereoisomers have different spatial arrangements but the same bonding order.
Enantiomers are mirror images of each other.
Diastereoisomers are not mirror images of each other.
Possible numbers of stereoisomers = 2ⁿ, where n is the number of asymmetric carbon atoms.

Common Monosaccharides

Epimers are diastereoisomers differing at only one asymmetric center.
Examples: D-ribose, 2-deoxy-D-ribose, D-glucose, D-mannose, D-galactose, D-fructose.

Cyclical Forms

Aldehydes and ketones can react with alcohols to form hemiacetals or hemiketals.
Monosaccharides exist primarily in their ring forms.
Pyranose and furanose are cyclic forms, similar to pyran and furan, respectively.
a-D-Glucopyranose and β-D-Glucopyranose are examples of pyranose forms of D-glucose.
α-D-Fructofuranose is an example of a furanose form of D-fructose

Anomers of Glucose

Anomers are diastereomers that differ in configuration at the anomeric carbon atom (C-1).
α-D-glucopyranose and β-D-glucopyranose are anomers, differing in the position of the hydroxyl group on C-1.

D-Glucose

D-glucose is an important fuel for most organisms.
It's the main blood sugar and used by the brain and red blood cells.
Glucose forms, a and β, are in equilibrium.
There's a roughly 2:1 ratio of β- to α-anomers in an equilibrium solution.
Glucose is a reducing sugar and reacts with oxidizing agents.

Reducing Sugars

Fehling's solution uses Cu²⁺ to test for reducing sugars.
Reducing sugars react with oxidizing agents and can adopt a linear structure in solution.

Glycation of Sugars

Glycation is the nonenzymatic addition of a carbohydrate to another molecule.
Reducing sugars often react with free amino groups on proteins.
This forms stable covalent bonds, potentially leading to advanced glycation end products (AGEs).
D-glucose tends to glycate proteins at very high concentrations for extended periods.

Advanced Glycation End Products (AGEs)

AGEs are products of cross-linking that result from primary glycation modification.
They are implicated in aging, arteriosclerosis, diabetes, and other pathologies.

Assessing Diabetes Treatments by A1c Levels

Glycated hemoglobin (hemoglobin A1c, A1c) forms by combining glucose and hemoglobin.
A1c levels can be monitored to assess diabetes treatment.
In nondiabetic individuals less than 6% of hemoglobin is glycated. . In uncontrolled diabetes, almost 10% of hemoglobins are glycated.

Oligosaccharides

Oligosaccharides are formed by linking two or more monosaccharides via O-glycosidic bonds.
They have a reducing end and a nonreducing end.

Section 11.1 Monosaccharides

A section covering the simple building blocks of carbohydrates, featuring examples, formulas, and important structural characteristics.

Maltose

This disaccharide is composed of two glucose units linked by an α-1,4-glycosidic bond, possessing a reducing end.

Sucrose, Lactose, and Maltose

Examples of disaccharides (two monosaccharides combined).
Sucrose combines glucose to fructose.
Lactose combines galactose to glucose.
Maltose combines two glucose units.

The Disaccharide Sucrose

Sucrose is a disaccharide of sugar cane or sugar beets.
It's formed by linking glucose and fructose.
It's not a reducing sugar.

The Disaccharide Lactose

Lactose is a disaccharide found in milk.
It's made of galactose and glucose linked by a β-1,4-glycosidic linkage.
It can be hydrolyzed by lactase in humans and β-galactosidase in bacteria.

The Disaccharide Maltose

Maltose is a disaccharide formed by the hydrolysis of large oligosaccharides, made from two linked glucose molecules.
It is joined by an α-1,4-glycosidic linkage.

Maltose Inhibitors

Inhibitors like Acarbose and Miglitol help control blood glucose by inhibiting maltase action.

Human Milk Oligosaccharides

Human milk contains over 150 different oligosaccharides.
They're not digested by infants but support growth and immunity.
They act as fuel for beneficial bacteria and prevent pathogen attachment to the intestinal wall.

Glycogen and Starch

Glycogen and starch are storage forms of glucose.
They consist of branched chains of glucose units.

Glycogen

Glycogen is a large, branched polymer of glucose residues.
It is the storage form of glucose in animals.

Starch

Starch serves as a nutritional reservoir in plants.
It is composed of amylose and amylopectin.

Cellulose

Cellulose is a structural polysaccharide in plants.
It's composed of unbranched chains of glucose joined by β-1,4-linkages.
Its structure allows for rigidity and support.

Glycosidic Linkages

O-glycosidic linkages bond a carbohydrate's anomeric carbon to an alcohol's oxygen atom.
N-glycosidic linkages bond a carbohydrate's anomeric carbon to an amine's nitrogen atom.

Section 11.3

This section explains how carbohydrates are linked to proteins to form glycoproteins.
Glycoproteins make up a significant portion of the human proteome.
Glycosylation alters the complexity of proteins.

Three Classes of Glycoproteins

Glycoproteins: predominantly proteins, with roles such as cell adhesion.
Proteoglycans: largely carbohydrates, acting as lubricants and structural components in connective tissues. Examples include aggrecan, important for cartilage.
Mucins: composed primarily of carbohydrates, playing roles as lubricants and protective barriers. Examples include those involved in mucus production.

Carbohydrates and Proteins

N-linkage connects carbohydrate sugars to the amide nitrogen of an Asn amino acid residue (specific Asn-X-Ser/Thr sequence).
O-linkage connects carbohydrate sugars to the oxygen of a Ser or Thr amino acid residue.

N-Linked Oligosaccharides

N-linked oligosaccharides possess a common core of three mannose and two N-acetylglucosamine residues.

Erythropoietin (EPO)

EPO is a glycoprotein hormone secreted by the kidneys to stimulate red blood cell production.
Glycosylation stabilizes the protein in the blood.

Oligosaccharides of Erythropoietin

Oligosaccharides are attached to EPO at specific Asn and Ser residues.
Carbohydrates constitute a significant portion of the protein's weight (approx. 40%).

Glycosylation Functions in Nutrient Sensing

GIcNAcylation is the post-translational addition of GIcNAc to specific Ser and Thr residues of proteins.
It occurs in response to nutrient abundance and is a reversible process.

###O-GlcNAc Transferase

O-GlcNAc transferase is an enzyme that adds GIcNAc groups to proteins.
Improper regulation of this enzyme is associated with insulin resistance, diabetes, cancer, and neurological conditions.

Proteoglycans

Proteoglycans are large molecules consisting primarily of glycosaminoglycans, which are structural components of connective tissues, functioning as lubricants and mediating cell adhesion.

Glycosaminoglycans

Glycosaminoglycans are composed of repeating disaccharide units containing an amino sugar derivative (glucosamine or galactosamine).
One of the sugars usually carries a negative charge (sulfate or carboxyl).

Proteoglycans and Cartilage

Cartilage contains proteins (such as collagen) and proteoglycans such as aggrecan.
Aggrecan serves as a shock absorber due to water binding and release.

Mucins

Mucins are glycoproteins with tandem repeat regions rich in O-glycosylated Ser and Thr residues.
Core carbohydrates are attached.

Functions of Mucins

Mucins bind to epithelial cells, acting as protective barriers.
They hydrate underlying cells.
They're also key for fertilization, immune responses, and cell adhesion.

Determining Oligosaccharide Structure

Oligosaccharide structure can be understood by combining enzymatic cleavage with mass spectrometry and chromatography.

Blood Groups

Blood groups are determined by the presence of specific carbohydrates (A, B, or O) on glycoproteins/glycolipids.

Cholera Toxin

Cholera is a disease induced by Vibrio cholerae toxin.
Blood type O is more sensitive to the disease, due to the toxin's stronger affinity for O-type antigens.

Errors in Glycosylation

Congenital disorders can result from improper glycosylation, leading to conditions like muscular dystrophy and I-cell disease.

I-Cell Disease

A type of lysosomal storage disease.
Lysosomes contain undigested glycosaminoglycans and glycolipids due to a lack of appropriate enzyme glycosylation.

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Description

Test your knowledge on the role of different types of dietary fibers in the mammalian diet. This quiz covers insoluble fibers, chitin, chitosan, and the digestibility of plant fibers. Understand the significance of soluble fiber in digestion and learn how mammals process various food components.