Unit 3: Carbohydrates

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Questions and Answers

What is a primary reason carbohydrates are named so?

They contain no chiral centers.

They are derived from simple sugars.

They are produced exclusively by animals.

They have a general formula of Cn(H2O)n. (correct)

What role do carbohydrates play in cell membranes?

They provide thermal insulation.

They serve as an energy source.

They act as structural components in cell walls. (correct)

They facilitate DNA replication.

Which statement about monosaccharides is true?

Dihydroxyacetone is the only monosaccharide without chiral centers. (correct)

They are always used for energy storage.

They all contain a chiral carbon atom.

Monosaccharides cannot exist in optically active forms.

What determines the interaction of carbohydrates with other biomolecules?

The arrangement of groups around their chiral carbons. Signup and view all the answers

What is the function of the TAS1R2 and TAS1R3 proteins?

They encode sweet-taste receptors. Signup and view all the answers

What is a characteristic of sugar stereoisomers?

They can be both D-series and L-series. Signup and view all the answers

Which type of carbohydrates serves as building blocks for larger polymers?

Monosaccharides Signup and view all the answers

What is one of the biological functions of glycoconjugates?

They are responsible for cell-cell signaling. Signup and view all the answers

Which of the following correctly describes an aldose?

It contains an aldehyde functionality. Signup and view all the answers

What type of sugar is sucrose?

Disaccharide Signup and view all the answers

Which sugar is considered a five-carbon standard sugar?

Ribose Signup and view all the answers

What defines an epimer?

Sugars that differ only in the configuration around one carbon atom. Signup and view all the answers

Which statement about the cyclic structures of monosaccharides is true?

The carbonyl carbon becomes the anomeric carbon. Signup and view all the answers

What type of carbohydrate is formed following the oxidation of aldoses?

Uronic acids Signup and view all the answers

What is the purpose of glucose oxidase in colorimetric glucose analysis?

It catalyzes the conversion of glucose to glucono-δ-lactone. Signup and view all the answers

How do intramolecular cyclic structures affect the reactivity of monosaccharides?

The anomeric carbon can act as a reducing agent. Signup and view all the answers

Which of the following is a characteristic of polysaccharides?

They are sugar polymers with ten or more monosaccharide units. Signup and view all the answers

What is the relationship between glucose and fructose?

Fructose is the ketose form of glucose. Signup and view all the answers

What are glycosaminoglycans primarily composed of?

Repeating disaccharide units Signup and view all the answers

Which component of the extracellular matrix provides strength and elasticity?

Collagen fibers Signup and view all the answers

What role do proteoglycans play in cellular function?

Regulate cell growth and interact with receptors Signup and view all the answers

Which of the following is a characteristic of glycoproteins?

They are primarily found in the plasma membrane and ECM. Signup and view all the answers

What is a primary function of glycolipids in cellular membranes?

Contribute to membrane structure Signup and view all the answers

What is the role of glycosphingolipids primarily found in neurons?

Play a role in signal transduction Signup and view all the answers

Which type of glycan is crucial for determining blood groups in vertebrates?

Gangliosides Signup and view all the answers

What principle underlines the function of molecular interactions in biological systems?

Molecular complementarity Signup and view all the answers

What bond type is involved in the formation of disaccharides?

Glycosidic bond Signup and view all the answers

Which of the following best describes glycogen?

A branched homopolysaccharide of glucose Signup and view all the answers

What type of polysaccharide is characterized by having no defined molecular weight?

Glycans Signup and view all the answers

Which enzyme is active in the small intestine after the pH is neutralized?

Pancreatic α-amylase Signup and view all the answers

What is the structure of amylopectin?

Long branched chains of monomers with α(1→4) and α(1→6) bonds Signup and view all the answers

How does salivary α-amylase affect starch and glycogen?

Acts on random α(1→4) bonds Signup and view all the answers

What can lead to lactose intolerance in the adult population?

Deficiency of digestive enzymes Signup and view all the answers

Which statement accurately describes the glycosidic bonds in polysaccharides?

They determine the properties and functions of the polymer Signup and view all the answers

What is maltose formed from?

Two glucose molecules linked by a 1,4 glycosidic bond Signup and view all the answers

Study Notes

Carbohydrates Overview

Named due to the general formula Cn(H2O)n.
Synthesized from CO2 and H2O through photosynthesis in plants.
Molecular weights range from glyceraldehyde (90 g/mol) to amylopectin (200,000,000 g/mol).
Sugar stereoisomers occur due to chiral centers, influencing interactions with enzymes.
Enzymes acting on sugars are stereospecific, demonstrating a preference for certain isomers.
Carbohydrates can form glycoproteins and proteoglycans via covalent links with proteins.

Functions and Properties of Carbohydrates

Serve as energy sources and storage.
Act as structural components in cell walls and exoskeletons.
Function as informational molecules for cell-cell signaling.

Monosaccharides and Their Characteristics

Monosaccharides are simple sugars with one polyhydroxy aldehyde or ketone unit (e.g., D-glucose).
Dihydroxyacetone is the only monosaccharide without chiral centers.
Exist in optically active forms; most common type is D-series.
Sweet taste perception is linked to TAS1R2 and TAS1R3 receptors.

Types of Carbohydrates

Disaccharides consist of two monosaccharides (e.g., sucrose = glucose + fructose).
Oligosaccharides are short chains of monosaccharides linked by glycosidic bonds.
Polysaccharides consist of 10+ monosaccharide units (examples include cellulose and glycogen).

Aldoses vs. Ketoses

Aldoses contain an aldehyde group.
Ketoses contain a ketone group.

Structural Variants of Sugars

Ribose and glucose are standard five- and six-carbon sugars, respectively.
Galactose is an epimer of glucose, differing at one carbon atom.
Fructose is the ketose form of glucose.
Monosaccharides can cyclize, forming new chiral centers (anomeric carbons).

Variants of Hexoses

Hexose derivatives include phosphate esters and oxidized forms (aldonic and uronic acids).
These derivatives can form lactones, which are stable intramolecular esters.

Glycosidic Bonds and Polysaccharides

Disaccharides form through glycosidic bonds between anomeric and hydroxyl carbons (e.g., maltose from two glucose units).
Polysaccharides can be homopolysaccharides or heteropolysaccharides and vary in branching and linear forms.

Storage Forms of Energy

Glycogen and starch are primary storage forms of carbohydrates.
Glycogen: branched structure of glucose with (α1→4) chains and (α1→6) branch points.
Starch consists of amylose (unbranched) and amylopectin (branched).

Digestion of Carbohydrates

Glycosidases in saliva and intestines hydrolyze glycosidic bonds, with specificity to structure.
Salivary α-amylase and pancreatic α-amylase are crucial for starch digestion.
Intestinal disaccharidases convert disaccharides to monosaccharides for absorption.

Absorption and Metabolism

Monosaccharides are absorbed in the small intestine via active and facilitated transport.
Disaccharidase deficiencies can lead to digestive disorders such as lactose intolerance.

Glycosaminoglycans and Extracellular Matrix

Glycosaminoglycans are linear polymers made of repeating disaccharide units (e.g., hyaluronan).
They play essential roles in the extracellular matrix, providing structure, strength, and elasticity.

Glycoconjugates

Biologically active molecules consisting of carbohydrates bound to proteins or lipids.
Include proteoglycans, glycoproteins, glycolipids, and glycosphingolipids.
Proteoglycans are involved in cell signaling and are integral to the extracellular matrix.

Molecular Complementarity

Fundamental to the function of glycosylated molecules, affecting interactions and recognition between biomolecules.

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Description

Explore the essential details of carbohydrates in this quiz. Learn about the structures, names, and biological functions of mono-, di-, and polysaccharides, as well as glycoconjugates. Test your knowledge on their properties and significance in biology.