Carbohydrates: Monosaccharides to Polysaccharides
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Questions and Answers

What is one major role of N-linked oligosaccharides in proteins?

  • To stabilize protein conformations (correct)
  • To enhance the color of proteins
  • To decrease protein mass
  • To increase protein digestibility

Why are most animals unable to digest cellulose?

  • They do not possess cellulase enzyme (correct)
  • Their digestive tracts are too acidic
  • Cellulose is too soluble
  • They lack dietary fibers

Which animals are known to efficiently digest cellulose?

  • Reptiles that consume plants
  • Carnivores like lions and tigers
  • Ruminant animals like cattle and deer (correct)
  • Birds which primarily eat seeds

What effect does glycosylation have on the properties of proteins?

<p>Alters solubility and electrical charge (B)</p> Signup and view all the answers

What does the enzyme cellulase do?

<p>It hydrolyzes cellulose's linkages (A)</p> Signup and view all the answers

What defines a disaccharide?

<p>Two monosaccharide units linked by a glycosidic bond (B)</p> Signup and view all the answers

Which of the following disaccharides is not a reducing sugar?

<p>Sucrose (B)</p> Signup and view all the answers

What type of polysaccharide contains only one kind of monosaccharide unit?

<p>Homopolysaccharide (C)</p> Signup and view all the answers

Which of the following statements about glycosidic bonds is true?

<p>They link monosaccharides through a condensation reaction. (D)</p> Signup and view all the answers

What is unique about N-linked glycoproteins?

<p>They always contain branched mannose triads. (D)</p> Signup and view all the answers

Which carbohydrate residue is commonly linked to proteins in O-linked saccharides?

<p>N-acetylgalactosamine (B)</p> Signup and view all the answers

What distinguishes a heteropolysaccharide from a homopolysaccharide?

<p>It contains more than one kind of monosaccharide. (B)</p> Signup and view all the answers

What are the simplest oligosaccharides?

<p>Disaccharides (A)</p> Signup and view all the answers

What role do N-linked oligosaccharides play in protein stability?

<p>They enhance the solubility of proteins. (B)</p> Signup and view all the answers

Which enzyme is explicitly missing in most animals that prevents them from digesting cellulose?

<p>Cellulase (D)</p> Signup and view all the answers

What effect does glycosylation have on the electrical charge of proteins?

<p>It increases negative charge. (D)</p> Signup and view all the answers

Why can ruminant animals digest cellulose effectively?

<p>They have a specialized stomach compartment for fermentation. (B)</p> Signup and view all the answers

What happens to glucose derived from cellulose in ruminant animals?

<p>It is metabolized in a fermentation process. (C)</p> Signup and view all the answers

What is the role of dehydration synthesis in the formation of glycosides?

<p>It forms a glycosidic bond between monosaccharides. (A)</p> Signup and view all the answers

Which statement correctly describes sucrose in relation to reducing sugars?

<p>Sucrose does not contain a free anomeric carbon. (B)</p> Signup and view all the answers

What are glycosidic bonds primarily formed from?

<p>Dehydration synthesis. (C)</p> Signup and view all the answers

What defines homopolysaccharides?

<p>Polymers made of only one kind of monosaccharide. (C)</p> Signup and view all the answers

Which type of polysaccharide can also be referred to as glycans?

<p>Polysaccharides. (D)</p> Signup and view all the answers

What distinguishes N-linked glycoproteins from O-linked glycoproteins?

<p>N-linked glycoproteins have a unique core structure with N-acetylglucosamine. (C)</p> Signup and view all the answers

Which of the following describes an aspect of polysaccharide structure?

<p>They are formed from glycosidic linkages between monosaccharides. (C)</p> Signup and view all the answers

What makes a disaccharide a reducing sugar, as opposed to one that is not?

<p>Presence of a free anomeric carbon. (C)</p> Signup and view all the answers

Flashcards

What is a glycosidic bond?

A glycosidic bond is a covalent bond formed between the anomeric carbon of one monosaccharide and the hydroxyl group of another. It is responsible for linking monosaccharide units together to form disaccharides and polysaccharides.

What are disaccharides?

Disaccharides are composed of two monosaccharide units joined by a glycosidic bond. Examples include lactose, sucrose, and maltose.

What is the structure of sucrose?

Sucrose is a disaccharide composed of glucose and fructose linked by an α(1→2)β glycosidic bond. This means the anomeric carbon of glucose is linked to the hydroxyl group at carbon 2 of fructose.

What is the structure of lactose?

Lactose is a disaccharide composed of galactose and glucose linked by a β(1→4) glycosidic bond. This means the anomeric carbon of galactose is linked to the hydroxyl group at carbon 4 of glucose.

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What is the structure of maltose?

Maltose is a disaccharide composed of two glucose units linked by an α(1→4) glycosidic bond. This means the anomeric carbon of one glucose molecule is linked to the hydroxyl group at carbon 4 of the other glucose molecule.

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What are polysaccharides?

Polysaccharides are polymers of monosaccharides linked together by glycosidic bonds. They can be homopolysaccharides (made of the same type of monosaccharide) or heteropolysaccharides (made of different types of monosaccharides).

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What are O-linked saccharides?

O-linked saccharides are a type of polysaccharide where the carbohydrate residue is linked to the hydroxyl group of an amino acid residue in a protein.

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What are N-linked saccharides?

N-linked saccharides are a type of polysaccharide where the carbohydrate residue is linked to the amide nitrogen of an asparagine residue in a protein.

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Why is cellulose indigestible?

Humans lack the enzyme 'cellulase' needed to break down the beta (1->4) linkages within cellulose.

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What is cellulase?

Cellulase is an enzyme that breaks down cellulose by cleaving the beta (1->4) linkages between glucose monomers.

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What is the significance of the beta (1->4) linkage in cellulose?

The beta (1->4) linkage in cellulose creates a linear, rigid structure that makes it resistant to hydrolysis by human enzymes.

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How do ruminants digest cellulose?

Ruminant animals have bacteria in their rumen that produce cellulase, allowing them to break down cellulose and benefit from the glucose generated.

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What are the consequences of cellulose indigestibility for humans?

Humans cannot extract energy from cellulose, limiting our ability to utilize this abundant plant-based carbohydrate.

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Why can't humans digest cellulose?

Humans lack the enzyme cellulase, which is necessary to break down the beta (1->4) linkages in cellulose. This means our bodies cannot extract energy from it effectively.

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What are N-linked oligosaccharides?

These are carbohydrate structures attached to the amide nitrogen of asparagine residues in proteins. They can influence protein properties and functions.

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What makes ( )-D glucose more reactive?

The presence of the hemiacetal group in cyclic ( )-D glucose makes it more reactive compared to open-chain glucose. This hemiacetal group can easily interconvert between α and β anomers, leading to greater participation in reactions.

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What makes sucrose a non-reducing sugar?

Sucrose lacks a free anomeric carbon, the carbon involved in the hemiacetal formation. This is because its glycosidic bond involves both anomeric carbons, making it unable to open into the open-chain form required for reducing properties.

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What are the three types of N-linked glycoproteins?

N-linked glycoproteins are categorized into high mannose, complex, and hybrid types. High mannose type has a core structure with only mannose residues. Complex has a more diverse structure with various sugars added. Hybrid combines features of both.

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Study Notes

Monosaccharides and their Reactions

  • Monosaccharides are the simplest carbohydrates
  • They are used to form disaccharides (e.g., maltose, sucrose, lactose) and polysaccharides via glycosidic bonds
  • Pyranose and furanose forms react with alcohols in dehydration synthesis to form glycosides, retaining the α or β configuration at C-1
  • The reaction results in a glycosidic bond via a condensation reaction and breaks by hydrolysis. The new bond is between an anomeric carbon and the oxygen of an alcohol.

Disaccharides

  • Disaccharides are oligosaccharides composed of two monosaccharide units linked by a glycosidic bond
  • Common examples include sucrose, maltose, and lactose
  • These are mixed acetals, with one intramolecular hydroxyl group and one from another monosaccharide
  • All except sucrose have a free anomeric carbon, making them reducing sugars
  • Sucrose is a non-reducing sugar due to no free anomeric carbon

Polysaccharides

  • Polysaccharides, also called glycans, are polymers of monosaccharides
  • Homopolysaccharides consist of only one type of monosaccharide
  • Heteropolysaccharides contain more than one type of monosaccharide

Glycosylation of Proteins

  • Proteins can be glycosylated, which involves the addition of carbohydrates (oligosaccharides)
  • O-linked glycosylation involves attaching carbohydrate residues (e.g., N-acetylgalactosamine, mannose, galactose, xylose) to the oxygen of hydroxyl groups on the protein.
  • N-linked glycosylation involves attaching carbohydrate residues to the amide nitrogen of an asparagine residue. The core structure always contains two N-acetylglucosamine residues linked to a branched mannose triad
  • N-linked glycoproteins can be high mannose, complex, or hybrid
  • O-linked oligosaccharides are often found in cell surface glycoproteins and mucins
  • N-linked oligosaccharides are found in various proteins, impacting their properties and functions, affecting solubility, mass and electrical charge
  • Glycosylation can stabilize protein conformations and protect from proteolysis

Cellulose Digestion

  • Cellulose is resistant to hydrolysis by acids and digestive enzymes because humans lack the enzyme cellulase, which breaks down β(1→4) linkages
  • Ruminant animals can digest cellulose due to cellulase-secreting bacteria in their rumen. These bacteria produce β-glucosidase which hydrolyzes the cellulose.

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Description

This quiz covers the basics of carbohydrates, including monosaccharides, disaccharides, and polysaccharides. It explores their structures, formation, and unique properties. Test your knowledge on glycosidic bonds and the characteristics of these essential biomolecules.

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